WorldWideScience

Sample records for food web linkages

  1. Pressure-Induced Shifts in Trophic Linkages in a Simplified Aquatic Food Web

    Directory of Open Access Journals (Sweden)

    Maarten Schrama

    2017-12-01

    Full Text Available It is essential to understand effects of existing and emerging anthropogenic stressors on the structure of aquatic food webs in more natural settings, to obtain realistic predictions on how they can affect major ecosystem properties and functioning. We therefore examined whether (1 realistic concentrations of key agricultural pesticides and nutrients induce shifts in trophic linkages (2 observed changes in trophic linkages are qualitatively different between the green (algal-based and brown (detritus-based part of the food web. To this end, we exposed a simplified, yet realistic freshwater invertebrate community to environmentally relevant concentrations of three anthropogenic pressures (eutrophication; the herbicide terbuthylazine; and the insecticide imidacloprid in a full factorial mesocosm design. Trophic linkages and the changes therein were assessed measuring stable isotopes of natural carbon and nitrogen. Results show that the green and brown part of the food web react qualitatively different to interacting pressures. Whereas, herbivorous species react mainly to the nutrients and herbicides and the synergistic interaction between these, species in the detritivore part of the food web were affected by insecticide applications and interactions with nutrients. These results suggest that agricultural pressures can induce shifts in trophic linkages, but that they can have contrasting effects on the different parts of the food web. Such antagonistic and synergistic interactions can provide powerful explanations for observed responses of ecosystems to interacting stressors. These findings may have important implications for our understanding on interactions of agricultural stressors and their propagation in aquatic food webs.

  2. Pressure-induced shifts in trophic linkages in a simplified aquatic food web

    NARCIS (Netherlands)

    Schrama, Maarten; Barmentlo, S. Henrik; Hunting, Ellard R.; van Logtestijn, Richard S.P.; Vijver, Martina G.; van Bodegom, Peter M.

    2017-01-01

    It is essential to understand effects of existing and emerging anthropogenic stressors on the structure of aquatic food webs in more natural settings, to obtain realistic predictions on how they can affect major ecosystem properties and functioning. We therefore examined whether (1) realistic

  3. Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

    Science.gov (United States)

    Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.

    2014-03-01

    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187-207 g C m-2 y-1, which are consistent with observed values (47-351 g C m-2 y-1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.

  4. Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

    Science.gov (United States)

    Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra L.; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.

    2014-01-01

    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187–207 g C m−2 y−1, which are consistent with observed values (47–351 g C m−2 y−1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.

  5. Taking the trophic bypass: aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web.

    Science.gov (United States)

    Bartrons, Mireia; Gratton, Claudio; Spiesman, Brian J; Vander Zanden, M Jake

    2015-01-01

    Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems.

  6. Ecosystem linkages revealed by experimental lake-derived isotope signal in heathland food webs.

    Science.gov (United States)

    Hoekman, David; Bartrons, Mireia; Gratton, Claudio

    2012-11-01

    Cross-ecosystem movement of nutrients and biomass can have important effects on recipient systems. Emerging aquatic insects are subsidies to terrestrial ecosystems and can influence foodweb interactions in riparian systems. In a 2-year field experiment, we simulated aquatic insect deposition by adding adult midge carcasses (150 g dry mass m(-2) year(-1)) to 1-m(2) heathland plots at a site with low natural midge deposition. We established four levels of midge-addition treatments and measured stable isotopes (δ(13)C and δ(15)N) in plants and arthropods within each treatment. We used a multiple-source isotope Bayesian mixing model to estimate the terrestrial versus aquatic contribution to the diets of arthropods. Aquatic resources were incorporated into plant, detritivore, and predator biomass. Detritivorous Collembola showed the greatest difference in isotope values (+3 ‰ δ(15)N and +4 ‰ δ(13)C) between midge-addition and reference treatments. Isotope values of small spiders followed the same trend of enrichment as Collembola while other arthropods (mites and large spiders) were only enriched after 2 years of midge addition. Although predator diets did not change, they became isotopically enriched via their likely prey (Collembola). Plants also had elevated δ(15)N (+1 ‰) in midge-addition treatments. The time required and amount of midge-derived C and N detected varied and depended on trophic position. Midge-derived nutrients were no longer present in arthropod biomass in the year following midge addition. Aquatic insect carcasses can be rapidly incorporated into terrestrial food webs in nearshore habitats, and repeated inputs can be detected at multiple trophic levels, thus highlighting the importance of the detrital pathway for aquatic to terrestrial cross-ecosystem subsidies.

  7. Historic Habitat Opportunities and Food-Web Linkages of Juvenile Salmon in the Columbia River Estuary, Annual Report of Research.

    Energy Technology Data Exchange (ETDEWEB)

    Bottom, Daniel L.; Simenstad, Charles A.; Campbell, Lance [Northwest Fisheries Science Center

    2009-05-15

    In 2002 with support from the U.S. Army Corps of Engineers (USACE), an interagency research team began investigating salmon life histories and habitat use in the lower Columbia River estuary to fill significant data gaps about the estuary's potential role in salmon decline and recovery . The Bonneville Power Administration (BPA) provided additional funding in 2004 to reconstruct historical changes in estuarine habitat opportunities and food web linkages of Columbia River salmon (Onchorhynchus spp.). Together these studies constitute the estuary's first comprehensive investigation of shallow-water habitats, including selected emergent, forested, and scrub-shrub wetlands. Among other findings, this research documented the importance of wetlands as nursery areas for juvenile salmon; quantified historical changes in the amounts and distributions of diverse habitat types in the lower estuary; documented estuarine residence times, ranging from weeks to months for many juvenile Chinook salmon (O. tshawytscha); and provided new evidence that contemporary salmonid food webs are supported disproportionately by wetland-derived prey resources. The results of these lower-estuary investigations also raised many new questions about habitat functions, historical habitat distributions, and salmon life histories in other areas of the Columbia River estuary that have not been adequately investigated. For example, quantitative estimates of historical habitat changes are available only for the lower 75 km of the estuary, although tidal influence extends 217 km upriver to Bonneville Dam. Because the otolith techniques used to reconstruct salmon life histories rely on detection of a chemical signature (strontium) for salt water, the estuarine residency information we have collected to date applies only to the lower 30 or 35 km of the estuary, where fish first encounter ocean water. We lack information about salmon habitat use, life histories, and growth within the long tidal

  8. Contrasting food web linkages for the grazing pathway in 3 temperate forested streams using {sup 15}N as a tracer

    Energy Technology Data Exchange (ETDEWEB)

    Tank, J.L.; Mulholland, P.J.; Meyer, J.L.; Bowden, W.B.; Webster, J.R.; Peterson, B.J.

    1998-11-01

    Nitrogen is a critical element controlling the productivity and dynamics of stream ecosystems and many streams are limited by the supply of biologically available nitrogen. The authors are learning more about the fate of inorganic nitrogen entering streams through {sup 15}N tracer additions. The Lotic Intersite Nitrogen Experiment (LINX) is studying the uptake, cycling, and fate of {sup 15}N-NH{sub 4} in the stream food web of 10 streams draining different biomes. Using the {sup 15}N tracer method and data from 3 sites in the study, the authors can differentiate patterns in the cycling of nitrogen through the grazing pathway (N from the epilithon to grazing macroinvertebrates) for 3 temperate forested streams. Here, they quantify the relationship between the dominant grazer and its proposed food resource, the epilithon, by comparing {sup 15}N levels of grazers with those of the epilithon, as well as the biomass, nitrogen content, and chlorophyll a standing stocks of the epilithon in 3 streams.

  9. The ecology of acidification and recovery: changes in herbivore-algal food web linkages across a stream pH gradient

    International Nuclear Information System (INIS)

    Ledger, M.E.; Hildrew, A.G.

    2005-01-01

    We examined the effects of acidification on herbivore-algal food web linkages in headwater streams. We determined the structure and abundance of consumer and benthic algal assemblages, and gauged herbivory, in 10 streams along a pH gradient (mean annual pH 4.6-6.4). Biofilm taxonomic composition changed with pH but total abundance did not vary systematically across the gradient. Mayflies and chironomids dominated under circumneutral conditions but declined with increasing acidity and their consumption of algae was strongly reduced. Contrary to expectations, several putative shredder species consumed algae, maintaining the herbivore-algal linkage where specialist grazers could not persist. These shifts in functioning could render the communities of acidified streams resistant to reinvasion when acidity ameliorates and water chemistry is restored to a pre-acidification condition. This hypothesis is discussed in the light of recent trends in the chemistry and biology of the UK Acid Waters Monitoring Network sites. - Generalist invertebrates maintain algae-herbivore interactions in acid streams

  10. DEEPWATER AND NEARSHORE FOOD WEB CHARACTERIZATIONS IN LAKE SUPERIOR

    Science.gov (United States)

    Due to the difficulty associated with sampling deep aquatic systems, food web relationships among deepwater fauna are often poorly known. We are characterizing nearshore versus offshore habitats in the Great Lakes and investigating food web linkages among profundal, pelagic, and ...

  11. Properties of food webs

    Energy Technology Data Exchange (ETDEWEB)

    Pimm, S.L.

    1980-04-01

    On the assumption that systems of interacting species, when perturbed from equilibrium, should return to equilibrium quickly, one can predict four properties of food webs: (1) food chains should be short, (2) species feeding on more than one trophic level (omnivores) should be rare, (3) those species that do feed on more than one trophic level should do so by feeding on species in adjacent trophic levels, and (4) host-parasitoid systems are likely to be exceptions to (1)-(3) when interaction coefficients permit greater trophic complexity. By generating random, model food webs (with many features identical to webs described from a variety of marine, freshwater, and terrestrial systems), it is possible to generate expected values for the number of trophic levels and the degree of omnivory within webs. When compared with these random webs, real world webs are shown to have fewer trophic levels, less omnivory, and very few omnivores feeding on nonadjacent trophic levels. Insect webs are shown to have a greater degree of omnivory than other webs. The confirmation of all these predictions from stability analyses suggests that system stability places necessary, though not sufficient, limitations on the possible shapes of food webs.

  12. Long-term increase in mesozooplankton biomass in the Sargasso Sea: Linkage to climate and implications for food web dynamics and biogeochemical cycling

    Science.gov (United States)

    Steinberg, Deborah K.; Lomas, Michael W.; Cope, Joseph S.

    2012-03-01

    microbial food web into mesozooplankton. Decreases in top-down control or expansion of the range of tropical species northward as a result of warming may also play a role.

  13. Complexity in quantitative food webs

    NARCIS (Netherlands)

    Banasek-Richter, C.; Bersier, L.F.; Cattin, M.F.; Baltensperger, R.; Gabriel, J.P.; Merz, Y.; Ulanowicz, R.E.; Tavares, A.F.; Williams, D.D.; Ruiter, de P.C.; Winemiller, K.O.; Naisbit, R.E.

    2009-01-01

    Food webs depict who eats whom in communities. Ecologists have examined statistical metrics and other properties of food webs, but mainly due to the uneven quality of the data, the results have proved controversial. The qualitative data on which those efforts rested treat trophic interactions as

  14. RLT-S: A Web System for Record Linkage.

    Directory of Open Access Journals (Sweden)

    Abdullah-Al Mamun

    Full Text Available Record linkage integrates records across multiple related data sources identifying duplicates and accounting for possible errors. Real life applications require efficient algorithms to merge these voluminous data sources to find out all records belonging to same individuals. Our recently devised highly efficient record linkage algorithms provide best-known solutions to this challenging problem.We have developed RLT-S, a freely available web tool, which implements our single linkage clustering algorithm for record linkage. This tool requires input data sets and a small set of configuration settings about these files to work efficiently. RLT-S employs exact match clustering, blocking on a specified attribute and single linkage based hierarchical clustering among these blocks.RLT-S is an implementation package of our sequential record linkage algorithm. It outperforms previous best-known implementations by a large margin. The tool is at least two times faster for any dataset than the previous best-known tools.RLT-S tool implements our record linkage algorithm that outperforms previous best-known algorithms in this area. This website also contains necessary information such as instructions, submission history, feedback, publications and some other sections to facilitate the usage of the tool.RLT-S is integrated into http://www.rlatools.com, which is currently serving this tool only. The tool is freely available and can be used without login. All data files used in this paper have been stored in https://github.com/abdullah009/DataRLATools. For copies of the relevant programs please see https://github.com/abdullah009/RLATools.

  15. Insect symbionts in food webs

    Czech Academy of Sciences Publication Activity Database

    McLean, A. H. C.; Parker, B. J.; Hrček, Jan; Henry, L. M.; Godfray, H. C. J.

    2016-01-01

    Roč. 371, č. 1702 (2016), article number 20150325 ISSN 0962-8436 Institutional support: RVO:60077344 Keywords : food web * symbiont * symbiosis Subject RIV: EE - Microbiology, Virology Impact factor: 5.846, year: 2016 http://rstb.royalsocietypublishing.org/content/371/1702/20150325

  16. A landscape theory for food web architecture.

    Science.gov (United States)

    Rooney, Neil; McCann, Kevin S; Moore, John C

    2008-08-01

    Ecologists have long searched for structures and processes that impart stability in nature. In particular, food web ecology has held promise in tackling this issue. Empirical patterns in food webs have consistently shown that the distributions of species and interactions in nature are more likely to be stable than randomly constructed systems with the same number of species and interactions. Food web ecology still faces two fundamental challenges, however. First, the quantity and quality of food web data required to document both the species richness and the interaction strengths among all species within food webs is largely prohibitive. Second, where food webs have been well documented, spatial and temporal variation in food web structure has been ignored. Conversely, research that has addressed spatial and temporal variation in ecosystems has generally ignored the full complexity of food web architecture. Here, we incorporate empirical patterns, largely from macroecology and behavioural ecology, into a spatially implicit food web structure to construct a simple landscape theory of food web architecture. Such an approach both captures important architectural features of food webs and allows for an exploration of food web structure across a range of spatial scales. Finally, we demonstrated that food webs are hierarchically organized along the spatial and temporal niche axes of species and their utilization of food resources in ways that stabilize ecosystems.

  17. Linkages among Key Actors in the Climate Change and Food ...

    African Journals Online (AJOL)

    The study used the innovation system approach to ascertain the intensity and trends of linkages among key actors in the climate change and food security innovation system in Nigeria, Sierra Leone and Liberia. Data were collected through the use of semi structured interview schedule, key informant interviews and focus ...

  18. Where are the parasites in food webs?

    Directory of Open Access Journals (Sweden)

    Sukhdeo Michael VK

    2012-10-01

    Full Text Available Abstract This review explores some of the reasons why food webs seem to contain relatively few parasite species when compared to the full diversity of free living species in the system. At present, there are few coherent food web theories to guide scientific studies on parasites, and this review posits that the methods, directions and questions in the field of food web ecology are not always congruent with parasitological inquiry. For example, topological analysis (the primary tool in food web studies focuses on only one of six important steps in trematode life cycles, each of which requires a stable community dynamic to evolve. In addition, these transmission strategies may also utilize pathways within the food web that are not considered in traditional food web investigations. It is asserted that more effort must be focused on parasite-centric models, and a central theme is that many different approaches will be required. One promising approach is the old energetic perspective, which considers energy as the critical resource for all organisms, and the currency of all food web interactions. From the parasitological point of view, energy can be used to characterize the roles of parasites at all levels in the food web, from individuals to populations to community. The literature on parasite energetics in food webs is very sparse, but the evidence suggests that parasite species richness is low in food webs because parasites are limited by the quantity of energy available to their unique lifestyles.

  19. Where are the parasites in food webs?

    Science.gov (United States)

    2012-01-01

    This review explores some of the reasons why food webs seem to contain relatively few parasite species when compared to the full diversity of free living species in the system. At present, there are few coherent food web theories to guide scientific studies on parasites, and this review posits that the methods, directions and questions in the field of food web ecology are not always congruent with parasitological inquiry. For example, topological analysis (the primary tool in food web studies) focuses on only one of six important steps in trematode life cycles, each of which requires a stable community dynamic to evolve. In addition, these transmission strategies may also utilize pathways within the food web that are not considered in traditional food web investigations. It is asserted that more effort must be focused on parasite-centric models, and a central theme is that many different approaches will be required. One promising approach is the old energetic perspective, which considers energy as the critical resource for all organisms, and the currency of all food web interactions. From the parasitological point of view, energy can be used to characterize the roles of parasites at all levels in the food web, from individuals to populations to community. The literature on parasite energetics in food webs is very sparse, but the evidence suggests that parasite species richness is low in food webs because parasites are limited by the quantity of energy available to their unique lifestyles. PMID:23092160

  20. Community food webs data and theory

    CERN Document Server

    Cohen, Joel E; Newman, Charles M

    1990-01-01

    Food webs hold a central place in ecology. They describe which organisms feed on which others in natural habitats. This book describes recently discovered empirical regularities in real food webs: it proposes a novel theory unifying many of these regularities, as well as extensive empirical data. After a general introduction, reviewing the empirical and theoretical discoveries about food webs, the second portion of the book shows that community food webs obey several striking phenomenological regularities. Some of these unify, regardless of habitat. Others differentiate, showing that habitat significantly influences structure. The third portion of the book presents a theoretical analysis of some of the unifying empirical regularities. The fourth portion of the book presents 13 community food webs. Collected from scattered sources and carefully edited, they are the empirical basis for the results in the volume. The largest available set of data on community food webs provides a valuable foundation for future s...

  1. Environmental controls on food web regimes: A fluvial perspective

    Science.gov (United States)

    Power, Mary E.

    2006-02-01

    Because food web regimes control the biomass of primary producers (e.g., plants or algae), intermediate consumers (e.g., invertebrates), and large top predators (tuna, killer whales), they are of societal as well as academic interest. Some controls over food web regimes may be internal, but many are mediated by conditions or fluxes over large spatial scales. To understand locally observed changes in food webs, we must learn more about how environmental gradients and boundaries affect the fluxes of energy, materials, or organisms through landscapes or seascapes that influence local species interactions. Marine biologists and oceanographers have overcome formidable challenges of fieldwork on the high seas to make remarkable progress towards this goal. In river drainage networks, we have opportunities to address similar questions at smaller spatial scales, in ecosystems with clear physical structure and organization. Despite these advantages, we still have much to learn about linkages between fluxes from watershed landscapes and local food webs in river networks. Longitudinal (downstream) gradients in productivity, disturbance regimes, and habitat structure exert strong effects on the organisms and energy sources of river food webs, but their effects on species interactions are just beginning to be explored. In fluid ecosystems with less obvious physical structure, like the open ocean, discerning features that control the movement of organisms and affect food web dynamics is even more challenging. In both habitats, new sensing, tracing and mapping technologies have revealed how landscape or seascape features (e.g., watershed divides, ocean fronts or circulation cells) channel, contain or concentrate organisms, energy and materials. Field experiments and direct in situ observations of basic natural history, however, remain as vital as ever in interpreting the responses of biota to these features. We need field data that quantify the many spatial and temporal scales of

  2. Integrating ecosystem engineering and food webs

    NARCIS (Netherlands)

    Sanders, D.; Jones, C.G.; Thébault, E.; Bouma, T.J.; van der Heide, T.; van Belzen, J.; Barot, S.

    2014-01-01

    Ecosystem engineering, the physical modification of the environment by organisms, is a common and often influential process whose significance to food web structure and dynamics is largely unknown. In the light of recent calls to expand food web studies to include non-trophic interactions, we

  3. Integrating ecosystem engineering and food webs

    NARCIS (Netherlands)

    Sanders, Dirk; Jones, Clive G.; Thebault, Elisa; Bouma, Tjeerd J.; van der Heide, Tjisse; van Belzen, Jim; Barot, Sebastien

    Ecosystem engineering, the physical modification of the environment by organisms, is a common and often influential process whose significance to food web structure and dynamics is largely unknown. In the light of recent calls to expand food web studies to include non-trophic interactions, we

  4. Graph Theory Approach for Studying Food Webs

    Science.gov (United States)

    Longjas, A.; Tejedor, A.; Foufoula-Georgiou, E.

    2017-12-01

    Food webs are complex networks of feeding interactions among species in ecological communities. Metrics describing food web structure have been proposed to compare and classify food webs ranging from food chain length, connectance, degree distribution, centrality measures, to the presence of motifs (distinct compartments), among others. However, formal methodologies for studying both food web topology and the dynamic processes operating on them are still lacking. Here, we utilize a quantitative framework using graph theory within which a food web is represented by a directed graph, i.e., a collection of vertices (species or trophic species defined as sets of species sharing the same predators and prey) and directed edges (predation links). This framework allows us to identify apex (environmental "source" node) to outlet (top predators) subnetworks and compute the steady-state flux (e.g., carbon, nutrients, energy etc.) in the food web. We use this framework to (1) construct vulnerability maps that quantify the relative change of flux delivery to the top predators in response to perturbations in prey species (2) identify keystone species, whose loss would precipitate further species extinction, and (3) introduce a suite of graph-theoretic metrics to quantify the topologic (imposed by food web connectivity) and dynamic (dictated by the flux partitioning and distribution) components of a food web's complexity. By projecting food webs into a 2D Topodynamic Complexity Space whose coordinates are given by Number of alternative paths (topologic) and Leakage Index (dynamic), we show that this space provides a basis for food web comparison and provide physical insights into their dynamic behavior.

  5. Impact of invasive plants on food webs and pathways

    OpenAIRE

    Sikai Wang; Qiang Sheng; Tianjiang Chu; Bo Li; Jiakuan Chen; Jihua Wu

    2013-01-01

    In natural ecosystems, energy mainly flows along food chains in food webs. Numerous studies have shown that plant invasions influence ecosystem functions through altering food webs. In recent decades, more attention has been paid to the effects of alien plants on local food webs. In this review, we analyze the influence of exotic plants on food webs and pathways, and explore the impacts of local food web characteristics on community invasibility. Invasive plants alter food webs mainly by chan...

  6. Food web topology and parasites in the pelagic zone of a subarctic lake

    Science.gov (United States)

    Amundsen, Per-Arne; Lafferty, K.D.; Knudsen, R.; Primicerio, R.; Klemetsen, A.; Kuris, A.M.

    2009-01-01

    Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3. More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4. For trophically transmitted parasites, the number of parasite-host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5. The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. ?? 2009 British Ecological Society.

  7. The Food Web of Potter Cove (Antarctica): complexity, structure and function

    Science.gov (United States)

    Marina, Tomás I.; Salinas, Vanesa; Cordone, Georgina; Campana, Gabriela; Moreira, Eugenia; Deregibus, Dolores; Torre, Luciana; Sahade, Ricardo; Tatián, Marcos; Barrera Oro, Esteban; De Troch, Marleen; Doyle, Santiago; Quartino, María Liliana; Saravia, Leonardo A.; Momo, Fernando R.

    2018-01-01

    Knowledge of the food web structure and complexity are central to better understand ecosystem functioning. A food-web approach includes both species and energy flows among them, providing a natural framework for characterizing species' ecological roles and the mechanisms through which biodiversity influences ecosystem dynamics. Here we present for the first time a high-resolution food web for a marine ecosystem at Potter Cove (northern Antarctic Peninsula). Eleven food web properties were analyzed in order to document network complexity, structure and topology. We found a low linkage density (3.4), connectance (0.04) and omnivory percentage (45), as well as a short path length (1.8) and a low clustering coefficient (0.08). Furthermore, relating the structure of the food web to its dynamics, an exponential degree distribution (in- and out-links) was found. This suggests that the Potter Cove food web may be vulnerable if the most connected species became locally extinct. For two of the three more connected functional groups, competition overlap graphs imply high trophic interaction between demersal fish and niche specialization according to feeding strategies in amphipods. On the other hand, the prey overlap graph shows also that multiple energy pathways of carbon flux exist across benthic and pelagic habitats in the Potter Cove ecosystem. Although alternative food sources might add robustness to the web, network properties (low linkage density, connectance and omnivory) suggest fragility and potential trophic cascade effects.

  8. Adaptive foraging and flexible food web topology

    Czech Academy of Sciences Publication Activity Database

    Křivan, Vlastimil; Schmitz, O.

    2003-01-01

    Roč. 5, - (2003), s. 623-652 ISSN 1522-0613 R&D Projects: GA ČR GA201/03/0091 Institutional research plan: CEZ:AV0Z5007907 Keywords : adaptive foraging * food chain * food web structure Subject RIV: EH - Ecology, Behaviour Impact factor: 1.587, year: 2003

  9. Zinc in an ultraoligotrophic lake food web.

    Science.gov (United States)

    Montañez, Juan Cruz; Arribére, María A; Rizzo, Andrea; Arcagni, Marina; Campbell, Linda; Ribeiro Guevara, Sergio

    2018-03-21

    Zinc (Zn) bioaccumulation and trophic transfer were analyzed in the food web of Lake Nahuel Huapi, a deep, unpolluted ultraoligotrophic system in North Patagonia. Benthic macroinvertebrates, plankton, and native and introduced fish were collected at three sites. The effect of pyroclastic inputs on Zn levels in lacustrine food webs was assessed by studying the impact of the eruption of Puyehue-Cordón Caulle volcanic complex (PCCVC) in 2011, by performing three sampling campaigns immediately before and after the PCCVC eruption, and after 2 years of recovery of the ecosystem. Zinc trophodynamics in L. Nahuel Huapi food web was assessed using nitrogen stable isotopes (δ 15 N). There was no significant increase of Zn concentrations ([Zn]) in L. Nahuel Huapi biota after the PCCVC eruption, despite the evidence of [Zn] increase in lake water that could be associated with volcanic ash leaching. The organisms studied exhibited [Zn] above the threshold level considered for dietary deficiency, regulating Zn adequately even under a catastrophic situations like PCCVC 2011 eruption. Zinc concentrations exhibited a biodilution pattern in the lake's food web. To the best of our knowledge, present research is the first report of Zn biodilution in lacustrine systems, and the first to study Zn transfer in a freshwater food web including both pelagic and benthic compartments.

  10. Food-Web Structure in Relation to Environmental Gradients and Predator-Prey Ratios in Tank-Bromeliad Ecosystems

    Science.gov (United States)

    Dézerald, Olivier; Leroy, Céline; Corbara, Bruno; Carrias, Jean-François; Pélozuelo, Laurent; Dejean, Alain; Céréghino, Régis

    2013-01-01

    Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators:prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests. PMID:23977128

  11. Keystone species and food webs.

    Science.gov (United States)

    Jordán, Ferenc

    2009-06-27

    Different species are of different importance in maintaining ecosystem functions in natural communities. Quantitative approaches are needed to identify unusually important or influential, 'keystone' species particularly for conservation purposes. Since the importance of some species may largely be the consequence of their rich interaction structure, one possible quantitative approach to identify the most influential species is to study their position in the network of interspecific interactions. In this paper, I discuss the role of network analysis (and centrality indices in particular) in this process and present a new and simple approach to characterizing the interaction structures of each species in a complex network. Understanding the linkage between structure and dynamics is a condition to test the results of topological studies, I briefly overview our current knowledge on this issue. The study of key nodes in networks has become an increasingly general interest in several disciplines: I will discuss some parallels. Finally, I will argue that conservation biology needs to devote more attention to identify and conserve keystone species and relatively less attention to rarity.

  12. Non-random food-web assembly at habitat edges increases connectivity and functional redundancy.

    Science.gov (United States)

    Peralta, Guadalupe; Frost, Carol M; Didham, Raphael K; Rand, Tatyana A; Tylianakis, Jason M

    2017-04-01

    Habitat fragmentation dramatically alters the spatial configuration of landscapes, with the creation of artificial edges affecting community structure and dynamics. Despite this, it is not known how the different food webs in adjacent habitats assemble at their boundaries. Here we demonstrate that the composition and structure of herbivore-parasitoid food webs across edges between native and plantation forests are not randomly assembled from those of the adjacent communities. Rather, elevated proportions of abundant, interaction-generalist parasitoid species at habitat edges allowed considerable interaction rewiring, which led to higher linkage density and less modular networks, with higher parasitoid functional redundancy. This was despite high overlap in host composition between edges and interiors. We also provide testable hypotheses for how food webs may assemble between habitats with lower species overlap. In an increasingly fragmented world, non-random assembly of food webs at edges may increasingly affect community dynamics at the landscape level. © 2016 by the Ecological Society of America.

  13. Parasites in the Wadden Sea food web

    NARCIS (Netherlands)

    Thieltges, D.W.; Engelsma, M.Y.; Wendling, C.C.; Wegner, K.M.

    2013-01-01

    While the free-living fauna of the Wadden Sea has received much interest, little is known on the distribution and effects of parasites in the Wadden Sea food web. However, recent studies on this special type of trophic interaction indicate a high diversity of parasites in the Wadden Sea and suggest

  14. Linking structure and function in food webs: maximization of different ecological functions generates distinct food web structures.

    Science.gov (United States)

    Yen, Jian D L; Cabral, Reniel B; Cantor, Mauricio; Hatton, Ian; Kortsch, Susanne; Patrício, Joana; Yamamichi, Masato

    2016-03-01

    Trophic interactions are central to ecosystem functioning, but the link between food web structure and ecosystem functioning remains obscure. Regularities (i.e. consistent patterns) in food web structure suggest the possibility of regularities in ecosystem functioning, which might be used to relate structure to function. We introduce a novel, genetic algorithm approach to simulate food webs with maximized throughput (a proxy for ecosystem functioning) and compare the structure of these simulated food webs to real empirical food webs using common metrics of food web structure. We repeat this analysis using robustness to secondary extinctions (a proxy for ecosystem resilience) instead of throughput to determine the relative contributions of ecosystem functioning and ecosystem resilience to food web structure. Simulated food webs that maximized robustness were similar to real food webs when connectance (i.e. levels of interaction across the food web) was high, but this result did not extend to food webs with low connectance. Simulated food webs that maximized throughput or a combination of throughput and robustness were not similar to any real food webs. Simulated maximum-throughput food webs differed markedly from maximum-robustness food webs, which suggests that maximizing different ecological functions can generate distinct food web structures. Based on our results, food web structure would appear to have a stronger relationship with ecosystem resilience than with ecosystem throughput. Our genetic algorithm approach is general and is well suited to large, realistically complex food webs. Genetic algorithms can incorporate constraints on structure and can generate outputs that can be compared directly to empirical data. Our method can be used to explore a range of maximization or minimization hypotheses, providing new perspectives on the links between structure and function in ecological systems. © 2015 The Authors. Journal of Animal Ecology © 2015 British

  15. Food-web dynamics under climate change

    DEFF Research Database (Denmark)

    Zhang, L.; Takahashi, M.; Hartvig, Martin

    2017-01-01

    Climate change affects ecological communities through its impact on the physiological performance of individuals. However, the population dynamic of species well inside their thermal niche is also determined by competitors, prey and predators, in addition to being influenced by temperature changes....... We use a trait-based food-web model to examine how the interplay between the direct physiological effects from temperature and the indirect effects due to changing interactions between populations shapes the ecological consequences of climate change for populations and for entire communities. Our...... climatically well-adapted species may be brought to extinction by the changed food-web topology. Our results highlight that the impact of climate change on specific populations is largely unpredictable, and apparently well-adapted species may be severely impacted...

  16. Food-web dynamics under climate change

    DEFF Research Database (Denmark)

    Zhang, L.; Takahashi, M.; Hartvig, Martin

    2017-01-01

    . We use a trait-based food-web model to examine how the interplay between the direct physiological effects from temperature and the indirect effects due to changing interactions between populations shapes the ecological consequences of climate change for populations and for entire communities. Our......Climate change affects ecological communities through its impact on the physiological performance of individuals. However, the population dynamic of species well inside their thermal niche is also determined by competitors, prey and predators, in addition to being influenced by temperature changes...... climatically well-adapted species may be brought to extinction by the changed food-web topology. Our results highlight that the impact of climate change on specific populations is largely unpredictable, and apparently well-adapted species may be severely impacted...

  17. Parasites in food webs: the ultimate missing links

    Science.gov (United States)

    Lafferty, Kevin D.; Allesina, Stefano; Arim, Matias; Briggs, Cherie J.; De Leo, Giulio A.; Dobson, Andrew P.; Dunne, Jennifer A.; Johnson, Pieter T.J.; Kuris, Armand M.; Marcogliese, David J.; Martinez, Neo D.; Memmott, Jane; Marquet, Pablo A.; McLaughlin, John P.; Mordecai, Eerin A.; Pascual, Mercedes; Poulin, Robert; Thieltges, David W.

    2008-01-01

    Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists.

  18. Detrital shadows: estuarine food web connectivity depends on fluvial influence and consumer feeding mode.

    Science.gov (United States)

    Howe, Emily; Simenstad, Charles A; Ogston, Andrea

    2017-10-01

    We measured the influence of landscape setting on estuarine food web connectivity in five macrotidal Pacific Northwest estuaries across a gradient of freshwater influence. We used stable isotopes (δ 13 C, δ 15 N, δ 34 S) in combination with a Bayesian mixing model to trace primary producer contributions to suspension- and deposit-feeding bivalve consumers (Mytilus trossulus and Macoma nasuta) transplanted into three estuarine vegetation zones: emergent marsh, mudflat, and eelgrass. Eelgrass includes both Japanese eelgrass (Zostera japonica) and native eelgrass (Zostera marina). Fluvial discharge and consumer feeding mode strongly influenced the strength and spatial scale of observed food web linkages, while season played a secondary role. Mussels displayed strong cross-ecosystem connectivity in all estuaries, with decreasing marine influence in the more fluvial estuaries. Mussel diets indicated homogenization of detrital sources within the water column of each estuary. In contrast, the diets of benthic deposit-feeding clams indicated stronger compartmentalization in food web connectivity, especially in the largest river delta where clam diets were trophically disconnected from marsh sources of detritus. This suggests detritus deposition is patchy across space, and less homogenous than the suspended detritus pool. In addition to fluvial setting, other estuary-specific environmental drivers, such as marsh area or particle transport speed, influenced the degree of food web linkages across space and time, often accounting for unexpected patterns in food web connectivity. Transformations of the estuarine landscape that alter river hydrology or availability of detritus sources can thus potentially disrupt natural food web connectivity at the landscape scale, especially for sedentary organisms, which cannot track their food sources through space. © 2017 by the Ecological Society of America.

  19. Food Insecurity and Conflict Dynamics: Causal Linkages and Complex Feedbacks

    Directory of Open Access Journals (Sweden)

    Cullen Hendrix

    2013-06-01

    Full Text Available This paper addresses two related topics: 1 the circular link between food insecurity and conflict, with particular emphasis on the Sahel, and 2 the potential role of food security interventions in reducing the risk of violent conflicts. While we eschew mono-causal explanations of conflict, acute food insecurity can be a factor in popular mobilization and a risk multiplier. Moreover, violent conflict itself is a major driver of acute food insecurity. If food insecurity is a threat multiplier for conflict, improving food security can reduce tensions and contribute to more stable environments. If these interventions are done right, the vicious cycle of food insecurity and conflict can be transformed into a virtuous cycle of food security and stability that provides peace dividends, reduces conflict drivers, enhances social cohesion, rebuilds social trust, and builds the legitimacy and capacity of governments.

  20. Food Enterprise Web Design Based on User Experience

    OpenAIRE

    Fei Wang

    2015-01-01

    Excellent auxiliary food enterprise web design conveyed good visual transmission effect through user experience. This study was based on the food enterprise managers and customers as the main operating object to get the performance of the web page creation, web page design not only focused on the function and work efficiency, the most important thing was that the user experience in the process of web page interaction.

  1. Mercury bioaccumulation in estuarine food webs.

    Science.gov (United States)

    Fry, Brian; Chumchal, Matthew M

    2012-03-01

    We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone, USA. Barataria Bay and Breton Sound are two neighboring deltaic estuaries that were isolated by levees from the Mississippi River about 100 years ago. These estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected > 2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: (H1) Background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and (H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and -2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (> 10 years) diversion inputs had -1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable-isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion

  2. Fostering sustainable urban-rural linkages through local food supply

    NARCIS (Netherlands)

    Viegas Preiss, Potira; Charão-Marques, Flávia; Wiskerke, Johannes S.C.

    2017-01-01

    The mainstream system of food supply has been heavily criticized in the last years due to its social and environmental impacts. Direct food purchasing schemes have emerged in recent decades as a form of supply that may be more ecologically sound and socially just, while allowing for a closer

  3. Food and beverage advertising on children's web sites.

    Science.gov (United States)

    Ustjanauskas, A E; Harris, J L; Schwartz, M B

    2014-10-01

    Food marketing contributes to childhood obesity. Food companies commonly place display advertising on children's web sites, but few studies have investigated this form of advertising. Document the number of food and beverage display advertisements viewed on popular children's web sites, nutritional quality of advertised brands and proportion of advertising approved by food companies as healthier dietary choices for child-directed advertising. Syndicated Internet exposure data identified popular children's web sites and food advertisements viewed on these web sites from July 2009 through June 2010. Advertisements were classified according to food category and companies' participation in food industry self-regulation. The percent of advertisements meeting government-proposed nutrition standards was calculated. 3.4 billion food advertisements appeared on popular children's web sites; 83% on just four web sites. Breakfast cereals and fast food were advertised most often (64% of ads). Most ads (74%) promoted brands approved by companies for child-directed advertising, but 84% advertised products that were high in fat, sugar and/or sodium. Ads for foods designated by companies as healthier dietary choices appropriate for child-directed advertising were least likely to meet independent nutrition standards. Most foods advertised on popular children's web sites do not meet independent nutrition standards. Further improvements to industry self-regulation are required. © 2013 The Authors. Pediatric Obesity © 2013 International Association for the Study of Obesity.

  4. Ecological networks--beyond food webs.

    Science.gov (United States)

    Ings, Thomas C; Montoya, José M; Bascompte, Jordi; Blüthgen, Nico; Brown, Lee; Dormann, Carsten F; Edwards, François; Figueroa, David; Jacob, Ute; Jones, J Iwan; Lauridsen, Rasmus B; Ledger, Mark E; Lewis, Hannah M; Olesen, Jens M; van Veen, F J Frank; Warren, Phil H; Woodward, Guy

    2009-01-01

    1. A fundamental goal of ecological network research is to understand how the complexity observed in nature can persist and how this affects ecosystem functioning. This is essential for us to be able to predict, and eventually mitigate, the consequences of increasing environmental perturbations such as habitat loss, climate change, and invasions of exotic species. 2. Ecological networks can be subdivided into three broad types: 'traditional' food webs, mutualistic networks and host-parasitoid networks. There is a recent trend towards cross-comparisons among network types and also to take a more mechanistic, as opposed to phenomenological, perspective. For example, analysis of network configurations, such as compartments, allows us to explore the role of co-evolution in structuring mutualistic networks and host-parasitoid networks, and of body size in food webs. 3. Research into ecological networks has recently undergone a renaissance, leading to the production of a new catalogue of evermore complete, taxonomically resolved, and quantitative data. Novel topological patterns have been unearthed and it is increasingly evident that it is the distribution of interaction strengths and the configuration of complexity, rather than just its magnitude, that governs network stability and structure. 4. Another significant advance is the growing recognition of the importance of individual traits and behaviour: interactions, after all, occur between individuals. The new generation of high-quality networks is now enabling us to move away from describing networks based on species-averaged data and to start exploring patterns based on individuals. Such refinements will enable us to address more general ecological questions relating to foraging theory and the recent metabolic theory of ecology. 5. We conclude by suggesting a number of 'dead ends' and 'fruitful avenues' for future research into ecological networks.

  5. Carbon Cycling in Floodplain Ecosystems: Out-Gassing and Photosynthesis Transmit Soil d13C Gradient Through Stream Food Webs

    DEFF Research Database (Denmark)

    Gray, Duncan P.; Harding, Jon S.; Elberling, Bo

    2011-01-01

    of carbon that drive these productive spring-fed systems are not well-known. We conducted field assessments and a manipulation, modeling, and a laboratory experiment to address this issue. Initially d13C values of both dissolved inorganic carbon (DIC) and food-web components of five springs were used...... to assess the sources of carbon to spring food webs. Partial pressures of CO2 in upwelling water ranged from 2 to 7 times atmospheric pressure, but rapidly approached equilibrium with the atmosphere downstream commensurate with 13C enrichment of DIC. Speciation modeling and a laboratory out...... was transmitted through three trophic levels of the spring food web. These findings indicate dependency on groundwater inorganic carbon by spring stream food webs and strong hydrologically mediated linkages connecting terrestrial, subsurface, and aquatic components of the floodplain....

  6. Characteristics of Food Industry Web Sites and "Advergames" Targeting Children

    Science.gov (United States)

    Culp, Jennifer; Bell, Robert A.; Cassady, Diana

    2010-01-01

    Objective: To assess the content of food industry Web sites targeting children by describing strategies used to prolong their visits and foster brand loyalty; and to document health-promoting messages on these Web sites. Design: A content analysis was conducted of Web sites advertised on 2 children's networks, Cartoon Network and Nickelodeon. A…

  7. Deep pelagic food web structure as revealed by in situ feeding observations.

    Science.gov (United States)

    Choy, C Anela; Haddock, Steven H D; Robison, Bruce H

    2017-12-06

    Food web linkages, or the feeding relationships between species inhabiting a shared ecosystem, are an ecological lens through which ecosystem structure and function can be assessed, and thus are fundamental to informing sustainable resource management. Empirical feeding datasets have traditionally been painstakingly generated from stomach content analysis, direct observations and from biochemical trophic markers (stable isotopes, fatty acids, molecular tools). Each approach carries inherent biases and limitations, as well as advantages. Here, using 27 years (1991-2016) of in situ feeding observations collected by remotely operated vehicles (ROVs), we quantitatively characterize the deep pelagic food web of central California within the California Current, complementing existing studies of diet and trophic interactions with a unique perspective. Seven hundred and forty-three independent feeding events were observed with ROVs from near-surface waters down to depths approaching 4000 m, involving an assemblage of 84 different predators and 82 different prey types, for a total of 242 unique feeding relationships. The greatest diversity of prey was consumed by narcomedusae, followed by physonect siphonophores, ctenophores and cephalopods. We highlight key interactions within the poorly understood 'jelly web', showing the importance of medusae, ctenophores and siphonophores as key predators, whose ecological significance is comparable to large fish and squid species within the central California deep pelagic food web. Gelatinous predators are often thought to comprise relatively inefficient trophic pathways within marine communities, but we build upon previous findings to document their substantial and integral roles in deep pelagic food webs. © 2017 The Authors.

  8. Species richness and trophic diversity increase decomposition in a co-evolved food web.

    Directory of Open Access Journals (Sweden)

    Benjamin Baiser

    Full Text Available Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators--larvae of the pitcher-plant mosquito--indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

  9. Infectious disease agents mediate interaction in food webs and ecosystems

    NARCIS (Netherlands)

    Selakovic, S.; Ruiter, de P.C.; Heesterbeek, J.A.P.

    2014-01-01

    Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows

  10. Gaining insight into food webs reconstructed by the inverse method

    NARCIS (Netherlands)

    Kones, J.; Soetaert, K.E.R.; Van Oevelen, D.; Owino, J.; Mavuti, K.

    2006-01-01

    The use of the inverse method to analyze flow patterns of organic components in ecological systems has had wide application in ecological modeling. Through this approach, an infinite number of food web flows describing the food web and satisfying biological constraints are generated, from which one

  11. Major dimensions in food-web structure properties

    NARCIS (Netherlands)

    Vermaat, J.E.; Dunne, J. A.; Gilbert, A.J.

    2009-01-01

    The covariance among a range of 20 network structural properties of food webs plus net primary productivity was assessed for 14 published food webs using principal components analysis. Three primary components explained 84% of the variability in the data sets, suggesting substantial covariance among

  12. Infectious disease agents mediate interaction in food webs and ecosystems.

    NARCIS (Netherlands)

    Selakovic, Sanja; de Ruiter, P.C.; Heesterbeek, Hans

    2014-01-01

    Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows

  13. Food web framework for size-structured populations

    DEFF Research Database (Denmark)

    Hartvig, Martin; Andersen, Ken Haste; Beyer, Jan

    2011-01-01

    We synthesise traditional unstructured food webs, allometric body size scaling, trait-based modelling, and physiologically structured modelling to provide a novel and ecologically relevant tool for size-structured food webs. The framework allows food web models to include ontogenetic growth....... Parameter values are determined from cross-species analysis of fish communities as life-history omnivory is widespread in aquatic systems, but may be reparameterised for other systems. An ensemble of food webs is generated and the resulting communities are analysed at four levels of organisation: community...... level, species level, trait level, and individual level. The model may be solved analytically by assuming that the community spectrum follows a power law. The analytical solution provides a baseline expectation of the results of complex food web simulations, and agrees well with the predictions...

  14. Using stable isotopes to differentiate trophic feeding channels within soil food webs.

    Science.gov (United States)

    Crotty, Felicity V; Adl, Sina M; Blackshaw, Rod P; Murray, Philip J

    2012-01-01

    The soil is probably the most diverse habitat there is, with organisms ranging in sizes from less than 1 μm to several metres in length. However, it is increasingly evident that we know little about the interactions occurring between these organisms, the functions that they perform as individual species, or together within their different feeding guilds. These interactions between groups of organisms and physical and chemical processes shape the soil as a habitat and influence the nature of the soil food web with consequences for the above-ground vegetation and food web. Protists are known as one of the most abundant groups of bacterivores within the soil; however, they are also consumers of a number of other food sources. Even though they are responsible for a large proportion of the mineralisation of bacterial biomass and have a large impact on the C and N cycles within the soil they are regularly overlooked when investigating the complete soil food web. Recently, stable isotopes have been used to determine trophic interactions and here we describe how this technique has been used to highlight linkages between protists and the soil food web. © 2012 The Author(s) Journal of Eukaryotic Microbiology © 2012 International Society of Protistologists.

  15. Soil food web changes during spontaneous succession at post mining sites: a possible ecosystem engineering effect on food web organization?

    Science.gov (United States)

    Frouz, Jan; Thébault, Elisa; Pižl, Václav; Adl, Sina; Cajthaml, Tomáš; Baldrián, Petr; Háněl, Ladislav; Starý, Josef; Tajovský, Karel; Materna, Jan; Nováková, Alena; de Ruiter, Peter C

    2013-01-01

    Parameters characterizing the structure of the decomposer food web, biomass of the soil microflora (bacteria and fungi) and soil micro-, meso- and macrofauna were studied at 14 non-reclaimed 1- 41-year-old post-mining sites near the town of Sokolov (Czech Republic). These observations on the decomposer food webs were compared with knowledge of vegetation and soil microstructure development from previous studies. The amount of carbon entering the food web increased with succession age in a similar way as the total amount of C in food web biomass and the number of functional groups in the food web. Connectance did not show any significant changes with succession age, however. In early stages of the succession, the bacterial channel dominated the food web. Later on, in shrub-dominated stands, the fungal channel took over. Even later, in the forest stage, the bacterial channel prevailed again. The best predictor of fungal bacterial ratio is thickness of fermentation layer. We argue that these changes correspond with changes in topsoil microstructure driven by a combination of plant organic matter input and engineering effects of earthworms. In early stages, soil is alkaline, and a discontinuous litter layer on the soil surface promotes bacterial biomass growth, so the bacterial food web channel can dominate. Litter accumulation on the soil surface supports the development of the fungal channel. In older stages, earthworms arrive, mix litter into the mineral soil and form an organo-mineral topsoil, which is beneficial for bacteria and enhances the bacterial food web channel.

  16. Food web structure in a harsh glacier-fed river.

    Directory of Open Access Journals (Sweden)

    Leonie R Clitherow

    Full Text Available Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the Ödenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13-22, highly connected individuals (directed connectance up to 0.19 and short mean food chain length (2.00-2.36. The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs.

  17. Food-web dynamics in a large river discontinuum

    Science.gov (United States)

    Cross, Wyatt F.; Baxter, Colden V.; Rosi-Marshall, Emma J.; Hall, Robert O.; Kennedy, Theodore A.; Donner, Kevin C.; Kelly, Holly A. Wellard; Seegert, Sarah E.Z.; Behn, Kathrine E.; Yard, Michael D.

    2013-01-01

    Nearly all ecosystems have been altered by human activities, and most communities are now composed of interacting species that have not co-evolved. These changes may modify species interactions, energy and material flows, and food-web stability. Although structural changes to ecosystems have been widely reported, few studies have linked such changes to dynamic food-web attributes and patterns of energy flow. Moreover, there have been few tests of food-web stability theory in highly disturbed and intensely managed freshwater ecosystems. Such synthetic approaches are needed for predicting the future trajectory of ecosystems, including how they may respond to natural or anthropogenic perturbations. We constructed flow food webs at six locations along a 386-km segment of the Colorado River in Grand Canyon (Arizona, USA) for three years. We characterized food-web structure and production, trophic basis of production, energy efficiencies, and interaction-strength distributions across a spatial gradient of perturbation (i.e., distance from Glen Canyon Dam), as well as before and after an experimental flood. We found strong longitudinal patterns in food-web characteristics that strongly correlated with the spatial position of large tributaries. Above tributaries, food webs were dominated by nonnative New Zealand mudsnails (62% of production) and nonnative rainbow trout (100% of fish production). The simple structure of these food webs led to few dominant energy pathways (diatoms to few invertebrate taxa to rainbow trout), large energy inefficiencies (i.e., Below large tributaries, invertebrate production declined ∼18-fold, while fish production remained similar to upstream sites and comprised predominately native taxa (80–100% of production). Sites below large tributaries had increasingly reticulate and detritus-based food webs with a higher prevalence of omnivory, as well as interaction strength distributions more typical of theoretically stable food webs (i

  18. Food marketing on popular children's web sites: a content analysis.

    Science.gov (United States)

    Alvy, Lisa M; Calvert, Sandra L

    2008-04-01

    In 2006 the Institute of Medicine (IOM) concluded that food marketing was a contributor to childhood obesity in the United States. One recommendation of the IOM committee was for research on newer marketing venues, such as Internet Web sites. The purpose of this cross-sectional study was to answer the IOM's call by examining food marketing on popular children's Web sites. Ten Web sites were selected based on market research conducted by KidSay, which identified favorite sites of children aged 8 to 11 years during February 2005. Using a standardized coding form, these sites were examined page by page for the existence, type, and features of food marketing. Web sites were compared using chi2 analyses. Although food marketing was not pervasive on the majority of the sites, seven of the 10 Web sites contained food marketing. The products marketed were primarily candy, cereal, quick serve restaurants, and snacks. Candystand.com, a food product site, contained a significantly greater amount of food marketing than the other popular children's Web sites. Because the foods marketed to children are not consistent with a healthful diet, nutrition professionals should consider joining advocacy groups to pressure industry to reduce online food marketing directed at youth.

  19. Landscape variation influences trophic cascades in dengue vector food webs.

    Science.gov (United States)

    Weterings, Robbie; Umponstira, Chanin; Buckley, Hannah L

    2018-02-01

    The epidemiology of vector-borne diseases is governed by a structured array of correlative and causative factors, including landscape (for example, rural versus urban), abiotic (for example, weather), and biotic (for example, food web) factors. Studies of mosquito-borne diseases rarely address these multiple factors at large spatial scales, which limits insights into how human alterations of landscapes and food webs alter mosquito abundance. We used structural equation modeling to identify the relative magnitude and direction of landscape, abiotic, and food web factors on Aedes larvae and adults across 70 sites in northern Thailand. Food web factors were modeled as mosquito-predator trophic cascades. Landscape context affected mosquito-predator communities in aquatic and terrestrial environments via cascading food web interactions. Several mosquito predators within these food webs showed potential as biocontrol agents in mosquito population control, but their potentials for control were landscape-dependent. In terrestrial food webs, the habitat-sensitive tokay gecko structured mosquito-predator communities, indicating that a conservation approach to vector control could be a useful addition to existing control efforts.

  20. Isotopic diversity indices: how sensitive to food web structure?

    Directory of Open Access Journals (Sweden)

    Anik Brind'Amour

    Full Text Available Recently revisited, the concept of niche ecology has lead to the formalisation of functional and trophic niches using stable isotope ratios. Isotopic diversity indices (IDI derived from a set of measures assessing the dispersion/distribution of points in the δ-space were recently suggested and increasingly used in the literature. However, three main critics emerge from the use of these IDI: 1 they fail to account for the isotopic sources overlap, 2 some indices are highly sensitive to the number of species and/or the presence of rare species, and 3 the lack of standardization prevents any spatial and temporal comparisons. Using simulations we investigated the ability of six commonly used IDI to discriminate among different trophic food web structures, with a focus on the first two critics. We tested the sensitivity of the IDI to five food web structures along a gradient of sources overlap, varying from two distinct food chains with differentiated sources to two superimposed food chains sharing two sources. For each of the food web structure we varied the number of species (from 10 to 100 species and the type of species feeding behaviour (i.e. random or selective feeding. Values of IDI were generally larger in food webs with distinct basal sources and tended to decrease as the superimposition of the food chains increased. This was more pronounced when species displayed food preferences in comparison to food webs where species fed randomly on any prey. The number of species composing the food web also had strong effects on the metrics, including those that were supposedly less sensitive to small sample size. In all cases, computing IDI on food webs with low numbers of species always increases the uncertainty of the metrics. A threshold of ~20 species was detected above which several metrics can be safely used.

  1. Isotopic diversity indices: how sensitive to food web structure?

    Science.gov (United States)

    Brind'Amour, Anik; Dubois, Stanislas F

    2013-01-01

    Recently revisited, the concept of niche ecology has lead to the formalisation of functional and trophic niches using stable isotope ratios. Isotopic diversity indices (IDI) derived from a set of measures assessing the dispersion/distribution of points in the δ-space were recently suggested and increasingly used in the literature. However, three main critics emerge from the use of these IDI: 1) they fail to account for the isotopic sources overlap, 2) some indices are highly sensitive to the number of species and/or the presence of rare species, and 3) the lack of standardization prevents any spatial and temporal comparisons. Using simulations we investigated the ability of six commonly used IDI to discriminate among different trophic food web structures, with a focus on the first two critics. We tested the sensitivity of the IDI to five food web structures along a gradient of sources overlap, varying from two distinct food chains with differentiated sources to two superimposed food chains sharing two sources. For each of the food web structure we varied the number of species (from 10 to 100 species) and the type of species feeding behaviour (i.e. random or selective feeding). Values of IDI were generally larger in food webs with distinct basal sources and tended to decrease as the superimposition of the food chains increased. This was more pronounced when species displayed food preferences in comparison to food webs where species fed randomly on any prey. The number of species composing the food web also had strong effects on the metrics, including those that were supposedly less sensitive to small sample size. In all cases, computing IDI on food webs with low numbers of species always increases the uncertainty of the metrics. A threshold of ~20 species was detected above which several metrics can be safely used.

  2. Compilation and network analyses of cambrian food webs.

    Directory of Open Access Journals (Sweden)

    Jennifer A Dunne

    2008-04-01

    Full Text Available A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid

  3. Using food-web theory to conserve ecosystems

    Science.gov (United States)

    McDonald-Madden, E.; Sabbadin, R.; Game, E. T.; Baxter, P. W. J.; Chadès, I.; Possingham, H. P.

    2016-01-01

    Food-web theory can be a powerful guide to the management of complex ecosystems. However, we show that indices of species importance common in food-web and network theory can be a poor guide to ecosystem management, resulting in significantly more extinctions than necessary. We use Bayesian Networks and Constrained Combinatorial Optimization to find optimal management strategies for a wide range of real and hypothetical food webs. This Artificial Intelligence approach provides the ability to test the performance of any index for prioritizing species management in a network. While no single network theory index provides an appropriate guide to management for all food webs, a modified version of the Google PageRank algorithm reliably minimizes the chance and severity of negative outcomes. Our analysis shows that by prioritizing ecosystem management based on the network-wide impact of species protection rather than species loss, we can substantially improve conservation outcomes. PMID:26776253

  4. Food Web Assembly Rules for Generalized Lotka-Volterra Equations

    DEFF Research Database (Denmark)

    Härter, Jan Olaf Mirko; Mitarai, Namiko; Sneppen, Kim

    2016-01-01

    In food webs, many interacting species coexist despite the restrictions imposed by the competitive exclusion principle and apparent competition. For the generalized Lotka-Volterra equations, sustainable coexistence necessitates nonzero determinant of the interaction matrix. Here we show that this...

  5. An experimental test of a fundamental food web motif.

    Science.gov (United States)

    Rip, Jason M K; McCann, Kevin S; Lynn, Denis H; Fawcett, Sonia

    2010-06-07

    Large-scale changes to the world's ecosystem are resulting in the deterioration of biostructure-the complex web of species interactions that make up ecological communities. A difficult, yet crucial task is to identify food web structures, or food web motifs, that are the building blocks of this baroque network of interactions. Once identified, these food web motifs can then be examined through experiments and theory to provide mechanistic explanations for how structure governs ecosystem stability. Here, we synthesize recent ecological research to show that generalist consumers coupling resources with different interaction strengths, is one such motif. This motif amazingly occurs across an enormous range of spatial scales, and so acts to distribute coupled weak and strong interactions throughout food webs. We then perform an experiment that illustrates the importance of this motif to ecological stability. We find that weak interactions coupled to strong interactions by generalist consumers dampen strong interaction strengths and increase community stability. This study takes a critical step by isolating a common food web motif and through clear, experimental manipulation, identifies the fundamental stabilizing consequences of this structure for ecological communities.

  6. Eelgrass (Zostera marina Food Web Structure in Different Environmental Settings.

    Directory of Open Access Journals (Sweden)

    Jonas Thormar

    Full Text Available This study compares the structure of eelgrass (Zostera marina L. meadows and associated food webs in two eelgrass habitats in Denmark, differing in exposure, connection to the open sea, nutrient enrichment and water transparency. Meadow structure strongly reflected the environmental conditions in each habitat. The eutrophicated, protected site had higher biomass of filamentous algae, lower eelgrass biomass and shoot density, longer and narrower leaves, and higher above to below ground biomass ratio compared to the less nutrient-enriched and more exposed site. The faunal community composition and food web structure also differed markedly between sites with the eutrophicated, enclosed site having higher biomass of consumers and less complex food web. These relationships resulted in a column shaped biomass distribution of the consumers at the eutrophicated site whereas the less nutrient-rich site showed a pyramidal biomass distribution of consumers coupled with a more diverse consumer community. The differences in meadow and food web structure of the two seagrass habitats, suggest how physical setting may shape ecosystem response and resilience to anthropogenic pressure. We encourage larger, replicated studies to further disentangle the effects of different environmental variables on seagrass food web structure.

  7. Global change in the trophic functioning of marine food webs.

    Directory of Open Access Journals (Sweden)

    Aurore Maureaud

    Full Text Available The development of fisheries in the oceans, and other human drivers such as climate warming, have led to changes in species abundance, assemblages, trophic interactions, and ultimately in the functioning of marine food webs. Here, using a trophodynamic approach and global databases of catches and life history traits of marine species, we tested the hypothesis that anthropogenic ecological impacts may have led to changes in the global parameters defining the transfers of biomass within the food web. First, we developed two indicators to assess such changes: the Time Cumulated Indicator (TCI measuring the residence time of biomass within the food web, and the Efficiency Cumulated Indicator (ECI quantifying the fraction of secondary production reaching the top of the trophic chain. Then, we assessed, at the large marine ecosystem scale, the worldwide change of these two indicators over the 1950-2010 time-periods. Global trends were identified and cluster analyses were used to characterize the variability of trends between ecosystems. Results showed that the most common pattern over the study period is a global decrease in TCI, while the ECI indicator tends to increase. Thus, changes in species assemblages would induce faster and apparently more efficient biomass transfers in marine food webs. Results also suggested that the main driver of change over that period had been the large increase in fishing pressure. The largest changes occurred in ecosystems where 'fishing down the marine food web' are most intensive.

  8. An isotopic investigation of mercury accumulation in terrestrial food webs adjacent to an Arctic seabird colony

    International Nuclear Information System (INIS)

    Choy, Emily S.; Gauthier, Martine; Mallory, Mark L.; Smol, John P.; Douglas, Marianne S.V.; Lean, David; Blais, Jules M.

    2010-01-01

    At Cape Vera (Devon Island, Nunavut, Canada), a seabird colony of northern fulmars (Fulmarus glacialis) congregates and releases nutrients through the deposition of guano to the coastal terrestrial environment, thus creating nutrient-fertilized habitats important to insects, birds, and mammals. Here we determined whether mercury was similarly enriched in various terrestrial food web components in this High Arctic coastal ecosystem due to seabird inputs. Stable isotopes (δ 15 N, δ 13 C) were used to identify trophic linkages and possible routes of contaminant transfer in the food web. Values of δ 15 N were significantly higher in lichens and certain plants collected closer to the bird colony, demonstrating a gradient of seabird influence, and were higher at Cape Vera than our reference site at Cape Herschel, on eastern Ellesmere Island, an area relatively unaffected by seabirds. In contrast, δ 13 C showed little variation among terrestrial species, suggesting minimal influence by seabirds. Concentrations of total mercury (THg) in primary producers and phyto/zooplankton were not significantly correlated with distance from the seabird colony or δ 15 N values, and were similar to other taxa from the High Arctic. Our results provide novel data on THg in several Arctic taxa where concentrations have not been reported previously. Moreover, the analyses indicate that δ 15 N is significantly enriched in the adjacent environment by guano fertilization, but our study was unable to show an enrichment of THg and δ 13 C in the terrestrial food web near the seabird colony.

  9. Key Features of Intertidal Food Webs That Support Migratory Shorebirds

    Science.gov (United States)

    Saint-Béat, Blanche; Dupuy, Christine; Bocher, Pierrick; Chalumeau, Julien; De Crignis, Margot; Fontaine, Camille; Guizien, Katell; Lavaud, Johann; Lefebvre, Sébastien; Montanié, Hélène; Mouget, Jean-Luc; Orvain, Francis; Pascal, Pierre-Yves; Quaintenne, Gwenaël; Radenac, Gilles; Richard, Pierre; Robin, Frédéric; Vézina, Alain F.; Niquil, Nathalie

    2013-01-01

    The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds. PMID:24204666

  10. Key features of intertidal food webs that support migratory shorebirds.

    Directory of Open Access Journals (Sweden)

    Blanche Saint-Béat

    Full Text Available The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds and July 2008 (absence of birds. To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain--Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.

  11. Global change in the trophic functioning of marine food webs

    DEFF Research Database (Denmark)

    Maureaud, Aurore; Gascuel, Didier; Colléter, Mathieu

    2017-01-01

    and life history traits of marine species, we tested the hypothesis that anthropogenic ecological impacts may have led to changes in the global parameters defining the transfers of biomass within the food web. First, we developed two indicators to assess such changes: the Time Cumulated Indicator (TCI......The development of fisheries in the oceans, and other human drivers such as climate warming, have led to changes in species abundance, assemblages, trophic interactions, and ultimately in the functioning of marine food webs. Here, using a trophodynamic approach and global databases of catches......) measuring the residence time of biomass within the food web, and the Efficiency Cumulated Indicator (ECI) quantifying the fraction of secondary production reaching the top of the trophic chain. Then, we assessed, at the large marine ecosystem scale, the worldwide change of these two indicators over the 1950...

  12. Functional group diversity increases with modularity in complex food webs.

    Science.gov (United States)

    Montoya, D; Yallop, M L; Memmott, J

    2015-06-10

    Biodiversity increases the ability of ecosystems to provide multiple functions. Most studies report a positive relationship between species richness and the number of ecosystem functions. However, it is not known whether the number of functional groups is related to the structure of the underlying species interaction network. Here we present food web data from 115 salt marsh islands and show that network structure is associated with the number of functional groups present. Functional group diversity is heterogeneously distributed across spatial scales, with some islands hosting more functional groups than others. Functional groups form modules within the community so that food webs with more modular architectures have more functional group diversity. Further, in communities with different interaction types, modularity can be seen as the multifunctional equivalent of trophic complementarity. Collectively, these findings reveal spatial heterogeneity in the number of functional groups that emerges from patterns in the structure of the food web.

  13. Size-based predictions of food web patterns

    DEFF Research Database (Denmark)

    Zhang, Lai; Hartvig, Martin; Knudsen, Kim

    2014-01-01

    We employ size-based theoretical arguments to derive simple analytic predictions of ecological patterns and properties of natural communities: size-spectrum exponent, maximum trophic level, and susceptibility to invasive species. The predictions are brought about by assuming that an infinite number...... simulations with varying species richness. To this end, we develop a new size- and trait-based food web model that can be simplified into an analytically solvable size-based model. We confirm existing solutions for the size distribution and derive novel predictions for maximum trophic level and invasion...... of species are continuously distributed on a size-trait axis. It is, however, an open question whether such predictions are valid for a food web with a finite number of species embedded in a network structure. We address this question by comparing the size-based predictions to results from dynamic food web...

  14. Soil food web structure after wood ash application

    DEFF Research Database (Denmark)

    Mortensen, L. H.; Qin, J.; Krogh, Paul Henning

    with varying intervals and subsequently analyzed. The food web analysis includes several trophic levels; bacteria/fungi, protozoa, nematodes, enchytraeids, microarthropods and arthropods. The initial results indicate that bacteria and protozoa are stimulated in the uppermost soil layer (0-3 cm) two months...... can facilitate an increase in the bacteria to fungi ratio with possible cascading effects for the soil food web structure. This is tested by applying ash of different concentrations to experimental plots in a coniferous forest. During the course of the project soil samples will be collected...

  15. THREaD Mapper Studio: a novel, visual web server for the estimation of genetic linkage maps.

    Science.gov (United States)

    Cheema, Jitender; Ellis, T H Noel; Dicks, Jo

    2010-07-01

    The estimation of genetic linkage maps is a key component in plant and animal research, providing both an indication of the genetic structure of an organism and a mechanism for identifying candidate genes associated with traits of interest. Because of this importance, several computational solutions to genetic map estimation exist, mostly implemented as stand-alone software packages. However, the estimation process is often largely hidden from the user. Consequently, problems such as a program crashing may occur that leave a user baffled. THREaD Mapper Studio (http://cbr.jic.ac.uk/threadmapper) is a new web site that implements a novel, visual and interactive method for the estimation of genetic linkage maps from DNA markers. The rationale behind the web site is to make the estimation process as transparent and robust as possible, while also allowing users to use their expert knowledge during analysis. Indeed, the 3D visual nature of the tool allows users to spot features in a data set, such as outlying markers and potential structural rearrangements that could cause problems with the estimation procedure and to account for them in their analysis. Furthermore, THREaD Mapper Studio facilitates the visual comparison of genetic map solutions from third party software, aiding users in developing robust solutions for their data sets.

  16. GLIDERS - A web-based search engine for genome-wide linkage disequilibrium between HapMap SNPs

    Directory of Open Access Journals (Sweden)

    Broxholme John

    2009-10-01

    Full Text Available Abstract Background A number of tools for the examination of linkage disequilibrium (LD patterns between nearby alleles exist, but none are available for quickly and easily investigating LD at longer ranges (>500 kb. We have developed a web-based query tool (GLIDERS: Genome-wide LInkage DisEquilibrium Repository and Search engine that enables the retrieval of pairwise associations with r2 ≥ 0.3 across the human genome for any SNP genotyped within HapMap phase 2 and 3, regardless of distance between the markers. Description GLIDERS is an easy to use web tool that only requires the user to enter rs numbers of SNPs they want to retrieve genome-wide LD for (both nearby and long-range. The intuitive web interface handles both manual entry of SNP IDs as well as allowing users to upload files of SNP IDs. The user can limit the resulting inter SNP associations with easy to use menu options. These include MAF limit (5-45%, distance limits between SNPs (minimum and maximum, r2 (0.3 to 1, HapMap population sample (CEU, YRI and JPT+CHB combined and HapMap build/release. All resulting genome-wide inter-SNP associations are displayed on a single output page, which has a link to a downloadable tab delimited text file. Conclusion GLIDERS is a quick and easy way to retrieve genome-wide inter-SNP associations and to explore LD patterns for any number of SNPs of interest. GLIDERS can be useful in identifying SNPs with long-range LD. This can highlight mis-mapping or other potential association signal localisation problems.

  17. Caught in the food web: complexity made simple?

    Directory of Open Access Journals (Sweden)

    Lawrence R. Pomeroy

    2001-12-01

    Full Text Available Several historically separate lines of food-web research are merging into a unified approach. Connections between microbial and metazoan food webs are significant. Interactions of control by predators, defenses against predation, and availability of organic and inorganic nutrition, not any one of these, shape food webs. The same principles of population ecology apply to metazoans and microorganisms, but microorganisms dominate the flux of energy in both marine and terrestrial systems. Microbial biomass often is a major fraction of total biomass, and very small organisms have a very large ratio of production and respiration to biomass. Assimilation efficiency of bacteria in natural systems is often not as high as in experimental systems, so more primary production is lost to microbial respiration than had been thought. Simulation has been a highly useful adjunct to experiments in both population theory and in studies of biogeochemical mass balance, but it does not fully encompass the complexity of real systems. A major challenge for the future is to find better ways to deal with the real complexity of food webs, both in modeling and in empirical observations, and to do a better job of bringing together conceptually the dynamics of population processes and biogeochemistry.

  18. Temporal and spatial variability in soil food web structure.

    NARCIS (Netherlands)

    Berg, M.P.; Bengtsson, J.

    2007-01-01

    Heterogeneity is a prominent feature of most ecosystems. As a result of environmental heterogeneity the distribution of many soil organisms shows a temporal as well as horizontal and vertical spatial patterning. In spite of this, food webs are usually portrayed as static networks with highly

  19. Stable isotope analysis of consumer food webs indicates ecosystem ...

    African Journals Online (AJOL)

    Assessing changes in food-web structure provides a useful monitoring tool for gauging the resilience of ecosystems in the face of climatic impacts. We consider the ecological resilience of a large estuarine lake (St Lucia Estuary, South Africa) in the wake of an extreme climatic event (prolonged drought). Using carbon and ...

  20. Food-web patterns and diversity in tropical fish communities

    NARCIS (Netherlands)

    Amarasinghe, U.S.; Vijverberg, J.; Weliange, W.S.; Vos, M.

    2014-01-01

    The food webs for three Sri Lankan reservoirs, Minneriya (ancient and shallow), Udawalawe (young and shallow) and Victoria (young and deep), were compared. The species richness of the fish communities was highest in Minneriya (30 species), intermediate in Udawalawe (21 species) and lowest in

  1. Riverine dominance of a nearshore marine demersal food web ...

    African Journals Online (AJOL)

    The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter ...

  2. Ecosystem Food Web Lift-The-Flap Pages

    Science.gov (United States)

    Atwood-Blaine, Dana; Rule, Audrey C.; Morgan, Hannah

    2016-01-01

    In the lesson on which this practical article is based, third grade students constructed a "lift-the-flap" page to explore food webs on the prairie. The moveable papercraft focused student attention on prairie animals' external structures and how the inferred functions of those structures could support further inferences about the…

  3. Soil food web structure during ecosystem development after land abandonment

    NARCIS (Netherlands)

    Holtkamp, R.; Kardol, P.; Van der Wal, A.; Dekker, S.C.; Van der Putten, W.H.; de Ruiter, P.C.

    2008-01-01

    The re-establishment of natural species rich heathlands on abandoned agricultural land is a common land use change in North-West Europe. However, it can take several decades to re-establish natural species rich heathland vegetation. The development rate has found to depend both on soil food web

  4. Stability in real food webs: weak links in long loops

    NARCIS (Netherlands)

    Neutel, A.-M.; Heesterbeek, J.A.P.; Ruiter, P.C. de

    2002-01-01

    Increasing evidence that the strengths of interactions among populations in biological communities form patterns that are crucial for system stability requires clarification of the precise form of these patterns, how they come about, and why they influence stability. We show that in real food webs,

  5. Theory of invasion extinction dynamics in minimal food webs

    Science.gov (United States)

    Haerter, Jan O.; Mitarai, Namiko; Sneppen, Kim

    2018-02-01

    When food webs are exposed to species invasion, secondary extinction cascades may be set off. Although much work has gone into characterizing the structure of food webs, systematic predictions on their evolutionary dynamics are still scarce. Here we present a theoretical framework that predicts extinctions in terms of an alternating sequence of two basic processes: resource depletion by or competitive exclusion between consumers. We first propose a conceptual invasion extinction model (IEM) involving random fitness coefficients. We bolster this IEM by an analytical, recursive procedure for calculating idealized extinction cascades after any species addition and simulate the long-time evolution. Our procedure describes minimal food webs where each species interacts with only a single resource through the generalized Lotka-Volterra equations. For such food webs ex- tinction cascades are determined uniquely and the system always relaxes to a stable steady state. The dynamics and scale invariant species life time resemble the behavior of the IEM, and correctly predict an upper limit for trophic levels as observed in the field.

  6. Assimilation of diazotrophic nitrogen into pelagic food webs.

    Directory of Open Access Journals (Sweden)

    Ryan J Woodland

    Full Text Available The fate of diazotrophic nitrogen (N(D fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N(D fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N(D (exuded from viable cyanobacterial cells by palatable phytoplankton or microbial consortia. Alternatively, N(D can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N(D (e.g., nitrate, ammonium by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom would be the primary pathway by which N(D was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of N(D by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of N(D from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of N(D to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-N(D pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that N(D can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes

  7. Linkages Among Water Vapor Flows, Food Production, and Terrestrial Ecosystem Services

    Directory of Open Access Journals (Sweden)

    Johan Rockström

    1999-12-01

    Full Text Available Global freshwater assessments have not addressed the linkages among water vapor flows, agricultural food production, and terrestrial ecosystem services. We perform the first bottom-up estimate of continental water vapor flows, subdivided into the major terrestrial biomes, and arrive at a total continental water vapor flow of 70,000 km3/yr (ranging from 56,000 to 84,000 km3/yr. Of this flow, 90% is attributed to forests, including woodlands (40,000 km3/yr, wetlands (1400 km3/yr, grasslands (15,100 km3/yr, and croplands (6800 km3/yr. These terrestrial biomes sustain society with essential welfare-supporting ecosystem services, including food production. By analyzing the freshwater requirements of an increasing demand for food in the year 2025, we discover a critical trade-off between flows of water vapor for food production and for other welfare-supporting ecosystem services. To reduce the risk of unintentional welfare losses, this trade-off must become embedded in intentional ecohydrological landscape management.

  8. Food Web Designer: a flexible tool to visualize interaction networks.

    Science.gov (United States)

    Sint, Daniela; Traugott, Michael

    Species are embedded in complex networks of ecological interactions and assessing these networks provides a powerful approach to understand what the consequences of these interactions are for ecosystem functioning and services. This is mandatory to develop and evaluate strategies for the management and control of pests. Graphical representations of networks can help recognize patterns that might be overlooked otherwise. However, there is a lack of software which allows visualizing these complex interaction networks. Food Web Designer is a stand-alone, highly flexible and user friendly software tool to quantitatively visualize trophic and other types of bipartite and tripartite interaction networks. It is offered free of charge for use on Microsoft Windows platforms. Food Web Designer is easy to use without the need to learn a specific syntax due to its graphical user interface. Up to three (trophic) levels can be connected using links cascading from or pointing towards the taxa within each level to illustrate top-down and bottom-up connections. Link width/strength and abundance of taxa can be quantified, allowing generating fully quantitative networks. Network datasets can be imported, saved for later adjustment and the interaction webs can be exported as pictures for graphical display in different file formats. We show how Food Web Designer can be used to draw predator-prey and host-parasitoid food webs, demonstrating that this software is a simple and straightforward tool to graphically display interaction networks for assessing pest control or any other type of interaction in both managed and natural ecosystems from an ecological network perspective.

  9. Designing Industrial Networks Using Ecological Food Web Metrics.

    Science.gov (United States)

    Layton, Astrid; Bras, Bert; Weissburg, Marc

    2016-10-18

    Biologically Inspired Design (biomimicry) and Industrial Ecology both look to natural systems to enhance the sustainability and performance of engineered products, systems and industries. Bioinspired design (BID) traditionally has focused on a unit operation and single product level. In contrast, this paper describes how principles of network organization derived from analysis of ecosystem properties can be applied to industrial system networks. Specifically, this paper examines the applicability of particular food web matrix properties as design rules for economically and biologically sustainable industrial networks, using an optimization model developed for a carpet recycling network. Carpet recycling network designs based on traditional cost and emissions based optimization are compared to designs obtained using optimizations based solely on ecological food web metrics. The analysis suggests that networks optimized using food web metrics also were superior from a traditional cost and emissions perspective; correlations between optimization using ecological metrics and traditional optimization ranged generally from 0.70 to 0.96, with flow-based metrics being superior to structural parameters. Four structural food parameters provided correlations nearly the same as that obtained using all structural parameters, but individual structural parameters provided much less satisfactory correlations. The analysis indicates that bioinspired design principles from ecosystems can lead to both environmentally and economically sustainable industrial resource networks, and represent guidelines for designing sustainable industry networks.

  10. Food web changes under ocean acidification promote herring larvae survival.

    Science.gov (United States)

    Sswat, Michael; Stiasny, Martina H; Taucher, Jan; Algueró-Muñiz, Maria; Bach, Lennart T; Jutfelt, Fredrik; Riebesell, Ulf; Clemmesen, Catriona

    2018-05-01

    Ocean acidification-the decrease in seawater pH due to rising CO 2 concentrations-has been shown to lower survival in early life stages of fish and, as a consequence, the recruitment of populations including commercially important species. To date, ocean-acidification studies with fish larvae have focused on the direct physiological impacts of elevated CO 2 , but largely ignored the potential effects of ocean acidification on food web interactions. In an in situ mesocosm study on Atlantic herring (Clupea harengus) larvae as top predators in a pelagic food web, we account for indirect CO 2 effects on larval survival mediated by changes in food availability. The community was exposed to projected end-of-the-century CO 2 conditions (~760 µatm pCO 2 ) over a period of 113 days. In contrast with laboratory studies that reported a decrease in fish survival, the survival of the herring larvae in situ was significantly enhanced by 19 ± 2%. Analysis of the plankton community dynamics suggested that the herring larvae benefitted from a CO 2 -stimulated increase in primary production. Such indirect effects may counteract the possible direct negative effects of ocean acidification on the survival of fish early life stages. These findings emphasize the need to assess the food web effects of ocean acidification on fish larvae before we can predict even the sign of change in fish recruitment in a high-CO 2 ocean.

  11. Pollen Stoichiometry May Influence Detrital Terrestrial and Aquatic Food Webs

    Directory of Open Access Journals (Sweden)

    Michał Filipiak

    2016-12-01

    Full Text Available Pollen rains may temporally mitigate nutritional limitations experienced by terrestrial and aquatic detritivores by supplying stoichiometrically balanced food during periods of detritivore growth and development (spring-summer. This may affect the functioning of food webs and thus influence fundamental processes, e.g., by enabling fungi to decompose nutritionally scarce litter. Nutritional limitation may be studied within the framework of ecological stoichiometry by comparing the stoichiometric mismatches experienced by organisms feeding on various foods. To this end, the elemental compositions of pine pollen, litter and detritivores (fungi, protozoans, worms, insects, mites, millipedes, isopods and slugs were compared, as were the stoichiometric mismatches experienced by the detritivores feeding on litter and pollen. Additionally, the contribution of pollen to the nutrient flow from the land to aquatic ecosystems was estimated through a literature review. Compared to litter, pine pollen is a stoichiometrically well-balanced food source in terms of its C:N:P ratio but also because of its high concentrations of K, S and Cu and its favorable Zn:Fe ratio. This characteristic is especially suitable to fungi, which may be responsible for the redistribution of pollen-derived nutrients in food webs, particularly aquatic ones. Pollen rains of various plant species act as temporal pulses of nutrients that are rapidly utilized and quickly introduced into the food web, so calculations of annual biomass input may be misleading. Pollen is an easily available, digestible and nutritious food for fungi, bacteria, protozoans and various groups of invertebrates, which suggests that pollen plays an important role in within- and cross-ecosystem nutrient cycling.

  12. Food web heterogeneity and succession in created saltmarshes

    Science.gov (United States)

    Nordstrom, M C; Demopoulos, Amanda W.J.; Whitcraft, CR; Rismondo, A.; McMillan, P.; Gonzales, J P; Levin, L A

    2015-01-01

    1. Ecological restoration must achieve functional as well as structural recovery. Functional metrics for reestablishment of trophic interactions can be used to complement traditional monitoring of structural attributes. In addition, topographic effects on food web structure provide added information within a restoration context; often, created sites may require spatial heterogeneity to effectively match structure and function of natural habitats. 2. We addressed both of these issues in our study of successional development of benthic food web structure, with focus on bottom–up driven changes in macroinvertebrate consumer assemblages in the salt marshes of the Venice Lagoon, Italy. We combined quantified estimates of the changing community composition with stable isotope data (13C:12C and 15N:14N) to compare the general trophic structure between created (2–14 years) marshes and reference sites and along topographic elevation gradients within salt marshes. 3. Macrofaunal invertebrate consumers exhibited local, habitat-specific trophic patterns. Stable isotope-based trophic structure changed with increasing marsh age, in particular with regards to mid-elevation (Salicornia) habitats. In young marshes, the mid-elevation consumer signatures resembled those of unvegetated ponds. The mid elevation of older and natural marshes had a more distinct Salicornia-zone food web, occasionally resembling that of the highest (Sarcocornia-dominated) elevation. In summary, this indicates that primary producers and availability of vascular plant detritus structure consumer trophic interactions and the flow of carbon. 4. Functionally different consumers, subsurface-feeding detritivores (Oligochaeta) and surface grazers (Hydrobia sp.), showed distinct but converging trajectories of isotopic change over time, indicating that successional development may be asymmetric between ‘brown’ (detrital) guilds and ‘green’ (grazing) guilds in the food web. 5. Synthesis and applications

  13. Benchmarking Successional Progress in a Quantitative Food Web

    Science.gov (United States)

    Boit, Alice; Gaedke, Ursula

    2014-01-01

    Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of

  14. Benchmarking successional progress in a quantitative food web.

    Science.gov (United States)

    Boit, Alice; Gaedke, Ursula

    2014-01-01

    Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of

  15. Benchmarking successional progress in a quantitative food web.

    Directory of Open Access Journals (Sweden)

    Alice Boit

    Full Text Available Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile

  16. A concept of food-web structure in organic arable farming systems

    NARCIS (Netherlands)

    Smeding, F.W.; Snoo, de G.R.

    2003-01-01

    A proposal for a descriptive or topological farm food web is derived from field observations and from references in literature. Important themes in the food-web theory are tentatively applied to this preliminary model, explaining differences between local farm food-web structures and how they are

  17. Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs.

    Science.gov (United States)

    Karlson, Agnes M L; Duberg, Jon; Motwani, Nisha H; Hogfors, Hedvig; Klawonn, Isabell; Ploug, Helle; Barthel Svedén, Jennie; Garbaras, Andrius; Sundelin, Brita; Hajdu, Susanna; Larsson, Ulf; Elmgren, Ragnar; Gorokhova, Elena

    2015-06-01

    Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.

  18. Web-Based Virtual Laboratory for Food Analysis Course

    Science.gov (United States)

    Handayani, M. N.; Khoerunnisa, I.; Sugiarti, Y.

    2018-02-01

    Implementation of learning on food analysis course in Program Study of Agro-industrial Technology Education faced problems. These problems include the availability of space and tools in the laboratory that is not comparable with the number of students also lack of interactive learning tools. On the other hand, the information technology literacy of students is quite high as well the internet network is quite easily accessible on campus. This is a challenge as well as opportunities in the development of learning media that can help optimize learning in the laboratory. This study aims to develop web-based virtual laboratory as one of the alternative learning media in food analysis course. This research is R & D (research and development) which refers to Borg & Gall model. The results showed that assessment’s expert of web-based virtual labs developed, in terms of software engineering aspects; visual communication; material relevance; usefulness and language used, is feasible as learning media. The results of the scaled test and wide-scale test show that students strongly agree with the development of web based virtual laboratory. The response of student to this virtual laboratory was positive. Suggestions from students provided further opportunities for improvement web based virtual laboratory and should be considered for further research.

  19. Evidence for the assimilation of ancient glacier organic carbon in a proglacial stream food web

    Science.gov (United States)

    Fellman, Jason; Hood, Eran; Raymond, Peter A.; Hudson, J.H.; Bozeman, Maura; Arimitsu, Mayumi L.

    2015-01-01

    We used natural abundance δ13C, δ15N, and Δ14C to compare trophic linkages between potential carbon sources (leaf litter, epilithic biofilm, and particulate organic matter) and consumers (aquatic macroinvertebrates and fish) in a nonglacial stream and two reaches of the heavily glaciated Herbert River. We tested the hypothesis that proglacial stream food webs are sustained by organic carbon released from glacial ecosystems. Carbon sources and consumers in the nonglacial stream had carbon isotope values that ranged from -30‰ to -25‰ for δ13C and from -14‰ to 53‰ for Δ14C reflecting a food web sustained mainly on contemporary primary production. In contrast, biofilm in the two glacial stream sites was highly Δ14C-depleted (-215‰ to 175‰) relative to the nonglacial stream consistent with the assimilation of ancient glacier organic carbon. IsoSource modeling showed that in upper Herbert River, macroinvertebrates (Δ14C = -171‰ to 22‰) and juvenile salmonids (Δ14C = −102‰ to 17‰) reflected a feeding history of both biofilm (~ 56%) and leaf litter (~ 40%). We estimate that in upper Herbert River on average 36% of the carbon incorporated into consumer biomass is derived from the glacier ecosystem. Thus, 14C-depleted glacial organic carbon was likely transferred to higher trophic levels through a feeding history of bacterial uptake of dissolved organic carbon and subsequent consumption of 14C-depleted biofilm by invertebrates and ultimately fish. Our findings show that the metazoan food web is sustained in part by glacial organic carbon such that future changes in glacial runoff could influence the stability and trophic structure of proglacial aquatic ecosystems.

  20. Influence of Black Mangrove Expansion on Salt Marsh Food Web Dynamics in Coastal Louisiana

    Science.gov (United States)

    Powell, C.; Baustian, M. M.; Polito, M. J.

    2017-12-01

    The range of black mangroves (Avicennia germinans) is projected to expand in the northern Gulf of Mexico due to reduced winter freeze events and an increased rate of droughts. The colonization of mangroves in salt marshes alters habitat structure and creates a novel basal carbon source for consumers. This addition may modify trophic linkages and the structure of estuarine food webs. To understand the implications of mangrove expansion on food web dynamics of traditional Spartina alterniflora marshes, two sites in coastal Louisiana with three habitat types, marsh-dominated, mangrove-dominated, and a transition or mix of the two, were studied. Community composition of juvenile nekton was sampled using fyke nets, minnow traps, and suction sampling and analyzed for abundance and diversity. Primary carbon sources (emergent vegetation, phytoplankton, macroalgae, benthic microalgae, submerged aquatic vegetation, and soil organic matter) and consumers ((blue crabs (Callinectes sapidus), brown shrimp (Farfantepenaeus aztecus), grass shrimp (Palaemonetes spp.), Gulf killifish (Fundulus grandis), periwinkle snails (Littoraria irrorata), eastern oysters (Crassostrea virginica), and southern ribbed mussels (Geukensia granosissima)) collected at each habitat type were measured using stable isotope analysis (δ13C, δ15N, δ34S) to identify trophic level, basal carbon sources, and assess how mangrove carbon is incorporated into salt marsh food webs. While data analysis is ongoing, preliminary results indicate that basal carbon sources supporting some marsh consumers (e.g., periwinkle snails) shift between habitat types, while others remain static (e.g., grass shrimp). This research will further develop our understanding of how climate induced shifts in vegetation influences valued marsh-dependent consumers in the estuarine ecosystems of northern Gulf of Mexico.

  1. Modeling food webs: exploring unexplained structure using latent traits.

    Science.gov (United States)

    Rohr, Rudolf Philippe; Scherer, Heike; Kehrli, Patrik; Mazza, Christian; Bersier, Louis-Félix

    2010-08-01

    Several stochastic models have tried to capture the architecture of food webs. This approach is interesting, but it is limited by the fact that different assumptions can yield similar results. To overcome this limitation, we develop a purely statistical approach. Body size in terms of an optimal ratio between prey and predator is used as explanatory variable. In 12 observed food webs, this model predicts, on average, 20% of interactions. To analyze the unexplained part, we introduce a latent term: each species is described by two latent traits, foraging and vulnerability, that represent nonmeasured characteristics of species once the optimal body size has been accounted for. The model now correctly predicts an average of 73% of links. The key features of our approach are that latent traits quantify the structure that is left unexplained by the explanatory variable and that this quantification allows a test of whether independent biological information, such as microhabitat use, camouflage, or phylogeny, explains this structure. We illustrate this method with phylogeny and find that it is linked to one or both latent traits in nine of 12 food webs. Our approach opens the door to the formulation of more complex models that can be applied to any kind of biological network.

  2. Successional dynamics in the seasonally forced diamond food web.

    Science.gov (United States)

    Klausmeier, Christopher A; Litchman, Elena

    2012-07-01

    Plankton seasonal succession is a classic example of nonequilibrium community dynamics. Despite the fact that it has been well studied empirically, it lacks a general quantitative theory. Here we investigate a food web model that includes a resource, two phytoplankton, and a shared grazer-the diamond food web-in a seasonal environment. The model produces a number of successional trajectories that have been widely discussed in the context of the verbal Plankton Ecology Group model of succession, such as a spring bloom of a good competitor followed by a grazer-induced clear-water phase, setting the stage for the late-season dominance of a grazer-resistant species. It also predicts a novel, counterintuitive trajectory where the grazer-resistant species has both early- and late-season blooms. The model often generates regular annual cycles but sometimes produces multiyear cycles or chaos, even with identical forcing each year. Parameterizing the model, we show how the successional trajectory depends on nutrient supply and the length of the growing season, two key parameters that vary among water bodies. This model extends nonequilibrium theory to food webs and is a first step toward a quantitative theory of plankton seasonal succession.

  3. Existence and construction of large stable food webs

    Science.gov (United States)

    Haerter, Jan O.; Mitarai, Namiko; Sneppen, Kim

    2017-09-01

    Ecological diversity is ubiquitous despite the restrictions imposed by competitive exclusion and apparent competition. To explain the observed richness of species in a given habitat, food-web theory has explored nonlinear functional responses, self-interaction, or spatial structure and dispersal—model ingredients that have proven to promote stability and diversity. We return instead here to classical Lotka-Volterra equations, where species-species interaction is characterized by a simple product and spatial restrictions are ignored. We quantify how this idealization imposes constraints on coexistence and diversity for many species. To this end, we introduce the concept of free and controlled species and use this to demonstrate how stable food webs can be constructed by the sequential addition of species. The resulting food webs can reach dozens of species and generally yield nonrandom degree distributions in accordance with the constraints imposed through the assembly process. Our model thus serves as a formal starting point for the study of sustainable interaction patterns between species.

  4. Fuelling women's empowerment? : An exploration of the linkages between gender, entrepreneurship and access to energy in the informal food sector

    NARCIS (Netherlands)

    de Groot, Jiska; Mohlakoana, Nthabiseng; Knox, Abigail; Bressers, Hans

    This interdisciplinary review paper explores linkages between access to energy, women's empowerment and entrepreneurship. This will be discussed in the context of the informal food sector. Despite expectations that access to energy for productive uses empowers women by enabling them to generate an

  5. New parasites and predators follow the introduction of two fish species to a subarctic lake: implications for food-web structure and functioning

    Science.gov (United States)

    Amundsen, Per-Arne; Lafferty, Kevin D.; Knudsen, Rune; Primicerio, Raul; Kristoffersen, Roar; Klemetsen, Anders; Kuris, Armand M.

    2012-01-01

    Introduced species can alter the topology of food webs. For instance, an introduction can aid the arrival of free-living consumers using the new species as a resource, while new parasites may also arrive with the introduced species. Food-web responses to species additions can thus be far more complex than anticipated. In a subarctic pelagic food web with free-living and parasitic species, two fish species (arctic charr Salvelinus alpinus and three-spined stickleback Gasterosteus aculeatus) have known histories as deliberate introductions. The effects of these introductions on the food web were explored by comparing the current pelagic web with a heuristic reconstruction of the pre-introduction web. Extinctions caused by these introductions could not be evaluated by this approach. The introduced fish species have become important hubs in the trophic network, interacting with numerous parasites, predators and prey. In particular, five parasite species and four predatory bird species depend on the two introduced species as obligate trophic resources in the pelagic web and could therefore not have been present in the pre-introduction network. The presence of the two introduced fish species and the arrival of their associated parasites and predators increased biodiversity, mean trophic level, linkage density, and nestedness; altering both the network structure and functioning of the pelagic web. Parasites, in particular trophically transmitted species, had a prominent role in the network alterations that followed the introductions.

  6. Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes.

    Science.gov (United States)

    Creed, Irena F; Bergström, Ann-Kristin; Trick, Charles G; Grimm, Nancy B; Hessen, Dag O; Karlsson, Jan; Kidd, Karen A; Kritzberg, Emma; McKnight, Diane M; Freeman, Erika C; Senar, Oscar E; Andersson, Agneta; Ask, Jenny; Berggren, Martin; Cherif, Mehdi; Giesler, Reiner; Hotchkiss, Erin R; Kortelainen, Pirkko; Palta, Monica M; Vrede, Tobias; Weyhenmeyer, Gesa A

    2018-03-15

    Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans. © 2018 John Wiley & Sons Ltd.

  7. Tracing biogeochemical subsidies from glacier runoff into Alaska's coastal marine food webs

    Science.gov (United States)

    Arimitsu, Mayumi L.; Hobson, Keith A.; Webber, D'Arcy N.; Piatt, John F.; Hood, Eran W.; Fellman, Jason B.

    2018-01-01

    Nearly half of the freshwater discharge into the Gulf of Alaska originates from landscapes draining glacier runoff, but the influence of the influx of riverine organic matter on the trophodynamics of coastal marine food webs is not well understood. We quantified the ecological impact of riverine organic matter subsidies to glacier-marine habitats by developing a multi-trophic level Bayesian three-isotope mixing model. We utilized large gradients in stable (δ13C, δ15N, δ2H) and radiogenic (Δ14C) isotopes that trace riverine and marine organic matter sources as they are passed from lower to higher trophic levels in glacial-marine habitats. We also compared isotope ratios between glacial-marine and more oceanic habitats. Based on isotopic measurements of potential baseline sources, ambient water and tissues of marine consumers, estimates of the riverine organic matter source contribution to upper trophic-level species including fish and seabirds ranged from 12% to 44%. Variability in resource use among similar taxa corresponded to variation in species distribution and life histories. For example, riverine organic matter assimilation by the glacier-nesting seabirds Kittlitz's murrelet (Brachyramphus brevirostris) was greater than that of the forest-nesting marbled murrelet (B. marmoratus). The particulate and dissolved organic carbon in glacial runoff and near surface coastal waters was aged (12100–1500 years BP 14C-age) but dissolved inorganic carbon and biota in coastal waters were young (530 years BP 14C-age to modern). Thus terrestrial-derived subsidies in marine food webs were primarily composed of young organic matter sources released from glacier ecosystems and their surrounding watersheds. Stable isotope compositions also revealed a divergence in food web structure between glacial-marine and oceanic sites. This work demonstrates linkages between terrestrial and marine ecosystems, and facilitates a greater understanding of how climate-driven changes

  8. Evolutionary conservation of species' roles in food webs.

    Science.gov (United States)

    Stouffer, Daniel B; Sales-Pardo, Marta; Sirer, M Irmak; Bascompte, Jordi

    2012-03-23

    Studies of ecological networks (the web of interactions between species in a community) demonstrate an intricate link between a community's structure and its long-term viability. It remains unclear, however, how much a community's persistence depends on the identities of the species present, or how much the role played by each species varies as a function of the community in which it is found. We measured species' roles by studying how species are embedded within the overall network and the subsequent dynamic implications. Using data from 32 empirical food webs, we find that species' roles and dynamic importance are inherent species attributes and can be extrapolated across communities on the basis of taxonomic classification alone. Our results illustrate the variability of roles across species and communities and the relative importance of distinct species groups when attempting to conserve ecological communities.

  9. Food-web stability signals critical transitions in temperate shallow lakes.

    Science.gov (United States)

    Kuiper, Jan J; van Altena, Cassandra; de Ruiter, Peter C; van Gerven, Luuk P A; Janse, Jan H; Mooij, Wolf M

    2015-07-15

    A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience.

  10. Microbial Food-Web Drivers in Tropical Reservoirs.

    Science.gov (United States)

    Domingues, Carolina Davila; da Silva, Lucia Helena Sampaio; Rangel, Luciana Machado; de Magalhães, Leonardo; de Melo Rocha, Adriana; Lobão, Lúcia Meirelles; Paiva, Rafael; Roland, Fábio; Sarmento, Hugo

    2017-04-01

    Element cycling in aquatic systems is driven chiefly by planktonic processes, and the structure of the planktonic food web determines the efficiency of carbon transfer through trophic levels. However, few studies have comprehensively evaluated all planktonic food-web components in tropical regions. The aim of this study was to unravel the top-down controls (metazooplankton community structure), bottom-up controls (resource availability), and hydrologic (water residence time) and physical (temperature) variables that affect different components of the microbial food web (MFW) carbon stock in tropical reservoirs, through structural equation models (SEM). We conducted a field study in four deep Brazilian reservoirs (Balbina, Tucuruí, Três Marias, and Funil) with different trophic states (oligo-, meso-, and eutrophic). We found evidence of a high contribution of the MFW (up to 50% of total planktonic carbon), especially in the less-eutrophic reservoirs (Balbina and Tucuruí). Bottom-up and top-down effects assessed through SEM indicated negative interactions between soluble reactive phosphorus and phototrophic picoplankton (PPP), dissolved inorganic nitrogen, and heterotrophic nanoflagellates (HNF). Copepods positively affected ciliates, and cladocerans positively affected heterotrophic bacteria (HB) and PPP. Higher copepod/cladoceran ratios and an indirect positive effect of copepods on HB might strengthen HB-HNF coupling. We also found low values for the degree of uncoupling (D) and a low HNF/HB ratio compared with literature data (mostly from temperate regions). This study demonstrates the importance of evaluating the whole size spectrum (including microbial compartments) of the different planktonic compartments, in order to capture the complex carbon dynamics of tropical aquatic ecosystems.

  11. Chemoattraction to dimethylsulfoniopropionate throughout the marine microbial food web.

    Science.gov (United States)

    Seymour, Justin R; Simó, Rafel; Ahmed, Tanvir; Stocker, Roman

    2010-07-16

    Phytoplankton-produced dimethylsulfoniopropionate (DMSP) provides underwater and atmospheric foraging cues for several species of marine invertebrates, fish, birds, and mammals. However, its role in the chemical ecology of marine planktonic microbes is largely unknown, and there is evidence for contradictory functions. By using microfluidics and image analysis of swimming behavior, we observed attraction toward microscale pulses of DMSP and related compounds among several motile strains of phytoplankton, heterotrophic bacteria, and bacterivore and herbivore microzooplankton. Because microbial DMSP cycling is the main natural source of cloud-forming sulfur aerosols, our results highlight how adaptations to microscale chemical seascapes shape planktonic food webs, while potentially influencing climate at the global scale.

  12. Soil food web structure after wood ash application

    DEFF Research Database (Denmark)

    Mortensen, Louise Hindborg; Qin, Jiayi; Cruz-Paredes, Carla

    concentrations to experimental plots in a coniferous forest the soil will be collected with varying intervals and subsequently analyzed. The food web included several trophic levels; bacteria/fungi, protozoa, nematodes, enchytraeids and microarthropods and arthropods. Results from 2014 indicated that bacteria...... the consequences of returning wood ash to biofuel producing coniferous forest. We that the change in pH and increased availability of nutrients after ash application to forest floor can facilitate an increase in the bacteria to fungi ratio with possible effects for the soil food by applying ash of different...... and protozoa were stimulated in the uppermost soil layer (0-3 cm) two months ash application, whereas the enchytraeids seemed to be slightly negatively affected. Generally, nematodes also appeared to be negatively affected, although it differed between feeding groups. On the higher trophic levels, no effect...

  13. Radiocobalt cycling in a small mammal food web

    International Nuclear Information System (INIS)

    Willard, W.K.

    1975-01-01

    Cobalt-60 seeping from a nearby radioactive liquid waste trench on the Oak Ridge reservation into a temperate deciduous forest ecosystem provided a source of environmental contamination where its dispersion through a small mammal food web could be studied. Maximum radiocobalt concentrations in the soil were found in the upper 5 cm of 15 cm cores. Transient mammals such as the opossum and the raccoon had small amounts of 60 Co in their tissues (0.5 and 1.0 pCi/gm, respectively), while the permanent mammal residents including the short-tailed shrew (80 pCi/g), white-footed mouse (50 pCi/g), golden mouse (50 pCi/g) and the eastern chipmunk (20 pCi/g) had from 27 to more than 100 times that of the transient mammals. The persistent occurrence of 60 Co in the small mammals tissues indicated its importance in the food web. Of the potential mammalian food items present in the area, only earthworms (Lumbricus rubellus) contained high levels of 60 Co activity (greater than 56 nCi/gm dry wt.). Earthworms collected from the seepage channel eliminated 70 percent of their body burden (gut contents) of 60 Co during the first 24-hour period, but retained the remaining 30 percent (tissue accumulation) for more than 11 weeks. Tissue retention by earthworms and the utilization of numerous burrows by mammals along the seepage channel during the summer months suggested that earthworms constituted a major link in the small mammal food chain. (U.S.)

  14. The ecological potentials of Phytomyxea ("plasmodiophorids") in aquatic food webs.

    Science.gov (United States)

    Neuhauser, Sigrid; Kirchmair, Martin; Gleason, Frank H

    2011-01-01

    The Phytomyxea ("plasmodiophorids") including both Plasmodiophorida and Phagomyxida is a monophyletic group of Eukaryotes composed of obligate biotrophic parasites of green plants, brown algae, diatoms and stramenopiles commonly found in many freshwater, soil and marine environments. However, most research on Phytomyxea has been restricted to plant pathogenic species with agricultural importance, thereby missing the huge ecological potential of this enigmatic group of parasites. Members of the Phytomyxea can induce changes in biomass in their hosts (e.g. hypertrophies of the host tissue) under suitable environmental conditions. Upon infection they alter the metabolism of their hosts, consequently changing the metabolic status of their host. This results in an altered chemical composition of the host tissue, which impacts the diversity of species which feed on the tissues of the infected host and on the zoospores produced by the parasites. Furthermore, significant amounts of nutrients derived from the hosts, both primary producers (plants and algae) and primary consumers (litter decomposers and plant parasites [Oomycetes]), can enter the food web at different trophic levels in form of zoospores and resting spores. Large numbers of zoospores and resting spores are produced which can be eaten by secondary and tertiary consumers, such as grazing zooplankton and metazoan filter-feeders. Therefore, these microbes can act as energy-rich nutrient resources which may significantly alter the trophic relationships in fresh water, soil and marine habitats. Based on the presented data, Phytomyxea can significantly contribute to the complexity and energy transfer within food webs.

  15. Application of information theory methods to food web reconstruction

    Science.gov (United States)

    Moniz, L.J.; Cooch, E.G.; Ellner, S.P.; Nichols, J.D.; Nichols, J.M.

    2007-01-01

    In this paper we use information theory techniques on time series of abundances to determine the topology of a food web. At the outset, the food web participants (two consumers, two resources) are known; in addition we know that each consumer prefers one of the resources over the other. However, we do not know which consumer prefers which resource, and if this preference is absolute (i.e., whether or not the consumer will consume the non-preferred resource). Although the consumers and resources are identified at the beginning of the experiment, we also provide evidence that the consumers are not resources for each other, and the resources do not consume each other. We do show that there is significant mutual information between resources; the model is seasonally forced and some shared information between resources is expected. Similarly, because the model is seasonally forced, we expect shared information between consumers as they respond to the forcing of the resources. The model that we consider does include noise, and in an effort to demonstrate that these methods may be of some use in other than model data, we show the efficacy of our methods with decreasing time series size; in this particular case we obtain reasonably clear results with a time series length of 400 points. This approaches ecological time series lengths from real systems.

  16. Enhancing food engineering education with interactive web-based simulations

    Directory of Open Access Journals (Sweden)

    Alexandros Koulouris

    2015-04-01

    Full Text Available In the traditional deductive approach in teaching any engineering topic, teachers would first expose students to the derivation of the equations that govern the behavior of a physical system and then demonstrate the use of equations through a limited number of textbook examples. This methodology, however, is rarely adequate to unmask the cause-effect and quantitative relationships between the system variables that the equations embody. Web-based simulation, which is the integration of simulation and internet technologies, has the potential to enhance the learning experience by offering an interactive and easily accessible platform for quick and effortless experimentation with physical phenomena.This paper presents the design and development of a web-based platform for teaching basic food engineering phenomena to food technology students. The platform contains a variety of modules (“virtual experiments” covering the topics of mass and energy balances, fluid mechanics and heat transfer. In this paper, the design and development of three modules for mass balances and heat transfer is presented. Each webpage representing an educational module has the following features: visualization of the studied phenomenon through graphs, charts or videos, computation through a mathematical model and experimentation.  The student is allowed to edit key parameters of the phenomenon and observe the effect of these changes on the outputs. Experimentation can be done in a free or guided fashion with a set of prefabricated examples that students can run and self-test their knowledge by answering multiple-choice questions.

  17. Regional Comparisons of Oceanic Food Web Structure Using Stable Isotopes

    Science.gov (United States)

    Choy, A.; Drazen, J.; Popp, B. N.; Robison, B. H.

    2016-02-01

    Food chain length, or the number of trophic steps between primary producers and apex predators within an ecosystem, is a key determinant of ecosystem structure, including overall efficiency, stability, and productivity. Here, we quantitatively estimate food chain length for three pelagic ecosystems characterized by distinct biogeochemical and oceanographic regimes: the Northern California Current (NCC), the North Pacific Subtropical Gyre (NPSG), and the Gulf of California (GoC). From each region, ecologically equivalent organisms were selected from each of four successive trophic steps, including zooplankton (primary consumers), zooplanktivores (secondary consumers), piscivores (tertiary consumers), and higher order predators. Bulk tissue δ15N values of the organisms from all four trophic steps spanned ranges of approximately 9.8‰ (NCC), 1.4‰ (NPSG), and 2.1‰ (GoC). Regional variations in nitrogen biogeochemistry, however, can alter isotopic baselines and food web dynamics, ultimately complicating bulk isotope measurements across regions. Thus, we apply amino acid nitrogen isotope measurements to quantitatively measure and compare food chain length across consumers from the three regions, accounting for biogeochemical disparities in isotopic baseline. Implications for ecosystem production and efficiency are discussed, including the potential for these different ecosystems to withstand environmental change, including shifting oxygen levels and surface productivity.

  18. Food web structure and the evolution of ecological communities

    Science.gov (United States)

    Quince, Christopher; Higgs, Paul G.; McKane, Alan J.

    Simulations of the coevolution of many interacting species are performed using the Webworld model. The model has a realistic set of predator-prey equations that describe the population dynamics of the species for any structure of the food web. The equations account for competition between species for the same resources, and for the diet choice of predators between alternative prey according to an evolutionarily stable strategy. The set of species present undergoes long-term evolution d ue to speciation and extinction events. We summarize results obtained on the macro-evolutionary dynamics of speciations and extinctions, and on the statistical properties of the food webs that are generated by the model. Simulations begin from small numbers of species and build up to larger webs with relatively constant species number on average. The rate of origination and extinction of species are relatively high, but remain roughly balanced throughout the simulations. When a 'parent' species undergoes sp eciation, the 'child' species usually adds to the same trophic level as the parent. The chance of the child species surviving is significantly higher if the parent is on the second or third trophic level than if it is on the first level, most likely due to a wider choice of possible prey for species on higher levels. Addition of a new species sometimes causes extinction of existing species. The parent species has a high probability of extinction because it has strong competition with the new species. Non-pa rental competitors of the new species also have a significantly higher extinction probability than average, as do prey of the new species. Predators of the new species are less likely than average to become extinct.

  19. Contamination of an arctic terrestrial food web with marine-derived persistent organic pollutants transported by breeding seabirds

    International Nuclear Information System (INIS)

    Choy, Emily S.; Kimpe, Linda E.; Mallory, Mark L.; Smol, John P.; Blais, Jules M.

    2010-01-01

    At Cape Vera, Devon Island (Nunavut, Canada), a colony of northern fulmars (Fulmarus glacialis) concentrates and releases contaminants through their guano to the environment. We determined whether persistent organic pollutants (POPs) from seabirds were transferred to coastal food webs. Snow buntings (Plectrophenax nivalis) were the most contaminated species, with ΣPCB and ΣDDT (mean: 168, 106 ng/g ww) concentrations surpassing environmental guidelines for protecting wildlife. When examined collectively, PCB congeners and DDT in jewel lichen (Xanthoria elegans) were lower in samples taken farther from the seabird colony, and increased with increasing δ 15 N values. However, only concentrations of p'p-DDE:ΣDDT and PCB-95 were significantly correlated inversely with distance from the seabird cliffs. Linkages between marine-derived POPs and their concentrations in terrestrial mammals were less clear. Our study provides novel contaminant data for these species and supports biovector transport as a source of organic contaminants to certain components of the terrestrial food web. - This study provides evidence of contaminant transport by seabirds to a coastal Arctic food web.

  20. Land use alters the resistance and resilience of soil food webs to drought

    Science.gov (United States)

    de Vries, Franciska T.; Liiri, Mira E.; Bjørnlund, Lisa; Bowker, Matthew A.; Christensen, Søren; Setälä, Heikki; Bardgett, Richard D.

    2012-01-01

    Soils deliver several ecosystem services including carbon sequestration and nutrient cycling, which are of central importance to climate mitigation and sustainable food production. Soil biota play an important role in carbon and nitrogen cycling, and, although the effects of land use on soil food webs are well documented the consequences for their resistance and resilience to climate change are not known. We compared the resistance and resilience to drought--which is predicted to increase under climate change of soil food webs of two common land-use systems: intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web. We found that the fungal-based food web, and the processes of C and N loss it governs, of grassland soil was more resistant, although not resilient, and better able to adapt to drought than the bacterial-based food web of wheat soil. Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss. Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change, and that extensively managed grassland promotes more resistant, and adaptable, fungal-based soil food webs.

  1. Parasitism and Food Web Structure in Defoliating Lepidoptera - Parasitoid Communities on Soybean.

    Science.gov (United States)

    Avalos, D S; Mangeaud, A; Valladares, G R

    2016-12-01

    Food webs are usually regarded as snapshots of community feeding interactions. Here, we describe the yearly and cumulative structure of parasitoid-caterpillar food webs on soybean in central Argentina, analyzing parasitism rates and their variability in relation to parasitoid diversity and food web vulnerability in the system. Lepidoptera larvae were collected along four seasons from soybean crops and reared in laboratory to obtain and identify adults and parasitoids. Eleven species of defoliating Lepidoptera and ten parasitoid species were recorded. Food web statistics showed rather low annual variability, with most variation coefficients in the order of 0.20 and generality showing the most stable values. Parasitism showed the highest variability, which was independent of parasitoid diversity and food web vulnerability, although parasitism rates were negatively related to parasitoid richness. Our study highlights the need to consider food web structure and variability in order to understand the functioning of ecological communities in general and in extensive agricultural ecosystems in particular.

  2. Global patterns in ecological indicators of marine food webs: a modelling approach.

    Directory of Open Access Journals (Sweden)

    Johanna Jacomina Heymans

    Full Text Available BACKGROUND: Ecological attributes estimated from food web models have the potential to be indicators of good environmental status given their capabilities to describe redundancy, food web changes, and sensitivity to fishing. They can be used as a baseline to show how they might be modified in the future with human impacts such as climate change, acidification, eutrophication, or overfishing. METHODOLOGY: In this study ecological network analysis indicators of 105 marine food web models were tested for variation with traits such as ecosystem type, latitude, ocean basin, depth, size, time period, and exploitation state, whilst also considering structural properties of the models such as number of linkages, number of living functional groups or total number of functional groups as covariate factors. PRINCIPAL FINDINGS: Eight indicators were robust to model construction: relative ascendency; relative overhead; redundancy; total systems throughput (TST; primary production/TST; consumption/TST; export/TST; and total biomass of the community. Large-scale differences were seen in the ecosystems of the Atlantic and Pacific Oceans, with the Western Atlantic being more complex with an increased ability to mitigate impacts, while the Eastern Atlantic showed lower internal complexity. In addition, the Eastern Pacific was less organised than the Eastern Atlantic although both of these systems had increased primary production as eastern boundary current systems. Differences by ecosystem type highlighted coral reefs as having the largest energy flow and total biomass per unit of surface, while lagoons, estuaries, and bays had lower transfer efficiencies and higher recycling. These differences prevailed over time, although some traits changed with fishing intensity. Keystone groups were mainly higher trophic level species with mostly top-down effects, while structural/dominant groups were mainly lower trophic level groups (benthic primary producers such as

  3. The robustness of keystone indices in food webs.

    Science.gov (United States)

    Fedor, Anna; Vasas, Vera

    2009-10-07

    Species that have outstanding importance in the functioning of a community are called keystone species. Network indices are increasingly used to identify them, e.g. for conservation biological purposes. The problem is that the calculation of these indices is based on the particular network model of the studied food web, which can include network construction errors. For example, additional, unnecessary trophic links can be built in, or, to the contrary, functional links can be left out. What is the effect of such errors on the result of network analysis, e.g. the centrality values of species? Can you rely on the importance rank of species that you calculated? We developed a robustness measure (R) for network indices to answer these questions. R is proportional to the likeliness that the importance rank of nodes in the given network according to a given index would not change due to possible errors in network construction. For calculating R, first the maximum expected error (P) has to be computed which represents the potential range of error in estimating the keystone index in question. Basically, R is calculated by comparing P to the keystone indices of species to assess the reliability of the importance rank of species based on the network model. We calculated the robustness of 13 different structural indices in 26 food webs of different size to test the P and R values. We found that fragmentation indices and the number of dominated nodes can be characterized by quite low R values, while betweenness, topological importance, keystoneness and mixed trophic impact have high R values, which means that they are relatively more reliable for assessing the importance rank of species in an uncertain network model. However, as R was found to be very variable, depending on the topology of a given network, a detailed description is provided for performing the actual calculations case-by-case.

  4. Food and Beverage Brands that Market to Children and Adolescents on the Internet: A Content Analysis of Branded Web Sites

    Science.gov (United States)

    Henry, Anna E.; Story, Mary

    2009-01-01

    Objective: To identify food and beverage brand Web sites featuring designated children's areas, assess marketing techniques present on those industry Web sites, and determine nutritional quality of branded food items marketed to children. Design: Systematic content analysis of food and beverage brand Web sites and nutrient analysis of food and…

  5. Plankton Food Web Responses to Experimental Nutrient Additions in a Subtropical Lake

    Directory of Open Access Journals (Sweden)

    Karl E. Havens

    2006-01-01

    Full Text Available During two controlled enclosure experiments using water from a subtropical lake, the plankton food web displayed a highly variable response to combined addition of nitrogen and phosphorus. In July, the nutrients stimulated growth of Cylindrospermopsis raciborskii, and the biomass of macrozooplankton and microbial food web components did not increase. In October, the same addition of nutrients stimulated growth of small edible Lyngbya spp., and there were coincident increases in biomass of macrozooplankton and components of the microbial web. Past generalizations that cyanobacteria blooms inhibit growth of other food web components may not always hold true.

  6. IMPORTANCE OF TEMPERATURE IN MODELLING PCB BIOACCUMULATION IN THE LAKE MICHIGAN FOOD WEB

    Science.gov (United States)

    In most food web models, the exposure temperature of a food web is typically defined using a single spatial compartment. This essentially assumes that the predator and prey are exposed to the same temperature. However, in a large water body such as Lake Michigan, due to the spati...

  7. Incorporating food web dynamics into ecological restoration: a modeling approach for river ecosystems

    Science.gov (United States)

    J. Ryan Bellmore; Joseph R. Benjamin; Michael Newsom; Jennifer A. Bountry; Daniel Dombroski

    2017-01-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration...

  8. Developing a broader scientific foundation for river restoration: Columbia River food webs.

    Science.gov (United States)

    Naiman, Robert J; Alldredge, J Richard; Beauchamp, David A; Bisson, Peter A; Congleton, James; Henny, Charles J; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N; Pearcy, William G; Rieman, Bruce E; Ruggerone, Gregory T; Scarnecchia, Dennis; Smouse, Peter E; Wood, Chris C

    2012-12-26

    Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure--without explicitly considering food webs--has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

  9. Exploring Fish Diversity as a Determinant of Ecosystem Properties in Aquatic Food Webs

    Science.gov (United States)

    Carey, Michael P.

    2009-01-01

    Dramatic biodiversity changes occurring globally from species loss and invasion have altered native food webs and ecosystem processes. My research objectives are to understand the consequences of fish diversity to freshwater systems by (1) examining the food web consequences of multiple top predators, (2) determining how biodiversity influences…

  10. What lies beneath? : Linking litter and canopy food webs to protect ornamental crops

    NARCIS (Netherlands)

    Muñoz Cárdenas, K.A.

    2017-01-01

    The main research question of this thesis was how interactions between above-ground and below-ground food webs affect biological control. Arthropod food webs associated with plants are commonly composed of several species of herbivores, the detritivore community, specialist and generalist predators

  11. Infochemicals structure marine, terrestrial and freshwater food webs: implications for ecological informatics

    NARCIS (Netherlands)

    Vos, Matthijs; Vet, L.E.M.; Wäckers, F.L.; Middelburg, J.J.; Van der Putten, W.H.; Mooij, W.M.; Heip, C.H.R.; Van Donk, E.

    2006-01-01

    Here we consider how information transfer shapes interactions in aquatic and terrestrial food webs. All organisms, whether they are dead or alive, release certain chemicals into their environment. These can be used as infochemicals by any other individual in the food web that has the biological

  12. Infochemicals structure marine, terrestrial and freshwater food webs: Implications for ecological informatics

    NARCIS (Netherlands)

    Vos, M.; Vet, L.E.M.; Wackers, F.L.; Middelburg, J.J.; Putten, van der W.H.; Mooij, W.M.; Heip, C.H.R.; Donk, van E.

    2006-01-01

    Here we consider how information transfer shapes interactions in aquatic and terrestrial food webs. All organisms, whether they are dead or alive, release certain chemicals into their environment. These can be used as infochemicals by any other individual in the food web that has the biological

  13. Benthic primary producers are key to sustain the Wadden Sea food web

    NARCIS (Netherlands)

    Christianen, M.J.A.; Middelburg, J.J.; Holthuijsen, S.J.; Jouta, J.; Compton, T.J.; Heide, van der T.; Piersma, T.; Sinninghe Damsté, J.S.; Veer, van der H.W.; Schouten, S.; Olff, H.

    2017-01-01

    Coastal food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Distinguishing between these energy sources is essential for our understanding of ecosystem functioning. However, the relative contribution of these components to the food web at the

  14. Inferring chemical effects on carbon flows in aquatic food webs: Methodology and case study

    NARCIS (Netherlands)

    De Laender, F.; Soetaert, K.E.R.; Middelburg, J.J.

    2010-01-01

    The majority of ecotoxicological enclosure experiments monitor species abundances at different chemical concentrations. Here, we present a new modelling approach that estimates changes in food web flows from such data and show that population- and food web level effects are revealed that are not

  15. Adaptive Food Webs : Stability and Transitions of Real and Model Ecosystems

    NARCIS (Netherlands)

    Moore, J.C.; de Ruiter, P.C.; McCann, K.S.; Wolters, V.

    2018-01-01

    Presenting new approaches to studying food webs, this book uses practical management and policy examples to demonstrate the theory behind ecosystem management decisions and the broader issue of sustainability. All the information that readers need to use food web analyses as a tool for understanding

  16. Oceanography and the base of the pelagic food web in the southern Indian Ocean

    DEFF Research Database (Denmark)

    Visser, Andre; Nielsen, Torkel Gissel; Middelboe, Mathias

    2015-01-01

    Processes governing productivity at the base of the pelagic food web of the southern Indian Ocean are influenced primarily by physical–chemical conditions with implications for the structure and function of the entire pelagic food web. Here, we report observations along a great circle transect from...

  17. Stable isotopes dissect aquatic food webs from the top to the bottom

    NARCIS (Netherlands)

    Middelburg, J.J.|info:eu-repo/dai/nl/079665373

    2014-01-01

    Stable isotopes have been used extensively to study food-web functioning, that is, the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of isotopes and are limited to larger organisms that can be physically separated from their environment.

  18. Divergent composition but similar function of soil food webs of individual plants

    DEFF Research Database (Denmark)

    Bezemer, T M; Fountain, M T; Barea, J M

    2010-01-01

    food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed...

  19. Food web architecture and basal resources interact to determine biomass and stoichiometric cascades along a benthic food web.

    Directory of Open Access Journals (Sweden)

    Rafael D Guariento

    Full Text Available Understanding the effects of predators and resources on primary producers has been a major focus of interest in ecology. Within this context, the trophic cascade concept especially concerning the pelagic zone of lakes has been the focus of the majority of these studies. However, littoral food webs could be especially interesting because base trophic levels may be strongly regulated by consumers and prone to be light limited. In this study, the availability of nutrients and light and the presence of an omnivorous fish (Hyphessobrycon bifasciatus were manipulated in enclosures placed in a humic coastal lagoon (Cabiúnas Lagoon, Macaé - RJ to evaluate the individual and interactive effects of resource availability (nutrients and light and food web configuration on the biomass and stoichiometry of periphyton and benthic grazers. Our findings suggest that light and nutrients interact to determine periphyton biomass and stoichiometry, which propagates to the consumer level. We observed a positive effect of the availability of nutrients on periphytic biomass and grazers' biomass, as well as a reduction of periphytic C∶N∶P ratios and an increase of grazers' N and P content. Low light availability constrained the propagation of nutrient effects on periphyton biomass and induced higher periphytic C∶N∶P ratios. The effects of fish presence strongly interacted with resource availability. In general, a positive effect of fish presence was observed for the total biomass of periphyton and grazer's biomass, especially with high resource availability, but the opposite was found for periphytic autotrophic biomass. Fish also had a significant effect on periphyton stoichiometry, but no effect was observed on grazers' stoichiometric ratios. In summary, we observed that the indirect effect of fish predation on periphyton biomass might be dependent on multiple resources and periphyton nutrient stoichiometric variation can affect consumers' stoichiometry.

  20. Divergent composition but similar function of soil food webs of individual plants

    DEFF Research Database (Denmark)

    Bezemer, T M; Fountain, M T; Barea, J M

    2010-01-01

    that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants......Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers...... and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity...

  1. Structure and dynamics of Lithocolletis ringoniella-Parasitoids food web in apple orchards of Shaanxi, China

    Directory of Open Access Journals (Sweden)

    Xin Li

    2014-09-01

    Full Text Available The formation and evolution of food web is a self-organizing process. A food web, L. ringoniella-Parasitoids food web, was proposed in present study. With the apple pest Lithocolletis ringoniella as the basic host, four parasitoids, Apanteles theivorae, Sympiesis sericeicornis, Ageniaspis testaceipes, and Sympiesis Foerst are included in the food web. In this food web, A. theivorae and A. testaceipes are primary parasitoids of L. ringoniella. A. theivorae mainly parasitizes apodous larva of L. ringoniella while A. testaceipes only chooses L. ringoniella egg to parasitize (egg-larva endoparasitization. S. Foerst and S. sericeicornis are facultative hyper-parasitoids. They can parasitize not only the larvae and pupae of L. ringoniella, but also A. theivorae. S. sericeicornis can be hyper-parasitized by S. Foerst. The occurrence mechanism and population dynamics of L. ringoniella and parasitoids, and parasitization effect of parasitoids in apple orchards of Shaanxi, China, were described in detail.

  2. Upland Forest Linkages to Seasonal Wetlands: Litter Flux, Processing, and Food Quality

    Science.gov (United States)

    Brian J. Palik; Darold P. Batzer; Christel Kern

    2005-01-01

    The flux of materials across ecosystem boundaries has significant effects on recipient systems. Because of edge effects, seasonal wetlands in upland forest are good systems to explore these linkages. The purpose of this study was to examine flux of coarse particulate organic matter as litter fall into seasonal wetlands in Minnesota, and the relationship of this flux to...

  3. IMPACT OF LINKAGES WITH SUPPLIERS AND CUSTOMERS IN SUPPLY CHAIN ON THE INNOVATION ACTIVITY OF FOOD INDUSTRY IN WESTERN POLAND

    Directory of Open Access Journals (Sweden)

    Piotr Dzikowski

    2015-06-01

    Full Text Available The article presents the results of a study which aims to determine the effect of the number of industrial vertical linkages and participation in the supply chain on innovation activity of food industry in western Poland. The main research hypothesis is the assumption that innovation processes in food industry are strongly determined by the intensity and nature of the linkages and membership in the supply chain. The scope of the survey relates to innovation in food industry, concerns innovation at the company level and takes into account the diffusion to the “new to the company”. Innovative activities are divided into three general groups including: expenditure on research and development and investments in fi xed assets not used so far (such as: buildings, premises and land, machinery and equipment, computer software, implementation of new products and processes, and innovative collaboration. The survey covers 422 industrial enterprises. The methodological part of the study uses probit modelling that enables to identify the probability of occurrence of innovation activity.

  4. The importance of nature's invisible fabric: food web structure mediates modeled responses to river restoration

    Science.gov (United States)

    Bellmore, R.; Benjamin, J.; Newsom, M.; Bountry, J.; Dombroski, D.

    2016-12-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration planning we constructed a food web model that links river food web dynamics to in-stream physical habitat and riparian vegetation conditions. We present an application of this model to the Methow River, Washington (USA), a location of on-going restoration aimed at recovering salmon. Three restoration strategies were simulated: riparian vegetation restoration, nutrient augmentation via salmon carcass addition, and floodplain reconnection. To explore how food web structure mediates responses to these actions, we modified the food web by adding populations of invasive aquatic snails and nonnative fish. Simulations suggest that floodplain reconnection may be a better strategy than carcass addition and vegetation planting for improving conditions for salmon in this river segment. However, modeled responses were strongly sensitive to changes in the structure of the food web. The addition of invasive snails and nonnative fishes modified pathways of energy through the food web, which negated restoration improvements. This finding illustrates that forecasting responses to restoration may require accounting for the structure of food webs, and that changes in this structure—as might be expected with the spread of invasive species—could compromise restoration outcomes. By elucidating the direct and indirect pathways by which restoration affects target species, dynamic food web models can improve restoration planning by fostering a deeper understanding of system connectedness and dynamics.

  5. Trophic levels and trophic tangles: the prevalence of omnivory in real food webs.

    Science.gov (United States)

    Thompson, Ross M; Hemberg, Martin; Starzomski, Brian M; Shurin, Jonathan B

    2007-03-01

    The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top-down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic-level-based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.

  6. Developing a broader scientific foundation for river restoration: Columbia River food webs

    Science.gov (United States)

    Naiman, Robert J.; Alldredge, Richard; Beauchamp, David A.; Bisson, Peter A.; Congleton, James; Henny, Charles J.; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N.; Pearcy, William G.; Rieman, Bruce E.; Ruggerone, Gregory T.; Scarnecchia, Dennis; Smouse, Peter E.; Wood, Chris C.

    2012-01-01

    Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure—without explicitly considering food webs—has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

  7. Road Salts as Environmental Constraints in Urban Pond Food Webs

    Science.gov (United States)

    Van Meter, Robin J.; Swan, Christopher M.

    2014-01-01

    Freshwater salinization is an emerging environmental filter in urban aquatic ecosystems that receive chloride road salt runoff from vast expanses of impervious surface cover. Our study was designed to evaluate the effects of chloride contamination on urban stormwater pond food webs through changes in zooplankton community composition as well as density and biomass of primary producers and consumers. From May – July 2009, we employed a 2×2×2 full-factorial design to manipulate chloride concentration (low = 177 mg L−1 Cl−/high = 1067 mg L−1 Cl−), gray treefrog (Hyla versicolor) tadpoles (presence/absence) and source of stormwater pond algae and zooplankton inoculum (low conductance/high conductance urban ponds) in 40, 600-L mesocosms. Road salt did serve as a constraint on zooplankton community structure, driving community divergence between the low and high chloride treatments. Phytoplankton biomass (chlorophyll [a] µg L−1) in the mesocosms was significantly greater for the high conductance inoculum (Psalts among algal resources and zooplankton taxa, and further suggest that road salts can act as a significant environmental constraint on urban stormwater pond communities. PMID:24587259

  8. Weighting and indirect effects identify keystone species in food webs.

    Science.gov (United States)

    Zhao, Lei; Zhang, Huayong; O'Gorman, Eoin J; Tian, Wang; Ma, Athen; Moore, John C; Borrett, Stuart R; Woodward, Guy

    2016-09-01

    Species extinctions are accelerating globally, yet the mechanisms that maintain local biodiversity remain poorly understood. The extinction of species that feed on or are fed on by many others (i.e. 'hubs') has traditionally been thought to cause the greatest threat of further biodiversity loss. Very little attention has been paid to the strength of those feeding links (i.e. link weight) and the prevalence of indirect interactions. Here, we used a dynamical model based on empirical energy budget data to assess changes in ecosystem stability after simulating the loss of species according to various extinction scenarios. Link weight and/or indirect effects had stronger effects on food-web stability than the simple removal of 'hubs', demonstrating that both quantitative fluxes and species dissipating their effects across many links should be of great concern in biodiversity conservation, and the potential for 'hubs' to act as keystone species may have been exaggerated to date. © 2016 The Authors Ecology Letters published by CNRS and John Wiley & Sons Ltd.

  9. Metal Bioaccumulation by Estuarine Food Webs in New England, USA

    Directory of Open Access Journals (Sweden)

    Celia Y. Chen

    2016-06-01

    Full Text Available Evaluating the degree of metal exposure and bioaccumulation in estuarine organisms is important for understanding the fate of metals in estuarine food webs. We investigated the bioaccumulation of Hg, methylmercury (MeHg, Cd, Se, Pb, and As in common intertidal organisms across a watershed urbanization gradient of coastal marsh sites in New England to relate metal exposure and bioaccumulation in fauna to both chemical and ecological factors. In sediments, we measured metal and metalloid concentrations, total organic carbon (TOC and SEM-AVS (Simultaneously extracted metal-acid volatile sulfides. In five different functional feeding groups of biota, we measured metal concentrations and delta 15N and delta 13C signatures. Concentrations of Hg and Se in biota for all sites were always greater than sediment concentrations whereas Pb in biota was always lower. There were positive relationships between biota Hg concentrations and sediment concentrations, and between biota MeHg concentrations and both pelagic feeding mode and trophic level. Bioavailability of all metals measured as SEM-AVS or Benthic-Sediment Accumulation Factor was lower in more contaminated sites, likely due to biogeochemical factors related to higher levels of sulfides and organic carbon in the sediments. Our study demonstrates that for most metals and metalloids, bioaccumulation is metal specific and not directly related to sediment concentrations or measures of bioavailability such as AVS-SEM.

  10. Transfer of heavy metals through terrestrial food webs: a review.

    Science.gov (United States)

    Gall, Jillian E; Boyd, Robert S; Rajakaruna, Nishanta

    2015-04-01

    Heavy metals are released into the environment by both anthropogenic and natural sources. Highly reactive and often toxic at low concentrations, they may enter soils and groundwater, bioaccumulate in food webs, and adversely affect biota. Heavy metals also may remain in the environment for years, posing long-term risks to life well after point sources of heavy metal pollution have been removed. In this review, we compile studies of the community-level effects of heavy metal pollution, including heavy metal transfer from soils to plants, microbes, invertebrates, and to both small and large mammals (including humans). Many factors contribute to heavy metal accumulation in animals including behavior, physiology, and diet. Biotic effects of heavy metals are often quite different for essential and non-essential heavy metals, and vary depending on the specific metal involved. They also differ for adapted organisms, including metallophyte plants and heavy metal-tolerant insects, which occur in naturally high-metal habitats (such as serpentine soils) and have adaptations that allow them to tolerate exposure to relatively high concentrations of some heavy metals. Some metallophyte plants are hyperaccumulators of certain heavy metals and new technologies using them to clean metal-contaminated soil (phytoextraction) may offer economically attractive solutions to some metal pollution challenges. These new technologies provide incentive to catalog and protect the unique biodiversity of habitats that have naturally high levels of heavy metals.

  11. Food Web Response to Habitat Restoration in Various Coastal Wetland Ecosystems

    Science.gov (United States)

    James, W. R.; Nelson, J. A.

    2017-12-01

    Coastal wetland habitats provide important ecosystem services, including supporting coastal food webs. These habitats are being lost rapidly. To combat the effects of these losses, millions of dollars have been invested to restore these habitats. However, the relationship between restoring habitat and restoring ecosystem functioning is poorly understood. Analyzing energy flow through food web comparisons between restored and natural habitats can give insights into ecosystem functioning. Using published stable isotope values from organisms in restored and natural habitats, we assessed the food web response of habitat restoration in salt marsh, mangrove, sea grass, and algal bed ecosystems. We ran Bayesian mixing models to quantify resource use by consumers and generated habitat specific niche hypervolumes for each ecosystem to assess food web differences between restored and natural habitats. Salt marsh, mangrove, and sea grass ecosystems displayed functional differences between restored and natural habitats. Salt marsh and mangrove food webs varied in the amount of each resource used, while the sea grass food web displayed more variation between individual organisms. The algal bed food web showed little variation between restored and natural habitats.

  12. Incorporating food web dynamics into ecological restoration: A modeling approach for river ecosystems

    Science.gov (United States)

    Bellmore, J. Ryan; Benjamin, Joseph R.; Newsom, Michael; Bountry, Jennifer A.; Dombroski, Daniel

    2017-01-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration planning we constructed a model that links river food web dynamics to in-stream physical habitat and riparian vegetation conditions. We present an application of the model to the Methow River, Washington (USA), a location of on-going restoration aimed at recovering salmon. Three restoration strategies were simulated: riparian vegetation restoration, nutrient augmentation via salmon carcass addition, and side-channel reconnection. We also added populations of nonnative aquatic snails and fish to the modeled food web to explore how changes in food web structure mediate responses to restoration. Simulations suggest that side-channel reconnection may be a better strategy than carcass addition and vegetation planting for improving conditions for salmon in this river segment. However, modeled responses were strongly sensitive to changes in the structure of the food web. The addition of nonnative snails and fish modified pathways of energy through the food web, which negated restoration improvements. This finding illustrates that forecasting responses to restoration may require accounting for the structure of food webs, and that changes in this structure—as might be expected with the spread of invasive species—could compromise restoration outcomes. Unlike habitat-based approaches to restoration assessment that focus on the direct effects of physical habitat conditions on single species of interest, our approach dynamically links the success of target organisms to the success of competitors, predators, and prey. By elucidating the direct and indirect pathways by which restoration affects target species

  13. Incorporating food web dynamics into ecological restoration: a modeling approach for river ecosystems.

    Science.gov (United States)

    Bellmore, J Ryan; Benjamin, Joseph R; Newsom, Michael; Bountry, Jennifer A; Dombroski, Daniel

    2017-04-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration planning, we constructed a model that links river food web dynamics to in-stream physical habitat and riparian vegetation conditions. We present an application of the model to the Methow River, Washington, USA, a location of on-going restoration aimed at recovering salmon. Three restoration strategies were simulated: riparian vegetation restoration, nutrient augmentation via salmon carcass addition, and side channel reconnection. We also added populations of nonnative aquatic snails and fish to the modeled food web to explore how changes in food web structure mediate responses to restoration. Simulations suggest that side channel reconnection may be a better strategy than carcass addition and vegetation planting for improving conditions for salmon in this river segment. However, modeled responses were strongly sensitive to changes in the structure of the food web. The addition of nonnative snails and fish modified pathways of energy through the food web, which negated restoration improvements. This finding illustrates that forecasting responses to restoration may require accounting for the structure of food webs, and that changes in this structure, as might be expected with the spread of invasive species, could compromise restoration outcomes. Unlike habitat-based approaches to restoration assessment that focus on the direct effects of physical habitat conditions on single species of interest, our approach dynamically links the success of target organisms to the success of competitors, predators, and prey. By elucidating the direct and indirect pathways by which restoration affects target species

  14. Dam regulation and riverine food-web structure in a Mediterranean river.

    Science.gov (United States)

    Mor, Jordi-René; Ruhí, Albert; Tornés, Elisabet; Valcárcel, Héctor; Muñoz, Isabel; Sabater, Sergi

    2018-06-01

    Flow regimes are a major driver of community composition and structure in riverine ecosystems, and flow regulation by dams often induces artificially-stable flow regimes downstream. This represents a major source of hydrological alteration, particularly in regions where biota is adapted to strong seasonal and interannual flow variability. We hypothesized that dam-induced hydrological stability should increase the availability of autochthonous resources at the base of the food web. This, in turn, should favour herbivorous over detritivorous strategies, increasing the diversity of primary consumers, and the food-web width and length. We tested this hypothesis by studying the longitudinal variation in food-web structure in a highly-seasonal Mediterranean river affected by an irrigation dam. We compared an unregulated reach to several reaches downstream of the dam. Hydrological and sedimentological stability increased downstream of the dam, and altered the type and quantity of available resources downstream, prompting a change from a detritus-based to an algae-based food web. The fraction of links between top and intermediate species also increased, and the food web became longer and wider at the intermediate trophic levels. Food-web structure did not recover 14km downstream of the dam, despite a partial restitution of the flow regime. Our results advance the notion that hydrologic alteration affects riverine food webs via additions/deletions of taxa and variation in the strength and distribution of food-web interactions. Thus, flow regulation by dams may not only impact individual facets of biodiversity, but also food-web level properties across river networks. Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

  15. Pulsed flows, tributary inputs, and food web structure in a highly regulated river

    Science.gov (United States)

    Sabo, John; Caron, Melanie; Doucett, Richard R.; Dibble, Kimberly L.; Ruhi, Albert; Marks, Jane; Hungate, Bruce; Kennedy, Theodore A.

    2018-01-01

    1.Dams disrupt the river continuum, altering hydrology, biodiversity, and energy flow. Although research indicates that tributary inputs have the potential to dilute these effects, knowledge at the food web level is still scarce.2.Here we examined the riverine food web structure of the Colorado River below Glen Canyon Dam, focusing on organic matter sources, trophic diversity, and food chain length. We asked how these components respond to pulsed flows from tributaries following monsoon thunderstorms that seasonally increase streamflow in the American Southwest.3.Tributaries increased the relative importance of terrestrial organic matter, particularly during the wet season below junctures of key tributaries. This contrasted with the algal-based food web present immediately below Glen Canyon Dam.4.Tributary inputs during the monsoon also increased trophic diversity and food chain length: food chain length peaked below the confluence with the largest tributary (by discharge) in Grand Canyon, increasing by >1 trophic level over a 4-5 kilometre reach possibly due to aquatic prey being flushed into the mainstem during heavy rain events.5.Our results illustrate that large tributaries can create seasonal discontinuities, influencing riverine food web structure in terms of allochthony, food web diversity, and food chain length.6.Synthesis and applications. Pulsed flows from unregulated tributaries following seasonal monsoon rains increase the importance of terrestrially-derived organic matter in large, regulated river food webs, increasing food chain length and trophic diversity downstream of tributary inputs. Protecting unregulated tributaries within hydropower cascades may be important if we are to mitigate food web structure alteration due to flow regulation by large dams. This is critical in the light of global hydropower development, especially in megadiverse, developing countries where dam placement (including completed and planned structures) is in tributaries.

  16. Anthropogenic and natural sources of acidity and metals and their influence on the structure of stream food webs

    International Nuclear Information System (INIS)

    Hogsden, Kristy L.; Harding, Jon S.

    2012-01-01

    We compared food web structure in 20 streams with either anthropogenic or natural sources of acidity and metals or circumneutral water chemistry in New Zealand. Community and diet analysis indicated that mining streams receiving anthropogenic inputs of acidic and metal-rich drainage had much simpler food webs (fewer species, shorter food chains, less links) than those in naturally acidic, naturally high metal, and circumneutral streams. Food webs of naturally high metal streams were structurally similar to those in mining streams, lacking fish predators and having few species. Whereas, webs in naturally acidic streams differed very little from those in circumneutral streams due to strong similarities in community composition and diets of secondary and top consumers. The combined negative effects of acidity and metals on stream food webs are clear. However, elevated metal concentrations, regardless of source, appear to play a more important role than acidity in driving food web structure. - Highlights: ► Food webs in acid mine drainage impacted streams are small and extremely simplified. ► Conductivity explained differences in food web properties between streams. ► Number of links and web size accounted for much dissimilarity between food webs. ► Food web structure was comparable in naturally acidic and circumneutral streams. - Food web structure differs in streams with anthropogenic and natural sources of acidity and metals.

  17. Mercury flow through an Asian rice-based food web.

    Science.gov (United States)

    Abeysinghe, Kasun S; Qiu, Guangle; Goodale, Eben; Anderson, Christopher W N; Bishop, Kevin; Evers, David C; Goodale, Morgan W; Hintelmann, Holger; Liu, Shengjie; Mammides, Christos; Quan, Rui-Chang; Wang, Jin; Wu, Pianpian; Xu, Xiao-Hang; Yang, Xiao-Dong; Feng, Xinbin

    2017-10-01

    Mercury (Hg) is a globally-distributed pollutant, toxic to humans and animals. Emissions are particularly high in Asia, and the source of exposure for humans there may also be different from other regions, including rice as well as fish consumption, particularly in contaminated areas. Yet the threats Asian wildlife face in rice-based ecosystems are as yet unclear. We sought to understand how Hg flows through rice-based food webs in historic mining and non-mining regions of Guizhou, China. We measured total Hg (THg) and methylmercury (MeHg) in soil, rice, 38 animal species (27 for MeHg) spanning multiple trophic levels, and examined the relationship between stable isotopes and Hg concentrations. Our results confirm biomagnification of THg/MeHg, with a high trophic magnification slope. Invertivorous songbirds had concentrations of THg in their feathers that were 15x and 3x the concentration reported to significantly impair reproduction, at mining and non-mining sites, respectively. High concentrations in specialist rice consumers and in granivorous birds, the later as high as in piscivorous birds, suggest rice is a primary source of exposure. Spiders had the highest THg concentrations among invertebrates and may represent a vector through which Hg is passed to vertebrates, especially songbirds. Our findings suggest there could be significant population level health effects and consequent biodiversity loss in sensitive ecosystems, like agricultural wetlands, across Asia, and invertivorous songbirds would be good subjects for further studies investigating this possibility. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Food web structure in oil sands reclaimed wetlands.

    Science.gov (United States)

    Kovalenko, K E; Ciborowski, J J H; Daly, C; Dixon, D G; Farwell, A J; Foote, A L; Frederick, K R; Costa, J M Gardner; Kennedy, K; Liber, K; Roy, M C; Slama, C A; Smits, J E G

    2013-07-01

    Boreal wetlands play an important role in global carbon balance. However, their ecosystem function is threatened by direct anthropogenic disturbance and climate change. Oil sands surface mining in the boreal regions of Western Canada denudes tracts of land of organic materials, leaves large areas in need of reclamation, and generates considerable quantities of extraction process-affected materials. Knowledge and validation of reclamation techniques that lead to self-sustaining wetlands has lagged behind development of protocols for reclaiming terrestrial systems. It is important to know whether wetlands reclaimed with oil sands process materials can be restored to levels equivalent to their original ecosystem function. We approached this question by assessing carbon flows and food web structure in naturally formed and oil sands-affected wetlands constructed in 1970-2004 in the postmining landscape. We evaluated whether a prescribed reclamation strategy, involving organic matter amendment, accelerated reclaimed wetland development, leading to wetlands that were more similar to their natural marsh counterparts than wetlands that were not supplemented with organic matter. We measured compartment standing stocks for bacterioplankton, microbial biofilm, macrophytes, detritus, and zoobenthos; concentrations of dissolved organic carbon and residual naphthenic acids; and microbial production, gas fluxes, and aquatic-terrestrial exports (i.e., aquatic insect emergence). The total biomass of several biotic compartments differed significantly between oil sands and reference wetlands. Submerged macrophyte biomass, macroinvertebrate trophic diversity, and predator biomass and richness were lower in oil sands-affected wetlands than in reference wetlands. There was insufficient evidence to conclude that wetland age and wetland amendment with peat-mineral mix mitigate effects of oil sands waste materials on the fully aquatic biota. Although high variability was observed within

  19. Integrating Ecosystem Engineering and Food Web Ecology: Testing the Effect of Biogenic Reefs on the Food Web of a Soft-Bottom Intertidal Area.

    Science.gov (United States)

    De Smet, Bart; Fournier, Jérôme; De Troch, Marleen; Vincx, Magda; Vanaverbeke, Jan

    2015-01-01

    The potential of ecosystem engineers to modify the structure and dynamics of food webs has recently been hypothesised from a conceptual point of view. Empirical data on the integration of ecosystem engineers and food webs is however largely lacking. This paper investigates the hypothesised link based on a field sampling approach of intertidal biogenic aggregations created by the ecosystem engineer Lanice conchilega (Polychaeta, Terebellidae). The aggregations are known to have a considerable impact on the physical and biogeochemical characteristics of their environment and subsequently on the abundance and biomass of primary food sources and the macrofaunal (i.e. the macro-, hyper- and epibenthos) community. Therefore, we hypothesise that L. conchilega aggregations affect the structure, stability and isotopic niche of the consumer assemblage of a soft-bottom intertidal food web. Primary food sources and the bentho-pelagic consumer assemblage of a L. conchilega aggregation and a control area were sampled on two soft-bottom intertidal areas along the French coast and analysed for their stable isotopes. Despite the structural impacts of the ecosystem engineer on the associated macrofaunal community, the presence of L. conchilega aggregations only has a minor effect on the food web structure of soft-bottom intertidal areas. The isotopic niche width of the consumer communities of the L. conchilega aggregations and control areas are highly similar, implying that consumer taxa do not shift their diet when feeding in a L. conchilega aggregation. Besides, species packing and hence trophic redundancy were not affected, pointing to an unaltered stability of the food web in the presence of L. conchilega.

  20. Soil fertility shapes belowground food webs across a regional climate gradient.

    Science.gov (United States)

    Laliberté, Etienne; Kardol, Paul; Didham, Raphael K; Teste, François P; Turner, Benjamin L; Wardle, David A

    2017-10-01

    Changes in soil fertility during pedogenesis affect the quantity and quality of resources entering the belowground subsystem. Climate governs pedogenesis, yet how climate modulates responses of soil food webs to soil ageing remains unexplored because of the paucity of appropriate model systems. We characterised soil food webs along each of four retrogressive soil chronosequences situated across a strong regional climate gradient to show that belowground communities are predominantly shaped by changes in fertility rather than climate. Basal consumers showed hump-shaped responses to soil ageing, which were propagated to higher-order consumers. There was a shift in dominance from bacterial to fungal energy channels with increasing soil age, while the root energy channel was most important in intermediate-aged soils. Our study highlights the overarching importance of soil fertility in regulating soil food webs, and indicates that belowground food webs will respond more strongly to shifts in soil resources than climate change. © 2017 John Wiley & Sons Ltd/CNRS.

  1. Direct and indirect effects of resource quality on food web structure

    NARCIS (Netherlands)

    Bukovinszky, T.; Veen, van F.; Jongema, Y.; Dicke, M.

    2008-01-01

    The diversity and complexity of food webs (the networks of feeding relationships within an ecological community) are considered to be important factors determining ecosystem function and stability. However, the biological processes driving these factors are poorly understood. Resource quality

  2. Food-web models predict species abundances in response to habitat change.

    Directory of Open Access Journals (Sweden)

    Nicholas J Gotelli

    2006-10-01

    Full Text Available Plant and animal population sizes inevitably change following habitat loss, but the mechanisms underlying these changes are poorly understood. We experimentally altered habitat volume and eliminated top trophic levels of the food web of invertebrates that inhabit rain-filled leaves of the carnivorous pitcher plant Sarracenia purpurea. Path models that incorporated food-web structure better predicted population sizes of food-web constituents than did simple keystone species models, models that included only autecological responses to habitat volume, or models including both food-web structure and habitat volume. These results provide the first experimental confirmation that trophic structure can determine species abundances in the face of habitat loss.

  3. Is benthic food web structure related to diversity of marine macrobenthic communities?

    NARCIS (Netherlands)

    Sokolowski, A.; Wolowicz, M.; Asmus, H.; Asmus, R.; Carlier, A.; Gasiunaité, Z.; Grémare, A.; Hummel, H.; Lesutiené, J.; Razinkovas, A.; Renaud, P.E.; Richard, P.; Kędra, M.

    2012-01-01

    Numerical structure and the organisation of food webs within macrozoobenthic communities has been assessed in the European waters (Svalbard, Barents Sea, Baltic Sea, North Sea, Atlantic Ocean and the Mediterranean Sea) to address the interactions between biodiversity and ecosystem functioning.

  4. Microbially mediated detrital food web: The link between mangroves and coastal aquatic animal communities

    Digital Repository Service at National Institute of Oceanography (India)

    RaghuKumar, S.

    be defined as any dead organic matter and its associated microbiota. The detrital pathway is the most important one through which the energy of coastal macrophytic primary producers is channelled into the food web of adjacent waters. The salient features...

  5. The rural-urban linkage in the use of traditional foods by peri-urban ...

    African Journals Online (AJOL)

    The article is based on the study that explored ways of reducing malnutrition amongst the inhabitants of South Africa through traditional foods. Traditional foods have been identified as one of the strategies that can be employed to lessen the problem in the community of Nompumelelo, in the Eastern Cape Province, and the ...

  6. Herbivore diet breadth mediates the cascading effects of carnivores in food webs

    OpenAIRE

    Singer, Michael S.; Lichter-Marck, Isaac H.; Farkas, Timothy E.; Aaron, Eric; Whitney, Kenneth D.; Mooney, Kailen A.

    2014-01-01

    Predicting the impact of carnivores on plants has challenged community and food web ecologists for decades. At the same time, the role of predators in the evolution of herbivore dietary specialization has been an unresolved issue in evolutionary ecology. Here, we integrate these perspectives by testing the role of herbivore diet breadth as a predictor of top-down effects of avian predators on herbivores and plants in a forest food web. Using experimental bird exclosures to study a complex co...

  7. Analysis on Transport of Food Logistics Based on Web and GIS Technology

    OpenAIRE

    Qiang Xu

    2015-01-01

    The transport of food logistics has higher requirements on the design and selection, path customer’s geographical information positioning, etc. The application of network and GIS technology in the field of logistics transportation of food will enhance the efficiency of delivering food logistics, which can lower the cost of the transportation logistic of food at the same time. This study is based on Web and GIS, taking them as the key point, through the analysis of the effect of network and GI...

  8. Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation

    Science.gov (United States)

    Hemraj, Deevesh A.; Hossain, A.; Ye, Qifeng; Qin, Jian G.; Leterme, Sophie C.

    2017-03-01

    Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong.

  9. Towards a framework for assessment and management of cumulative human impacts on marine food webs.

    Science.gov (United States)

    Giakoumi, Sylvaine; Halpern, Benjamin S; Michel, Loïc N; Gobert, Sylvie; Sini, Maria; Boudouresque, Charles-François; Gambi, Maria-Cristina; Katsanevakis, Stelios; Lejeune, Pierre; Montefalcone, Monica; Pergent, Gerard; Pergent-Martini, Christine; Sanchez-Jerez, Pablo; Velimirov, Branko; Vizzini, Salvatrice; Abadie, Arnaud; Coll, Marta; Guidetti, Paolo; Micheli, Fiorenza; Possingham, Hugh P

    2015-08-01

    Effective ecosystem-based management requires understanding ecosystem responses to multiple human threats, rather than focusing on single threats. To understand ecosystem responses to anthropogenic threats holistically, it is necessary to know how threats affect different components within ecosystems and ultimately alter ecosystem functioning. We used a case study of a Mediterranean seagrass (Posidonia oceanica) food web and expert knowledge elicitation in an application of the initial steps of a framework for assessment of cumulative human impacts on food webs. We produced a conceptual seagrass food web model, determined the main trophic relationships, identified the main threats to the food web components, and assessed the components' vulnerability to those threats. Some threats had high (e.g., coastal infrastructure) or low impacts (e.g., agricultural runoff) on all food web components, whereas others (e.g., introduced carnivores) had very different impacts on each component. Partitioning the ecosystem into its components enabled us to identify threats previously overlooked and to reevaluate the importance of threats commonly perceived as major. By incorporating this understanding of system vulnerability with data on changes in the state of each threat (e.g., decreasing domestic pollution and increasing fishing) into a food web model, managers may be better able to estimate and predict cumulative human impacts on ecosystems and to prioritize conservation actions. © 2015 Society for Conservation Biology.

  10. The web-buffet--development and validation of an online tool to measure food choice.

    Science.gov (United States)

    Bucher, Tamara; Keller, Carmen

    2015-08-01

    To date, no data exist on the agreement of food choice measured using an online tool with subsequent actual consumption. This needs to be shown before food choice, measured by means of an online tool, is used as a dependent variable to examine intake in the general population. A 'web-buffet' was developed to assess food choice. Choice was measured as planned meal composition from photographic material; respondents chose preferred foods and proportions for a main meal (out of a possible 144 combinations) online and the validity was assessed by comparison of a meal composed from a web-buffet with actual food intake 24-48 h later. Furthermore, correlations of food preferences, energy needs and health interest with meals chosen from the web-buffet were analysed. Students: n 106 (Study I), n 32 (Study II). Meals chosen from the web-buffet (mean = 2998 kJ, SD = 471 kJ) agreed with actual consumption (rs = 0.63, P choice in the web-buffet agrees sufficiently well with actual intake to measure food choice as a dependent variable in online surveys. However, we found an average underestimation of subsequent consumption. High correlations of preferences with chosen amounts and an inverse association of health interest with total energy further indicate the validity of the tool. Applications in behavioural nutrition research are discussed.

  11. The impact of nonlinear functional responses on the long-term evolution of food web structure.

    Science.gov (United States)

    Drossel, Barbara; McKane, Alan J; Quince, Christopher

    2004-08-21

    We investigate the long-term web structure emerging in evolutionary food web models when different types of functional responses are used. We find that large and complex webs with several trophic layers arise only if the population dynamics is such that it allows predators to focus on their best prey species. This can be achieved using modified Lotka-Volterra or Holling/Beddington functional responses with effective couplings that depend on the predator's efficiency at exploiting the prey, or a ratio-dependent functional response with adaptive foraging. In contrast, if standard Lotka-Volterra or Holling/Beddington functional responses are used, long-term evolution generates webs with almost all species being basal, and with additionally many links between these species. Interestingly, in all cases studied, a large proportion of weak links result naturally from the evolution of the food webs.

  12. Community food web, decomposition and nitrogen mineralisation in a stratified Scots pine forest soil

    NARCIS (Netherlands)

    Berg, M.; Ruiter, de P.C.; Didden, W.; Janssen, M.; Schouten, T.; Verhoef, H.

    2001-01-01

    A soil community food web model was used to improve the understanding of what factors govern the mineralisation of nutrients and carbon and the decay of dead organic matter. The model derives the rates of C and N mineralisation by organisms by splitting their uptake rate of food resources into a

  13. Comparing Food Label Experiments Using Samples from Web Panels versus Mall Intercepts

    Science.gov (United States)

    Chang, LinChiat; Lin, Chung-Tung Jordan

    2015-01-01

    To regulate health messages on food labels, the U.S. Food and Drug Administration (FDA) traditionally relied on mall intercepts to collect consumer data. In recent years, web surveys have presented a viable alternative for presenting visual stimuli with more control and efficiency in data collection. However, there is a paucity of empirical data…

  14. Food Chains & Webs. A Multimedia CD-ROM. [CD-ROM].

    Science.gov (United States)

    2001

    This CD-ROM is designed for classroom and individual use to teach and learn about food chains and food webs. Integrated animations, custom graphics, three-dimensional representations, photographs, and sound are featured for use in user-controlled activities. Interactive lessons are available to reinforce the subject material. Pre- and post-testing…

  15. Trophic Magnification of Parabens and Their Metabolites in a Subtropical Marine Food Web.

    Science.gov (United States)

    Xue, Xiaohong; Xue, Jingchuan; Liu, Wenbin; Adams, Douglas H; Kannan, Kurunthachalam

    2017-01-17

    Despite the widespread use of parabens in a range of consumer products, little is known about bioaccumulation of these chemicals in aquatic environments. In this study, six parabens and four of their common metabolites were measured in abiotic (water, sediment) and biotic (fish including sharks, invertebrates, plants) samples collected from a subtropical marine food web in coastal Florida. Methyl paraben (MeP) was found in all abiotic (100%) and a majority of biotic (87%) samples. 4-Hydroxy benzoic acid (4-HB) was the most abundant metabolite, found in 97% of biotic and all abiotic samples analyzed. The food chain accumulation of MeP and 4-HB was investigated for this food web. The trophic magnification factor (TMF) of MeP was estimated to be 1.83, which suggests considerable bioaccumulation and biomagnification of this compound in the marine food web. In contrast, a low TMF value was found for 4-HB (0.30), indicating that this compound is metabolized and excreted along the food web. This is the first study to document the widespread occurrence of parabens and their metabolites in fish, invertebrates, seagrasses, marine macroalgae, mangroves, seawater, and ocean sediments and to elucidate biomagnification potential of MeP in a marine food web.

  16. Reconciling the role of terrestrial leaves in pond food webs: a whole-ecosystem experiment.

    Science.gov (United States)

    Holgerson, Meredith A; Post, David M; Skelly, David K

    2016-07-01

    Terrestrial carbon and nutrients can subsidize the detrital pool of freshwater ecosystems; yet, the importance of terrestrial subsidies to lake and pond food webs is uncertain and debated. Terrestrial detritus is expected to have the greatest impact on food webs when water bodies are small and shallow with low levels of incident light. Temporary forested ponds fit this description and are often assumed to have a leaf detritus-based food web, but this has not been quantified. In a whole-ecosystem experiment, we traced the flow of isotopically enriched leaf litter to primary producers and consumers in a small, forested pond. We found that terrestrial leaves provided nutrients to algae, offering an indirect pathway in which leaf litter can enter the food web. Terrestrial leaves were also consumed directly, and larval caddisfly (Limnephilus sp.) shredders likely mobilized leaf nutrients to other consumers, a process overlooked in many previous small-scale experiments that did not incorporate shredders. Unexpectedly, most consumers relied heavily upon algal food pathways despite low light and net heterotrophic conditions. Overall, our study highlights the interconnectedness of algal and leaf litter pathways in small pond food webs, and emphasizes that algal pathways are prevalent and important even in small, shaded ponds with high loads of terrestrial leaf litter. © 2016 by the Ecological Society of America.

  17. The linkages between food and nutrition security in lowland and coastal villages in the Philippines

    NARCIS (Netherlands)

    Balatibat, E.M.

    2004-01-01

    Philippinesis endowed with many natural resources but it is also confronted with a climate that annually poses threats to livelihood, food and

  18. Energy and Food Commodity Prices Linkage: An Examination with Mixed-Frequency Data

    NARCIS (Netherlands)

    Trujillo Barrera, A.A.; Pennings, J.M.E.

    2013-01-01

    Abstract Is the relationship between energy and agricultural commodities an important factor in the increasing price variability of food commodities? Findings from the literature appear to be mixed and highly influenced by the data frequency used in those analysis. A recurrent task in time series

  19. Mercury and other trace elements in a pelagic Arctic marine food web (Northwater Polynya, Baffin Bay)

    International Nuclear Information System (INIS)

    Campbell, Linda M.; Norstrom, Ross J.; Hobson, Keith A.; Muir, Derek C.G.; Backus, Sean; Fisk, Aaron T.

    2005-01-01

    Total mercury (THg), methylmercury (MeHg) and 22 other trace elements were measured in ice algae, three species of zooplankton, mixed zooplankton samples, Arctic cod (Boreogadus saida), ringed seals (Phoca hispida) and eight species of seabirds to examine the trophodynamics of these metals in an Arctic marine food web. All samples were collected in 1998 in the Northwater Polynya (NOW) located between Ellesmere Island and Greenland in Baffin Bay. THg and MeHg were found to biomagnify through the NOW food web, based on significant positive relationships between log THg and log MeHg concentrations vs. δ 15 N muscle and liver . The slope of these relationships for muscle THg and MeHg concentrations (slope = 0.197 and 0.223, respectively) were similar to those reported for other aquatic food webs. The food web behavior of THg and δ 15 N appears constant, regardless of trophic state (eutrophic vs. oligotrophic), latitude (Arctic vs. tropical) or salinity (marine vs. freshwater) of the ecosystem. Rb in both liver and muscle tissue and Zn in muscle tissue were also found to biomagnify through this food web, although at a rate that is approximately 25% of that of THg. A number of elements (Cd, Pb and Ni in muscle tissue and Cd and Li in seabird liver tissue) were found to decrease trophically through the food web, as indicated by significantly negative relationships with tissue-specific δ 15 N. A diverse group of metals (Ag, Ba, La, Li, Sb, Sr, U and V) were found to have higher concentrations in zooplankton than seabirds or marine mammals due to bioconcentration from seawater. The remaining metals (As, Co, Cu, Ga, Mn, Mo and Se in muscle tissue) showed no relationship with trophic position, as indicated by δ 15 N values, although As in liver tissue showed significant biomagnification in the seabird portion of the food web

  20. The meaning of functional trait composition of food webs for ecosystem functioning.

    Science.gov (United States)

    Gravel, Dominique; Albouy, Camille; Thuiller, Wilfried

    2016-05-19

    There is a growing interest in using trait-based approaches to characterize the functional structure of animal communities. Quantitative methods have been derived mostly for plant ecology, but it is now common to characterize the functional composition of various systems such as soils, coral reefs, pelagic food webs or terrestrial vertebrate communities. With the ever-increasing availability of distribution and trait data, a quantitative method to represent the different roles of animals in a community promise to find generalities that will facilitate cross-system comparisons. There is, however, currently no theory relating the functional composition of food webs to their dynamics and properties. The intuitive interpretation that more functional diversity leads to higher resource exploitation and better ecosystem functioning was brought from plant ecology and does not apply readily to food webs. Here we appraise whether there are interpretable metrics to describe the functional composition of food webs that could foster a better understanding of their structure and functioning. We first distinguish the various roles that traits have on food web topology, resource extraction (bottom-up effects), trophic regulation (top-down effects), and the ability to keep energy and materials within the community. We then discuss positive effects of functional trait diversity on food webs, such as niche construction and bottom-up effects. We follow with a discussion on the negative effects of functional diversity, such as enhanced competition (both exploitation and apparent) and top-down control. Our review reveals that most of our current understanding of the impact of functional trait diversity on food web properties and functioning comes from an over-simplistic representation of network structure with well-defined levels. We, therefore, conclude with propositions for new research avenues for both theoreticians and empiricists. © 2016 The Author(s).

  1. Impact of nitrogen deposition on forest and lake food webs in nitrogen-limited environments.

    Science.gov (United States)

    Meunier, Cédric L; Gundale, Michael J; Sánchez, Irene S; Liess, Antonia

    2016-01-01

    Increased reactive nitrogen (Nr ) deposition has raised the amount of N available to organisms and has greatly altered the transfer of energy through food webs, with major consequences for trophic dynamics. The aim of this review was to: (i) clarify the direct and indirect effects of Nr deposition on forest and lake food webs in N-limited biomes, (ii) compare and contrast how aquatic and terrestrial systems respond to increased Nr deposition, and (iii) identify how the nutrient pathways within and between ecosystems change in response to Nr deposition. We present that Nr deposition releases primary producers from N limitation in both forest and lake ecosystems and raises plants' N content which in turn benefits herbivores with high N requirements. Such trophic effects are coupled with a general decrease in biodiversity caused by different N-use efficiencies; slow-growing species with low rates of N turnover are replaced by fast-growing species with high rates of N turnover. In contrast, Nr deposition diminishes below-ground production in forests, due to a range of mechanisms that reduce microbial biomass, and decreases lake benthic productivity by switching herbivore growth from N to phosphorus (P) limitation, and by intensifying P limitation of benthic fish. The flow of nutrients between ecosystems is expected to change with increasing Nr deposition. Due to higher litter production and more intense precipitation, more terrestrial matter will enter lakes. This will benefit bacteria and will in turn boost the microbial food web. Additionally, Nr deposition promotes emergent insects, which subsidize the terrestrial food web as prey for insectivores or by dying and decomposing on land. So far, most studies have examined Nr -deposition effects on the food web base, whereas our review highlights that changes at the base of food webs substantially impact higher trophic levels and therefore food web structure and functioning. © 2015 John Wiley & Sons Ltd.

  2. Production and food web efficiency decrease as fishing activity increases in a coastal ecosystem

    Science.gov (United States)

    Anh, Pham Viet; Everaert, Gert; Goethals, Peter; Vinh, Chu Tien; De Laender, Frederik

    2015-11-01

    Fishing effort in the Vietnamese coastal ecosystem has rapidly increased from the 1990s to the 2000s, with unknown consequences for local ecosystem structure and functioning. Using ecosystem models that integrate fisheries and food webs we found profound differences in the production of six functional groups, the food web efficiency, and eight functional food web indices between the 1990s (low fishing intensity) and the 2000s (high fishing intensity). The functional attributes (e.g. consumption) of high trophic levels (e.g. predators) were lower in the 2000s than in the 1990s while primary production did not vary, causing food web efficiency to decrease up to 40% with time for these groups. The opposite was found for lower trophic levels (e.g. zooplankton): the functional attributes and food web efficiency increased with time (22 and 10% for the functional attributes and food web efficiency, respectively). Total system throughput, a functional food web index, was about 10% higher in the 1990s than in the 2000s, indicating a reduction of the system size and activity with time. The network analyses further indicated that the Vietnamese coastal ecosystem in the 1990s was more developed (higher ascendancy and capacity), more stable (higher overhead) and more mature (higher ratio of ascendancy and capacity) than in the 2000s. In the 1990s the recovery time of the ecosystem was shorter than in 2000s, as indicated by a higher Finn's cycling index in the 1990s (7.8 and 6.5% in 1990s and 2000s, respectively). Overall, our results demonstrate that the Vietnamese coastal ecosystem has experienced profound changes between the 1990s and 2000s, and emphasise the need for a closer inspection of the ecological impact of fishing.

  3. Defining ecospace of Arctic marine food webs using a novel quantitative approach

    Science.gov (United States)

    Gale, M.; Loseto, L. L.

    2011-12-01

    The Arctic is currently facing unprecedented change with developmental, physical and climatological changes. Food webs within the marine Arctic environment are highly susceptible to anthropogenic stressors and have thus far been understudied. Stable isotopes, in conjunction with a novel set of metrics, may provide a framework that allows us to understand which areas of the Arctic are most vulnerable to change. The objective of this study was to use linear distance metrics applied to stable isotopes to a) define and quantify four Arctic marine food webs in ecospace; b) enable quantifiable comparisons among the four food webs and with other ecosystems; and, c) evaluate vulnerability of the four food webs to anthropogenic stressors such as climate change. The areas studied were Hudson Bay, Beaufort Sea, Lancaster Sound and North Water Polynya. Each region was selected based on the abundance of previous research and published and available stable isotope data in peer-review literature. We selected species to cover trophic levels ranging from particulate matter to polar bears with consideration of pelagic, benthic and ice-associated energy pathways. We interpret higher diversity in baseline carbon energy as signifying higher stability in food web structure. Based on this, the Beaufort Sea food web had the highest stability; the Beaufort Sea food web occupied the largest isotopic niche space and was supported by multiple carbon sources. Areas with top-down control system, such as Lancaster Sound and North Water Polynya, would be the first to experience an increase in trophic redundancy and possible hardships from external stressors, as they have fewer basal carbon sources and greater numbers of mid-high level consumers. We conclude that a diverse carbon energy based ecosystem such as the Beaufort Sea and Hudson Bay regions are more resilient to change than a top down control system.

  4. Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation.

    Science.gov (United States)

    Ullah, Hadayet; Nagelkerken, Ivan; Goldenberg, Silvan U; Fordham, Damien A

    2018-01-01

    Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems worldwide. However, most of these projections are based on ecological proxies or experiments on single species or simplified food webs. How energy fluxes are likely to change in marine food webs in response to future climates remains unclear, hampering forecasts of ecosystem functioning. Using a sophisticated mesocosm experiment, we model energy flows through a species-rich multilevel food web, with live habitats, natural abiotic variability, and the potential for intra- and intergenerational adaptation. We show experimentally that the combined stress of acidification and warming reduced energy flows from the first trophic level (primary producers and detritus) to the second (herbivores), and from the second to the third trophic level (carnivores). Warming in isolation also reduced the energy flow from herbivores to carnivores, the efficiency of energy transfer from primary producers and detritus to herbivores and detritivores, and the living biomass of detritivores, herbivores, and carnivores. Whilst warming and acidification jointly boosted primary producer biomass through an expansion of cyanobacteria, this biomass was converted to detritus rather than to biomass at higher trophic levels-i.e., production was constrained to the base of the food web. In contrast, ocean acidification affected the food web positively by enhancing trophic flow from detritus and primary producers to herbivores, and by increasing the biomass of carnivores. Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer-consumer dynamics, both of which have important implications for the structuring of benthic communities.

  5. Comparing the Ecological Stoichiometry in Green and Brown Food Webs – A Review and Meta-analysis of Freshwater Food Webs

    Directory of Open Access Journals (Sweden)

    Michelle A. Evans-White

    2017-06-01

    Full Text Available The framework of ecological stoichiometry was developed primarily within the context of “green” autotroph-based food webs. While stoichiometric principles also apply in “brown” detritus-based systems, these systems have been historically understudied and differ from green ones in several important aspects including carbon (C quality and the nutrient [nitrogen (N and phosphorus (P] contents of food resources for consumers. In this paper, we review work over the last decade that has advanced the application of ecological stoichiometry from green to brown food webs, focusing on freshwater ecosystems. We first review three focal areas where green and brown food webs differ: (1 bottom–up controls by light and nutrient availability, (2 stoichiometric constraints on consumer growth and nutritional regulation, and (3 patterns in consumer-driven nutrient dynamics. Our review highlights the need for further study of how light and nutrient availability affect autotroph–heterotroph interactions on detritus and the subsequent effects on consumer feeding and growth. To complement this conceptual review, we formally quantified differences in stoichiometric principles between green and brown food webs using a meta-analysis across feeding studies of freshwater benthic invertebrates. From 257 datasets collated across 46 publications and several unpublished studies, we compared effect sizes (Pearson’s r of resource N:C and P:C on growth, consumption, excretion, and egestion between herbivorous and detritivorous consumers. The meta-analysis revealed that both herbivore and detritivore growth are limited by resource N:C and P:C contents, but effect sizes only among detritivores were significantly above zero. Consumption effect sizes were negative among herbivores but positive for detritivores in the case of both N:C and P:C, indicating distinct compensatory feeding responses across resource stoichiometry gradients. Herbivore P excretion rates responded

  6. FoodPro: A Web-Based Tool for Evaluating Covariance and Correlation NMR Spectra Associated with Food Processes

    Directory of Open Access Journals (Sweden)

    Eisuke Chikayama

    2016-10-01

    Full Text Available Foods from agriculture and fishery products are processed using various technologies. Molecular mixture analysis during food processing has the potential to help us understand the molecular mechanisms involved, thus enabling better cooking of the analyzed foods. To date, there has been no web-based tool focusing on accumulating Nuclear Magnetic Resonance (NMR spectra from various types of food processing. Therefore, we have developed a novel web-based tool, FoodPro, that includes a food NMR spectrum database and computes covariance and correlation spectra to tasting and hardness. As a result, FoodPro has accumulated 236 aqueous (extracted in D2O and 131 hydrophobic (extracted in CDCl3 experimental bench-top 60-MHz NMR spectra, 1753 tastings scored by volunteers, and 139 hardness measurements recorded by a penetrometer, all placed into a core database. The database content was roughly classified into fish and vegetable groups from the viewpoint of different spectrum patterns. FoodPro can query a user food NMR spectrum, search similar NMR spectra with a specified similarity threshold, and then compute estimated tasting and hardness, covariance, and correlation spectra to tasting and hardness. Querying fish spectra exemplified specific covariance spectra to tasting and hardness, giving positive covariance for tasting at 1.31 ppm for lactate and 3.47 ppm for glucose and a positive covariance for hardness at 3.26 ppm for trimethylamine N-oxide.

  7. Nutrition Content of Food and Beverage Products on Web Sites Popular With Children

    Science.gov (United States)

    Lingas, Elena O.; Bukofzer, Eliana

    2009-01-01

    We assessed the nutritional quality of branded food and beverage products advertised on 28 Web sites popular with children. Of the 77 advertised products for which nutritional information was available, 49 met Institute of Medicine criteria for foods to avoid, 23 met criteria for foods to neither avoid nor encourage, and 5 met criteria for foods to encourage. There is a need for further research on the nature and extent of food and beverage advertising online to aid policymakers as they assess the impact of this marketing on children. PMID:19443816

  8. Nutrition content of food and beverage products on Web sites popular with children.

    Science.gov (United States)

    Lingas, Elena O; Dorfman, Lori; Bukofzer, Eliana

    2009-11-01

    We assessed the nutritional quality of branded food and beverage products advertised on 28 Web sites popular with children. Of the 77 advertised products for which nutritional information was available, 49 met Institute of Medicine criteria for foods to avoid, 23 met criteria for foods to neither avoid nor encourage, and 5 met criteria for foods to encourage. There is a need for further research on the nature and extent of food and beverage advertising online to aid policymakers as they assess the impact of this marketing on children.

  9. Seasonal variation in mercury and food web biomagnification in Lake Ontario, Canada

    International Nuclear Information System (INIS)

    Zhang Liang; Campbell, Linda M.; Johnson, Timothy B.

    2012-01-01

    Seasonal variation in mercury (Hg) concentrations and food web structure was assessed for eastern Lake Ontario. Hg concentrations, measured in 6 species of invertebrates and 8 species of fishes, tended to be highest in the spring and lowest in the summer for most biota. Yellow perch (Perca flavescens) exhibited significant ontogenetic shifts in diet and Hg, although such patterns were not evident for other species. Food web structure, as indicated by stable isotope values (δ 15 N, δ 13 C) was not static. Log-transformed Hg data were strongly and consistently correlated with δ 15 N values for the whole food web in each of the three seasons (slopes, 0.17–0.24) and across the entire year (slope, 0.2). While significantly different between seasons, the regression slope values are still consistent with published global Hg biomagnification rates. Our results indicate that the assessment of Hg trends in Great Lakes must take into account seasonal patterns and time of sampling. - Graphical abstract: Total mercury concentrations and trophic level (δ 15 N) regressions for organisms from the littoral Lake Ontario food web of Waupoos in 2009. Filled circles represent invertebrates while open circles represent fish. Dashed lines represents the regression between δ 15 N and THg of “whole” food web (log-Hg-δ 15 N regression equations in the upper left hand corner in each plot), and solid lines represents the regression between δ 15 N and THg of “fish-only” food web (log-Hg-δ 15 N regression equations in the lower right hand corner of each plot). Note that the y-axis is untransformed Hg concentrations plotted along a logarithmic scale, while the equations are based on log-transformed Hg values. Highlights: ► Most fish in littoral Lake Ontario had higher Hg concentrations in spring and lower Hg in summer. ► Log Hg consistently biomagnified throughout the food web in each season and for the year. ► Biomagnification rates (e.g., log Hg-δ 15 N slopes) vary

  10. A new modeling approach to define marine ecosystems food-web status with uncertainty assessment

    Science.gov (United States)

    Chaalali, Aurélie; Saint-Béat, Blanche; Lassalle, Géraldine; Le Loc'h, François; Tecchio, Samuele; Safi, Georges; Savenkoff, Claude; Lobry, Jérémy; Niquil, Nathalie

    2015-06-01

    Ecosystem models are currently one of the most powerful approaches used to project and analyse the consequences of anthropogenic and climate-driven changes in food web structure and function. The modeling community is however still finding the effective representation of microbial processes as challenging and lacks of techniques for assessing flow uncertainty explicitly. A linear inverse model of the Bay of Biscay continental shelf was built using a Monte Carlo method coupled with a Markov Chain (LIM-MCMC) to characterize the system's trophic food-web status and its associated structural and functional properties. By taking into account the natural variability of ecosystems (and their associated flows) and the lack of data on these environments, this innovative approach enabled the quantification of uncertainties for both estimated flows and derived food-web indices. This uncertainty assessment constituted a real improvement on the existing Ecopath model for the same area and both models results were compared. Our results suggested a food web characterized by main flows at the basis of the food web and a high contribution of primary producers and detritus to the entire system input flows. The developmental stage of the ecosystem was characterized using estimated Ecological Network Analysis (ENA) indices; the LIM-MCMC produced a higher estimate of flow specialization (than the estimate from Ecopath) owing to better consideration of bacterial processes. The results also pointed to a detritus-based food-web with a web-like structure and an intermediate level of internal flow complexity, confirming the results of previous studies. Other current research on ecosystem model comparability is also presented.

  11. Functional redundancy and food web functioning in linuron-exposed ecosystems

    International Nuclear Information System (INIS)

    De Laender, F.; Van den Brink, P.J.; Janssen, C.R.

    2011-01-01

    An extensive data set describing effects of the herbicide linuron on macrophyte-dominated microcosms was analysed with a food web model to assess effects on ecosystem functioning. We showed that sensitive phytoplankton and periphyton groups in the diets of heterotrophs were gradually replaced by more tolerant phytoplankton species as linuron concentrations increased. This diet shift - showing redundancy among phytoplankton species - allowed heterotrophs to maintain their functions in the contaminated microcosms. On an ecosystem level, total gross primary production was up to hundred times lower in the treated microcosms but the uptake of dissolved organic carbon by bacteria and mixotrophs was less sensitive. Food web efficiency was not consistently lower in the treated microcosms. We conclude that linuron predominantly affected the macrophytes but did not alter the overall functioning of the surrounding planktonic food web. Therefore, a risk assessment that protects macrophyte growth also protects the functioning of macrophyte-dominated microcosms. - Highlights: → Food web modelling reveals the functional response of species and ecosystem to linuron. → Primary production was more sensitive to linuron than bacterial production. → Linuron replaced sensitive phytoplankton by tolerant phytoplankton in heterotrophs' diets. → Linuron did not change the functioning of heterotrophs. - Food web modelling reveals functional redundancy of the planktonic community in microcosms treated with linuron.

  12. Effects of alien plants on insect abundance and biomass: a food-web approach.

    Science.gov (United States)

    Heleno, Rúben H; Ceia, Ricardo S; Ramos, Jaime A; Memmott, Jane

    2009-04-01

    The replacement of native plants by alien species is likely to affect other trophic levels, particularly phytophagous insects. Nevertheless, the effect of alien plants on insect biomass has not yet been quantified. Given their critical role in transferring energy from plants to higher trophic levels, if alien plants do affect insect biomass, this could have far-reaching consequences for community structure. We used 35 food webs to evaluate the impacts of alien plants on insect productivity in a native forest in the Azores. Our food webs quantified plants, insect herbivores, and their parasitoids, which allowed us to test the effects of alien plants on species richness and evenness, insect abundance, insect biomass, and food-web structure. Species richness of plants and insects, along with plant species evenness, declined as the level of plant invasion increased. Nevertheless, none of the 4 quantitative food-web descriptors (number of links, link density, connectance, and interaction evenness) varied significantly with plant invasion independent of the size of the food web. Overall, insect abundance was not significantly affected by alien plants, but insect biomass was significantly reduced. This effect was due to the replacement of large insects on native plants with small insects on alien plants. Furthermore, the impact of alien plants was sufficiently severe to invert the otherwise expected pattern of species-richness decline with increased elevation. We predict a decrease in insect productivity by over 67% if conservation efforts fail to halt the invasion of alien plants in the Azores.

  13. How habitat-modifying organisms structure the food web of two coastal ecosystems

    Science.gov (United States)

    van der Zee, Els M.; Angelini, Christine; Govers, Laura L.; Christianen, Marjolijn J. A.; Altieri, Andrew H.; van der Reijden, Karin J.; Silliman, Brian R.; van de Koppel, Johan; van der Geest, Matthijs; van Gils, Jan A.; van der Veer, Henk W.; Piersma, Theunis; de Ruiter, Peter C.; Olff, Han; van der Heide, Tjisse

    2016-01-01

    The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity. PMID:26962135

  14. Internet food marketing strategies aimed at children and adolescents: a content analysis of food and beverage brand web sites.

    Science.gov (United States)

    Weber, Kristi; Story, Mary; Harnack, Lisa

    2006-09-01

    Americans are spending an increasing amount of time using "new media" like the Internet. There has been little research examining food and beverage Web sites' content and marketing practices, especially those that attract children and adolescents. The purpose of this study was to conduct a content analysis of food- and beverage-brand Web sites and the marketing techniques and advertising strategies present on these sites. The top five brands in eight food and beverage categories, 40 brands in total, were selected based on annual sales data from Brandweek magazine's annual "Superbrands" report. Data were collected using a standardized coding form. The results show a wide variety of Internet marketing techniques and advertising strategies targeting children and adolescents. "Advergaming" (games in which the advertised product is part of the game) was present on 63% of the Web sites. Half or more of the Web sites used cartoon characters (50%) or spokescharacters (55%), or had a specially designated children's area (58%) with a direct link from the homepage. With interactive media still in its developmental stage, there is a need to develop safeguards for children. Food and nutrition professionals need to advocate for responsible marketing techniques that will support the health of children.

  15. Concomitant predation on parasites is highly variable but constrains the ways in which parasites contribute to food web structure

    OpenAIRE

    Cirtwill, Alyssa R.; Stouffer, Daniel B.

    2015-01-01

    Summary Previous analyses of empirical food webs (the networks of who eats whom in a community) have revealed that parasites exert a strong influence over observed food web structure and alter many network properties such as connectance and degree distributions. It remains unclear, however, whether these community?level effects are fully explained by differences in the ways that parasites and free?living species interact within a food web. To rigorously quantify the interrelationship between ...

  16. STRUCTURE OF SOIL FOOD WEB IN SMALLHOLDER COCOA PLANTATION, SOUTH KONAWE DISTRICT, SOUTHEAST SULAWESI, INDONESIA

    Directory of Open Access Journals (Sweden)

    Laode Muhammad Harjoni Kilowasid

    2014-02-01

    Full Text Available An understanding of the structure of the soil food web is critical in determining the practices of soil fertility management based on the biological processes in tropical agricultural regions. The objectives of the study were to assess the variation in trophic level biomass and to analyze the dynamics of the energy channels on the increasing age of cocoa plantation. The characteristics of soil food web structure in smallholder cocoa plantation aged 4, 5, 7, 10, and 16 years were analyzed. The results showed that only biomass at the third trophic level increased with plantation age, but not for the biomass at the lower trophic levels. Biomass in all energy channels did not increased as well along with plantation age. We concluded that variation in the soil food web structure was more influenced by biotic factors of macro-arthropods group, such as facilitation, recolonization capabilities and accessibility in the soil habitat of smallholder cocoa plantation.

  17. The structure of the pelagic food web in relation to water column structure in the Skagerrak

    DEFF Research Database (Denmark)

    Kiørboe, Thomas; Kaas, H.; Kruse, B.

    1990-01-01

    by a doming of the pycnocline, with a deep mixed layer along the periphery and a very shallow pycnocline in central parts. Average phytoplankton size increased with the depth of the upper mixed layer, and the central stratified area was characterized by small flagellates while large and chain-forming diatoms...... on particle surface area rather than particle volume or chl a, and showed a distributional pattern that was nearly the inverse of the distribution of copepod activity. That is, peak bacterial growth rates occurred in central, stratified parts and lower rates were found along the margin with a deep mixed layer....... Thus a 'microbial loop' type of food web seemed to be evolving in the central, strongly stratified parts of the Skagerrak, while a shorter 'classical' type of food web appeared to dominate along the margin. The relation between food web structure and vertical mixing processes observed on oceanwide...

  18. Determination of keystone species in CSM food web: A topological analysis of network structure

    Directory of Open Access Journals (Sweden)

    LiQin Jiang

    2015-03-01

    Full Text Available The importance of a species is correlated with its topological properties in a food web. Studies of keystone species provide the valuable theory and evidence for conservation ecology, biodiversity, habitat management, as well as the dynamics and stability of the ecosystem. Comparing with biological experiments, network methods based on topological structure possess particular advantage in the identification of keystone species. In present study, we quantified the relative importance of species in Carpinteria Salt Marsh food web by analyzing five centrality indices. The results showed that there were large differences in rankings species in terms of different centrality indices. Moreover, the correlation analysis of those centralities was studied in order to enhance the identifying ability of keystone species. The results showed that the combination of degree centrality and closeness centrality could better identify keystone species, and the keystone species in the CSM food web were identified as, Stictodora hancocki, small cyathocotylid, Pygidiopsoides spindalis, Phocitremoides ovale and Parorchis acanthus.

  19. More than a meal: integrating non-feeding interactions into food webs

    Science.gov (United States)

    Kéfi, Sonia; Berlow, Eric L.; Wieters, Evie A.; Navarrete, Sergio A.; Petchey, Owen L.; Wood, Spencer A.; Boit, Alice; Joppa, Lucas N.; Lafferty, Kevin D.; Williams, Richard J.; Martinez, Neo D.; Menge, Bruce A.; Blanchette, Carol A.; Iles, Alison C.; Brose, Ulrich

    2012-01-01

    Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.

  20. Impacts of food web structure and feeding behavior on mercury exposure in Greenland Sharks (Somniosus microcephalus).

    Science.gov (United States)

    McMeans, Bailey C; Arts, Michael T; Fisk, Aaron T

    2015-03-15

    Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks (Somniosus microcephalus) via both bottom-up food web transfer and top-down shark feeding behavior. Log10THg increased significantly with δ(15)N and trophic position from invertebrates (0.01 ± 0.01 μg · g(-1) [113 ± 1 ng · g(-1)] dw in copepods) to Greenland Sharks (3.54 ± 1.02 μg · g(-1)). The slope of the log10THg vs. δ(15)N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas. Copyright © 2014 Elsevier B.V. All rights reserved.

  1. Parasites affect food web structure primarily through increased diversity and complexity.

    Directory of Open Access Journals (Sweden)

    Jennifer A Dunne

    Full Text Available Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity, particularly when including concomitant links (links from predators to parasites of their prey. However, we clarify prior claims that parasites "dominate" food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic

  2. Unraveling the intricate dynamics of planktonic Arctic marine food webs. A sensitivity analysis of a well-documented food web model

    Science.gov (United States)

    Saint-Béat, Blanche; Maps, Frédéric; Babin, Marcel

    2018-01-01

    The extreme and variable environment shapes the functioning of Arctic ecosystems and the life cycles of its species. This delicate balance is now threatened by the unprecedented pace and magnitude of global climate change and anthropogenic pressure. Understanding the long-term consequences of these changes remains an elusive, yet pressing, goal. Our work was specifically aimed at identifying which biological processes impact Arctic planktonic ecosystem functioning, and how. Ecological Network Analysis (ENA) indices reveal emergent ecosystem properties that are not accessible through simple in situ observation. These indices are based on the architecture of carbon flows within food webs. But, despite the recent increase in in situ measurements from Arctic seas, many flow values remain unknown. Linear inverse modeling (LIM) allows missing flow values to be estimated from existing flow observations and, subsequent reconstruction of ecosystem food webs. Through a sensitivity analysis on a LIM model of the Amundsen Gulf in the Canadian Arctic, we were able to determine which processes affected the emergent properties of the planktonic ecosystem. The analysis highlighted the importance of an accurate knowledge of the various processes controlling bacterial production (e.g. bacterial growth efficiency and viral lysis). More importantly, a change in the fate of the microzooplankton within the food web can be monitored through the trophic level of mesozooplankton. It can be used as a "canary in the coal mine" signal, a forewarner of larger ecosystem change.

  3. Legacy effects of drought on plant growth and the soil food web

    DEFF Research Database (Denmark)

    de Vries, Franciska; Liiri, Mira; Strandmark, Lisa Bjørnlund

    2012-01-01

    Soils deliver important ecosystem services, such as nutrient provision for plants and the storage of carbon (C) and nitrogen (N), which are greatly impacted by drought. Both plants and soil biota affect soil C and N availability, which might in turn affect their response to drought, offering...... the potential to feed back on each other's performance. In a greenhouse experiment, we compared legacy effects of repeated drought on plant growth and the soil food web in two contrasting land-use systems: extensively managed grassland, rich in C and with a fungal-based food web, and intensively managed wheat...

  4. Mangrove detrital system: decomposition processes and their role in estuarine food webs

    Energy Technology Data Exchange (ETDEWEB)

    Fell, J.W.

    1978-01-01

    The report describes a research program directed to the role of the decomposition of leaf material from the red mangrove (Rhizophora mangle) in the food web of estuaries, how these processes work and what alterations can be expected with environmental perturbations. The program was designed to examine the following components of the decomposition process involving carbon and nitrogen inputs/outputs: (1) the role of nitrogen fixation in the decomposition process; (2) the role of fungi in the secondary phase of decomposition; (3) the fate of detrital particles via /sup 13/C//sup 12/C; (4) the role leachates in food webs; and (5) invertebrate utilization of detritus. 19 references. (ACR)

  5. Adaptive behaviour, tri-trophic food-web stability and damping of chaos

    DEFF Research Database (Denmark)

    Visser, Andre; Mariani, Patrizio; Pigolotti, Simone

    2012-01-01

    We examine the effect of adaptive foraging behaviour within a tri-trophic food web with intra-guild predation. The intra-guild prey is allowed to adjust its foraging effort so as to achieve an optimal per capita growth rate in the face of realized feeding, predation risk and foraging cost. Adaptive...... fitness-seeking behaviour of the intra-guild prey has a stabilizing effect on the tri-trophic food-web dynamics provided that (i) a finite optimal foraging effort exists and (ii) the trophic transfer efficiency from resource to predator via the intra-guild prey is greater than that from the resource...

  6. Stable isotope evidence of long-term changes in North Sea food web structure

    DEFF Research Database (Denmark)

    Richardson, Katherine; Christensen, Jens Tang

    2008-01-01

    coast. Porpoises collected after ~1960 had significantly lower d15N than porpoises collected earlier. This change in d15N implies that fundamental changes in food web structure in, or nutrient availability to, the North Sea have taken place over the last ~150 yr and that most of the change occurred over...... reported here may be a reflection of a change in the isotope signature of nitrogen entering the food web. Regardless of its underlying cause, the recorded change in isotopic signature in harbour porpoises is noteworthy as it represents the first fisheries-independent documentation of a long-term temporal...

  7. Enhancing Linkages Between Healthy Diets, Local Agriculture, and Sustainable Food Systems: The School Meals Planner Package in Ghana.

    Science.gov (United States)

    Fernandes, Meenakshi; Galloway, Rae; Gelli, Aulo; Mumuni, Daniel; Hamdani, Salha; Kiamba, Josephine; Quarshie, Kate; Bhatia, Rita; Aurino, Elisabetta; Peel, Francis; Drake, Lesley

    2016-12-01

    Interventions that enhance linkages between healthy diets and local agriculture can promote sustainable food systems. Home-grown school feeding programs present a promising entry point for such interventions, through the delivery of nutritious menus and meals. To describe the adaptation of the School Meals Planner Package to the programmatic and environmental reality in Ghana during the 2014 to 2015 school year. Guided by a conceptual framework highlighting key considerations and trade-offs in menu design, an open-source software was developed that could be easily understood by program implementers. Readily available containers from markets were calibrated into "handy measures" to support the provision of adequate quantities of food indicated by menus. Schools and communities were sensitized to the benefits of locally sourced, nutrient-rich diets. A behavior change communication campaign including posters and songs promoting healthy diets was designed and disseminated in schools and communities. The School Meals Planner Package was introduced in 42 districts in Ghana, reaching more than 320 000 children. Monitoring reports and feedback on its use were positive, demonstrating how the tool can be used by planners and implementers alike to deliver nutritious, locally-sourced meals to schoolchildren. The value of the tool has been recognized at the highest levels by Ghana's government who have adopted it as official policy. The School Meals Planner Package supported the design of nutritious, locally sourced menus for the school feeding program in Ghana. The tool can be similarly adapted for other countries to meet context-specific needs. © The Author(s) 2016.

  8. Climate change-contaminant interactions in marine food webs: Toward a conceptual framework.

    Science.gov (United States)

    Alava, Juan José; Cheung, William W L; Ross, Peter S; Sumaila, U Rashid

    2017-10-01

    Climate change is reshaping the way in which contaminants move through the global environment, in large part by changing the chemistry of the oceans and affecting the physiology, health, and feeding ecology of marine biota. Climate change-associated impacts on structure and function of marine food webs, with consequent changes in contaminant transport, fate, and effects, are likely to have significant repercussions to those human populations that rely on fisheries resources for food, recreation, or culture. Published studies on climate change-contaminant interactions with a focus on food web bioaccumulation were systematically reviewed to explore how climate change and ocean acidification may impact contaminant levels in marine food webs. We propose here a conceptual framework to illustrate the impacts of climate change on contaminant accumulation in marine food webs, as well as the downstream consequences for ecosystem goods and services. The potential impacts on social and economic security for coastal communities that depend on fisheries for food are discussed. Climate change-contaminant interactions may alter the bioaccumulation of two priority contaminant classes: the fat-soluble persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), as well as the protein-binding methylmercury (MeHg). These interactions include phenomena deemed to be either climate change dominant (i.e., climate change leads to an increase in contaminant exposure) or contaminant dominant (i.e., contamination leads to an increase in climate change susceptibility). We illustrate the pathways of climate change-contaminant interactions using case studies in the Northeastern Pacific Ocean. The important role of ecological and food web modeling to inform decision-making in managing ecological and human health risks of chemical pollutants contamination under climate change is also highlighted. Finally, we identify the need to develop integrated policies that manage the

  9. Organochlorine pollution in tropical rivers (Guadeloupe): Role of ecological factors in food web bioaccumulation

    Energy Technology Data Exchange (ETDEWEB)

    Coat, Sophie, E-mail: coatsophie@gmail.com [EA 926 DYNECAR, Laboratoire de Biologie Marine, UFR Sciences, Universite des Antilles et de la Guyane, BP592, 97159 Pointe-a-Pitre Cedex (France); Monti, Dominique, E-mail: dominique.monti@univ-ag.fr [EA 926 DYNECAR, Laboratoire de Biologie Marine, UFR Sciences, Universite des Antilles et de la Guyane, BP592, 97159 Pointe-a-Pitre Cedex (France); Legendre, Pierre, E-mail: pierre.legendre@umontreal.ca [Departement de Sciences Biologique, Universite de Montreal, C.P. 6128, succursale A, Montreal, Quebec H3C 3J7 (Canada); Bouchon, Claude, E-mail: claude.bouchon@univ-ag.fr [EA 926 DYNECAR, Laboratoire de Biologie Marine, UFR Sciences, Universite des Antilles et de la Guyane, BP592, 97159 Pointe-a-Pitre Cedex (France); Massat, Felix, E-mail: fmassat@ladrome.fr [LDA26, laboratoire Departemental d' Analyses de la Drome, 27 avenue Lautagne, 26000 Valence (France); Lepoint, Gilles, E-mail: g.lepoint@ulg.ac.be [MARE Centre, Laboratoire d' Oceanologie, Universite de Liege, Bat. B6, 4000 Sart Tilman, Belgique (Belgium)

    2011-06-15

    Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of diadromous fishes and shrimps, as they re-enter the river. The role of ecological factors in the bioaccumulation of pesticides was evaluated. Whereas the most persistent pollutants (chlordecone and monohydro-chlordecone) were related to the organisms diet and habitat, bioaccumulation of {beta}-HCH was only influenced by animal lipid content. The biomagnification potential of chlordecone through the food chain has been demonstrated. It highlighted the importance of trophic transfer in this compound bioaccumulation process. In contrast, bioconcentration by passive diffusion from water seemed to be the main exposure route of biota to {beta}-HCH. - Highlights: > We measured OC pesticides and stable isotope ratios in a tropical stream. > Results showed a strong and ubiquitous contamination of the entire food web. > Diadromous juveniles strongly accumulated pollutants when they re-enter the river. > The most persistent pollutant (chlordecone) was related to species diet and habitat. > {beta}-HCH was only influenced by animal lipid content. - This paper determines the bioaccumulation and transfer processes of organochlorine pesticides within the stream food web in Guadeloupe (Caribbean).

  10. Warming alters energetic structure and function but not resilience of soil food webs

    Science.gov (United States)

    Schwarz, Benjamin; Barnes, Andrew D.; Thakur, Madhav P.; Brose, Ulrich; Ciobanu, Marcel; Reich, Peter B.; Rich, Roy L.; Rosenbaum, Benjamin; Stefanski, Artur; Eisenhauer, Nico

    2017-12-01

    Climate warming is predicted to alter the structure, stability, and functioning of food webs1-5. Yet, despite the importance of soil food webs for energy and nutrient turnover in terrestrial ecosystems, the effects of warming on these food webs—particularly in combination with other global change drivers—are largely unknown. Here, we present results from two complementary field experiments that test the interactive effects of warming with forest canopy disturbance and drought on energy flux in boreal-temperate ecotonal forest soil food webs. The first experiment applied a simultaneous above- and belowground warming treatment (ambient, +1.7 °C, +3.4 °C) to closed-canopy and recently clear-cut forest, simulating common forest disturbance6. The second experiment crossed warming with a summer drought treatment (-40% rainfall) in the clear-cut habitats. We show that warming reduces energy flux to microbes, while forest canopy disturbance and drought facilitates warming-induced increases in energy flux to higher trophic levels and exacerbates the reduction in energy flux to microbes, respectively. Contrary to expectations, we find no change in whole-network resilience to perturbations, but significant losses in ecosystem functioning. Warming thus interacts with forest disturbance and drought, shaping the energetic structure of soil food webs and threatening the provisioning of multiple ecosystem functions in boreal-temperate ecotonal forests.

  11. Fish introductions and light modulate food web fluxes in tropical streams: a whole-ecosystem experimental approach.

    Science.gov (United States)

    Collins, Sarah M; Thomas, Steven A; Heatherly, Thomas; MacNeill, Keeley L; Leduc, Antoine O H C; López-Sepulcre, Andrés; Lamphere, Bradley A; El-Sabaawi, Rana W; Reznick, David N; Pringle, Catherine M; Flecker, Alexander S

    2016-11-01

    Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen ( 15 N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. control) and consumer treatments (guppy introduction vs. control). The thinned canopy stream had higher primary production than the natural canopy control, leading to increased N fluxes to invertebrates that feed on benthic biofilms (grazers), fine benthic organic matter (collector-gatherers), and organic particles suspended in the water column (filter feeders). Stream reaches with guppies also had higher primary productivity and higher N fluxes to grazers and filter feeders. In contrast, N fluxes to collector-gatherers were reduced in guppy introduction reaches relative to upstream controls. N fluxes to leaf-shredding invertebrates, predatory invertebrates, and the other fish species present (Hart's killifish, Anablepsoides hartii) did not differ across light or guppy treatments, suggesting that effects on detritus-based linkages and upper trophic levels were not as strong. Effect sizes of guppy and canopy treatments on N flux rates were similar for most taxa, though guppy effects were the strongest for filter feeding invertebrates while canopy effects were the strongest for collector-gatherer invertebrates. Combined, these results extend previous knowledge about top-down and bottom-up controls on ecosystems by providing experimental, reach-scale evidence that both pathways can

  12. Trophic state changes can affect the importance of methane-derived carbon in aquatic food webs

    NARCIS (Netherlands)

    Schilder, Jos; Van Hardenbroek, M.; Bodelier, P.L.E.; Kirilova, Emiliya P.; Leuenberger, Markus; Lotter, A.F.; Heiri, O.

    2017-01-01

    Methane-derived carbon, incorporated by methane-oxidizing bacteria, has been identified as a significant source of carbon in food webs of many lakes. By measuring the stable carbon isotopic composition (δ13C values) of particulate organic matter, Chironomidae and Daphnia spp. and their resting eggs

  13. The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient

    Science.gov (United States)

    Estuarine food webs function within a heterogeneous mosaic and are supported by a mix of primary producers from both local and distant sources. Processes governing the exchange and consumption of organic matter (OM), however, are poorly understood. To study the contribution of ...

  14. Feeding environment and other traits shape species' roles in marine food webs.

    Science.gov (United States)

    Cirtwill, Alyssa R; Eklöf, Anna

    2018-04-02

    Food webs and meso-scale motifs allow us to understand the structure of ecological communities and define species' roles within them. This species-level perspective on networks permits tests for relationships between species' traits and their patterns of direct and indirect interactions. Such relationships could allow us to predict food-web structure based on more easily obtained trait information. Here, we calculated the roles of species (as vectors of motif position frequencies) in six well-resolved marine food webs and identified the motif positions associated with the greatest variation in species' roles. We then tested whether the frequencies of these positions varied with species' traits. Despite the coarse-grained traits we used, our approach identified several strong associations between traits and motifs. Feeding environment was a key trait in our models and may shape species' roles by affecting encounter probabilities. Incorporating environment into future food-web models may improve predictions of an unknown network structure. © 2018 John Wiley & Sons Ltd/CNRS.

  15. The delivery of organic contaminants to the Arctic food web: Why sea ice matters

    DEFF Research Database (Denmark)

    Pucko, M.; Stern, Gary; Macdonald, Robie

    2015-01-01

    For decades sea ice has been perceived as a physical barrier for the loading of contaminants to the Arctic Ocean. We show that sea ice, in fact, facilitates the delivery of organic contaminants to the Arctic marine food web through processes that: 1) are independent of contaminant physical...

  16. Microcystin in aquatic food webs of the Baltic and Chesapeake Bay regions

    Science.gov (United States)

    Bukaveckas, Paul A.; Lesutienė, Jūratė; Gasiūnaitė, Zita R.; Ložys, Linas; Olenina, Irina; Pilkaitytė, Renata; Pūtys, Žilvinas; Tassone, Spencer; Wood, Joseph

    2017-05-01

    We undertook a comparative study of the James River Estuary, a sub-estuary of Chesapeake Bay, and the Curonian Lagoon, a sub-estuary of the Baltic Sea, to better understand the factors that determine the presence and persistence of algal toxins in food webs. Over a 2-year period, we measured microcystin concentrations in water, sediment and biota (fish and shellfish) at both sites. Across both food webs we found highest levels of microcystin among consumers of suspended particulate matter, including planktivorous fishes and filter-feeding shellfish, and lower levels of toxin among piscivores, scavengers and benthic omnivores. Despite similar levels of microcystin in the water column at the two sites, we observed higher toxin levels in fish and sediments of the Curonian Lagoon. We attribute this difference to the legacy of prior toxic cyanobacteria blooms in the Curonian Lagoon and hydrologic factors that result in a predominance of autochthonously-derived organic matter in the sediments at this site. Our results suggest that a consideration of species-specific differences in feeding habits, and organic matter sources supporting food webs are important to understanding the accumulation and persistence of algal toxins in food webs and should therefore be considered in assessment of risks to aquatic biota and human health.

  17. Effects of labile carbon addition on a headwater stream food web

    Science.gov (United States)

    Heidi S. Wilcox; J. Bruce Wallace; Judy L. Meyer; Jonathan P. Benstead

    2005-01-01

    We added dextrose for two 8-week periods (summer and autumn) to a highly heterotrophic headwater stream in North Carolina, U.S.A., to examine the responses of its benthic food web to increased labile carbon. We hypothesized that addition of labile carbon would elevate microbial abundance and activity, resulting in greater resource availability and higher...

  18. The role of a water bug, Sigara striata, in freshwater food webs

    Czech Academy of Sciences Publication Activity Database

    Klečka, Jan

    2014-01-01

    Roč. 2, č. 1 (2014), e389 ISSN 2167-8359 Grant - others:Student Grant Agency of the Faculty of Biological Sciences, University of South Bohemia(CZ) SGA 2008 Institutional support: RVO:60077344 Keywords : predation * predator-prey interactions * food webs Subject RIV: EH - Ecology, Behaviour Impact factor: 2.112, year: 2014 https://peerj.com/articles/389.pdf

  19. Status and trends in the structure of Arctic benthic food webs

    Directory of Open Access Journals (Sweden)

    Monika Kędra

    2015-05-01

    Full Text Available Ongoing climate warming is causing a dramatic loss of sea ice in the Arctic Ocean, and it is projected that the Arctic Ocean will become seasonally ice-free by 2040. Many studies of local Arctic food webs now exist, and with this review paper we aim to synthesize these into a large-scale assessment of the current status of knowledge on the structure of various Arctic marine food webs and their response to climate change, and to sea-ice retreat in particular. Key drivers of ecosystem change and potential consequences for ecosystem functioning and Arctic marine food webs are identified along the sea-ice gradient, with special emphasis on the following regions: seasonally ice-free Barents and Chukchi seas, loose ice pack zone of the Polar Front and Marginal Ice Zone, and permanently sea-ice covered High Arctic. Finally, we identify knowledge gaps in different Arctic marine food webs and provide recommendations for future studies.

  20. Verifying Food Web Bioaccumulation Models by Tracking Fish Exposure and Contaminant Uptake

    Science.gov (United States)

    2012-03-01

    chemical: employing poisons or homeostasis disrupters The suitability of these mechanisms for the tag under development was evaluated from a number...Arnot, J. A. and F. A. P. C. Gobas (2004). "A Food Web Bioaccumulation Model for Organic Chemicals in Aquatic Ecosystems ." Environmental Toxicology

  1. Estuarine consumers utilize marine, estuarine and terrestrial organic matter and provide connectivity among these food webs

    Science.gov (United States)

    The flux of organic matter (OM) across ecosystem boundaries can influence estuarine food web dynamics and productivity. However, this process is seldom investigated taking into account all the adjacent ecosystems (e.g. ocean, river, land) and different hydrological settings (i.e....

  2. Food-web structure in the hypertrophic Rietvlei Dam based on ...

    African Journals Online (AJOL)

    ... major planktonic (phytoplankton, zooplankton), benthic (submerged macrophytes and associated epiphytes, benthic macro-invertebrates) and nektonic (fish) food-web components, collected from 3 to 7 shallow inshore locations (with additional plankton samples at 1 or 2 deep offshore sites) in Rietvlei Dam over a period ...

  3. Columbia River food webs: Developing a broader scientific foundation for river restoration

    Science.gov (United States)

    Alldredge, J. Richard; Beauchamp, David; Bisson, Peter A.; Congleton, James; Henny, Charles; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Naiman, Robert J.; Pearcy, William; Rieman, Bruce; Ruggerone, Greg; Scarnecchia, Dennis; Smouse, Peter; Wood, Chris C.

    2011-01-01

    The objectives of this report are to provide a fundamental understanding of aquatic food webs in the Columbia River Basin and to illustrate and summarize their influences on native fish restoration efforts. The spatial scope addresses tributaries, impoundments, the free-flowing Columbia and Snake rivers, as well as the estuary and plume. Achieving the Council's vision for the Columbia River Fish and Wildlife Program (NPCC 2009-09) of sustaining a "productive and diverse community" that provides "abundant" harvest, is best accomplished through a time-prioritized action plan, one that complements other approaches while addressing important challenges and uncertainties related to the Basin's food webs. Note that the oceanic food webs, although of immense importance in sustaining fish populations, are not considered beyond the plume since they involve an additional set of complex and rapidly evolving issues. An analysis of oceanic food webs of relevance to the Columbia River requires a separately focused effort (e.g., Hoegh- Guldberg and Bruno 2010).

  4. Nutrient enrichment reduces constraints on material flows in a detritus-based food web

    Science.gov (United States)

    Wyatt F. Cross; Bruce Wallace; Amy D. Rosemond

    2007-01-01

    Most aquatic and terrestrial ecosystems are experiencing increased nutrient availability, which is affecting their structure and function. By altering community composition and productivity of consumers, enrichment can indirectly cause changes in the pathways and magnitude of material flows in food webs. These changes, in turn, have major consequences for material...

  5. Food Web Structure and Basal Resource Utilization along a Tropical Island Stream Continuum, Puerto Rico.

    Science.gov (United States)

    James G. March; Catherine M. Pringle

    2003-01-01

    Tropical stream food webs are thought to be based primarily on terrestrial resources (leaf litter) in small forested headwater streams and algal resources in larger, wider streams. In tropical island streams, the dominant consumers are often omnivorous freshwater shrimps that consume algae, leaf litter, insects, and other shrimps. We used stable isotope analysis...

  6. Stable isotope evidence of food web connectivity by a top predatory ...

    African Journals Online (AJOL)

    In this study, food web connectivity within the Kowie Estuary on the south-east coast of South Africa was evidenced by the trophic behaviour of the predominantly piscivorous Argyrosomus japonicus. We examined stable isotopes of carbon (δ 13C) and nitrogen (δ 15N) in the dominant consumers (zooplankton, invertebrates ...

  7. Towards ecosystem-based management: Identifying operational food-web indicators for marine ecosystems

    DEFF Research Database (Denmark)

    Tam, Jamie C.; Link, Jason S.; Rossberg, Axel G.

    2017-01-01

    Modern approaches to Ecosystem-Based Management and sustainable use of marine resources must account for the myriad of pressures (interspecies, human and environmental) affecting marine ecosystems. The network of feeding interactions between co-existing species and populations (food webs) are an ...

  8. Status and trends in the structure of Arctic benthic food webs

    NARCIS (Netherlands)

    Kędra, M.; Moritz, C.; Choy, E.S.; David, C.; Degen, R.; Duerksen, S.; Ellingsen, I.; Górska, B.; Grebmeier, J.M.; Kirievskaya, D.; van Oevelen, D.; Piwosz, K.; Samuelsen, A.; We? slawski, J.M.

    2015-01-01

    Ongoing climate warming is causing a dramatic loss of sea ice in the Arctic Ocean, and it is projected that the Arctic Ocean will become seasonally ice-free by 2040. Many studies of local Arctic food webs now exist, and with this review paper we aim to synthesize these into a large-scale assessment

  9. Parasites Affect Food Web Structure Primarily through Increased Diversity and Complexity

    NARCIS (Netherlands)

    Dunne, J.A.; Lafferty, K.D.; Dobson, A.P.; Hechinger, R.F.; Kuris, A.M.; Martinez, N.D.; McLaughlin, J.P.; Mouritsen, K.N.; Poulin, R.; Reise, K.; Stouffer, D.B.; Thieltges, D.W.; Williams, R.J.; Zander, C.D.

    2013-01-01

    Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters

  10. Food-web stability signals critical transitions in temperate shallow lakes

    NARCIS (Netherlands)

    Kuiper, Jan J.; van Altena, Cassandra; de Ruiter, P.C.; Van Gerven, Luuk P.A.; Janse, Jan H.; Mooij, Wolf M.

    2015-01-01

    A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it

  11. Food-web stability signals critical transitions in temperate shallow lakes

    NARCIS (Netherlands)

    Kuiper, J.J.; Altena, Van Cassandra; Ruiter, De P.C.; Gerven, Van L.P.A.; Janse, J.H.; Mooij, W.M.

    2015-01-01

    A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet,

  12. Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)

    NARCIS (Netherlands)

    Van Oevelen, D.; Bergmann, M.; Soetaert, K.E.R.; Bauerfeind, E.; Hasemann, C.; Klages, M.; Schewe, I.; Soltwedel, T.; Budaeva, N.E.

    2011-01-01

    The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central

  13. The soil food web revisited: Diverse and widespread mycophagous soil protists

    NARCIS (Netherlands)

    Geisen, Stefan; Koller, R.; Hünninghaus, M.; Dumack, K.; Urich, T.; Bonkowski, M.

    2016-01-01

    Soil protists are commonly suggested being solely bacterivorous, serving together with bacterivorous nematodes as the main controllers of the bacterial energy channel in soil food webs. In contrast, the fungal energy channel is assumed to be controlled by arthropods and mycophagous nematodes. This

  14. Food web assembly at the landscape scale : Using stable isotopes to reveal changes in trophic structure during succession

    NARCIS (Netherlands)

    Schrama, Maarten; Jouta, Jeltje; Berg, Matty P.; Olff, Han

    Food webs are increasingly evaluated at the landscape scale, accounting for spatial interactions involving different nutrient and energy channels. Also, while long viewed as static, food webs are increasingly seen as dynamic entities that assemble during vegetation succession. The next necessary

  15. Benthic primary producers are key to sustain the Wadden Sea food web : Stable carbon isotope analysis at landscape scale

    NARCIS (Netherlands)

    Christianen, M J A; Middelburg, J J; Holthuijsen, S J; Jouta, J; Compton, T J; van der Heide, T; Piersma, T.; Sinninghe Damsté, J S; van der Veer, H W; Schouten, S; Olff, H

    Coastal food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Distinguishing between these energy sources is essential for our understanding of ecosystem functioning. However, the relative contribution of these components to the food web at the

  16. Benthic primary producers are key to sustain the Wadden Sea food web: stable carbon isotope analysis at landscape scale

    NARCIS (Netherlands)

    Christianen, M.J.A.; Middelburg, J.J.; Holthuijsen, S.J.; Jouta, J.; Compton, T.J.; van der Heide, T.; Piersma, T.; Sinninghe Damsté, J.S.; van der Veer, H.W.; Schouten, S.; Olff, H.

    2017-01-01

    Coastal food webs can be supported by local benthic or pelagic primary produc-ers and by the import of organic matter. Distinguishing between these energy sources is essen-tial for our understanding of ecosystem functioning. However, the relative contribution ofthese components to the food web at

  17. Benthic primary producers are key to sustain the Wadden Sea food web : stable carbon isotope analysis at landscape scale

    NARCIS (Netherlands)

    Christianen, M.J.A.; Middelburg, Jack J.; Holthuijsen, S.J.; Jouta, J.; Compton, T.J.; van der Heide, T.; Piersma, T.; Sinninghe Damsté, Jaap S.; van der Veer, H.W.; Schouten, Stefan; Olff, H.

    Coastal food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Distinguishing between these energy sources is essential for our understanding of ecosystem functioning. However, the relative contribution of these components to the food web at the

  18. Structure and functioning of intertidal food webs along an avian flyway : A comparative approach using stable isotopes

    NARCIS (Netherlands)

    Catry, Teresa; Lourenço, Pedro M.; Lopes, Ricardo J.; Carneiro, Camilo; Alves, José A.; Costa, Joana; Rguibi-Idrissi, Hamid; Bearhop, Stuart; Piersma, Theunis; Granadeiro, José P.

    1. Food webs and trophic dynamics of coastal systems have been the focus of intense research throughout the world, as they prove to be critical in understanding ecosystem processes and functions. However, very few studies have undertaken a quantitative comparison of entire food webs from a key

  19. Structure and functioning of intertidal food webs along an avian flyway: a omparative approach using stable isotopes

    NARCIS (Netherlands)

    Catry, T.; Lourenco, P.M.; Lopes, R.J.; Carneiro, C.; Alves, J.A.; Costa, J.; Rguibi-Idrissi, H.; Bearhop, S.; Piersma, T.; Granadeiro, J.P.

    2016-01-01

    Food webs and trophic dynamics of coastal systems have been the focus of intense research throughout the world, as they prove to be critical in understanding ecosystem processes and functions. However, very few studies have undertaken a quantitative comparison of entire food webs from a key consumer

  20. Impacts of food web structure and feeding behavior on mercury exposure in Greenland Sharks (Somniosus microcephalus)

    International Nuclear Information System (INIS)

    McMeans, Bailey C.; Arts, Michael T.; Fisk, Aaron T.

    2015-01-01

    Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks (Somniosus microcephalus) via both bottom-up food web transfer and top-down shark feeding behavior. Log 10 THg increased significantly with δ 15 N and trophic position from invertebrates (0.01 ± 0.01 μg·g −1 [113 ± 1 ng·g −1 ] dw in copepods) to Greenland Sharks (3.54 ± 1.02 μg·g −1 ). The slope of the log 10 THg vs. δ 15 N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas. - Highlights: • THg significantly increased with δ 15 N from invertebrates to Greenland Sharks. • THg increased with δ 15 N at a faster rate through the pelagic than benthic food web. • Benthic primary

  1. Impacts of food web structure and feeding behavior on mercury exposure in Greenland Sharks (Somniosus microcephalus)

    Energy Technology Data Exchange (ETDEWEB)

    McMeans, Bailey C., E-mail: bcmcmeans@gmail.com [Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4 (Canada); Arts, Michael T. [Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4 (Canada); National Water Research Institute, Environment Canada, 867 Lakeshore Road, PO Box 5050, Burlington, Ontario L7R 4A6 (Canada); Fisk, Aaron T. [Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4 (Canada)

    2015-03-15

    Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks (Somniosus microcephalus) via both bottom-up food web transfer and top-down shark feeding behavior. Log{sub 10}THg increased significantly with δ{sup 15}N and trophic position from invertebrates (0.01 ± 0.01 μg·g{sup −1} [113 ± 1 ng·g{sup −1}] dw in copepods) to Greenland Sharks (3.54 ± 1.02 μg·g{sup −1}). The slope of the log{sub 10}THg vs. δ{sup 15}N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas. - Highlights: • THg significantly increased with δ{sup 15}N from invertebrates to Greenland Sharks. • THg increased with δ{sup 15}N at a faster rate through the pelagic than

  2. Plankton food-webs: to what extent can they be simplified?

    Directory of Open Access Journals (Sweden)

    Domenico D'Alelio

    2016-05-01

    Full Text Available Plankton is a hugely diverse community including both unicellular and multicellular organisms, whose individual dimensions span over seven orders of magnitude. Plankton is a fundamental part of biogeochemical cycles and food-webs in aquatic systems. While knowledge has progressively accumulated at the level of single species and single trophic processes, the overwhelming biological diversity of plankton interactions is insufficiently known and a coherent and unifying trophic framework is virtually lacking. We performed an extensive review of the plankton literature to provide a compilation of data suitable for implementing food-web models including plankton trophic processes at high taxonomic resolution. We identified the components of the plankton community at the Long Term Ecological Research Station MareChiara in the Gulf of Naples. These components represented the sixty-three nodes of a plankton food-web. To each node we attributed biomass and vital rates, i.e. production, consumption, assimilation rates and ratio between autotrophy and heterotrophy in mixotrophic protists. Biomasses and rates values were defined for two opposite system’s conditions; relatively eutrophic and oligotrophic states. We finally identified 817 possible trophic links within the web and provided each of them with a relative weight, in order to define a diet-matrix, valid for both trophic states, which included all consumers, fromn anoflagellates to carnivorous plankton. Vital rates for plankton resulted, as expected, very wide; this strongly contrasts with the narrow ranges considered in plankton system models implemented so far. Moreover, the amount and variety of trophic links highlighted by our review is largely excluded by state-of-the-art biogeochemical and food-web models for aquatic systems. Plankton models could potentially benefit from the integration of the trophic diversity outlined in this paper: first, by using more realistic rates; second, by better

  3. Nearshore energy subsidies support Lake Michigan fishes and invertebrates following major changes in food web structure

    Science.gov (United States)

    Turschak, Benjamin A; Bunnell, David B.; Czesny, Sergiusz J.; Höök, Tomas O.; Janssen, John; Warner, David M.; Bootsma, Harvey A

    2014-01-01

    Aquatic food webs that incorporate multiple energy channels (e.g. nearshore benthic or pelagic) with varying productivity and turnover rates convey stability to biological communities by providing multiple independent energy sources. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and potentially altered the channels through which consumers acquire energy. We used stable C and N isotopes to determine how Lake Michigan food web structure has changed in the past decade, coincident with the expansion of dreissenid mussels, decreased pelagic phytoplankton production and increased nearshore benthic algal production. Fish and invertebrate samples collected from sites around Lake Michigan were analyzed to determine taxa-specific 13C:12C (delta 13C) and 15N:14N (delta 15N) ratios. Sampling took place during two distinct periods, 2002-2003 and 2010-2012, that spanned the period of dreissenid expansion, and included nearshore, pelagic and profundal fish and invertebrate taxa. Magnitude and direction of the 13C shift indicated significantly greater reliance upon nearshore benthic energy sources among nearly all fish taxa as well as profundal invertebrates. Although the mechanisms underlying this 13C shift likely varied among species, possible causes include the transport of benthic algal production to offshore waters and an increased reliance on nearshore prey items. Delta 15N shifts were more variable and of smaller magnitude across taxa although declines in delta 15N among some pelagic fishes may indicate a shift to alternative prey resources. Lake Michigan fishes and invertebrates appear to have responded to dreissenid induced changes in nutrient and energy pathways by switching from pelagic to alternative nearshore energy subsidies. Although large shifts in energy allocation (i.e. pelagic to nearshore benthic) resulting from invasive species appear to have affected total production at upper trophic

  4. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    Directory of Open Access Journals (Sweden)

    Hannah B Vander Zanden

    2016-03-01

    Full Text Available The measurement of stable carbon (δ13C and nitrogen (δ15N isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H and oxygen (δ18O isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applications using δ2H and, to a lesser extent, δ18O values have demonstrated potential for these elements to provide novel insights in modern food web studies. We explore the advantages and challenges associated with three applications of δ2H and δ18O values in food web studies. First, large δ2H differences between aquatic and terrestrial ecosystem end members can permit the quantification of energy inputs and nutrient fluxes between these two sources, with potential applications for determining allochthonous vs. autochthonous nutrient sources in freshwater systems and relative aquatic habitat utilization by terrestrial organisms. Next, some studies have identified a relationship between δ2H values and trophic position, which suggests that this marker may serve as a trophic indicator, in addition to the more commonly used δ15N values. Finally, coupled measurements of δ2H and δ18O values are increasing as a result of reduced analytical challenges to measure both simultaneously and may provide additional ecological information over single element measurements. In some organisms, the isotopic ratios of these two elements are tightly coupled, whereas the isotopic disequilibrium in other organisms may offer insight into the diet and physiology of individuals. Although a coherent framework for interpreting δ2H and δ18O data in the context of food web studies is emerging, many fundamental uncertainties remain. We highlight directions for targeted research that

  5. Using sulfur stable isotopes to assess mercury bioaccumulation and biomagnification in temperate lake food webs.

    Science.gov (United States)

    Clayden, Meredith G; Lescord, Gretchen L; Kidd, Karen A; Wang, Xiaowa; Muir, Derek C G; O'Driscoll, Nelson J

    2017-03-01

    Nitrogen and carbon stable isotopes (δ 15 N, δ 13 C) are commonly used to understand mercury (Hg) bioaccumulation and biomagnification in freshwater food webs. Though sulfur isotopes (δ 34 S) can distinguish between energy sources from the water column (aqueous sulfate) and from sediments to freshwater organisms, little is known about whether δ 34 S can help interpret variable Hg concentrations in aquatic species or food webs. Seven acidic lakes in Kejimkujik National Park (Nova Scotia, Canada) were sampled for biota, water, and sediments in 2009 and 2010. Fishes, zooplankton, and macroinvertebrates were analyzed for δ 34 S, δ 15 N, δ 13 C, and Hg (methyl Hg in invertebrates, total Hg in fishes); aqueous sulfate and profundal sediments were analyzed for δ 34 S. Within lakes, mean δ 34 S values in sediments and sulfate differed between 0.53‰ and 1.98‰, limiting their use as tracers of energy sources to the food webs. However, log-Hg and δ 34 S values were negatively related (slopes -0.14 to -0.35, R 2 0.20-0.39, p < 0.001-0.01) through each food web, and slopes were significantly different among lakes (analysis of covariance, lake × δ 34 S interaction term p = 0.04). Despite these relationships, multiple regression analyses within each taxon showed that biotic Hg concentrations were generally better predicted by δ 15 N and/or δ 13 C. The results indicate that δ 34 S values are predictive of Hg concentrations in these food webs, although the mechanisms underlying these relationships warrant further study. Environ Toxicol Chem 2017;36:661-670. © 2016 SETAC. © 2016 SETAC.

  6. Food Webs of the Delta, Suisun Bay, and Suisun Marsh: An Update on Current Understanding and Possibilities for Management

    Directory of Open Access Journals (Sweden)

    Larry R. Brown

    2016-10-01

    Full Text Available This paper reviews and highlights recent research findings on food web processes since an earlier review by Kimmerer et al. (2008. We conduct this review within a conceptual framework of the Delta–Suisun food web, which includes both temporal and spatial components. The temporal component of our framework is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to food web function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the south Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic food web processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: (1 synthesis of factors responsible for low pelagic biomass; (2 monitoring and research on effects of harmful algal blooms; (3 broadening the scope of long-term monitoring; (4 determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and (5 interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.

  7. A major food web component in the orinoco river channel: evidence from planktivorous electric fishes.

    Science.gov (United States)

    Lundberg, J G; Lewis, W M; Saunders, J F; Mago-Leccia, F

    1987-07-03

    Deep-water sampling of the Orinoco River main channel resulted in the collection of an unexpectedly high abundance and diversity of specialized fishes. Twenty-eight of the more than 60 species collected belong to the Gymnotiformes(New World electric or knife fishes). One of the more numerous of these, a recently described species of the genus Rhabdolichops, consumes large numbers of very small planktonic Crustacea and insect larvae. These items are captured in the very swift, turbid, and deep waters of the Orinoco. Although the strong dependence of the river food web on terrestrial and floodplain food sources is well known, the specialized capabilities of Rhabdolichops and of other fishes that occur with it indicate a significant extension of the river food web into the main channel.

  8. Interaction strength combinations and the overfishing of a marine food web.

    Science.gov (United States)

    Bascompte, Jordi; Melián, Carlos J; Sala, Enric

    2005-04-12

    The stability of ecological communities largely depends on the strength of interactions between predators and their prey. Here we show that these interaction strengths are structured nonrandomly in a large Caribbean marine food web. Specifically, the cooccurrence of strong interactions on two consecutive levels of food chains occurs less frequently than expected by chance. Even when they occur, these strongly interacting chains are accompanied by strong omnivory more often than expected by chance. By using a food web model, we show that these interaction strength combinations reduce the likelihood of trophic cascades after the overfishing of top predators. However, fishing selectively removes predators that are overrepresented in strongly interacting chains. Hence, the potential for strong community-wide effects remains a threat.

  9. Protozoan pulses unveil their pivotal position within the soil food web.

    Science.gov (United States)

    Crotty, Felicity V; Adl, Sina M; Blackshaw, Rod P; Murray, Philip J

    2012-05-01

    Protozoa are one of the most abundant groups of bacterivores within the soil and are responsible for mineralisation of bacterial biomass, having a large impact on C and N cycling. Little is known of their contribution to soil nutrient transfers or the identity of their consumers. Here, for the first time indigenous flagellates and ciliates, enriched to 83 atom% for (13)C and 10 atom% for (15)N, were introduced to soil cores from two different land managements, grassland and woodland with the same soil type, to trace the flow of protozoan C and N through the soil food web. Nematodes, Collembola, earthworms and insect larvae obtained the greatest amounts of C and N of protozoan origin, either through direct consumption or uptake of biomass post-cell death. Our results show that changes in management, affect the functioning of the soil food web and the utilisation of protozoa as a food source.

  10. Tundra fire disturbance homogonizes belowground food web structure, function and dynamics

    Science.gov (United States)

    Moore, J. C.; Pressler, Y.; Koltz, A.; Asmus, A.; Simpson, R.

    2016-12-01

    Tundra fires on Alaska's North Slope are on the rise due to increased lightning strikes since 2000. On July 16, 2007 lightning ignited the Anaktuvuk River fire, burning a 40-by-10 mile swath of tundra about 24 miles north of Toolik Field Station. The fire burned 401 square miles, was visible from space, and released more than 2.3 million tons of carbon into the atmosphere. A large amount of the organic layer of the soil was burned, changing the over all composition of the site and exposing deeper soil horizons. Due to fundamental transitions in soil characteristics and vegetation we hypothesized that the belowground food web community would be affected both in terms of biomass and location within the soil profile. Microbial biomass was reduced with burn severity. In the lower organic horizon there was a significant reduction in fungal biomass but we did not observe this effect in the upper organic soil. We did not observe a significant effect of burn severity on individual group biomass within higher trophic levels. Canonical Discriminant Analysis using the biomass estimates of the functional groups in the food webs found that the webs are becoming increasingly homogenized in the severely burned site compared to the moderately burned and unburned sites. The unburned soils differed significantly from soil at both burn sites; the greatest effects on food web structure were at the lower organic depth, whereas. We modeled the effects of the fire on soil organic matter processing rates and energy flow through the three food webs. The model estimated a decrease in C and N mineralization with fire severity, due in large part to the loss of organic material. While the organic horizon at the unburned site had 12 times greater C and N mineralization than the mineral soils, we observed little to no difference in C and N mineralization between the organic and mineral soil horizons in the moderately and severely burned sites. Our results show that the fire significantly altered

  11. Feeding by larvae of intertidal invertebrates: assessing their position in pelagic food webs.

    Science.gov (United States)

    Vargas, Cristian A; Manríquez, Patricio H; Navarrete, Sergio A

    2006-02-01

    One of the leading determinants of the structure and dynamics of marine populations is the rate of arrival of new individuals to local sites. While physical transport processes play major roles in delivering larvae to the shore, these processes become most important after larvae have survived the perils of life in the plankton, where they usually suffer great mortality. The lack of information regarding larval feeding makes it difficult to assess the effects of food supply on larval survival, or the role larvae may play in nearshore food webs. Here, we examine the spectrum of food sizes and food types consumed by the larvae of two intertidal barnacle species and of the predatory gastropod Concholepas concholepas. We conducted replicated experiments in which larvae were exposed to the food size spectrum (phytoplankton, microprotozoan and autotrophic picoplankton) found in nearshore waters in central Chile. Results show that barnacle nauplii and gastropod veligers are omnivorous grazers, incorporating significant fractions of heterotrophs in their diets. In accordance with their feeding mechanisms and body size, barnacle nauplii were able to feed on autotrophic picoplankton (concholepas larvae also consumed picoplankton cells, while competent larvae of this species ingested mostly the largest phytoplankton cells and heterotrophic protozoans. Results suggest that persistent changes in the structure of pelagic food webs can have important effects on the species-specific food availability for invertebrate larvae, which can result in large-scale differences in recruitment rates of a given species, and in the relative recruitment success of the different species that make up benthic communities.

  12. Food web structure in exotic and native mangroves: A Hawaii-Puerto Rico comparison

    Science.gov (United States)

    Demopoulos, A.W.J.; Fry, B.; Smith, C.R.

    2007-01-01

    Plant invasions can fundamentally alter detrital inputs and the structure of detritus-based food webs. We examined the detrital pathways in mangrove food webs in native (Puerto Rican) and introduced (Hawaiian) Rhizophora mangle forests using a dual isotope approach and a mixing model. Based on trophic-level fractionation of 0-1??? for ?? 13C and 2-3??? for ?? 15N, among the invertebrates, only nematodes, oligochaetes, and nereid polychaetes from native mangroves exhibited stable isotopes consistent with a mangrove-derived diet. Certain fauna, in particular tubificid oligochaetes, had ?? 13C values consistent with the consumption of mangrove leaves, but they were depleted in 15N, suggesting their primary nitrogen source was low in 15N, and was possibly N 2-fixing bacteria. In introduced mangroves, all feeding groups appeared to rely heavily on non-mangrove sources, especially phytoplankton inputs. Mixing model results and discriminant analysis showed clear separation of introduced and native mangrove sites based on differential food source utilization within feeding groups, with stronger and more diverse use of benthic foods observed in native forests. Observed differences between native and invasive mangrove food webs may be due to Hawaiian detritivores being poorly adapted to utilizing the tannin-rich, nitrogen-poor mangrove detritus. In addition, differential utilization of mangrove detritus between native and introduced mangroves may be a consequence of forest age. We postulate that increasing mangrove forest age may promote diversification of bacterial food webs important in N and S cycling. Our results also suggest a potentially important role for sulfur bacteria in supporting the most abundant infaunal consumers, nematodes, in the most mature systems. ?? 2007 Springer-Verlag.

  13. River food web response to large-scale riparian zone manipulations.

    Directory of Open Access Journals (Sweden)

    J Timothy Wootton

    Full Text Available Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks.

  14. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

    International Nuclear Information System (INIS)

    Davis, J.A.; Looker, R.E.; Yee, D.; Marvin-Di Pasquale, M.; Grenier, J.L.; Austin, C.M.; McKee, L.J.; Greenfield, B.K.; Brodberg, R.; Blum, J.D.

    2012-01-01

    San Francisco Bay (California, USA) and its local watersheds present an interesting case study in estuarine mercury (Hg) contamination. This review focuses on the most promising avenues for attempting to reduce methylmercury (MeHg) contamination in Bay Area aquatic food webs and identifying the scientific information that is most urgently needed to support these efforts. Concern for human exposure to MeHg in the region has led to advisories for consumption of sport fish. Striped bass from the Bay have the highest average Hg concentration measured for this species in USA estuaries, and this degree of contamination has been constant for the past 40 years. Similarly, largemouth bass in some Bay Area reservoirs have some of the highest Hg concentrations observed in the entire US. Bay Area wildlife, particularly birds, face potential impacts to reproduction based on Hg concentrations in the tissues of several Bay species. Source control of Hg is one of the primary possible approaches for reducing MeHg accumulation in Bay Area aquatic food webs. Recent findings (particularly Hg isotope measurements) indicate that the decades-long residence time of particle-associated Hg in the Bay is sufficient to allow significant conversion of even the insoluble forms of Hg into MeHg. Past inputs have been thoroughly mixed throughout this shallow and dynamic estuary. The large pool of Hg already present in the ecosystem dominates the fraction converted to MeHg and accumulating in the food web. Consequently, decreasing external Hg inputs can be expected to reduce MeHg in the food web, but it will likely take many decades to centuries before those reductions are achieved. Extensive efforts to reduce loads from the largest Hg mining source (the historic New Almaden mining district) are underway. Hg is spread widely across the urban landscape, but there are a number of key sources, source areas, and pathways that provide opportunities to capture larger quantities of Hg and reduce loads

  15. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

    Energy Technology Data Exchange (ETDEWEB)

    Davis, J.A., E-mail: jay@sfei.org [San Francisco Estuary Institute, 4911 Central Avenue, Richmond, CA 94804 (United States); Looker, R.E. [San Francisco Bay Regional Water Quality Control Board, 1515 Clay Street, Suite 1400, Oakland, CA 94612 (United States); Yee, D. [San Francisco Estuary Institute, 4911 Central Avenue, Richmond, CA 94804 (United States); Marvin-Di Pasquale, M. [U.S. Geological Survey, Water Resources Division/MS 480, 345 Middlefield Road, Menlo Park, CA 94025 (United States); Grenier, J.L. [San Francisco Estuary Institute, 4911 Central Avenue, Richmond, CA 94804 (United States); Austin, C.M. [San Francisco Bay Regional Water Quality Control Board, 1515 Clay Street, Suite 1400, Oakland, CA 94612 (United States); McKee, L.J.; Greenfield, B.K. [San Francisco Estuary Institute, 4911 Central Avenue, Richmond, CA 94804 (United States); Brodberg, R. [California Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, 1001 I Street, Sacramento, CA 95812 (United States); Blum, J.D. [Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109 (United States)

    2012-11-15

    San Francisco Bay (California, USA) and its local watersheds present an interesting case study in estuarine mercury (Hg) contamination. This review focuses on the most promising avenues for attempting to reduce methylmercury (MeHg) contamination in Bay Area aquatic food webs and identifying the scientific information that is most urgently needed to support these efforts. Concern for human exposure to MeHg in the region has led to advisories for consumption of sport fish. Striped bass from the Bay have the highest average Hg concentration measured for this species in USA estuaries, and this degree of contamination has been constant for the past 40 years. Similarly, largemouth bass in some Bay Area reservoirs have some of the highest Hg concentrations observed in the entire US. Bay Area wildlife, particularly birds, face potential impacts to reproduction based on Hg concentrations in the tissues of several Bay species. Source control of Hg is one of the primary possible approaches for reducing MeHg accumulation in Bay Area aquatic food webs. Recent findings (particularly Hg isotope measurements) indicate that the decades-long residence time of particle-associated Hg in the Bay is sufficient to allow significant conversion of even the insoluble forms of Hg into MeHg. Past inputs have been thoroughly mixed throughout this shallow and dynamic estuary. The large pool of Hg already present in the ecosystem dominates the fraction converted to MeHg and accumulating in the food web. Consequently, decreasing external Hg inputs can be expected to reduce MeHg in the food web, but it will likely take many decades to centuries before those reductions are achieved. Extensive efforts to reduce loads from the largest Hg mining source (the historic New Almaden mining district) are underway. Hg is spread widely across the urban landscape, but there are a number of key sources, source areas, and pathways that provide opportunities to capture larger quantities of Hg and reduce loads

  16. Spatial guilds in the Serengeti food web revealed by a Bayesian group model.

    Directory of Open Access Journals (Sweden)

    Edward B Baskerville

    2011-12-01

    Full Text Available Food webs, networks of feeding relationships in an ecosystem, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. A standard approach in food-web analysis, and network analysis in general, has been to identify compartments, or modules, defined by many links within compartments and few links between them. This approach can identify large habitat boundaries in the network but may fail to identify other important structures. Empirical analyses of food webs have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure using a flexible definition that can describe both functional trophic roles and standard compartments. We apply this method to a newly compiled plant-mammal food web from the Serengeti ecosystem that includes high taxonomic resolution at the plant level, allowing a simultaneous examination of the signature of both habitat and trophic roles in network structure. We find that groups at the plant level reflect habitat structure, coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial pattern, in contrast to the standard compartments typically identified. The network topology supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence. Furthermore, our Bayesian approach provides a powerful, flexible framework for the study of network structure, and we believe it will prove instrumental in a variety of biological contexts.

  17. Spatial guilds in the Serengeti food web revealed by a Bayesian group model.

    Science.gov (United States)

    Baskerville, Edward B; Dobson, Andy P; Bedford, Trevor; Allesina, Stefano; Anderson, T Michael; Pascual, Mercedes

    2011-12-01

    Food webs, networks of feeding relationships in an ecosystem, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. A standard approach in food-web analysis, and network analysis in general, has been to identify compartments, or modules, defined by many links within compartments and few links between them. This approach can identify large habitat boundaries in the network but may fail to identify other important structures. Empirical analyses of food webs have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure using a flexible definition that can describe both functional trophic roles and standard compartments. We apply this method to a newly compiled plant-mammal food web from the Serengeti ecosystem that includes high taxonomic resolution at the plant level, allowing a simultaneous examination of the signature of both habitat and trophic roles in network structure. We find that groups at the plant level reflect habitat structure, coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial pattern, in contrast to the standard compartments typically identified. The network topology supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence. Furthermore, our Bayesian approach provides a powerful, flexible framework for the study of network structure, and we believe it will prove instrumental in a variety of biological contexts.

  18. FoodWiki: a Mobile App Examines Side Effects of Food Additives Via Semantic Web.

    Science.gov (United States)

    Çelik Ertuğrul, Duygu

    2016-02-01

    In this article, a research project on mobile safe food consumption system (FoodWiki) is discussed that performs its own inferencing rules in its own knowledge base. Currently, the developed rules examines the side effects that are causing some health risks: heart disease, diabetes, allergy, and asthma as initial. There are thousands compounds added to the processed food by food producers with numerous effects on the food: to add color, stabilize, texturize, preserve, sweeten, thicken, add flavor, soften, emulsify, and so forth. Those commonly used ingredients or compounds in manufactured foods may have many side effects that cause several health risks such as heart disease, hypertension, cholesterol, asthma, diabetes, allergies, alzheimer etc. according to World Health Organization. Safety in food consumption, especially by patients in these risk groups, has become crucial, given that such health problems are ranked in the top ten health risks around the world. It is needed personal e-health knowledge base systems to help patients take control of their safe food consumption. The systems with advanced semantic knowledge base can provide recommendations of appropriate foods before consumption by individuals. The proposed FoodWiki system is using a concept based search mechanism that performs on thousands food compounds to provide more relevant information.

  19. Stability lies in flowers: Plant diversification mediating shifts in arthropod food webs.

    Directory of Open Access Journals (Sweden)

    Marcelo Mendes Haro

    Full Text Available Arthropod community composition in agricultural landscapes is dependent on habitat characteristics, such as plant composition, landscape homogeneity and the presence of key resources, which are usually absent in monocultures. Manipulating agroecosystems through the insertion of in-field floral resources is a useful technique to reduce the deleterious effects of habitat simplification. Food web analysis can clarify how the community reacts to the presence of floral resources which favour ecosystem services such as biological control of pest species. Here, we reported quantitative and qualitative alterations in arthropod food web complexity due to the presence of floral resources from the Mexican marigold (Tagetes erecta L. in a field scale lettuce community network. The presence of marigold flowers in the field successfully increased richness, body size, and the numerical and biomass abundance of natural enemies in the lettuce arthropod community, which affected the number of links, vulnerability, generality, omnivory rate and food chain length in the community, which are key factors for the stability of relationships between species. Our results reinforce the notion that diversification through insertion of floral resources may assist in preventing pest outbreaks in agroecosystems. This community approach to arthropod interactions in agricultural landscapes can be used in the future to predict the effect of different management practices in the food web to contribute with a more sustainable management of arthropod pest species.

  20. Methylmercury enters an aquatic food web through acidophilic microbial mats in Yellowstone National Park, Wyoming.

    Science.gov (United States)

    Boyd, Eric S; King, Susan; Tomberlin, Jeffery K; Nordstrom, D Kirk; Krabbenhoft, David P; Barkay, Tamar; Geesey, Gill G

    2009-04-01

    Microbial mats are a visible and abundant life form inhabiting the extreme environments in Yellowstone National Park (YNP), WY, USA. Little is known of their role in food webs that exist in the Park's geothermal habitats. Eukaryotic green algae associated with a phototrophic green/purple Zygogonium microbial mat community that inhabits low-temperature regions of acidic (pH approximately 3.0) thermal springs were found to serve as a food source for stratiomyid (Diptera: Stratiomyidae) larvae. Mercury in spring source water was taken up and concentrated by the mat biomass. Monomethylmercury compounds (MeHg(+)), while undetectable or near the detection limit (0.025 ng l(-1)) in the source water of the springs, was present at concentrations of 4-7 ng g(-1) dry weight of mat biomass. Detection of MeHg(+) in tracheal tissue of larvae grazing the mat suggests that MeHg(+) enters this geothermal food web through the phototrophic microbial mat community. The concentration of MeHg(+) was two to five times higher in larval tissue than mat biomass indicating MeHg(+) biomagnification occurred between primary producer and primary consumer trophic levels. The Zygogonium mat community and stratiomyid larvae may also play a role in the transfer of MeHg(+) to species in the food web whose range extends beyond a particular geothermal feature of YNP.

  1. The structure of salt marsh soil mesofauna food webs - The prevalence of disturbance.

    Science.gov (United States)

    Haynert, Kristin; Kiggen, Mirijam; Klarner, Bernhard; Maraun, Mark; Scheu, Stefan

    2017-01-01

    Mesofauna taxa fill key trophic positions in soil food webs, even in terrestrial-marine boundary habitats characterized by frequent natural disturbances. Salt marshes represent such boundary habitats, characterized by frequent inundations increasing from the terrestrial upper to the marine pioneer zone. Despite the high abundance of soil mesofauna in salt marshes and their important function by facilitating energy and carbon flows, the structure, trophic ecology and habitat-related diet shifts of mesofauna species in natural salt marsh habitats is virtually unknown. Therefore, we investigated the effects of natural disturbance (inundation frequency) on community structure, food web complexity and resource use of soil mesofauna using stable isotope analysis (15N, 13C) in three salt marsh zones. In this intertidal habitat, the pioneer zone is exposed to inundations twice a day, but lower and upper salt marshes are less frequently inundated based on shore height. The mesofauna comprised 86 species / taxa dominated by Collembola, Oribatida and Mesostigmata. Shifts in environmental disturbances influenced the structure of food webs, diversity and density declined strongly from the land to the sea pointing to the importance of increasing levels of inundation frequency. Accordingly, the reduced diversity and density was associated by a simplification of the food web in the pioneer zone as compared to the less inundated lower and upper salt marsh with a higher number of trophic levels. Strong variations in δ15N signatures demonstrated that mesofauna species are feeding at multiple trophic levels. Primary decomposers were low and most mesofauna species functioned as secondary decomposers or predators including second order predators or scavengers. The results document that major decomposer taxa, such as Collembola and Oribatida, are more diverse than previously assumed and predominantly dwell on autochthonous resources of the respective salt marsh zone. The results further

  2. Food-Web Complexity in Guaymas Basin Hydrothermal Vents and Cold Seeps.

    Science.gov (United States)

    Portail, Marie; Olu, Karine; Dubois, Stanislas F; Escobar-Briones, Elva; Gelinas, Yves; Menot, Lénaick; Sarrazin, Jozée

    In the Guaymas Basin, the presence of cold seeps and hydrothermal vents in close proximity, similar sedimentary settings and comparable depths offers a unique opportunity to assess and compare the functioning of these deep-sea chemosynthetic ecosystems. The food webs of five seep and four vent assemblages were studied using stable carbon and nitrogen isotope analyses. Although the two ecosystems shared similar potential basal sources, their food webs differed: seeps relied predominantly on methanotrophy and thiotrophy via the Calvin-Benson-Bassham (CBB) cycle and vents on petroleum-derived organic matter and thiotrophy via the CBB and reductive tricarboxylic acid (rTCA) cycles. In contrast to symbiotic species, the heterotrophic fauna exhibited high trophic flexibility among assemblages, suggesting weak trophic links to the metabolic diversity of chemosynthetic primary producers. At both ecosystems, food webs did not appear to be organised through predator-prey links but rather through weak trophic relationships among co-occurring species. Examples of trophic or spatial niche differentiation highlighted the importance of species-sorting processes within chemosynthetic ecosystems. Variability in food web structure, addressed through Bayesian metrics, revealed consistent trends across ecosystems. Food-web complexity significantly decreased with increasing methane concentrations, a common proxy for the intensity of seep and vent fluid fluxes. Although high fluid-fluxes have the potential to enhance primary productivity, they generate environmental constraints that may limit microbial diversity, colonisation of consumers and the structuring role of competitive interactions, leading to an overall reduction of food-web complexity and an increase in trophic redundancy. Heterogeneity provided by foundation species was identified as an additional structuring factor. According to their biological activities, foundation species may have the potential to partly release the

  3. Food-Web Complexity in Guaymas Basin Hydrothermal Vents and Cold Seeps

    Science.gov (United States)

    Olu, Karine; Dubois, Stanislas F.; Escobar-Briones, Elva; Gelinas, Yves; Menot, Lénaick; Sarrazin, Jozée

    2016-01-01

    In the Guaymas Basin, the presence of cold seeps and hydrothermal vents in close proximity, similar sedimentary settings and comparable depths offers a unique opportunity to assess and compare the functioning of these deep-sea chemosynthetic ecosystems. The food webs of five seep and four vent assemblages were studied using stable carbon and nitrogen isotope analyses. Although the two ecosystems shared similar potential basal sources, their food webs differed: seeps relied predominantly on methanotrophy and thiotrophy via the Calvin-Benson-Bassham (CBB) cycle and vents on petroleum-derived organic matter and thiotrophy via the CBB and reductive tricarboxylic acid (rTCA) cycles. In contrast to symbiotic species, the heterotrophic fauna exhibited high trophic flexibility among assemblages, suggesting weak trophic links to the metabolic diversity of chemosynthetic primary producers. At both ecosystems, food webs did not appear to be organised through predator-prey links but rather through weak trophic relationships among co-occurring species. Examples of trophic or spatial niche differentiation highlighted the importance of species-sorting processes within chemosynthetic ecosystems. Variability in food web structure, addressed through Bayesian metrics, revealed consistent trends across ecosystems. Food-web complexity significantly decreased with increasing methane concentrations, a common proxy for the intensity of seep and vent fluid fluxes. Although high fluid-fluxes have the potential to enhance primary productivity, they generate environmental constraints that may limit microbial diversity, colonisation of consumers and the structuring role of competitive interactions, leading to an overall reduction of food-web complexity and an increase in trophic redundancy. Heterogeneity provided by foundation species was identified as an additional structuring factor. According to their biological activities, foundation species may have the potential to partly release the

  4. Food-Web Complexity in Guaymas Basin Hydrothermal Vents and Cold Seeps.

    Directory of Open Access Journals (Sweden)

    Marie Portail

    Full Text Available In the Guaymas Basin, the presence of cold seeps and hydrothermal vents in close proximity, similar sedimentary settings and comparable depths offers a unique opportunity to assess and compare the functioning of these deep-sea chemosynthetic ecosystems. The food webs of five seep and four vent assemblages were studied using stable carbon and nitrogen isotope analyses. Although the two ecosystems shared similar potential basal sources, their food webs differed: seeps relied predominantly on methanotrophy and thiotrophy via the Calvin-Benson-Bassham (CBB cycle and vents on petroleum-derived organic matter and thiotrophy via the CBB and reductive tricarboxylic acid (rTCA cycles. In contrast to symbiotic species, the heterotrophic fauna exhibited high trophic flexibility among assemblages, suggesting weak trophic links to the metabolic diversity of chemosynthetic primary producers. At both ecosystems, food webs did not appear to be organised through predator-prey links but rather through weak trophic relationships among co-occurring species. Examples of trophic or spatial niche differentiation highlighted the importance of species-sorting processes within chemosynthetic ecosystems. Variability in food web structure, addressed through Bayesian metrics, revealed consistent trends across ecosystems. Food-web complexity significantly decreased with increasing methane concentrations, a common proxy for the intensity of seep and vent fluid fluxes. Although high fluid-fluxes have the potential to enhance primary productivity, they generate environmental constraints that may limit microbial diversity, colonisation of consumers and the structuring role of competitive interactions, leading to an overall reduction of food-web complexity and an increase in trophic redundancy. Heterogeneity provided by foundation species was identified as an additional structuring factor. According to their biological activities, foundation species may have the potential to

  5. The structure of salt marsh soil mesofauna food webs – The prevalence of disturbance

    Science.gov (United States)

    Kiggen, Mirijam; Klarner, Bernhard; Maraun, Mark; Scheu, Stefan

    2017-01-01

    Mesofauna taxa fill key trophic positions in soil food webs, even in terrestrial–marine boundary habitats characterized by frequent natural disturbances. Salt marshes represent such boundary habitats, characterized by frequent inundations increasing from the terrestrial upper to the marine pioneer zone. Despite the high abundance of soil mesofauna in salt marshes and their important function by facilitating energy and carbon flows, the structure, trophic ecology and habitat-related diet shifts of mesofauna species in natural salt marsh habitats is virtually unknown. Therefore, we investigated the effects of natural disturbance (inundation frequency) on community structure, food web complexity and resource use of soil mesofauna using stable isotope analysis (15N, 13C) in three salt marsh zones. In this intertidal habitat, the pioneer zone is exposed to inundations twice a day, but lower and upper salt marshes are less frequently inundated based on shore height. The mesofauna comprised 86 species / taxa dominated by Collembola, Oribatida and Mesostigmata. Shifts in environmental disturbances influenced the structure of food webs, diversity and density declined strongly from the land to the sea pointing to the importance of increasing levels of inundation frequency. Accordingly, the reduced diversity and density was associated by a simplification of the food web in the pioneer zone as compared to the less inundated lower and upper salt marsh with a higher number of trophic levels. Strong variations in δ15N signatures demonstrated that mesofauna species are feeding at multiple trophic levels. Primary decomposers were low and most mesofauna species functioned as secondary decomposers or predators including second order predators or scavengers. The results document that major decomposer taxa, such as Collembola and Oribatida, are more diverse than previously assumed and predominantly dwell on autochthonous resources of the respective salt marsh zone. The results

  6. The structure of salt marsh soil mesofauna food webs - The prevalence of disturbance.

    Directory of Open Access Journals (Sweden)

    Kristin Haynert

    Full Text Available Mesofauna taxa fill key trophic positions in soil food webs, even in terrestrial-marine boundary habitats characterized by frequent natural disturbances. Salt marshes represent such boundary habitats, characterized by frequent inundations increasing from the terrestrial upper to the marine pioneer zone. Despite the high abundance of soil mesofauna in salt marshes and their important function by facilitating energy and carbon flows, the structure, trophic ecology and habitat-related diet shifts of mesofauna species in natural salt marsh habitats is virtually unknown. Therefore, we investigated the effects of natural disturbance (inundation frequency on community structure, food web complexity and resource use of soil mesofauna using stable isotope analysis (15N, 13C in three salt marsh zones. In this intertidal habitat, the pioneer zone is exposed to inundations twice a day, but lower and upper salt marshes are less frequently inundated based on shore height. The mesofauna comprised 86 species / taxa dominated by Collembola, Oribatida and Mesostigmata. Shifts in environmental disturbances influenced the structure of food webs, diversity and density declined strongly from the land to the sea pointing to the importance of increasing levels of inundation frequency. Accordingly, the reduced diversity and density was associated by a simplification of the food web in the pioneer zone as compared to the less inundated lower and upper salt marsh with a higher number of trophic levels. Strong variations in δ15N signatures demonstrated that mesofauna species are feeding at multiple trophic levels. Primary decomposers were low and most mesofauna species functioned as secondary decomposers or predators including second order predators or scavengers. The results document that major decomposer taxa, such as Collembola and Oribatida, are more diverse than previously assumed and predominantly dwell on autochthonous resources of the respective salt marsh zone

  7. Climate change alters the structure of arctic marine food webs due to poleward shifts of boreal generalists

    Science.gov (United States)

    Kortsch, Susanne; Primicerio, Raul; Fossheim, Maria; Dolgov, Andrey V.; Aschan, Michaela

    2015-01-01

    Climate-driven poleward shifts, leading to changes in species composition and relative abundances, have been recently documented in the Arctic. Among the fastest moving species are boreal generalist fish which are expected to affect arctic marine food web structure and ecosystem functioning substantially. Here, we address structural changes at the food web level induced by poleward shifts via topological network analysis of highly resolved boreal and arctic food webs of the Barents Sea. We detected considerable differences in structural properties and link configuration between the boreal and the arctic food webs, the latter being more modular and less connected. We found that a main characteristic of the boreal fish moving poleward into the arctic region of the Barents Sea is high generalism, a property that increases connectance and reduces modularity in the arctic marine food web. Our results reveal that habitats form natural boundaries for food web modules, and that generalists play an important functional role in coupling pelagic and benthic modules. We posit that these habitat couplers have the potential to promote the transfer of energy and matter between habitats, but also the spread of pertubations, thereby changing arctic marine food web structure considerably with implications for ecosystem dynamics and functioning. PMID:26336179

  8. Climate change alters the structure of arctic marine food webs due to poleward shifts of boreal generalists.

    Science.gov (United States)

    Kortsch, Susanne; Primicerio, Raul; Fossheim, Maria; Dolgov, Andrey V; Aschan, Michaela

    2015-09-07

    Climate-driven poleward shifts, leading to changes in species composition and relative abundances, have been recently documented in the Arctic. Among the fastest moving species are boreal generalist fish which are expected to affect arctic marine food web structure and ecosystem functioning substantially. Here, we address structural changes at the food web level induced by poleward shifts via topological network analysis of highly resolved boreal and arctic food webs of the Barents Sea. We detected considerable differences in structural properties and link configuration between the boreal and the arctic food webs, the latter being more modular and less connected. We found that a main characteristic of the boreal fish moving poleward into the arctic region of the Barents Sea is high generalism, a property that increases connectance and reduces modularity in the arctic marine food web. Our results reveal that habitats form natural boundaries for food web modules, and that generalists play an important functional role in coupling pelagic and benthic modules. We posit that these habitat couplers have the potential to promote the transfer of energy and matter between habitats, but also the spread of pertubations, thereby changing arctic marine food web structure considerably with implications for ecosystem dynamics and functioning. © 2015 The Authors.

  9. Spatial variations in food web structures with alternative stable states: evidence from stable isotope analysis in a large eutrophic lake

    Science.gov (United States)

    Li, Yunkai; Zhang, Yuying; Xu, Jun; Zhang, Shuo

    2017-05-01

    Food web structures are well known to vary widely among ecosystems. Moreover, many food web studies of lakes have generally attempted to characterize the overall food web structure and have largely ignored internal spatial and environmental variations. In this study, we hypothesize that there is a high degree of spatial heterogeneity within an ecosystem and such heterogeneity may lead to strong variations in environmental conditions and resource availability, in turn resulting in different trophic pathways. Stable carbon and nitrogen isotopes were employed for the whole food web to describe the structure of the food web in different sub-basins within Taihu Lake. This lake is a large eutrophic freshwater lake that has been intensively managed and highly influenced by human activities for more than 50 years. The results show significant isotopic differences between basins with different environmental characteristics. Such differences likely result from isotopic baseline differences combining with a shift in food web structure. Both are related to local spatial heterogeneity in nutrient loading in waters. Such variation should be explicitly considered in future food web studies and ecosystem-based management in this lake ecosystem.

  10. From ontology selection and semantic web to an integrated information system for food-borne diseases and food safety.

    Science.gov (United States)

    Yan, Xianghe; Peng, Yun; Meng, Jianghong; Ruzante, Juliana; Fratamico, Pina M; Huang, Lihan; Juneja, Vijay; Needleman, David S

    2011-01-01

    Several factors have hindered effective use of information and resources related to food safety due to inconsistency among semantically heterogeneous data resources, lack of knowledge on profiling of food-borne pathogens, and knowledge gaps among research communities, government risk assessors/managers, and end-users of the information. This paper discusses technical aspects in the establishment of a comprehensive food safety information system consisting of the following steps: (a) computational collection and compiling publicly available information, including published pathogen genomic, proteomic, and metabolomic data; (b) development of ontology libraries on food-borne pathogens and design automatic algorithms with formal inference and fuzzy and probabilistic reasoning to address the consistency and accuracy of distributed information resources (e.g., PulseNet, FoodNet, OutbreakNet, PubMed, NCBI, EMBL, and other online genetic databases and information); (c) integration of collected pathogen profiling data, Foodrisk.org ( http://www.foodrisk.org ), PMP, Combase, and other relevant information into a user-friendly, searchable, "homogeneous" information system available to scientists in academia, the food industry, and government agencies; and (d) development of a computational model in semantic web for greater adaptability and robustness.

  11. ARCTOX: a pan-Arctic sampling network to track mercury contamination across Arctic marine food webs

    DEFF Research Database (Denmark)

    Fort, Jerome; Helgason, Halfdan; Amelineau, Francoise

    and is still a source of major environmental concerns. In that context, providing a large-scale and comprehensive understanding of the Arctic marine food-web contamination is essential to better apprehend impacts of anthropogenic activities and climate change on the exposure of Arctic species and humans to Hg....... In 2015, an international sampling network (ARCTOX) has been established, allowing the collection seabird samples all around the Arctic. Seabirds are indeed good indicators of Hg contamination of marine food webs at large spatial scale. Gathering researchers from 10 countries, ARCTOX allowed......, pelagic, epontic, coastal, oceanic). By relying on this new network and by combining Hg analyses with biotelemetry, we aim at (1) monitoring spatio-temporal variations of Hg in Arctic biota. (2) Defining Arctic hotspots of Hg contamination and highlighting sensitive areas that require particular attention...

  12. Bridging food webs, ecosystem metabolism, and biogeochemistry using ecological stoichiometry theory

    DEFF Research Database (Denmark)

    Welti, Nina; Striebel, Maren; Ulseth, Amber J.

    2017-01-01

    stoichiometry is important for both biogeochemical and ecological research. Nonetheless, assessments of ecological stoichiometry (ES) often focus on the elemental content of biota rather than taking a more holistic view by examining both elemental pools and fluxes (e. g., organismal stoichiometry and ecosystem...... process rates). ES theory holds the promise to be a unifying concept to link across hierarchical scales of patterns and processes in ecology, but this has not been fully achieved. Therefore, we propose connecting the expertise of aquatic ecologists and biogeochemists with ES theory as a common currency...... to connect food webs, ecosystem metabolism, and biogeochemistry, as they are inherently concatenated by the transfer of carbon, nitrogen, and phosphorous through biotic and abiotic nutrient transformation and fluxes. Several new studies exist that demonstrate the connections between food web ecology...

  13. Identity effects dominate the impacts of multiple species extinctions on the functioning of complex food webs.

    Science.gov (United States)

    Harvey, Eric; Séguin, Annie; Nozais, Christian; Archambault, Philippe; Gravel, Dominique

    2013-01-01

    Understanding the impacts of species extinctions on the functioning of food webs is a challenging task because of the complexity of ecological interactions. We report the impacts of experimental species extinctions on the functioning of two food webs of freshwater and marine systems. We used a linear model to partition the variance among the multiple components of the diversity effect (linear group richness, nonlinear group richness, and identity). The identity of each functional group was the best explaining variable of ecosystem functioning for both systems. We assessed the contribution of each functional group in multifunctional space and found that, although the effect of functional group varied across ecosystem functions, some functional groups shared common effects on functions. This study is the first experimental demonstration that functional identity dominates the effects of extinctions on ecosystem functioning, suggesting that generalizations are possible despite the inherent complexity of interactions.

  14. Community diversity, structure and carbon footprint of nematode food web following reforestation on degraded Karst soil

    Science.gov (United States)

    Hu, Ning; Li, Hui; Tang, Zheng; Li, Zhongfang; Tian, Jing; Lou, Yilai; Li, Jianwei; Li, Guichun; Hu, Xiaomin

    2016-01-01

    We examined community diversity, structure and carbon footprint of nematode food web along a chronosequence of T. Sinensis reforestation on degraded Karst. In general, after the reforestation: a serious of diversity parameters and community indices (Shannon-Weinier index (H′), structure index (SI), etc.) were elevated; biomass ratio of fungivores to bacterivores (FFC/BFC), and fungi to bacteria (F/B) were increased, and nematode channel ratio (NCR) were decreased; carbon footprints of all nematode trophic groups, and biomass of bacteria and fungi were increased. Our results indicate that the Karst aboveground vegetation restoration was accompanied with belowground nematode food web development: increasing community complexity, function and fungal dominance in decomposition pathway, and the driving forces included the bottom-up effect (resource control), connectedness of functional groups, as well as soil environments. PMID:27311984

  15. Community diversity, structure and carbon footprint of nematode food web following reforestation on degraded Karst soil.

    Science.gov (United States)

    Hu, Ning; Li, Hui; Tang, Zheng; Li, Zhongfang; Tian, Jing; Lou, Yilai; Li, Jianwei; Li, Guichun; Hu, Xiaomin

    2016-06-17

    We examined community diversity, structure and carbon footprint of nematode food web along a chronosequence of T. Sinensis reforestation on degraded Karst. In general, after the reforestation: a serious of diversity parameters and community indices (Shannon-Weinier index (H'), structure index (SI), etc.) were elevated; biomass ratio of fungivores to bacterivores (FFC/BFC), and fungi to bacteria (F/B) were increased, and nematode channel ratio (NCR) were decreased; carbon footprints of all nematode trophic groups, and biomass of bacteria and fungi were increased. Our results indicate that the Karst aboveground vegetation restoration was accompanied with belowground nematode food web development: increasing community complexity, function and fungal dominance in decomposition pathway, and the driving forces included the bottom-up effect (resource control), connectedness of functional groups, as well as soil environments.

  16. Impact of biodiversity loss on production in complex marine food webs mitigated by prey-release.

    Science.gov (United States)

    Fung, Tak; Farnsworth, Keith D; Reid, David G; Rossberg, Axel G

    2015-03-23

    Public concern over biodiversity loss is often rationalized as a threat to ecosystem functioning, but biodiversity-ecosystem functioning (BEF) relations are hard to empirically quantify at large scales. We use a realistic marine food-web model, resolving species over five trophic levels, to study how total fish production changes with species richness. This complex model predicts that BEF relations, on average, follow simple Michaelis-Menten curves when species are randomly deleted. These are shaped mainly by release of fish from predation, rather than the release from competition expected from simpler communities. Ordering species deletions by decreasing body mass or trophic level, representing 'fishing down the food web', accentuates prey-release effects and results in unimodal relationships. In contrast, simultaneous unselective harvesting diminishes these effects and produces an almost linear BEF relation, with maximum multispecies fisheries yield at ≈40% of initial species richness. These findings have important implications for the valuation of marine biodiversity.

  17. Carbon dynamics, food web structure and reclamation strategies in Athabasca oil sands wetlands (CRFAW)

    International Nuclear Information System (INIS)

    Ciborowski, J.; Dixon, G.; Foote, L.; Liber, K.; Smits, J.

    2010-01-01

    This abstract provided details of the Carbon Dynamics, Food Web Structure and Reclamation Strategies in Athabasca Oil Sands Wetlands (CFRAW) program, a collaboration between oil sands industry partners and university laboratories. CFRAW researchers are investigating the effects of mine tailings and process waters on the development, health, and function of wetland communities in post-mining landscapes. The aim of the program is to accurately predict how quickly the reclaimed wetlands will approach conditions seen in reference wetland systems. The program is also examining the effects of hydrocarbons as a surrogate source of carbon after they are metabolized by bacteria. The biological uptake, pathways, and movement through the food web of materials used by the biota in constructed wetlands are also being studied. Flux estimates will be used to determine if wetlands amended with peat will maintain their productivity. A conceptual model of carbon pathways and budgets is also being developed.

  18. Community diversity, structure and carbon footprint of nematode food web following reforestation on degraded Karst soil

    Science.gov (United States)

    Hu, Ning; Li, Hui; Tang, Zheng; Li, Zhongfang; Tian, Jing; Lou, Yilai; Li, Jianwei; Li, Guichun; Hu, Xiaomin

    2016-06-01

    We examined community diversity, structure and carbon footprint of nematode food web along a chronosequence of T. Sinensis reforestation on degraded Karst. In general, after the reforestation: a serious of diversity parameters and community indices (Shannon-Weinier index (H‧), structure index (SI), etc.) were elevated; biomass ratio of fungivores to bacterivores (FFC/BFC), and fungi to bacteria (F/B) were increased, and nematode channel ratio (NCR) were decreased; carbon footprints of all nematode trophic groups, and biomass of bacteria and fungi were increased. Our results indicate that the Karst aboveground vegetation restoration was accompanied with belowground nematode food web development: increasing community complexity, function and fungal dominance in decomposition pathway, and the driving forces included the bottom-up effect (resource control), connectedness of functional groups, as well as soil environments.

  19. Polycyclic aromatic hydrocarbons alter the structure of oceanic and oligotrophic microbial food webs

    KAUST Repository

    Cerezo, Maria Isabel

    2015-11-01

    One way organic pollutants reach remote oceanic regions is by atmospheric transport. During the Malaspina-2010 expedition, across the Atlantic, Indian, and Pacific Oceans, we analyzed the polycyclic aromatic hydrocarbon (PAH) effects on oceanic microbial food webs. We performed perturbation experiments adding PAHs to classic dilution experiments. The phytoplankton growth rates were reduced by more than 5 times, being Prochlorococcus spp. the most affected. 62% of the experiments showed a reduction in the grazing rates due to the presence of PAHs. For the remaining experiments, grazing usually increased likely due to cascading effects. We identified changes in the slope of the relation between the growth rate and the dilution fraction induced by the pollutants, moving from no grazing to V-shape, or to negative slope, indicative of grazing increase by cascade effects and alterations of the grazers\\' activity structure. Our perturbation experiments indicate that PAHs could influence the structure oceanic food-webs structure.

  20. Visualizing the Food-Web Effects of Fishing for Tunas in the Pacific Ocean

    Directory of Open Access Journals (Sweden)

    Jefferson T. Hinke

    2004-06-01

    Full Text Available We use food-web models to develop visualizations to compare and evaluate the interactions of tuna fisheries with their supporting food webs in the eastern tropical Pacific (ETP and the central north Pacific (CNP Oceans. In the ETP and CNP models, individual fisheries use slightly different food webs that are defined by the assemblage of targeted tuna species. Distinct energy pathways are required to support different tuna species and, consequently, the specific fisheries that target different tuna assemblages. These simulations suggest that catches of tunas, sharks, and billfishes have lowered the biomass of the upper trophic levels in both systems, whereas increases in intermediate and lower trophic level animals have accompanied the decline of top predators. Trade-offs between fishing and predation mortality rates that occur when multiple fisheries interact with their respective food webs may lead to smaller changes in biomass than if only the effect of a single fishery is considered. Historical simulations and hypothetical management scenarios further demonstrate that the effects of longline and purse seine fisheries have been strongest in upper trophic levels, but that lower trophic levels may respond more strongly to purse-seine fisheries. The apex predator guild has responded most strongly to longlining. Simulations of alternative management strategies that attempt to rebuild shark and billfish populations in each ecosystem reveal that (1 changes in longlining more effectively recover top predator populations than do changes in purse seining and (2 restrictions on both shallow-set longline gear and shark finning may do more to recover top predators than do simple reductions in fishing effort.

  1. Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past.

    Directory of Open Access Journals (Sweden)

    Fabiana Saporiti

    Full Text Available The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs.

  2. Determination of keystone species in CSM food web: A topological analysis of network structure

    OpenAIRE

    LiQin Jiang; WenJun Zhang

    2015-01-01

    The importance of a species is correlated with its topological properties in a food web. Studies of keystone species provide the valuable theory and evidence for conservation ecology, biodiversity, habitat management, as well as the dynamics and stability of the ecosystem. Comparing with biological experiments, network methods based on topological structure possess particular advantage in the identification of keystone species. In present study, we quantified the relative importance of specie...

  3. Rainfall and hydrological stability alter the impact of top predators on food web structure and function.

    Science.gov (United States)

    Marino, Nicholas A C; Srivastava, Diane S; MacDonald, A Andrew M; Leal, Juliana S; Campos, Alice B A; Farjalla, Vinicius F

    2017-02-01

    Climate change will alter the distribution of rainfall, with potential consequences for the hydrological dynamics of aquatic habitats. Hydrological stability can be an important determinant of diversity in temporary aquatic habitats, affecting species persistence and the importance of predation on community dynamics. As such, prey are not only affected by drought-induced mortality but also the risk of predation [a non-consumptive effect (NCE)] and actual consumption by predators [a consumptive effect (CE)]. Climate-induced changes in rainfall may directly, or via altered hydrological stability, affect predator-prey interactions and their cascading effects on the food web, but this has rarely been explored, especially in natural food webs. To address this question, we performed a field experiment using tank bromeliads and their aquatic food web, composed of predatory damselfly larvae, macroinvertebrate prey and bacteria. We manipulated the presence and consumption ability of damselfly larvae under three rainfall scenarios (ambient, few large rainfall events and several small rainfall events), recorded the hydrological dynamics within bromeliads and examined the effects on macroinvertebrate colonization, nutrient cycling and bacterial biomass and turnover. Despite our large perturbations of rainfall, rainfall scenario had no effect on the hydrological dynamics of bromeliads. As a result, macroinvertebrate colonization and nutrient cycling depended on the hydrological stability of bromeliads, with no direct effect of rainfall or predation. In contrast, rainfall scenario determined the direction of the indirect effects of predators on bacteria, driven by both predator CEs and NCEs. These results suggest that rainfall and the hydrological stability of bromeliads had indirect effects on the food web through changes in the CEs and NCEs of predators. We suggest that future studies should consider the importance of the variability in hydrological dynamics among habitats as

  4. Modeling food web interactions in benthic deep-sea ecosystems: a practical guide

    OpenAIRE

    Soetaert, K.

    2009-01-01

    Deep-sea benthic systems are notoriously difficult to sample. Even more than for other benthic systems, many flows among biological groups cannot be directly measured, and data sets remain incomplete and uncertain. In such cases, mathematical models are often used to quantify unmeasured biological interactions. Here, we show how to use so-called linear inverse models (LIMs) to reconstruct material and energy flows through food webs in which the number of measurements is a fraction of the tota...

  5. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    OpenAIRE

    Hannah B Vander Zanden; David X Soto; Gabriel J Bowen; Keith A Hobson; Keith A Hobson

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicat...

  6. Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

    OpenAIRE

    Vander Zanden, Hannah B.; Soto, David X.; Bowen, Gabriel J.; Hobson, Keith A.

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicatio...

  7. Mathematical modelling and analysis for a three-tiered microbial food web in a chemostat

    Directory of Open Access Journals (Sweden)

    Miled El hajji

    2017-10-01

    Full Text Available In this article, we present a mathematical six-dimensional dynamical system involving a three-tiered microbial food web without maintenance. We give a qualitative analysis of the model, and an analysis of the local stability of equilibrium points. Under general assumptions of monotonicity, we prove the uniqueness and the local stability of the positive equilibrium point corresponding to the persistence of the three bacteria. Possibilities of periodic orbits are not excluded and asymptotic coexistence is satisfied.

  8. Lipids of Prokaryotic Origin at the Base of Marine Food Webs

    OpenAIRE

    de Carvalho, Carla C. C. R.; Caramujo, Maria José

    2012-01-01

    In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered “extremophiles” and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, hig...

  9. Diet breadth influences how the impact of invasive plants is propagated through food webs.

    Science.gov (United States)

    Carvalheiro, Luisa G; Buckley, Yvonne M; Memmott, Jane

    2010-04-01

    Invasive plants are considered a major cause of ecosystem degradation worldwide. While their impacts on native plants have been widely reported, there is little information on how these impacts propagate through food webs and affect species at higher trophic levels. Using a quantitative food web approach we evaluated the impacts of an invasive plant on plant-herbivore-parasitoid communities, asking specifically how diet breadth influences the propagation of such impacts. Measuring the impact of the alien plant at the plant level seriously underestimated the community-level effect of this weed as it also caused changes in the abundance of native herbivores and parasitoids, along with a decrease in parasitoid species richness. The invading plant affected specialist and generalist subsets of communities differently, having significant and strong negative impacts on the abundance of all specialists with no negative effect on generalist consumers. Specialist consumer decline led to further disruptions of top-down regulatory mechanisms, releasing generalist species from competition via shared natural enemies. Plant invasion also significantly increased the evenness of species abundance of all trophic levels in the food webs, as well as the evenness of species interaction frequency. Extending impact evaluation to higher trophic levels and considering changes in trophic diversity within levels is hence essential for a full evaluation of the consequences of invasion by alien plants. Moreover, information on diet breadth of species in the invaded community should be taken into account when evaluating/predicting the impacts on any introduced species.

  10. Lipids of Prokaryotic Origin at the Base of Marine Food Webs

    Directory of Open Access Journals (Sweden)

    Maria José Caramujo

    2012-11-01

    Full Text Available In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered “extremophiles” and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, high/low salinity and pH. Bacterial cells are even able to produce polyunsaturated fatty acids, contrarily to what was considered until the 1990s, helping the regulation of the membrane fluidity triggered by temperature and pressure and providing protection from oxidative stress. In marine ecosystems, bacteria may either act as a sink of carbon, contribute to nutrient recycling to photo-autotrophs or bacterial organic matter may be transferred to other trophic links in aquatic food webs. The present work aims to provide a comprehensive review on lipid production in bacteria and archaea and to discuss how their lipids, of both heterotrophic and chemoautotrophic origin, contribute to marine food webs.

  11. Mangrove clearing impacts on macrofaunal assemblages and benthic food webs in a tropical estuary.

    Science.gov (United States)

    Bernardino, Angelo Fraga; Gomes, Luiz Eduardo de Oliveira; Hadlich, Heliatrice Louise; Andrades, Ryan; Correa, Lucas Barreto

    2018-01-01

    Despite over 21,000ha of mangrove forests being removed per year in Brazil, ecological changes following mangrove deforestation have been overlooked. Here we evaluated changes in benthic macrofaunal assemblages and food-webs at a mangrove removal and natural sites in a tropical estuary in Eastern Brazil. The impacted site had coarser sediment particle sizes suggesting significant changes in sedimentation processes after forest clearing. Spatial differences in macrofaunal abundance, biomass and diversity were not directly associated with the removal of mangrove forests, supporting recolonization of impacted areas by estuarine fauna. However, benthic assemblage composition, infaunal δ 13 C signatures and food-web diversity markedly differed at the impacted site being strongly related to sedimentary changes. The loss of infaunal trophic diversity that followed mangrove removal suggests that large-scale forest clearing may impact estuarine food webs, with potential consequences to nearby coastal ecosystems given the high clearing rate of mangrove forests in Brazil. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Mercury bioaccumulation in bats reflects dietary connectivity to aquatic food webs.

    Science.gov (United States)

    Becker, Daniel J; Chumchal, Matthew M; Broders, Hugh G; Korstian, Jennifer M; Clare, Elizabeth L; Rainwater, Thomas R; Platt, Steven G; Simmons, Nancy B; Fenton, M Brock

    2018-02-01

    Mercury (Hg) is a persistent and widespread heavy metal with neurotoxic effects in wildlife. While bioaccumulation of Hg has historically been studied in aquatic food webs, terrestrial consumers can become contaminated with Hg when they feed on aquatic organisms (e.g., emergent aquatic insects, fish, and amphibians). However, the extent to which dietary connectivity to aquatic ecosystems can explain patterns of Hg bioaccumulation in terrestrial consumers has not been well studied. Bats (Order: Chiroptera) can serve as a model system for illuminating the trophic transfer of Hg given their high dietary diversity and foraging links to both aquatic and terrestrial food webs. Here we quantitatively characterize the dietary correlates of long-term exposure to Hg across a diverse local assemblage of bats in Belize and more globally across bat species from around the world with a comparative analysis of hair samples. Our data demonstrate considerable interspecific variation in hair total Hg concentrations in bats that span three orders of magnitude across species, ranging from 0.04 mg/kg in frugivorous bats (Artibeus spp.) to 145.27 mg/kg in the piscivorous Noctilio leporinus. Hg concentrations showed strong phylogenetic signal and were best explained by dietary connectivity of bat species to aquatic food webs. Our results highlight that phylogeny can be predictive of Hg concentrations through similarity in diet and how interspecific variation in feeding strategies influences chronic exposure to Hg and enables movement of contaminants from aquatic to terrestrial ecosystems. Copyright © 2017 Elsevier Ltd. All rights reserved.

  13. Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake.

    Directory of Open Access Journals (Sweden)

    Päivi Rinta

    Full Text Available Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰, consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.

  14. Mercury Bioavailability and Bioaccumulation in Estuarine Food Webs in the Gulf of Maine

    Science.gov (United States)

    Chen, Celia Y.; Dionne, Michele; Mayes, Brandon M.; Ward, Darren M.; Sturup, Stefan; Jackson, Brian P.

    2009-01-01

    Marine food webs are important links between Hg in the environment and human exposure via consumption of fish. Estuaries contain sediment repositories of Hg and are also critical habitat for marine fish and shellfish species consumed by humans. MeHg biotransfers from sites of production in estuarine sediments to higher trophic levels via both benthic and pelagic pathways. In this study, we investigated the potential for Hg biotransfer to estuarine food webs across a Hg contamination gradient in the Gulf of Maine. Despite the variation in sediment Hg concentrations across sites (>100 fold), Hg concentrations in biota ranged by only 2–4 fold for each species across sites. Sediment contamination alone explained some variation in Hg and MeHg concentrations in biota across sites. However, biogeochemical and ecological factors also explained significant variation in Hg bioaccumulation across species. Contaminated sites had higher total organic carbon concentrations in sediments, which related to a decrease in Hg bioaccumulation (measured as biota-sediment concentration factors, BSCF). Moreover, concentrations of MeHg were higher in pelagic-feeding than benthic-feeding fauna (determined from delta 13C) indicating the importance of pelagic pathways in transferring MeHg. Lastly, the proportion of total Hg as MeHg increased with trophic level (measured as delta 15N). These results reveal the importance of both biogeochemical and ecological factors in determining the bioavailability and trophic transfer of MeHg in estuarine food webs. PMID:19368175

  15. Lipids of prokaryotic origin at the base of marine food webs.

    Science.gov (United States)

    de Carvalho, Carla C C R; Caramujo, Maria José

    2012-12-01

    In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered "extremophiles" and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, high/low salinity and pH. Bacterial cells are even able to produce polyunsaturated fatty acids, contrarily to what was considered until the 1990s, helping the regulation of the membrane fluidity triggered by temperature and pressure and providing protection from oxidative stress. In marine ecosystems, bacteria may either act as a sink of carbon, contribute to nutrient recycling to photo-autotrophs or bacterial organic matter may be transferred to other trophic links in aquatic food webs. The present work aims to provide a comprehensive review on lipid production in bacteria and archaea and to discuss how their lipids, of both heterotrophic and chemoautotrophic origin, contribute to marine food webs.

  16. Trophic state changes can affect the importance of methane-derived carbon in aquatic food webs.

    Science.gov (United States)

    Schilder, Jos; van Hardenbroek, Maarten; Bodelier, Paul; Kirilova, Emiliya P; Leuenberger, Markus; Lotter, André F; Heiri, Oliver

    2017-06-28

    Methane-derived carbon, incorporated by methane-oxidizing bacteria, has been identified as a significant source of carbon in food webs of many lakes. By measuring the stable carbon isotopic composition (δ 13 C values) of particulate organic matter, Chironomidae and Daphnia spp. and their resting eggs (ephippia), we show that methane-derived carbon presently plays a relevant role in the food web of hypertrophic Lake De Waay, The Netherlands. Sediment geochemistry, diatom analyses and δ 13 C measurements of chironomid and Daphnia remains in the lake sediments indicate that oligotrophication and re-eutrophication of the lake during the twentieth century had a strong impact on in-lake oxygen availability. This, in turn, influenced the relevance of methane-derived carbon in the diet of aquatic invertebrates. Our results show that, contrary to expectations, methane-derived relative to photosynthetically produced organic carbon became more relevant for at least some invertebrates during periods with higher nutrient availability for algal growth, indicating a proportionally higher use of methane-derived carbon in the lake's food web during peak eutrophication phases. Contributions of methane-derived carbon to the diet of the investigated invertebrates are estimated to have ranged from 0-11% during the phase with the lowest nutrient availability to 13-20% during the peak eutrophication phase. © 2017 The Author(s).

  17. Evolution mediates the effects of apex predation on aquatic food webs.

    Science.gov (United States)

    Urban, Mark C

    2013-07-22

    Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.

  18. Antibiotic Pollution in Marine Food Webs in Laizhou Bay, North China: Trophodynamics and Human Exposure Implication.

    Science.gov (United States)

    Liu, Sisi; Zhao, Hongxia; Lehmler, Hans-Joachim; Cai, Xiyun; Chen, Jingwen

    2017-02-21

    Little information is available about the bioaccumulation and biomagnification of antibiotics in marine food webs. Here, we investigate the levels and trophic transfer of 9 sulfonamide (SA), 5 fluoroquinolone (FQ), and 4 macrolide (ML) antibiotics, as well as trimethoprim in nine invertebrate and ten fish species collected from a marine food web in Laizhou Bay, North China in 2014 and 2015. All the antibiotics were detected in the marine organisms, with SAs and FQs being the most abundant antibiotics. Benthic fish accumulated more SAs than invertebrates and pelagic fish, while invertebrates exhibited higher FQ levels than fish. Generally, SAs and trimethoprim biomagnified in the food web, while the FQs and MLs were biodiluted. Trophic magnification factors (TMF) were 1.2-3.9 for SAs and trimethoprim, 0.3-1.0 for FQs and MLs. Limited biotransformation and relatively high assimilation efficiencies are the likely reasons for the biomagnification of SAs. The pH dependent distribution coefficients (log D) but not the lipophilicity (log K OW ) of SAs and FQs had a significant correlation (r = 0.73; p < 0.05) with their TMFs. Although the calculated estimated daily intakes (EDI) for antibiotics suggest that consumption of seafood from Laizhou Bay is not associated with significant human health risks, this study provides important insights into the guidance of risk management of antibiotics.

  19. Spatial complexity reduces interaction strengths in the meta-food web of a river floodplain mosaic

    Science.gov (United States)

    Bellmore, James Ryan; Baxter, Colden Vance; Connolly, Patrick J.

    2015-01-01

    Theory states that both the spatial complexity of landscapes and the strength of interactions between consumers and their resources are important for maintaining biodiversity and the 'balance of nature.' Spatial complexity is hypothesized to promote biodiversity by reducing potential for competitive exclusion; whereas, models show weak trophic interactions can enhance stability and maintain biodiversity by dampening destabilizing oscillations associated with strong interactions. Here we show that spatial complexity can reduce the strength of consumer-resource interactions in natural food webs. By sequentially aggregating food webs of individual aquatic habitat patches across a floodplain mosaic, we found that increasing spatial complexity resulted in decreases in the strength of interactions between predators and prey, owing to a greater proportion of weak interactions and a reduced proportion of strong interactions in the meta-food web. The main mechanism behind this pattern was that some patches provided predation refugia for species which were often strongly preyed upon in other patches. If weak trophic interactions do indeed promote stability, then our findings may signal an additional mechanism by which complexity and stability are linked in nature. In turn, this may have implications for how the values of landscape complexity, and the costs of biophysical homogenization, are assessed.

  20. Determinants of Web-based CSR Disclosure in the Food Industry

    Directory of Open Access Journals (Sweden)

    Florian Sommer

    2015-01-01

    Full Text Available Purpose –Web-based CSR disclosure provides a variety of advantages for firms. Determining factors for web-based CSR disclosure have been analyzed in several papers. However, only limited research has been conducted on both, the food industry and small and midsized enterprises. This paper is one contribution to fill this gap as we investigate web-based CSR communication of food processors including SME.Design/methodology/approach – We analyzed corporate communication on the websites of 71 food producers from North Rhine-Westphalia, Germany using dictionary-based content analysis. Based on an ordered logit model the relationship between CSR communication and size, profitability, indebtedness and closeness to market was estimated. Economic data were obtained from the commercial database DAFNE.Findings – Our results reveal that larger firms provide relatively more CSR information than smaller firms. There was no significant relationship between CSR disclosure and profitability or indebtedness of a company and an ambiguous relationship with regard to the determinant ‘closeness to market’. Regarding the different areas of communication we found that social compared to environmental aspects were underrepresented.Practical implications – Social aspects of CSR could be used for differentiation in the market. Furthermore, as smaller firms provide relatively less information on CSR it might be worthwhile to analyze the central impediments for CSR communication for those companies.Originality/Value – This paper contributes to the ongoing discussion about firms’ CSR communication. From a convenience sample of 71 food processing firms, including SME, it provides insight regarding the determinants for CSR disclosure on firms’ websites. With the focus on the food industry and the inclusion of SME we contribute with our study to two under-researched areas.

  1. Food-web complexity across hydrothermal vents on the Azores triple junction

    Science.gov (United States)

    Portail, Marie; Brandily, Christophe; Cathalot, Cécile; Colaço, Ana; Gélinas, Yves; Husson, Bérengère; Sarradin, Pierre-Marie; Sarrazin, Jozée

    2018-01-01

    The assessment and comparison of food webs across various hydrothermal vent sites can enhance our understanding of ecological processes involved in the structure and function of biodiversity. The Menez Gwen, Lucky Strike and Rainbow vent fields are located on the Azores triple junction of the Mid-Atlantic Ridge. These fields have distinct depths (from 850 to 2320 m) and geological contexts (basaltic and ultramafic), but share similar faunal assemblages defined by the presence of foundation species that include Bathymodiolus azoricus, alvinocarid shrimp and gastropods. We compared the food webs of 13 faunal assemblages at these three sites using carbon and nitrogen stable isotope analyses (SIA). Results showed that photosynthesis-derived organic matter is a negligible basal source for vent food webs, at all depths. The contribution of methanotrophy versus autotrophy based on Calvin-Benson-Bassham (CBB) or reductive tricarboxylic acid (rTCA) cycles varied between and within vent fields according to the concentrations of reduced compounds (e.g. CH4, H2S). Species that were common to vent fields showed high trophic flexibility, suggesting weak trophic links to the metabolism of chemosynthetic primary producers. At the community level, a comparison of SIA-derived metrics between mussel assemblages from two vent fields (Menez Gwen & Lucky Strike) showed that the functional structure of food webs was highly similar in terms of basal niche diversification, functional specialization and redundancy. Coupling SIA to functional trait approaches included more variability within the analyses, but the functional structures were still highly comparable. These results suggest that despite variable environmental conditions (physico-chemical factors and basal sources) and faunal community structure, functional complexity remained relatively constant among mussel assemblages. This functional similarity may be favoured by the propensity of species to adapt to fluid variations and

  2. Convergence of trophic interaction strengths in grassland food webs through metabolic scaling of herbivore biomass.

    Science.gov (United States)

    Schmitz, Oswald J; Price, Jessica R

    2011-11-01

    1. Food web theory hypothesizes that trophic interaction strengths of consumers should vary with consumer metabolic body mass (mass(0·75) ) rather than simply with consumer body mass (mass(1·0) ) owing to constraints on consumption imposed by metabolic demand for and metabolic capacity to process nutrients and energy. Accordingly, species with similar metabolic body masses should have similar trophic interaction strengths. 2. We experimentally tested this hypothesis by assembling food webs comprised of species of arthropod predators, small sap-feeding and large leaf-chewing insect herbivores and herbaceous plants in a New England, USA meadow grassland. The experiment comprised of a density-matching treatment where herbivore species were stocked into field mesocosms at equal densities to quantify baseline species identity and metabolic body mass effects. The experiment also comprised of a metabolic biomass-matching treatment where smaller sap-feeding herbivore (SH) species were stocked into mesocosms such that the product of their density and metabolic body mass (metabolic biomass) was equal to the large herbivore (LH) species. We compared the magnitude of the direct effects of herbivore species on plants in the different treatments. We also compared the magnitude of indirect effects between predators and plants mediated by herbivores in the different treatments. 3. Consistent with the hypothesis, we found that increasing metabolic biomass translated into a 9-14-fold increase in magnitude of herbivore direct effects and up to a fivefold increase in indirect effects on plants. Moreover, metabolic biomass matching caused interaction strengths among herbivore species to converge. This result came about through increases in the herbivore mean effects as well as decreases in variation in effects among treatment replicates as herbivore metabolic biomass increased. 4. We found, however, that herbivore feeding mode rather than herbivore metabolic biomass explained

  3. A freshwater food web model for the combined effects of nutrients and insecticide stress and subsequent recovery

    NARCIS (Netherlands)

    Traas, T.P.; Janse, J.H.; Brink, van den P.J.; Brock, T.C.M.; Aldenberg, T.

    2004-01-01

    A microcosm experiment that addressed the interaction between eutrophication processes and contaminants was analyzed using a food web model. Both direct and indirect effects of nutrient additions and a single insecticide application (chlorpyrifos) on biomass dynamics and recovery of functional

  4. Potential impacts of ocean acidification on the Puget Sound food web from a model study (NCEI Accession 0134852)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This archival package contains output from a study designed to evaluate the impacts of ocean acidification on the food web of Puget Sound, a large estuary in the...

  5. 'David and Goliath' of the soil food web - Flagellates that kill nematodes

    DEFF Research Database (Denmark)

    Strandmark, Lisa Bjørnlund; Rønn, Regin

    2008-01-01

    Nematodes and flagellates are important bacterial predators in soil and sediments. Generally, these organisms are considered to be competitors for bacterial food. We studied the interaction among flagellates and nematodes using axenic liquid cultures amended with heat-killed bacteria as food...... and showed for the first time that a small and common soil flagellate (Cercomonas sp.) is able to attack and kill the much larger nematode Caenorhabditis elegans. The killing process is not caused by soluble metabolites but requires direct contact between the flagellate cells and the nematode surface...... bacterial feeder can control the abundance of another, suggests a new perspective on how bacterial diversity and trophic interactions are linked in the soil food web. (C) 2008 Elsevier Ltd. All rights reserved Udgivelsesdato: 2008...

  6. Seasonality in contaminant accumulation in Arctic marine pelagic food webs using trophic magnification factor as a measure of bioaccumulation.

    Science.gov (United States)

    Hallanger, Ingeborg G; Warner, Nicholas A; Ruus, Anders; Evenset, Anita; Christensen, Guttorm; Herzke, Dorte; Gabrielsen, Geir W; Borgå, Katrine

    2011-05-01

    Seasonality in biomagnification of persistent organic pollutants (POPs; polychlorinated biphenyls, chlorinated pesticides, and brominated flame retardants) in Arctic marine pelagic food webs was investigated in Kongsfjorden, Svalbard, Norway. Trophic magnification factors (TMFs; average factor change in concentration between two trophic levels) were used to measure food web biomagnification in biota in May, July, and October 2007. Pelagic zooplankton (seven species), fish (five species), and seabirds (two species) were included in the study. For most POP compounds, highest TMFs were found in July and lowest were in May. Seasonally changing TMFs were a result of seasonally changing POP concentrations and the δ¹⁵N-derived trophic positions of the species included in the food web. These seasonal differences in TMFs were independent of inclusion/exclusion of organisms based on physiology (i.e., warm- versus cold-blooded organisms) in the food web. The higher TMFs in July, when the food web consisted of a higher degree of boreal species, suggest that future warming of the Arctic and increased invasion by boreal species can result in increased food web magnification. Knowledge of the seasonal variation in POP biomagnification is a prerequisite for understanding changes in POP biomagnification caused by climate change. Copyright © 2011 SETAC.

  7. The impact of 850,000 years of climate changes on the structure and dynamics of mammal food webs.

    Directory of Open Access Journals (Sweden)

    Hedvig K Nenzén

    Full Text Available Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans on Iberian Holocene mammal communities.

  8. Isotopic evidence for the spatial heterogeneity of the planktonic food webs in the transition zone between river and lake ecosystems

    Directory of Open Access Journals (Sweden)

    Hideyuki Doi

    2013-12-01

    Full Text Available Resources and organisms in food webs are distributed patchily. The spatial structure of food webs is important and critical to understanding their overall structure. However, there is little available information about the small-scale spatial structure of food webs. We investigated the spatial structure of food webs in a lake ecosystem at the littoral transition zone between an inflowing river and a lake. We measured the carbon isotope ratios of zooplankton and particulate organic matter (POM; predominantly phytoplankton in the littoral zone of a saline lake. Parallel changes in the δ 13C values of zooplankton and their respective POMs indicated that there is spatial heterogeneity of the food web in this study area. Lake ecosystems are usually classified at the landscape level as either pelagic or littoral habitats. However, we showed small-scale spatial heterogeneity among planktonic food webs along an environmental gradient. Stable isotope data is useful for detecting spatial heterogeneity of habitats, populations, communities, and ecosystems.

  9. Nutrient enrichment and food web composition affect ecosystem metabolism in an experimental seagrass habitat.

    Science.gov (United States)

    Spivak, Amanda C; Canuel, Elizabeth A; Duffy, J Emmett; Richardson, J Paul

    2009-10-15

    Food web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood. Using an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1) Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2) Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution) correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments. Overall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in the face of

  10. Nutrient enrichment and food web composition affect ecosystem metabolism in an experimental seagrass habitat.

    Directory of Open Access Journals (Sweden)

    Amanda C Spivak

    2009-10-01

    Full Text Available Food web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood.Using an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1 Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2 Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments.Overall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in

  11. Food web flows through a sub-arctic deep-sea benthic community

    Science.gov (United States)

    Gontikaki, E.; van Oevelen, D.; Soetaert, K.; Witte, U.

    2011-11-01

    The benthic food web of the deep Faroe-Shetland Channel (FSC) was modelled by using the linear inverse modelling methodology. The reconstruction of carbon pathways by inverse analysis was based on benthic oxygen uptake rates, biomass data and transfer of labile carbon through the food web as revealed by a pulse-chase experiment. Carbon deposition was estimated at 2.2 mmol C m -2 d -1. Approximately 69% of the deposited carbon was respired by the benthic community with bacteria being responsible for 70% of the total respiration. The major fraction of the labile detritus flux was recycled within the microbial loop leaving merely 2% of the deposited labile phytodetritus available for metazoan consumption. Bacteria assimilated carbon at high efficiency (0.55) but only 24% of bacterial production was grazed by metazoans; the remaining returned to the dissolved organic matter pool due to viral lysis. Refractory detritus was the basal food resource for nematodes covering ∼99% of their carbon requirements. On the contrary, macrofauna seemed to obtain the major part of their metabolic needs from bacteria (49% of macrofaunal consumption). Labile detritus transfer was well-constrained, based on the data from the pulse-chase experiment, but appeared to be of limited importance to the diet of the examined benthic organisms (preferred prey, in this case, was other macrofaunal animals rather than nematodes. Bacteria and detritus contributed 53% and 12% to the total carbon ingestion of carnivorous polychaetes suggesting a high degree of omnivory among higher consumers in the FSC benthic food web. Overall, this study provided a unique insight into the functioning of a deep-sea benthic community and demonstrated how conventional data can be exploited further when combined with state-of-the-art modelling approaches.

  12. Effects of anthropogenic nitrogen input on the aquatic food webs of river ecosystem in central Japan

    Science.gov (United States)

    Ohte, N.; Togashi, H.; Tokuchi, N.; Yoshimura, M.; Kato, Y.; Ishikawa, N. F.; Osaka, K.; Kondo, M.; Tayasu, I.

    2014-12-01

    To evaluate the impact of the anthropogenic nitrogen input to the river ecosystem, we conducted the monitoring on nutrient status of river waters and food web structures of aquatic organisms. Especially, changes of sources and concentration of nitrate (NO3-) in river water were focused to evaluate the impact of anthropogenic nitrogen loadings from agricultural and residential areas. Stable nitrogen isotope ratio (δ15N) of aquatic organisms has also intensively been monitored not only to describe their food web structure, but also to detect the influences of extraneous nitrogen inputs. Field samplings an observation campaigns were conducted in the Arida river watershed located in central part of Japan at four different seasons from September 2011 to October 2012. Five observation points were set from headwaters to the point just above the brackish waters starts. Water samples for chemical analysis were taken at the observation points for each campaign. Organisms including leaf litters, benthic algae, aquatic insects, crustacean, and fishes were sampled at each point quantitatively. Results of the riverine survey utilizing 5 regular sampling points showed that δ15N of nitrate (NO3-) increased from forested upstream (˜2 ‰) to the downstream (˜7 ‰) due to the sewage loads and fertilizer effluents from agricultural area. Correspondingly the δ15N of benthic algae and aquatic insects increased toward the downstream. This indicates that primary producers of each reach strongly relied on the local N sources and it was utilized effectively in their food web. Simulation using a GIS based mixing model considering the spatial distributions of human population density and fertilizer effluents revealed that strongest impacts of N inputs was originated from organic fertilizers applied to orchards in the middle to lower parts of catchment. Differences in δ15N between primary producers and predators were 6-7 ‰ similarly at all sampling points. Food web structural

  13. Mobilizing the regional eco-economy: evolving webs of agri-food and rural development in the UK

    OpenAIRE

    Terry Marsden

    2010-01-01

    The paper traces the emergence of the regional eco-economy with reference to a new conceptual model called the rural web. These webs are embedded into the fabric of regional systems of production and consumption and provide a key driver for both rural development generally and eco-economic development more specifically. Relocalized agri-food networks are playing a key integrating role in mobilizing the web and the regional eco-economy more generally. The web concept is used to (i) assess the ...

  14. Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal.

    Directory of Open Access Journals (Sweden)

    Olena Glavatska

    Full Text Available Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of

  15. Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal.

    Science.gov (United States)

    Glavatska, Olena; Müller, Karolin; Butenschoen, Olaf; Schmalwasser, Andreas; Kandeler, Ellen; Scheu, Stefan; Totsche, Kai Uwe; Ruess, Liliane

    2017-01-01

    Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter

  16. Molecular trophic markers in marine food webs and their potential use for coral ecology.

    Science.gov (United States)

    Leal, Miguel Costa; Ferrier-Pagès, Christine

    2016-10-01

    Notable advances in ecological genomics have been driven by high-throughput sequencing technology and taxonomically broad sequence repositories that allow us to accurately assess species interactions with great taxonomic resolution. The use of DNA as a marker for ingested food is particularly relevant to address predator-prey interactions and disentangle complex marine food webs. DNA-based methods benefit from reductionist molecular approaches to address ecosystem scale processes, such as community structure and energy flow across trophic levels, among others. Here we review how molecular trophic markers have been used to better understand trophic interactions in the marine environment and their advantages and limitations. We focus on animal groups where research has been focused, such as marine mammals, seabirds, fishes, pelagic invertebrates and benthic invertebrates, and use case studies to illustrate how DNA-based methods unraveled food-web interactions. The potential of molecular trophic markers for disentangling the complex trophic ecology of corals is also discussed. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Organochlorine pollution in tropical rivers (Guadeloupe): role of ecological factors in food web bioaccumulation.

    Science.gov (United States)

    Coat, Sophie; Monti, Dominique; Legendre, Pierre; Bouchon, Claude; Massat, Félix; Lepoint, Gilles

    2011-06-01

    Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of diadromous fishes and shrimps, as they re-enter the river. The role of ecological factors in the bioaccumulation of pesticides was evaluated. Whereas the most persistent pollutants (chlordecone and monohydro-chlordecone) were related to the organisms diet and habitat, bioaccumulation of β-HCH was only influenced by animal lipid content. The biomagnification potential of chlordecone through the food chain has been demonstrated. It highlighted the importance of trophic transfer in this compound bioaccumulation process. In contrast, bioconcentration by passive diffusion from water seemed to be the main exposure route of biota to β-HCH. Copyright © 2011 Elsevier Ltd. All rights reserved.

  18. Effects of zebra mussels on food webs: Interactions with juvenile bluegill and water residence time

    Science.gov (United States)

    Richardson, W.B.; Bartsch, L.A.

    1997-01-01

    We evaluated how water residence time mediated the impact of zebra mussels Dreissena polymorpha and bluegill sunfish Lepomis macrochirus on experimental food webs established in 1100-1 outdoor mesocosms. Water residence time was manipulated as a surrogate for seston resupply - a critical variable affecting growth and survival of suspension-feeding invertebrates. We used a 2 x 2 x 2 factorial experimental design with eight treatment combinations (3 replicates/treatment) including the presence or absence of Dreissena (2000 per m2), juvenile bluegill (40 per mesocosm), and short (1100 1 per d) or long (220 1 per d) water residence time. Measures of seston concentration (chlorophyll a, turbidity and suspended solids) were greater in the short- compared to long water-residence mesocosms, but intermediate in short water-residence mesocosms containing Dreissena. Abundance of rotifers (Keratella and Polyarthra) was reduced in Dreissena mesocosms and elevated in short residence time mesocosms. Cladocera abundance, in general, was unaffected by the presence of Dreissena; densities were higher in short-residence time mesocosms, and reduced in the presence of Lepomis. The growth of juvenile Lepomis were unaffected by Dreissena because of abundant benthic food. The final total mass of Dreissena was significantly greater in short- than long-residence mesocosms. Impacts of Dreissena on planktonic food webs may not only depend on the density of zebra mussels but also on the residence time of the surrounding water and the resupply of seston. ?? 1997 Kluwer Academic Publishers.

  19. Chironomidae feeding habits in different habitats from a Neotropical floodplain: exploring patterns in aquatic food webs.

    Science.gov (United States)

    Butakka, C M M; Ragonha, F H; Train, S; Pinha, G D; Takeda, A M

    2016-02-01

    Ecological studies on food webs have considerably increased in recent decades, especially in aquatic communities. Because Chironomidae family are highly specious, occurring in almost all aquatic habitats is considered organisms-key to initiate studies on ecological relationships and trophic webs. We tested the hypothesis that the diversity of the morphospecies diet reflects differences on both the food items available among habitats and the preferences of larval feeding. We analyzed the gut content of the seven most abundant Chironomidae morphospecies of the different habitats from the Upper Paraná River. We categorized the food items found into algae, fungal spores, fragments of plants, algae and animal fragments and sponge spicules. We observed the algae predominance in the gut content of morphospecies from lakes. Considering the different regions from each lake, we registered the highest food abundance in the littoral regions in relation to the central regions. From the variety of feeding habits (number of item kinds), we classified Chironomus strenzkei, Tanytarsus sp.1, Procladius sp.1 as generalist morphospecies. We found a nested pattern between food items and Chironomidae morphospecies, where some items were common to all taxa (e.g., Bacillariophyceae algae, especially), while others were found in specific morphospecies (e.g., animals fragments found in Procladius sp.1). The algae represented the most percentage of gut contents of Chironomidae larvae. This was especially true for the individuals from littoral regions, which is probably due to the major densities of algae associated to macrophytes, which are abundant in these regions. Therefore, the feeding behavior of these morphospecies was generalist and not selective, depending only of the available resources.

  20. Parasites reduce food web robustness because they are sensitive to secondary extinction as illustrated by an invasive estuarine snail

    Science.gov (United States)

    Lafferty, Kevin D.; Kuris, Armand M.

    2009-01-01

    A robust food web is one in which few secondary extinctions occur after removing species. We investigated how parasites affected the robustness of the Carpinteria Salt Marsh food web by conducting random species removals and a hypothetical, but plausible, species invasion. Parasites were much more likely than free-living species to suffer secondary extinctions following the removal of a free-living species from the food web. For this reason, the food web was less robust with the inclusion of parasites. Removal of the horn snail, Cerithidea californica, resulted in a disproportionate number of secondary parasite extinctions. The exotic Japanese mud snail, Batillaria attramentaria, is the ecological analogue of the native California horn snail and can completely replace it following invasion. Owing to the similarities between the two snail species, the invasion had no effect on predator–prey interactions. However, because the native snail is host for 17 host-specific parasites, and the invader is host to only one, comparison of a food web that includes parasites showed significant effects of invasion on the native community. The hypothetical invasion also significantly reduced the connectance of the web because the loss of 17 native trematode species eliminated many links.

  1. Micro-Food Web Structure Shapes Rhizosphere Microbial Communities and Growth in Oak

    Directory of Open Access Journals (Sweden)

    Hazel R. Maboreke

    2018-03-01

    Full Text Available The multitrophic interactions in the rhizosphere impose significant impacts on microbial community structure and function, affecting nutrient mineralisation and consequently plant performance. However, particularly for long-lived plants such as forest trees, the mechanisms by which trophic structure of the micro-food web governs rhizosphere microorganisms are still poorly understood. This study addresses the role of nematodes, as a major component of the soil micro-food web, in influencing the microbial abundance and community structure as well as tree growth. In a greenhouse experiment with Pedunculate Oak seedlings were grown in soil, where the nematode trophic structure was manipulated by altering the proportion of functional groups (i.e., bacterial, fungal, and plant feeders in a full factorial design. The influence on the rhizosphere microbial community, the ectomycorrhizal symbiont Piloderma croceum, and oak growth, was assessed. Soil phospholipid fatty acids were employed to determine changes in the microbial communities. Increased density of singular nematode functional groups showed minor impact by increasing the biomass of single microbial groups (e.g., plant feeders that of Gram-negative bacteria, except fungal feeders, which resulted in a decline of all microorganisms in the soil. In contrast, inoculation of two or three nematode groups promoted microbial biomass and altered the community structure in favour of bacteria, thereby counteracting negative impact of single groups. These findings highlight that the collective action of trophic groups in the soil micro-food web can result in microbial community changes promoting the fitness of the tree, thereby alleviating the negative effects of individual functional groups.

  2. Changes in the Lake Michigan food web following dreissenid mussel invasions: A synthesis

    Science.gov (United States)

    Madenjian, Charles P.; Bunnell, David B.; Warner, David M.; Pothoven, Steven A.; Fahnenstiel, Gary L.; Nalepa, Thomas F.; Vanderploeg, Henry A.; Tsehaye, Iyob; Claramunt, Randall M.; Clark, Richard D

    2015-01-01

    Using various available time series for Lake Michigan, we examined changes in the Lake Michigan food web following the dreissenid mussel invasions and identified those changes most likely attributable to these invasions, thereby providing a synthesis. Expansion of the quagga mussel (Dreissena rostriformis bugensis) population into deeper waters, which began around 2004, appeared to have a substantial predatory effect on both phytoplankton abundance and primary production, with annual primary production in offshore (> 50 m deep) waters being reduced by about 35% by 2007. Primary production likely decreased in nearshore waters as well, primarily due to predatory effects exerted by the quagga mussel expansion. The drastic decline inDiporeia abundance in Lake Michigan during the 1990s and 2000s has been attributed to dreissenid mussel effects, but the exact mechanism by which the mussels were negatively affecting Diporeia abundance remains unknown. In turn, decreased Diporeiaabundance was associated with reduced condition, growth, and/or energy density in alewife (Alosa pseudoharengus), lake whitefish (Coregonus clupeaformis), deepwater sculpin (Myoxocephalus thompsonii), and bloater (Coregonus hoyi). However, lake-wide biomass of salmonines, top predators in the food web, remained high during the 2000s, and consumption of alewives by salmonines actually increased between the 1980–1995 and 1996–2011 time periods. Moreover, abundance of the lake whitefish population, which supports Lake Michigan's most valuable commercial fishery, remained at historically high levels during the 2000s. Apparently, counterbalancing mechanisms operating within the complex Lake Michigan food web have enabled salmonines and lake whitefish to retain relatively high abundances despite reduced primary production.

  3. Are algae relevant to the detritus-based food web in tank-bromeliads?

    Directory of Open Access Journals (Sweden)

    Olivier Brouard

    Full Text Available We assessed the occurrence of algae in five species of tank-bromeliads found in contrasting environmental sites in a Neotropical, primary rainforest around the Nouragues Research Station, French Guiana. The distributions of both algal abundance and biomass were examined based on physical parameters, the morphological characteristics of bromeliad species and with regard to the structure of other aquatic microbial communities held in the tanks. Algae were retrieved in all of the bromeliad species with mean densities ranging from ∼10(2 to 10(4 cells/mL. Their biomass was positively correlated to light exposure and bacterial biomass. Algae represented a tiny component of the detrital food web in shaded bromeliads but accounted for up to 30 percent of the living microbial carbon in the tanks of Catopsis berteroniana, located in a highly exposed area. Thus, while nutrient supplies are believed to originate from wind-borne particles and trapped insects (i.e., allochtonous organic matter, our results indicate that primary producers (i.e., autochtonous organic matter are present in this insectivorous bromeliad. Using a 24-h incubation of size-fractionated and manipulated samples from this plant, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated that the dominant algal taxon, Bumilleriopsis sp., like protozoa and rotifers, is a significant part of the diet of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C. berteroniana and might form the basis of a complementary non-detrital food web.

  4. Microbial food web dynamics along a soil chronosequence of a glacier forefield

    Directory of Open Access Journals (Sweden)

    J. Esperschütz

    2011-11-01

    Full Text Available Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web dynamics in soils at different developmental stages. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland. 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L. Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA and phospholipid ether lipids (PLEL. Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PLFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria, especially actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain.

  5. Nutrient enrichment reduces constraints on material flows in a detritus-based food web.

    Science.gov (United States)

    Cross, Wyatt F; Wallace, J Bruce; Rosemond, Amy D

    2007-10-01

    Most aquatic and terrestrial ecosystems are experiencing increased nutrient availability, which is affecting their structure and function. By altering community composition and productivity of consumers, enrichment can indirectly cause changes in the pathways and magnitude of material flows in food webs. These changes, in turn, have major consequences for material storage and cycling in the ecosystem. Understanding mechanisms and predicting consequences of nutrient-induced changes in material flows requires a quantitative food web approach that combines information on consumer energetics and consumer-resource stoichiometry. We examined effects of a whole-system experimental nutrient enrichment on the trophic basis of production and the magnitude and pathways of carbon (C), nitrogen (N), and phosphorus (P) flows in a detritus-based stream food web. We compared the response of the treated stream to an adjacent reference stream throughout the study. Dietary composition and elemental flows varied considerably among invertebrate functional feeding groups. During nutrient enrichment, increased flows of leaf litter and amorphous detritus to shredders and gatherers accounted for most of the altered flows of C from basal resources to consumers. Nutrient enrichment had little effect on patterns of material flows but had large positive effects on the magnitude of C, N, and P flows to consumers (mean increase of 97% for all elements). Nutrient-specific food webs revealed similar flows of N and P to multiple functional groups despite an order of magnitude difference among groups in consumption of C. Secondary production was more strongly related to consumption of nutrients than C, and increased material flows were positively related to the degree of consumer-resource C:P and C:N imbalances. Nutrient enrichment resulted in an increased proportion of detrital C inputs consumed by primary consumers (from -15% to 35%) and a decreased proportion of invertebrate prey consumed by

  6. Trophic significance of the kelp Laminaria digitata (Lamour.) for the associated food web: a between-sites comparison

    Science.gov (United States)

    Schaal, Gauthier; Riera, Pascal; Leroux, Cédric

    2009-12-01

    This study aimed at establishing the trophic significance of the kelp Laminaria digitata for consumers inhabiting two rocky shores of Northern Brittany (France), displaying contrasted ecological conditions. The general trophic structure did not vary between these two sites, with a wide diversity of filter-feeders and predators, and only 14% of the species sampled belonging to the grazers' trophic group. The diversity of food sources fueling the food web appeared also similar. The food webs comprised four trophic levels and the prevalence of omnivory appeared relatively low compared to previous studies in the same area. Conversely, to the food web structure, which did not differ, the biochemical composition of L. digitata differed between the two sites, and was correlated to a larger diversity of grazers feeding on this kelp in sheltered conditions. This indicated that the spatial variability occurring in the nutritive value of L. digitata is likely to deeply affect the functioning of kelp-associated food webs. The contribution of L. digitata-derived organic matter to the diet of filter-feeders inhabiting these two environments was assessed using the mixing model Isosource, which showed the higher contribution of kelp matter in sheltered conditions. These results highlight the spatial variability that may occur in the functioning of kelp-associated food webs. Moreover, this suggests that hydrodynamics is likely to control the availability of kelp-derived organic matter to local filter-feeders, probably through an increase of detritus export in exposed areas.

  7. Food webs of the Delta, Suisun Bay and Suisun Marsh: an update on current understanding and possibilities for management

    Science.gov (United States)

    Brown, Larry R.; Kimmerer, Wim J.; Conrad, Louise; Lesmeister, Sarah; Mueller-Solger, Anke

    2016-01-01

    This paper reviews and highlights recent research findings on foodweb processes since an earlier review by Kimmerer et al. (2008). We conduct this review within a conceptual framework of the Delta-Suisun food web, which includes both temporal and spatial components. The temporal component is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to foodweb function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the South Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic foodweb processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: 1) synthesis of factors responsible for low pelagic biomass; 2) monitoring and research on effects of harmful algal blooms; 3) broadening the scope of long-term monitoring; 4) determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and 5) interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.

  8. Stable nitrogen and carbon isotopes in sediments and biota from three tropical marine food webs: Application to chemical bioaccumulation assessment.

    Science.gov (United States)

    Zhang, Hui; Teng, Yun; Doan, Tra Thi Thanh; Yat, Yun Wei; Chan, Sheot Harn; Kelly, Barry C

    2017-09-01

    Studies of trophodynamics and contaminant bioaccumulation in tropical marine ecosystems are limited. The present study employed stable isotope and trace contaminant analysis to assess sources of primary productivity, trophic interactions, and chemical bioaccumulation behavior in 2 mangrove food webs and 1 offshore coastal marine food web in Singapore. Samples of sediment, phytoplankton, mangrove leaves, clams, snails, crabs, worms, prawns, and fishes were analyzed for stable carbon and nitrogen isotope values, as well as concentrations of persistent organic pollutants. In the mangrove food webs, consumers exhibited similar δ 13 C values, probably because of the well-mixed nature of these systems. However, the 2 primary consumers (common nerite and rodong snail) exhibited distinct δ 13 C values (-21.6‰ vs -17.7‰), indicating different carbon sources. Fish from Singapore Strait exhibited similar δ 13 C values, indicating common carbon sources in this offshore marine food web. The highest trophic level was found in glass perchlet (trophic level = 3.3) and tilapia (trophic level = 3.4) in the 2 mangrove food webs and grunter (trophic level = 3.7) in the Singapore Strait food web. Concentrations of polychlorinated biphenyl (PCB 153) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) concentrations ranged from 0.9 to 84.6 ng/g lipid weight and from factors of PCB 153 and p,p'-DDE ranged between 1.63 and 4.62, indicating biomagnification in these tropical marine food webs. The findings provide important information that will aid future chemical bioaccumulation assessment initiatives. Environ Toxicol Chem 2017;36:2521-2532. © 2017 SETAC. © 2017 SETAC.

  9. Food-web structure and ecosystem services: insights from the Serengeti.

    Science.gov (United States)

    Dobson, Andy

    2009-06-27

    The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year. The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species. Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web. The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that

  10. Prey or predator – expanding the food web role of sandeel (Ammodytes marinus)

    DEFF Research Database (Denmark)

    Eigaard, Ole Ritzau; Deurs, Mikael van; Behrens, Jane

    2014-01-01

    in marine food webs. In 2012 and 2013 the stomachs of 748 sandeels from 36 different commercial sandeel hauls in the central North Sea were opened. 9% of these stomachs contained late stage sandeel larvae. In order to better understand the cannibalistic nature of sandeels, we made a detailed analysis...... of another 450 sandeels from a single haul with a high frequency of apparent cannibals. One-third of the stomachs contained a minimum of one young sandeel (mean length 2.7 cm; max. length 4.9 cm), 10 percent contained 5 or more, and one stomach contained 18. Analyses of sample DNA confirmed that predator...... in North Sea sandeel stocks, but it may also add a new element to the complexity of energy flow in marine food chains...

  11. The Role of Highly Unsaturated Fatty Acids in Aquatic Food Webs

    Science.gov (United States)

    Perhar, G.; Arhonditsis, G. B.

    2009-05-01

    Highly unsaturated fatty acids (HUFAs) are important molecules transferred across the plant-animal interface in aquatic food webs. Defined here as carbon chains of length 18 (carbons) or more, with a double bond in the third (Omega 3) or sixth (Omega 6) bond from the methyl end, HUFAs are formed in primary producers (phytoplankton). With limited abilities to synthesize de novo, consumers and higher trophic organisms are required to obtain their HUFAs primarily from diet. Bioconversion of HUFAs from one form to another is in theory possible, as is synthesis via elongation and the transformation of a saturated to highly saturated fatty acid, but the enzymes required for these processes are absent in most species. HUFAs are hypothesized to be somatic growth limiting compounds for herbivorous zooplankton and have been shown to be critical for juvenile fish growth and wellbeing. Zooplankton tend to vary their fatty acid concentrations, collection strategies and utilization methods based on taxonomy, and various mechanisms have been suggested to account for these differences i.e., seasonal and nervous system hypotheses. Considering also the facts that copepods overwinter in an active state while daphnids overwinter as resting eggs, and that copepods tend to accumulate Docosahexaenoic acid (DHA) through collection and bioconversion, while daphnids focus on Eicosapentaenoic acid (EPA), one can link high DHA concentrations to active overwintering; but both EPA and DHA have similar melting points, putting DHA's cold weather adaptation abilities into question. Another characteristic setting copepods apart from daphnids is nervous system complexity: copepod axons are coated in thick myelin sheaths, permitting rapid neural processing, such as rapid prey attack and intelligent predator avoidance; DHA may be required for the proper functioning of copepod neurons. Recent modeling results have suggested food webs with high quality primary producers (species high in HUFAs, i

  12. A stable isotope ( δ13C, δ15N) model for the North Water food web: implications for evaluating trophodynamics and the flow of energy and contaminants

    Science.gov (United States)

    Hobson, Keith A.; Fisk, Aaron; Karnovsky, Nina; Holst, Meike; Gagnon, Jean-Marc; Fortier, Martin

    The North Water Polynya is an area of high biological activity that supports large numbers of higher trophic-level organisms such as seabirds and marine mammals. An overall objective of the Upper Trophic-Level Group of the International North Water Polynya Study (NOW) was to evaluate carbon and contaminant flux through these high trophic-level (TL) consumers. Crucial to an evaluation of the role of such consumers, however, was the establishment of primary trophic linkages within the North Water food web. We used δ15N values of food web components from particulate organic matter (POM) through polar bears ( Ursus maritimus) to create a trophic-level model based on the assumptions that Calanus hyperboreus occupies TL 2.0 and there is a 2.4‰ trophic enrichment in 15N between birds and their diets, and a 3.8‰ trophic enrichment for all other components. This model placed the planktivorous dovekie ( Alle alle) at TL 3.3, ringed seal ( Phoca hispida) at TL 4.5, and polar bear at TL 5.5. The copepods C. hyperboreus, Chiridius glacialis and Euchaeta glacialis formed a trophic continuum (TL 2.0-3.0) from primary herbivore through omnivore to primary carnivore. Invertebrates were generally sorted according to planktonic, benthic and epibenthic feeding groups. Seabirds formed three trophic groups, with dovekie occupying the lowest, black-legged kittiwake ( Rissa tridactyla), northern fulmar ( Fulmarus glacialis), thick-billed murre ( Uria aalge), and ivory gull ( Pagophilia eburnea) intermediate (TL 3.9-4.0), and glaucous gull ( Larus hyperboreus) the highest (TL 4.6) trophic positions. Among marine mammals, walrus ( Odobenus rosmarus) occupied the lowest (TL 3.2) and bearded seal ( Erignathus barbatus), ringed seal, beluga whale ( Delphinapterus leucas), and narwhal ( Monodon monoceros) intermediate positions (TL 4.1-4.6). In addition to arctic cod ( Boreogadus saida), we suggest that lower trophic-level prey, in particular the amphipod Themisto libellula, contribute

  13. Simple rules describe bottom-up and top-down control in food webs with alternative energy pathways.

    Science.gov (United States)

    Wollrab, Sabine; Diehl, Sebastian; De Roos, André M

    2012-09-01

    Many human influences on the world's ecosystems have their largest direct impacts at either the top or the bottom of the food web. To predict their ecosystem-wide consequences we must understand how these impacts propagate. A long-standing, but so far elusive, problem in this endeavour is how to reduce food web complexity to a mathematically tractable, but empirically relevant system. Simplification to main energy channels linking primary producers to top consumers has been recently advocated. Following this approach, we propose a general framework for the analysis of bottom-up and top-down forcing of ecosystems by reducing food webs to two energy pathways originating from a limiting resource shared by competing guilds of primary producers (e.g. edible vs. defended plants). Exploring dynamical models of such webs we find that their equilibrium responses to nutrient enrichment and top consumer harvesting are determined by only two easily measurable topological properties: the lengths of the component food chains (odd-odd, odd-even, or even-even) and presence vs. absence of a generalist top consumer reconnecting the two pathways (yielding looped vs. branched webs). Many results generalise to other looped or branched web structures and the model can be easily adapted to include a detrital pathway. © 2012 Blackwell Publishing Ltd/CNRS.

  14. Combining food web and species distribution models for improved community projections.

    Science.gov (United States)

    Pellissier, Loïc; Rohr, Rudolf P; Ndiribe, Charlotte; Pradervand, Jean-Nicolas; Salamin, Nicolas; Guisan, Antoine; Wisz, Mary

    2013-11-01

    The ability to model biodiversity patterns is of prime importance in this era of severe environmental crisis. Species assemblage along environmental gradients is subject to the interplay of biotic interactions in complement to abiotic filtering and stochastic forces. Accounting for complex biotic interactions for a wide array of species remains so far challenging. Here, we propose using food web models that can infer the potential interaction links between species as a constraint in species distribution models. Using a plant-herbivore (butterfly) interaction dataset, we demonstrate that this combined approach is able to improve species distribution and community forecasts. The trophic interaction network between butterfly larvae and host plant was phylogenetically structured and driven by host plant nitrogen content allowing forecasting the food web model to unknown interactions links. This combined approach is very useful in rendering models of more generalist species that have multiple potential interaction links, where gap in the literature may occur. Our combined approach points toward a promising direction for modeling the spatial variation in entire species interaction networks.

  15. Herbivore diet breadth mediates the cascading effects of carnivores in food webs.

    Science.gov (United States)

    Singer, Michael S; Lichter-Marck, Isaac H; Farkas, Timothy E; Aaron, Eric; Whitney, Kenneth D; Mooney, Kailen A

    2014-07-01

    Predicting the impact of carnivores on plants has challenged community and food web ecologists for decades. At the same time, the role of predators in the evolution of herbivore dietary specialization has been an unresolved issue in evolutionary ecology. Here, we integrate these perspectives by testing the role of herbivore diet breadth as a predictor of top-down effects of avian predators on herbivores and plants in a forest food web. Using experimental bird exclosures to study a complex community of trees, caterpillars, and birds, we found a robust positive association between caterpillar diet breadth (phylodiversity of host plants used) and the strength of bird predation across 41 caterpillar and eight tree species. Dietary specialization was associated with increased enemy-free space for both camouflaged (n = 33) and warningly signaled (n = 8) caterpillar species. Furthermore, dietary specialization was associated with increased crypsis (camouflaged species only) and more stereotyped resting poses (camouflaged and warningly signaled species), but was unrelated to caterpillar body size. These dynamics in turn cascaded down to plants: a metaanalysis (n = 15 tree species) showed the beneficial effect of birds on trees (i.e., reduced leaf damage) decreased with the proportion of dietary specialist taxa composing a tree species' herbivore fauna. We conclude that herbivore diet breadth is a key functional trait underlying the trophic effects of carnivores on both herbivores and plants.

  16. Contrasting food web factor and body size relationships with Hg and Se concentrations in marine biota.

    Directory of Open Access Journals (Sweden)

    Roxanne Karimi

    Full Text Available Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by δ(15N and degree of pelagic feeding (measured by δ(13C. Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans.

  17. UV effects on marine planktonic food webs: A synthesis of results from mesocosm studies.

    Science.gov (United States)

    Belzile, Claude; Demers, Serge; Ferreyra, Gustavo A; Schloss, Irene; Nozais, Christian; Lacoste, Karine; Mostajir, Behzad; Roy, Suzanne; Gosselin, Michel; Pelletier, Emilien; Gianesella, Sônia M F; Vernet, Maria

    2006-01-01

    UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical, chemical and light conditions mimicking those of the natural environment. In allowing the manipulation of UV intensities and light spectral composition, the experimental mesocosm approach has proven to be especially useful in assessing the impacts at the community level. This review of mesocosm studies shows that, although a UV increase even well above natural intensities often has subtle effects on bulk biomass (carbon and chlorophyll), it can significantly impact the food-web structure because of different sensitivity to UV among planktonic organisms. Given the complexity of UV impacts, as evidenced by results of mesocosm studies, interactions between UV and changing environmental conditions (e.g. eutrophication and climate change) are likely to have significant effects on the function of marine ecosystems.

  18. Dynamically Coupled Food-web and Hydrodynamic Modeling with ADH-CASM

    Science.gov (United States)

    Piercy, C.; Swannack, T. M.

    2012-12-01

    Oysters and freshwater mussels are "ecological engineers," modifying the local water quality by filtering zooplankton and other suspended particulate matter from the water column and flow hydraulics by impinging on the near-bed flow environment. The success of sessile, benthic invertebrates such as oysters depends on environmental factors including but not limited to temperature, salinity, and flow regime. Typically food-web and other types of ecological models use flow and water quality data as direct input without regard to the feedback between the ecosystem and the physical environment. The USACE-ERDC has developed a coupled hydrodynamic-ecological modeling approach that dynamically couples a 2-D hydrodynamic and constituent transport model, Adaptive Hydraulics (ADH), with a bioenergetics food-web model, the Comprehensive Aquatics Systems Model (CASM), which captures the dynamic feedback between aquatic ecological systems and the environment. We present modeling results from restored oyster reefs in the Great Wicomico River on the western shore of the Chesapeake Bay, which quantify ecosystem services such as the influence of the benthic ecosystem on water quality. Preliminary results indicate that while the influence of oyster reefs on bulk flow dynamics is limited due to the localized influence of oyster reefs, large reefs and the associated benthic ecosystem can create measurable changes in the concentrations of nitrogen, phosphorus, and carbon in the areas around reefs. We also present a sensitivity analysis to quantify the relative sensitivity of the coupled ADH-CASM model to both hydrodynamic and ecological parameter choice.

  19. The roles and impacts of human hunter-gatherers in North Pacific marine food webs.

    Science.gov (United States)

    Dunne, Jennifer A; Maschner, Herbert; Betts, Matthew W; Huntly, Nancy; Russell, Roly; Williams, Richard J; Wood, Spencer A

    2016-02-17

    There is a nearly 10,000-year history of human presence in the western Gulf of Alaska, but little understanding of how human foragers integrated into and impacted ecosystems through their roles as hunter-gatherers. We present two highly resolved intertidal and nearshore food webs for the Sanak Archipelago in the eastern Aleutian Islands and use them to compare trophic roles of prehistoric humans to other species. We find that the native Aleut people played distinctive roles as super-generalist and highly-omnivorous consumers closely connected to other species. Although the human population was positioned to have strong effects, arrival and presence of Aleut people in the Sanak Archipelago does not appear associated with long-term extinctions. We simulated food web dynamics to explore to what degree introducing a species with trophic roles like those of an Aleut forager, and allowing for variable strong feeding to reflect use of hunting technology, is likely to trigger extinctions. Potential extinctions decreased when an invading omnivorous super-generalist consumer focused strong feeding on decreasing fractions of its possible resources. This study presents the first assessment of the structural roles of humans as consumers within complex ecological networks, and potential impacts of those roles and feeding behavior on associated extinctions.

  20. Biomagnification of persistent organic pollutants in a deep-sea, temperate food web.

    Science.gov (United States)

    Romero-Romero, Sonia; Herrero, Laura; Fernández, Mario; Gómara, Belén; Acuña, José Luis

    2017-12-15

    Polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) were measured in a temperate, deep-sea ecosystem, the Avilés submarine Canyon (AC; Cantabrian Sea, Southern Bay of Biscay). There was an increase of contaminant concentration with the trophic level of the organisms, as calculated from stable nitrogen isotope data (δ 15 N). Such biomagnification was only significant for the pelagic food web and its magnitude was highly dependent on the type of top predators included in the analysis. The trophic magnification factor (TMF) for PCB-153 in the pelagic food web (spanning four trophic levels) was 6.2 or 2.2, depending on whether homeotherm top predators (cetaceans and seabirds) were included or not in the analysis, respectively. Since body size is significantly correlated with δ 15 N, it can be used as a proxy to estimate trophic magnification, what can potentially lead to a simple and convenient method to calculate the TMF. In spite of their lower biomagnification, deep-sea fishes showed higher concentrations than their shallower counterparts, although those differences were not significant. In summary, the AC fauna exhibits contaminant levels comparable or lower than those reported in other systems. Copyright © 2017 Elsevier B.V. All rights reserved.

  1. Mercury biomagnification through food webs along a salinity gradient down-estuary from a biological hotspot

    Science.gov (United States)

    Rumbold, Darren G.; Lange, Ted R.; Richard, Doug; DelPizzo, Gina; Hass, Nicole

    2018-01-01

    To examine down-estuary effects and how differences in food webs along a salinity gradient might influence mercury (Hg) biomagnification, we conducted a study from 2010 to 2015 in an estuary with a known biological hotspot at its headwaters. Over 907 samples of biota, representing 92 different taxa of fish and invertebrates, seston and sediments were collected from the upper, middle and lower reach for Hg determination and for stable nitrogen and carbon isotope analyses. Trophic magnification slopes (TMS; log Hg versus δ15N), as a measure of biomagnification efficiency, ranged from 0.23 to 0.241 but did not differ statistically among reaches. Hg concentrations were consistently highest, ranging as high as 4.9 mg/kg in top predatory fish, in the upper-reach of the estuary where basal Hg entering the food web was also highest, as evidenced by methylmercury concentrations in suspension feeders. Top predatory fish at the mouth of the estuary contained relatively low [THg], likely due to lower basal Hg. This was nonetheless surprising given the potential for down-estuary biotransport.

  2. Human Impacts and Climate Change Influence Nestedness and Modularity in Food-Web and Mutualistic Networks.

    Science.gov (United States)

    Takemoto, Kazuhiro; Kajihara, Kosuke

    2016-01-01

    Theoretical studies have indicated that nestedness and modularity-non-random structural patterns of ecological networks-influence the stability of ecosystems against perturbations; as such, climate change and human activity, as well as other sources of environmental perturbations, affect the nestedness and modularity of ecological networks. However, the effects of climate change and human activities on ecological networks are poorly understood. Here, we used a spatial analysis approach to examine the effects of climate change and human activities on the structural patterns of food webs and mutualistic networks, and found that ecological network structure is globally affected by climate change and human impacts, in addition to current climate. In pollination networks, for instance, nestedness increased and modularity decreased in response to increased human impacts. Modularity in seed-dispersal networks decreased with temperature change (i.e., warming), whereas food web nestedness increased and modularity declined in response to global warming. Although our findings are preliminary owing to data-analysis limitations, they enhance our understanding of the effects of environmental change on ecological communities.

  3. Human Impacts and Climate Change Influence Nestedness and Modularity in Food-Web and Mutualistic Networks.

    Directory of Open Access Journals (Sweden)

    Kazuhiro Takemoto

    Full Text Available Theoretical studies have indicated that nestedness and modularity-non-random structural patterns of ecological networks-influence the stability of ecosystems against perturbations; as such, climate change and human activity, as well as other sources of environmental perturbations, affect the nestedness and modularity of ecological networks. However, the effects of climate change and human activities on ecological networks are poorly understood. Here, we used a spatial analysis approach to examine the effects of climate change and human activities on the structural patterns of food webs and mutualistic networks, and found that ecological network structure is globally affected by climate change and human impacts, in addition to current climate. In pollination networks, for instance, nestedness increased and modularity decreased in response to increased human impacts. Modularity in seed-dispersal networks decreased with temperature change (i.e., warming, whereas food web nestedness increased and modularity declined in response to global warming. Although our findings are preliminary owing to data-analysis limitations, they enhance our understanding of the effects of environmental change on ecological communities.

  4. Insect-damaged fossil leaves record food web response to ancient climate change and extinction.

    Science.gov (United States)

    Wilf, P

    2008-01-01

    Plants and herbivorous insects have dominated terrestrial ecosystems for over 300 million years. Uniquely in the fossil record, foliage with well-preserved insect damage offers abundant and diverse information both about producers and about ecological and sometimes taxonomic groups of consumers. These data are ideally suited to investigate food web response to environmental perturbations, and they represent an invaluable deep-time complement to neoecological studies of global change. Correlations between feeding diversity and temperature, between herbivory and leaf traits that are modulated by climate, and between insect diversity and plant diversity can all be investigated in deep time. To illustrate, I emphasize recent work on the time interval from the latest Cretaceous through the middle Eocene (67-47 million years ago (Ma)), including two significant events that affected life: the end-Cretaceous mass extinction (65.5 Ma) and its ensuing recovery; and globally warming temperatures across the Paleocene-Eocene boundary (55.8 Ma). Climatic effects predicted from neoecology generally hold true in these deep-time settings. Rising temperature is associated with increased herbivory in multiple studies, a result with major predictive importance for current global warming. Diverse floras are usually associated with diverse insect damage; however, recovery from the end-Cretaceous extinction reveals uncorrelated plant and insect diversity as food webs rebuilt chaotically from a drastically simplified state. Calibration studies from living forests are needed to improve interpretation of the fossil data.

  5. Tracing carbon sources through aquatic and terrestrial food webs using amino acid stable isotope fingerprinting.

    Directory of Open Access Journals (Sweden)

    Thomas Larsen

    Full Text Available Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring δ(13C patterns among amino acids (δ(13CAA could distinguish between multiple aquatic and terrestrial primary production sources. We found that δ(13CAA patterns in contrast to bulk δ(13C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their δ(13CAA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk δ(13C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer δ(13C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

  6. Molecular detection of trophic links in a complex insect host-parasitoid food web.

    Science.gov (United States)

    Hrcek, Jan; Miller, Scott E; Quicke, Donald L J; Smith, M Alex

    2011-09-01

    Previously, host-parasitoid links have been unveiled almost exclusively by time-intensive rearing, while molecular methods were used only in simple agricultural host-parasitoid systems in the form of species-specific primers. Here, we present a general method for the molecular detection of these links applied to a complex caterpillar-parasitoid food web from tropical rainforest of Papua New Guinea. We DNA barcoded hosts, parasitoids and their tissue remnants and matched the sequences to our extensive library of local species. We were thus able to match 87% of host sequences and 36% of parasitoid sequences to species and infer subfamily or family in almost all cases. Our analysis affirmed 93 hitherto unknown trophic links between 37 host species from a wide range of Lepidoptera families and 46 parasitoid species from Hymenoptera and Diptera by identifying DNA sequences for both the host and the parasitoid involved in the interaction. Molecular detection proved especially useful in cases where distinguishing host species in caterpillar stage was difficult morphologically, or when the caterpillar died during rearing. We have even detected a case of extreme parasitoid specialization in a pair of Choreutis species that do not differ in caterpillar morphology and ecology. Using the molecular approach outlined here leads to better understanding of parasitoid host specificity, opens new possibilities for rapid surveys of food web structure and allows inference of species associations not already anticipated. Published 2011. This article is a US Government work and is in the public domain in the USA.

  7. Interested in Pelagic Food Webs? BCO-DMO has your Data.

    Science.gov (United States)

    Chandler, C. L.; Groman, R. C.; Kinkade, D.; Rauch, S.; Allison, M. D.; Gegg, S. R.; Shepherd, A.; Wiebe, P. H.; Glover, D. M.

    2016-02-01

    Interdisciplinary research collaborations that address complex, global research themes such as the interactive effects of global warming and studies of pelagic food webs require access to a broad range of data types from all disciplines of oceanography, from all platforms (e.g. ships, gliders, floats, moorings), with the in situ observations complementing and being complemented by laboratory and model results. In an effort to build a comprehensive database of marine ecosystem research data, the National Science Foundation (NSF) funded the Biological and Chemical Oceanography Data Management Office (BCO-DMO; bco-dmo.org) to support the data management requirements of investigators funded by the NSF's Polar Programs (PLR) and Biological and Chemical Oceanography Sections (OCE). Since 2006, investigators funded by NSF PLR and OCE have been working with support from BCO-DMO data scientists, to build a data system that now includes the full range of ocean biogeochemistry data resulting from decades of research. In addition to data from recently funded PIs, the BCO-DMO data system also serves data from legacy programs (e.g. US Joint Global Ocean Flux Study and US Global Ocean Ecosystem Dynamics). The data are open-access, available for download in a variety of user-selectable formats, and accompanied by sufficient documentation to enable re-use. This presentation will highlight the diversity of data available from the BCO-DMO system and demonstrate some of the features that enable discovery, access and download of data relevant to studies of pelagic food webs.

  8. Contrasting Food Web Factor and Body Size Relationships with Hg and Se Concentrations in Marine Biota

    Science.gov (United States)

    Karimi, Roxanne; Frisk, Michael; Fisher, Nicholas S.

    2013-01-01

    Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by δ15N) and degree of pelagic feeding (measured by δ13C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans. PMID:24019976

  9. Donor-Control of Scavenging Food Webs at the Land-Ocean Interface.

    Directory of Open Access Journals (Sweden)

    Thomas A Schlacher

    Full Text Available Food webs near the interface of adjacent ecosystems are potentially subsidised by the flux of organic matter across system boundaries. Such subsidies, including carrion of marine provenance, are predicted to be instrumental on open-coast sandy shores where in situ productivity is low and boundaries are long and highly permeable to imports from the sea. We tested the effect of carrion supply on the structure of consumer dynamics in a beach-dune system using broad-scale, repeated additions of carcasses at the strandline of an exposed beach in eastern Australia. Carrion inputs increased the abundance of large invertebrate scavengers (ghost crabs, Ocypode spp., a numerical response most strongly expressed by the largest size-class in the population, and likely due to aggregative behaviour in the short term. Consumption of carrion at the beach-dune interface was rapid and efficient, driven overwhelmingly by facultative avian scavengers. This guild of vertebrate scavengers comprises several species of birds of prey (sea eagles, kites, crows and gulls, which reacted strongly to concentrations of fish carrion, creating hotspots of intense scavenging activity along the shoreline. Detection of carrion effects at several trophic levels suggests that feeding links arising from carcasses shape the architecture and dynamics of food webs at the land-ocean interface.

  10. Hydrogen Isotope Fractionation in Aquatic Primary Producers: Implications for Food Web Studies

    Science.gov (United States)

    Hondula, K. L.; Pace, M. L.; Cole, J. J.; Batt, R. D.

    2011-12-01

    Hydrogen in the organic matter of aquatic plants has a lower relative abundance of the deuterium isotope in comparison to hydrogen in the surrounding water due to a series of fractionation processes including photosynthesis and the biosynthesis of lipids. Expected differences between the deuterium values of different types of plant tissue have been used to observe terrestrial contributions to aquatic food webs and to discriminate organic matter sources in 3-isotope studies with more precision than in 2-isotope studies, however some values used in these studies are derived from an estimated fractionation value (ɛ) between water and plant tissue. We found significant differences in fractionation values between different groups of aquatic plants sampled from three system types: lakes, river, and coastal lagoon. Fractionation values between water and plant tissue of macrophytes and marine macroalgae were more similar to those of terrestrial plants and distinctly different than those of benthic microalgae and phytoplankton. Incorporating the variability in fractionation values between plant types will improve models and experimental designs used in isotopic food web studies for aquatic systems.

  11. Qualitative Analysis of Cognitive Interviews With School Children: A Web-Based Food Intake Questionnaire.

    Science.gov (United States)

    Fernandes Davies, Vanessa; Kupek, Emil; Faria Di Pietro, Patricia; Altenburg de Assis, Maria Alice; Gk Vieira, Francilene; Perucchi, Clarice; Mafra, Rafaella; Thompson, Debbe; Baranowski, Thomas

    2016-11-28

    The use of computers to administer dietary assessment questionnaires has shown potential, particularly due to the variety of interactive features that can attract and sustain children's attention. Cognitive interviews can help researchers to gain insights into how children understand and elaborate their response processes in this type of questionnaire. To present the cognitive interview results of children who answered the WebCAAFE, a Web-based questionnaire, to obtain an in-depth understanding of children's response processes. Cognitive interviews were conducted with children (using a pretested interview script). Analyses were carried out using thematic analysis within a grounded theory framework of inductive coding. A total of 40 children participated in the study, and 4 themes were identified: (1) the meaning of words, (2) understanding instructions, (3) ways to resolve possible problems, and (4) suggestions for improving the questionnaire. Most children understood questions that assessed nutritional intake over the past 24 hours, although the structure of the questionnaire designed to facilitate recall of dietary intake was not always fully understood. Younger children (7 and 8 years old) had more difficulty relating the food images to mixed dishes and foods eaten with bread (eg, jam, cheese). Children were able to provide suggestions for improving future versions of the questionnaire. More attention should be paid to children aged 8 years or below, as they had the greatest difficulty completing the WebCAAFE. ©Vanessa Fernandes Davies, Emil Kupek, Patricia Faria Di Pietro, Maria Alice Altenburg de Assis, Francilene GK Vieira, Clarice Perucchi, Rafaella Mafra, Debbe Thompson, Thomas Baranowski. Originally published in JMIR Public Health and Surveillance (http://publichealth.jmir.org), 28.11.2016.

  12. Short-term effects of different genetically modified maize varieties on arthropod food web properties: an experimental field assessment.

    Science.gov (United States)

    Szénási, Ágnes; Pálinkás, Zoltán; Zalai, Mihály; Schmitz, Oswald J; Balog, Adalbert

    2014-06-17

    There is concern that genetically modified (GM) plants may have adverse affects on the arthropod biodiversity comprising agricultural landscapes. The present study report on a two year field experimental test of whether four different genotypic lines, some are novel with no previous field tests, of GM maize hybrids alter the structure of arthropod food webs that they harbour, relative to non-GM maize (control) that is widely used in agriculture. The different GM genotypes produced either Bt toxins, conferred glyphosate tolerance or a combination of the two traits. Quantitative food web analysis, based on short-term assessment assigning a total of 243,896 arthropod individuals collected from the treatments to their positions in food webs, revealed that complex and stable food webs persisted in each maize treatment. Moreover, food web structure remained relatively unchanged by the GM-genotype. The results suggest that at least in short-term period these particular GM maize genotypes will not have adverse effects on arthropod biota of agricultural landscapes.

  13. Biomagnification of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls in a highly contaminated freshwater food web from South China

    International Nuclear Information System (INIS)

    Wu Jiangping; Luo Xiaojun; Zhang Ying; Yu Mei; Chen Shejun; Mai Bixian; Yang Zhongyi

    2009-01-01

    To evaluate the biomagnification extent of polybrominated diphenyls ethers (PBDEs) and polychlorinated biphenyls (PCBs) in a highly contaminated freshwater food web from South China, trophic magnification factors (TMFs) for 18 PBDE congeners and 53 PCB congeners were calculated. The TMF values ranged 0.26-4.47 for PBDEs and 0.75-5.10 for PCBs. Forty-five of 53 PCBs and BDEs 47, 100 and 154 had TMFs greater than one, suggesting their biomagnification in the present food web. The TMFs for PBDEs were generally smaller than those for PCBs with the same degree of halogenation, indicating a lower biomagnification potential for PBDEs compared to PCBs. For PCBs, it followed a parabolic relationship between TMFs and log K OW (octanol-water partition coefficient). However, this relationship was not significant for PBDEs, possibly due to the more complex behaviors of PBDEs in the food web (e.g., metabolism), compared to that of PCBs. - Forty-five of 53 PCBs magnified in the freshwater food web, while only BDEs 47, 100 and 154 significantly magnified in the same food web

  14. Evaluation of web-based, self-administered, graphical food frequency questionnaire.

    Science.gov (United States)

    Kristal, Alan R; Kolar, Ann S; Fisher, James L; Plascak, Jesse J; Stumbo, Phyllis J; Weiss, Rick; Paskett, Electra D

    2014-04-01

    Computer-administered food frequency questionnaires (FFQs) can address limitations inherent in paper questionnaires by allowing very complex skip patterns, portion size estimation based on food pictures, and real-time error checking. We evaluated a web-based FFQ, the Graphical Food Frequency System (GraFFS). Participants completed the GraFFS, six telephone-administered 24-hour dietary recalls over the next 12 weeks, followed by a second GraFFS. Participants were 40 men and 34 women, aged 18 to 69 years, living in the Columbus, OH, area. Intakes of energy, macronutrients, and 17 micronutrients/food components were estimated from the GraFFS and the mean of all recalls. Bias (second GraFFS minus recalls) was -9%, -5%, +4%, and -4% for energy and percentages of energy from fat, carbohydrate, and protein, respectively. De-attenuated, energy-adjusted correlations (intermethod reliability) between the recalls and the second GraFFS for fat, carbohydrate, protein, and alcohol were 0.82, 0.79, 0.67, and 0.90, respectively; for micronutrients/food components the median was 0.61 and ranged from 0.40 for zinc to 0.92 for beta carotene. The correlations between the two administrations of the GraFFS (test-retest reliability) for fat, carbohydrate, protein, and alcohol were 0.60, 0.63, 0.73, and 0.87, respectively; among micronutrients/food components the median was 0.67 and ranged from 0.49 for vitamin B-12 to 0.82 for fiber. The measurement characteristics of the GraFFS were at least as good as those reported for most paper FFQs, and its high intermethod reliability suggests that further development of computer-administered FFQs is warranted. Copyright © 2014 Academy of Nutrition and Dietetics. Published by Elsevier Inc. All rights reserved.

  15. Seasonal variation in accumulation of persistent organic pollutants in an Arctic marine benthic food web

    Energy Technology Data Exchange (ETDEWEB)

    Evenset, A., E-mail: anita.evenset@akvaplan.niva.no [Akvaplan-niva. Fram Centre, Tromsø (Norway); University of Tromsø, The Arctic University of Norway, Tromsø (Norway); Hallanger, I.G. [University of Tromsø, The Arctic University of Norway, Tromsø (Norway); Tessmann, M. [Akvaplan-niva. Fram Centre, Tromsø (Norway); Institute for Hydrobiology and Fisheries Research, University of Hamburg (Germany); Warner, N. [Norwegian Institute for Air Research, Fram Centre, Tromsø (Norway); Ruus, A. [Norwegian Institute for Water Research, Oslo (Norway); Borgå, K. [Norwegian Institute for Water Research, Oslo (Norway); Department of Biosciences, P.O. Box 1066, Blindern 0316, Oslo (Norway); Gabrielsen, G.W. [Norwegian Polar Institute, Fram Centre, Tromsø (Norway); Christensen, G. [Akvaplan-niva. Fram Centre, Tromsø (Norway); Renaud, P.E. [Akvaplan-niva. Fram Centre, Tromsø (Norway); University Centre in Svalbard, Longyearbyen (Norway)

    2016-01-15

    The aim of the present study was to investigate seasonal variation in persistent organic pollutant (POP) concentrations, as well as food-web biomagnification, in an Arctic, benthic marine community. Macrozoobenthos, demersal fish and common eiders were collected both inside and outside of Kongsfjorden, Svalbard, during May, July and October 2007. The samples were analysed for a selection of legacy chlorinated POPs. Overall, low levels of POPs were measured in all samples. Although POP levels and accumulation patterns showed some seasonal variation, the magnitude and direction of change was not consistent among species. Overall, seasonality in bioaccumulation in benthic biota was less pronounced than in the pelagic system in Kongsfjorden. In addition, the results indicate that δ{sup 15}N is not a good predictor for POP-levels in benthic food chains. Other factors, such as feeding strategy (omnivory, necrophagy versus herbivory), degree of contact with the sediment, and a high dependence on particulate organic matter (POM), with low POP-levels and high δ{sup 15}N-values (due to bacterial isotope enrichment), seem to govern the uptake of the different POPs and result in loads deviating from what would be expected consulting the trophic position alone. - Highlights: • Seasonal variation in POP biomagnification was investigated in a benthic food web. • Levels of POPs are generally low in benthic species from Kongsfjorden, Svalbard. • POP-concentrations varied with season, but direction of change varied among taxa. • No POP-biomagnification, except for cis-nonachlor, was detected in this study. • δ{sup 15}N-values does not seem to be a good proxy for trophic level in macrozoobenthos.

  16. Trophic relationships in an Arctic food web and implications for trace metal transfer

    International Nuclear Information System (INIS)

    Dehn, Larissa-A.; Follmann, Erich H.; Thomas, Dana L.; Sheffield, Gay G.; Rosa, Cheryl; Duffy, Lawrence K.; O'Hara, Todd M.

    2006-01-01

    Tissues of subsistence-harvested Arctic mammals were analyzed for silver (Ag), cadmium (Cd), and total mercury (THg). Muscle (or total body homogenates of potential fish and invertebrate prey) was analyzed for stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes to establish trophic interactions within the Arctic food chain. Food web magnification factors (FWMFs) and biomagnification factors for selected predator-prey scenarios (BMFs) were calculated to describe pathways of heavy metals in the Alaskan Arctic. FWMFs in this study indicate that magnification of selected heavy metals in the Arctic food web is not significant. Biomagnification of Cd occurs mainly in kidneys; calculated BMFs are higher for hepatic THg than renal THg for all predator-prey scenarios with the exception of polar bears (Ursus maritimus). In bears, the accumulation of renal THg is approximately 6 times higher than in liver. Magnification of hepatic Ag is minimal for all selected predator-prey scenarios. Though polar bears occupy a higher trophic level than belugas (Delphinapterus leucas), based on δ 15 N, the metal concentrations are either not statistically different between the two species or lower for bears. Similarly, concentrations of renal and hepatic Cd are significantly lower or not statistically different in polar bears compared to ringed (Phoca hispida) and bearded seals (Erignathus barbatus), their primary prey. THg, on the other hand, increased significantly from seal to polar bear tissues. Mean δ 15 N was lowest in muscle of Arctic fox (Alopex lagopus) and foxes also show the lowest levels of Hg, Cd and Ag in liver and kidney compared to the other species analyzed. These values are in good agreement with a diet dominated by terrestrial prey. Metal deposition in animal tissues is strongly dependent on biological factors such as diet, age, sex, body condition and health, and caution should be taken when interpreting magnification of dynamic and actively regulated trace metals

  17. Trophic relationships in an Arctic food web and implications for trace metal transfer

    Energy Technology Data Exchange (ETDEWEB)

    Dehn, Larissa-A. [Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-7000 (United States)]. E-mail: ftld@uaf.edu; Follmann, Erich H. [Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-7000 (United States); Thomas, Dana L. [Department of Mathematical Sciences, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-6660 (United States); Sheffield, Gay G. [Alaska Department of Fish and Game, Fairbanks, Division of Wildlife Conservation, Fairbanks, Alaska, 99701-1599 (United States); Rosa, Cheryl [Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-7000 (United States); Duffy, Lawrence K. [Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-7000 (United States); O' Hara, Todd M. [Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775-7000 (United States)

    2006-06-01

    Tissues of subsistence-harvested Arctic mammals were analyzed for silver (Ag), cadmium (Cd), and total mercury (THg). Muscle (or total body homogenates of potential fish and invertebrate prey) was analyzed for stable carbon ({delta} {sup 13}C) and nitrogen ({delta} {sup 15}N) isotopes to establish trophic interactions within the Arctic food chain. Food web magnification factors (FWMFs) and biomagnification factors for selected predator-prey scenarios (BMFs) were calculated to describe pathways of heavy metals in the Alaskan Arctic. FWMFs in this study indicate that magnification of selected heavy metals in the Arctic food web is not significant. Biomagnification of Cd occurs mainly in kidneys; calculated BMFs are higher for hepatic THg than renal THg for all predator-prey scenarios with the exception of polar bears (Ursus maritimus). In bears, the accumulation of renal THg is approximately 6 times higher than in liver. Magnification of hepatic Ag is minimal for all selected predator-prey scenarios. Though polar bears occupy a higher trophic level than belugas (Delphinapterus leucas), based on {delta} {sup 15}N, the metal concentrations are either not statistically different between the two species or lower for bears. Similarly, concentrations of renal and hepatic Cd are significantly lower or not statistically different in polar bears compared to ringed (Phoca hispida) and bearded seals (Erignathus barbatus), their primary prey. THg, on the other hand, increased significantly from seal to polar bear tissues. Mean {delta} {sup 15}N was lowest in muscle of Arctic fox (Alopex lagopus) and foxes also show the lowest levels of Hg, Cd and Ag in liver and kidney compared to the other species analyzed. These values are in good agreement with a diet dominated by terrestrial prey. Metal deposition in animal tissues is strongly dependent on biological factors such as diet, age, sex, body condition and health, and caution should be taken when interpreting magnification of

  18. Food Web Responses to Artificial Mixing in a Small Boreal Lake

    Directory of Open Access Journals (Sweden)

    Lauri Arvola

    2017-07-01

    Full Text Available In order to simulate food web responses of small boreal lakes to changes in thermal stratification due to global warming, a 4 year whole-lake manipulation experiment was performed. Within that time, period lake mixing was intensified artificially during two successive summers. Complementary data from a nearby lake of similar size and basic water chemistry were used as a reference. Phytoplankton biomass and chlorophyll a did not respond to the greater mixing depth but an increase was observed in the proportional abundance of diatoms, and the proportional abundance of cryptophytes also increased immediately after the onset of mixing. Obligate anoxic green sulphur bacteria vanished at the onset of mixing but gradually recovered after re-establishment of hypolimnetic anoxic conditions. No major effect on crustacean zooplankton was found, but their diversity increased in the metalimnion. During the mixing, the density of rotifers declined but protozoan density increased in the hypolimnion. Littoral benthic invertebrate density increased during the mixing due to Ephemeroptera, Asellus aquaticus and Chironomidae, whereas the density of Chaoborus larvae declined during mixing and lower densities were still recorded one year after the treatment. No structural changes in fish community were found although gillnet catches increased after the onset of the study. The early growth of perch (Perca fluviatilis increased compared to the years before the mixing and in comparison to the reference lake, suggesting improved food availability in the experimental lake. Although several food web responses to the greater mixing depth were found, their persistence and ecological significance were strongly dependent on the extent of the disturbance. To better understand the impacts of wind stress on small lakes, long term whole-lake experiments are needed.

  19. Exposure and food web transfer of pharmaceuticals in ospreys (Pandion haliaetus): Predictive model and empirical data

    Science.gov (United States)

    Lazarus, Rebecca S.; Rattner, Barnett A.; Du, Bowen; McGowan, Peter C.; Blazer, Vicki; Ottinger, Mary Ann

    2015-01-01

    The osprey (Pandion haliaetus) is a well-known sentinel of environmental contamination, yet no studies have traced pharmaceuticals through the water–fish–osprey food web. A screening-level exposure assessment was used to evaluate the bioaccumulation potential of 113 pharmaceuticals and metabolites, and an artificial sweetener in this food web. Hypothetical concentrations in water reflecting “wastewater effluent dominated” or “dilution dominated” scenarios were combined with pH-specific bioconcentration factors (BCFs) to predict uptake in fish. Residues in fish and osprey food intake rate were used to calculate the daily intake (DI) of compounds by an adult female osprey. Fourteen pharmaceuticals and a drug metabolite with a BCF greater than 100 and a DI greater than 20 µg/kg were identified as being most likely to exceed the adult human therapeutic dose (HTD). These 15 compounds were also evaluated in a 40 day cumulative dose exposure scenario using first-order kinetics to account for uptake and elimination. Assuming comparable absorption to humans, the half-lives (t1/2) for an adult osprey to reach the HTD within 40 days were calculated. For 3 of these pharmaceuticals, the estimated t1/2 in ospreys was less than that for humans, and thus an osprey might theoretically reach or exceed the HTD in 3 to 7 days. To complement the exposure model, 24 compounds were quantified in water, fish plasma, and osprey nestling plasma from 7 potentially impaired locations in Chesapeake Bay. Of the 18 analytes detected in water, 8 were found in fish plasma, but only 1 in osprey plasma (the antihypertensive diltiazem). Compared to diltiazem detection rate and concentrations in water (10/12 detects, time, and there is no evidence to suggest adverse effects. This screening-level exposure model can help identify those compounds that warrant further investigation in high-trophic level species.

  20. Arsenic in stream waters is bioaccumulated but neither biomagnified through food webs nor biodispersed to land.

    Science.gov (United States)

    Hepp, Luiz U; Pratas, João A M S; Graça, Manuel A S

    2017-05-01

    Human activities such as mining have contributed substantially to the increase of metals in aquatic environments worldwide. These metals are bioaccumulated by aquatic organisms and can be biomagnified along trophic webs. The dispersal of contaminants from water to land has been little investigated, even though most aquatic invertebrates in streams have aerial stages. We used field and laboratory approaches to investigate the effects of arsenic pollution on stream invertebrate assemblages, and its bioaccumulation, biomagnification and trophic transfer from aquatic to terrestrial environments by emergent insects. We conducted the study in an arsenic-impacted stream (40μgL -1 As at the most polluted site) and a reference stream (0.3μgL -1 As). Invertebrate abundance and richness were lowest at the most impacted site. Arsenic in biofilm and in invertebrates increased with the arsenic content in the water. The highest arsenic accumulators were bryophytes (1760μgg -1 ), followed by the biofilm (449μgg -1 ) and shredder invertebrates (313μgg -1 ); predators had the lowest arsenic concentration. Insects emerging from water and spiders along streambanks sampled from the reference and the impacted stream did not differ in their body arsenic concentrations. In the laboratory, the shredder Sericostoma vittatum had reduced feeding rates when exposed to water from the impacted stream in comparison with the reference stream (15.6 vs. 19.0mg leaves mg body mass -1 day -1 ; parsenic from food, not through contact with water. We concluded that although arsenic is bioaccumulated, mainly by food ingestion, it is not biomagnified through food webs and is not transported from the aquatic to terrestrial environment when insects leave the stream water. Copyright © 2017. Published by Elsevier Inc.

  1. Food web de-synchronization in England's largest lake: an assessment based on multiple phenological metrics.

    Science.gov (United States)

    Thackeray, Stephen J; Henrys, Peter A; Feuchtmayr, Heidrun; Jones, Ian D; Maberly, Stephen C; Winfield, Ian J

    2013-12-01

    Phenological changes have been observed globally for marine, freshwater and terrestrial species, and are an important element of the global biological 'fingerprint' of climate change. Differences in rates of change could desynchronize seasonal species interactions within a food web, threatening ecosystem functioning. Quantification of this risk is hampered by the rarity of long-term data for multiple interacting species from the same ecosystem and by the diversity of possible phenological metrics, which vary in their ecological relevance to food web interactions. We compare phenological change for phytoplankton (chlorophyll a), zooplankton (Daphnia) and fish (perch, Perca fluviatilis) in two basins of Windermere over 40 years and determine whether change has differed among trophic levels, while explicitly accounting for among-metric differences in rates of change. Though rates of change differed markedly among the nine metrics used, seasonal events shifted earlier for all metrics and trophic levels: zooplankton advanced most, and fish least, rapidly. Evidence of altered synchrony was found in both lake basins, when combining information from all phenological metrics. However, comparisons based on single metrics did not consistently detect this signal. A multimetric approach showed that across trophic levels, earlier phenological events have been associated with increasing water temperature. However, for phytoplankton and zooplankton, phenological change was also associated with changes in resource availability. Lower silicate, and higher phosphorus, concentrations were associated with earlier phytoplankton growth, and earlier phytoplankton growth was associated with earlier zooplankton growth. The developing trophic mismatch detected between the dominant fish species in Windermere and important zooplankton food resources may ultimately affect fish survival and portend significant impacts upon ecosystem functioning. We advocate that future studies on phenological

  2. Seasonal variation in accumulation of persistent organic pollutants in an Arctic marine benthic food web

    International Nuclear Information System (INIS)

    Evenset, A.; Hallanger, I.G.; Tessmann, M.; Warner, N.; Ruus, A.; Borgå, K.; Gabrielsen, G.W.; Christensen, G.; Renaud, P.E.

    2016-01-01

    The aim of the present study was to investigate seasonal variation in persistent organic pollutant (POP) concentrations, as well as food-web biomagnification, in an Arctic, benthic marine community. Macrozoobenthos, demersal fish and common eiders were collected both inside and outside of Kongsfjorden, Svalbard, during May, July and October 2007. The samples were analysed for a selection of legacy chlorinated POPs. Overall, low levels of POPs were measured in all samples. Although POP levels and accumulation patterns showed some seasonal variation, the magnitude and direction of change was not consistent among species. Overall, seasonality in bioaccumulation in benthic biota was less pronounced than in the pelagic system in Kongsfjorden. In addition, the results indicate that δ 15 N is not a good predictor for POP-levels in benthic food chains. Other factors, such as feeding strategy (omnivory, necrophagy versus herbivory), degree of contact with the sediment, and a high dependence on particulate organic matter (POM), with low POP-levels and high δ 15 N-values (due to bacterial isotope enrichment), seem to govern the uptake of the different POPs and result in loads deviating from what would be expected consulting the trophic position alone. - Highlights: • Seasonal variation in POP biomagnification was investigated in a benthic food web. • Levels of POPs are generally low in benthic species from Kongsfjorden, Svalbard. • POP-concentrations varied with season, but direction of change varied among taxa. • No POP-biomagnification, except for cis-nonachlor, was detected in this study. • δ 15 N-values does not seem to be a good proxy for trophic level in macrozoobenthos.

  3. Food microbe tracker: a web-based tool for storage and comparison of food-associated microbes.

    Science.gov (United States)

    Vangay, Pajau; Fugett, Eric B; Sun, Qi; Wiedmann, Martin

    2013-02-01

    Large amounts of molecular subtyping information are generated by the private sector, academia, and government agencies. However, use of subtype data is limited by a lack of effective data storage and sharing mechanisms that allow comparison of subtype data from multiple sources. Currently available subtype databases are generally limited in scope to a few data types (e.g., MLST. net) or are not publicly available (e.g., PulseNet). We describe the development and initial implementation of Food Microbe Tracker, a public Web-based database that allows archiving and exchange of a variety of molecular subtype data that can be cross-referenced with isolate source data, genetic data, and phenotypic characteristics. Data can be queried with a variety of search criteria, including DNA sequences and banding pattern data (e.g., ribotype or pulsed-field gel electrophoresis type). Food Microbe Tracker allows the deposition of data on any bacterial genus and species, bacteriophages, and other viruses. The bacterial genera and species that currently have the most entries in this database are Listeria monocytogenes, Salmonella, Streptococcus spp., Pseudomonas spp., Bacillus spp., and Paenibacillus spp., with over 40,000 isolates. The combination of pathogen and spoilage microorganism data in the database will facilitate source tracking and outbreak detection, improve discovery of emerging subtypes, and increase our understanding of transmission and ecology of these microbes. Continued addition of subtyping, genetic or phenotypic data for a variety of microbial species will broaden the database and facilitate large-scale studies on the diversity of food-associated microbes.

  4. Carbon dynamics, food web structure and reclamation strategies in Athabasca oil sands wetlands (CFRAW) : overview and progress

    International Nuclear Information System (INIS)

    Ciborowski, J.; Dixon, D.G.; Foote, L.; Liber, K.; Smits, J.E.

    2009-01-01

    Seven oil sand mining partners and 5 university labs have joined forces to study the effects of mine tailings and process waters on development, health and function of wetland communities formed in post-mining landscapes. The collaborative effort, know as the carbon dynamics, food web structure and reclamation strategies in Athabasca oil sands wetlands (CRFAW), aims to identify the materials and strategies most effective and economical in producing a functioning reclamation landscape. This presentation reported on part of the study that tested predictions about how quickly wetlands amended with reclamation materials approach the conditions of reference wetland systems. It provided a conceptual model of carbon pathways and budgets to assess how the allocation of carbon among compartments changes as newly formed wetlands mature in the boreal system. It was assumed that stockpiling constructed wetlands with peat or topsoil would accelerate succession and community development. Although the bitumen and the naphthenic acids found in constructed wetlands are initially toxic, they may serve as an alternate source of carbon once they degrade. This study also assessed the sources, biological uptake, pathways, and movement through the food web of materials used by the biota in constructed wetlands. Additional studies are examining how the productivity of new wetlands is maintained. Net ecosystem productivity is being monitored along with rates of organic carbon accumulation from microbial, algal, and macrophyte production, and influx of outside materials. The rates of leaf litter breakdown and microbial respiration are being compared to determine how constituents speed or slow food web processes of young and older wetlands. Carbon and nitrogen isotope values in food web compartments indicate which sources are incorporated into the food web as wetlands age. The values are used to determine how this influences community development, food web structure and complexity, and the

  5. Fire affects root decomposition, soil food web structure, and carbon flow in tallgrass prairie

    Science.gov (United States)

    Shaw, E. Ashley; Denef, Karolien; Milano de Tomasel, Cecilia; Cotrufo, M. Francesca; Wall, Diana H.

    2016-05-01

    Root litter decomposition is a major component of carbon (C) cycling in grasslands, where it provides energy and nutrients for soil microbes and fauna. This is especially important in grasslands where fire is common and removes aboveground litter accumulation. In this study, we investigated whether fire affects root decomposition and C flow through the belowground food web. In a greenhouse experiment, we applied 13C-enriched big bluestem (Andropogon gerardii) root litter to intact tallgrass prairie soil cores collected from annually burned (AB) and infrequently burned (IB) treatments at the Konza Prairie Long Term Ecological Research (LTER) site. Incorporation of 13C into microbial phospholipid fatty acids and nematode trophic groups was measured on six occasions during a 180-day decomposition study to determine how C was translocated through the soil food web. Results showed significantly different soil communities between treatments and higher microbial abundance for IB. Root decomposition occurred rapidly and was significantly greater for AB. Microbes and their nematode consumers immediately assimilated root litter C in both treatments. Root litter C was preferentially incorporated in a few groups of microbes and nematodes, but depended on burn treatment: fungi, Gram-negative bacteria, Gram-positive bacteria, and fungivore nematodes for AB and only omnivore nematodes for IB. The overall microbial pool of root-litter-derived C significantly increased over time but was not significantly different between burn treatments. The nematode pool of root-litter-derived C also significantly increased over time, and was significantly higher for the AB treatment at 35 and 90 days after litter addition. In conclusion, the C flow from root litter to microbes to nematodes is not only measurable but also significant, indicating that higher nematode trophic levels are critical components of C flow during root decomposition, which, in turn, is significantly affected by fire. Not

  6. The bioenergetic consequences of invasive-induced food web disruption to Lake Ontario alewives

    Science.gov (United States)

    Stewart, Thomas J.; O'Gorman, Robert; Sprules, W. Gary; Lantry, B.F.

    2010-01-01

    Alewives Alosa pseudoharengus are the dominant prey fish in Lake Ontario, and their response to ecological change can alter the structure and function of the Lake Ontario food web. Using stochastic population-based bioenergetic models of Lake Ontario alewives for 1987–1991 and 2001–2005, we evaluated changes to alewife production, consumption, and associated bioenergetic ratios after invasive-induced food web disruption. After the disruption, mean biomass of alewives declined from 28.0 to 14.6 g/m2, production declined from 40.8 to 13.6 g·m−2·year−1, and consumption declined from 342.1 to 137.2 g·m−2·year−1, but bootstrapping of error sources suggested that the changes were not statistically significant. Population-based bioenergetic ratios of production to biomass (P/B ratio), total consumption to biomass (Q/B ratio), and production efficiency did not change. Pathways of energy flow measured as prey-group-specific Q/B ratios changed significantly between the two time periods for invasive predatory cladocerans (from 0.6 to 1.3), Mysis diluviana (from 0.4 to 2.5), and other prey (from 0.8 to 0.1), but the observed decline in the zooplankton Q/B ratio (from 10.6 to 5.5) was not significant. Gross production efficiency did not change; values ranged from 8% to 15%. Age-group mean gross conversion efficiency (GCE) declined with age; GCE ranged from 7.5% to 11.0% for yearlings, was approximately 5% for age-2 alewives, and was less than 2% for age-3 and older alewives. The GCE increased significantly between the time periods for yearling alewives. Our analyses support the hypothesis that after 2003, alewives could not sustain their growth while feeding on zooplankton closer to shore. Modeling of observed spatial variation in diet and alternative occupied temperatures demonstrates the potential for reducing consumption by alewives. Our results suggest that Lake Ontario alewives can exploit spatial heterogeneity in resource patches and thermal habitat to

  7. Rural food insecurity and poverty mappings and their linkage with water resources in the Limpopo River Basin

    Science.gov (United States)

    Magombeyi, M. S.; Taigbenu, A. E.; Barron, J.

    2016-04-01

    The mappings of poverty and food insecurity were carried out for the rural districts of the four riparian countries (Botswana, Mozambique, South Africa and Zimbabwe) of the Limpopo river basin using the results of national surveys that were conducted between 2003 and 2013. The analysis shows lower range of food insecure persons (0-40%) than poverty stricken persons (0-95%) that is attributable to enhanced government and non-government food safety networks in the basin countries, the dynamic and transitory nature of food insecurity which depends on the timings of the surveys in relation to harvests, markets and food prices, and the limited dimension of food insecurity in relation to poverty which tends to be a more structural and pervasive socio-economic condition. The usefulness of this study in influencing policies and strategies targeted at alleviating poverty and improving rural livelihoods lies with using food insecurity mappings to address short-term socio-economic conditions and poverty mappings to address more structural and long-term deprivations. Using the poverty line of 1.25/day per person (2008-2013) in the basin, Zimbabwe had the highest percentage of 68.7% of its rural population classified as poor, followed by Mozambique with 68.2%, South Africa with 56.1% and Botswana with 20%. While average poverty reduction of 6.4% was observed between 2003 and 2009 in Botswana, its population growth of 20.1% indicated no real poverty reduction. Similar observations are made about Mozambique and Zimbabwe where population growth outstripped poverty reductions. In contrast, both average poverty levels and population increased by 4.3% and 11%, respectively, in South Africa from 2007 to 2010. While areas of high food insecurity and poverty consistently coincide with low water availability, it does not indicate a simple cause-effect relationship between water, poverty and food insecurity. With limited water resources, rural folks in the basin require stronger

  8. Zinc isotope ratios of bones and teeth as new dietary indicators: results from a modern food web (Koobi Fora, Kenya)

    OpenAIRE

    Jaouen, Klervia; Beasley, Melanie; Schoeninger, Margaret; Hublin, Jean-Jacques; Richards, Michael P.

    2016-01-01

    In order to explore the possibilities of using zinc (Zn) stable isotope ratios as dietary indicators, we report here on the measurements of the ratio of stable isotopes of zinc (66Zn/64Zn, expressed here as ?66Zn) in bioapatite (bone and dental enamel) of animals from a modern food web in the Koobi Fora region of the Turkana Basin in Kenya. We demonstrate that ?66Zn values in both bone and enamel allow a clear distinction between carnivores and herbivores from this food web. Differences were ...

  9. Cubic exact solutions for the estimation of pairwise haplotype frequencies: implications for linkage disequilibrium analyses and a web tool 'CubeX'

    Directory of Open Access Journals (Sweden)

    Day Ian NM

    2007-11-01

    Full Text Available Abstract Background The frequency of a haplotype comprising one allele at each of two loci can be expressed as a cubic equation (the 'Hill equation', the solution of which gives that frequency. Most haplotype and linkage disequilibrium analysis programs use iteration-based algorithms which substitute an estimate of haplotype frequency into the equation, producing a new estimate which is repeatedly fed back into the equation until the values converge to a maximum likelihood estimate (expectation-maximisation. Results We present a program, "CubeX", which calculates the biologically possible exact solution(s and provides estimated haplotype frequencies, D', r2 and χ2 values for each. CubeX provides a "complete" analysis of haplotype frequencies and linkage disequilibrium for a pair of biallelic markers under situations where sampling variation and genotyping errors distort sample Hardy-Weinberg equilibrium, potentially causing more than one biologically possible solution. We also present an analysis of simulations and real data using the algebraically exact solution, which indicates that under perfect sample Hardy-Weinberg equilibrium there is only one biologically possible solution, but that under other conditions there may be more. Conclusion Our analyses demonstrate that lower allele frequencies, lower sample numbers, population stratification and a possible |D'| value of 1 are particularly susceptible to distortion of sample Hardy-Weinberg equilibrium, which has significant implications for calculation of linkage disequilibrium in small sample sizes (eg HapMap and rarer alleles (eg paucimorphisms, q

  10. The floodplain food web mosaic: a study of its importance to salmon and steelhead with implications for their recovery

    Science.gov (United States)

    Bellmore, J. Ryan; Baxter, Colden V.; Martens, Kyle; Connolly, Patrick J.

    2013-01-01

    Although numerous studies have attempted to place species of interest within the context of food webs, such efforts have generally occurred at small scales or disregard potentially important spatial heterogeneity. If food web approaches are to be employed to manage species, studies are needed that evaluate the multiple habitats and associated webs of interactions in which these species participate. Here, we quantify the food webs that sustain rearing salmon and steelhead within a floodplain landscape of the Methow River, Washington, USA, a location where restoration has been proposed to restore side channels in an attempt to recover anadromous fishes. We combined year-long measures of production, food demand, and diet composition for the fish assemblage with estimates of invertebrate prey productivity to quantify food webs within the main channel and five different, intact, side channels; ranging from channels that remained connected to the main channel at low flow to those reduced to floodplain ponds. Although we found that habitats within the floodplain had similar invertebrate prey production, these habitats hosted different local food webs. In the main channel, 95% of total prey consumption flowed to fishes that are not the target of proposed restoration. These fishes consumed 64% and 47% of the prey resources that were found to be important to fueling chinook and steelhead production in the main channel, respectively. Conversely, in side channels, a greater proportion of prey was consumed by anadromous salmonids. As a result, carrying capacity estimates based on food were 251% higher, on average, for anadromous salmonids in side channels than the main channel. However, salmon and steelhead production was generally well below estimated capacity in both the main and side channels, suggesting these habitats are under-seeded with respect to food, and that much larger populations could be supported. Overall, this study demonstrates that floodplain heterogeneity is

  11. Measuring terrestrial subsidies to aquatic food webs using stable isotopes of hydrogen.

    Science.gov (United States)

    Doucett, Richard R; Marks, Jane C; Blinn, Dean W; Caron, Melanie; Hungate, Bruce A

    2007-06-01

    Understanding river food webs requires distinguishing energy derived from primary production in the river itself (autochthonous) from that produced externally (allochthonous), yet there are no universally applicable and reliable techniques for doing so. We compared the natural abundance stable isotope ratios of hydrogen (deltaD) of allochthonous and autochthonous energy sources in four different aquatic ecosystems. We found that autochthonous organic matter is uniformly far more depleted in deuterium (lower deltaD values) than allochthonous: an average difference of approximately 100% per hundred. We also found that organisms at higher trophic levels, including both aquatic invertebrates and fish, have deltaD values intermediate between aquatic algae and terrestrial plants. The consistent differences between leaves and algae in deltaD among these four watersheds, along with the intermediate values in higher trophic levels, indicate that natural abundance hydrogen isotope signatures are a powerful tool for partitioning energy flow in aquatic ecosystems.

  12. Organic matter flow in the food web at a temperate heath under multifactorial climate change

    DEFF Research Database (Denmark)

    Andresen, Louise C.; Konestabo, Heidi S.; Maraldo, Kristine

    2011-01-01

    of the microbial biomass, a likely major food source, and the climatic factors. Furthermore, the natural abundance δ13C of enchytraeids was significantly altered in CO2‐fumigated plots, showing that even small changes in δ13C‐CO2 can be used to detect transfer of carbon from primary producers to detritivores. We....../omnivore → predator food‐web for one year after amendment with 15N13C2‐glycine. Isotope ratio mass spectrometry (IRMS) measurement of 15N/14N and 13C/12C in soil extracts and functional ecosystem compartments revealed that the recovery of 15N sometimes decreased through the chain of consumption, with the largest...

  13. Population regulation and role of mesozooplankton in shaping marine pelagic food webs

    DEFF Research Database (Denmark)

    Kiørboe, Thomas

    1998-01-01

    Copepods constitute the majority of the mesozooplankton in the oceans. By eating and being eaten copepods have implications for the flow of matter and energy in the pelagic environment. I first consider population regulation mechanisms in copepods by briefly reviewing estimates of growth and mort...... activity for plankton food webs, particularly their role in retarding vertical fluxes and, thus, the loss of material from the euphotic zone......Copepods constitute the majority of the mesozooplankton in the oceans. By eating and being eaten copepods have implications for the flow of matter and energy in the pelagic environment. I first consider population regulation mechanisms in copepods by briefly reviewing estimates of growth...... to variations in fecundity. This is consistent with the observed tremendous variation in copepod fecundity rates, relatively low and constant mortality rates and with morphological and behavioral characteristics of pelagic copepods (e.g., predator perception and escape capability, vertical migration), which can...

  14. Species response to environmental change: impacts of food web interactions and evolution.

    Science.gov (United States)

    Harmon, Jason P; Moran, Nancy A; Ives, Anthony R

    2009-03-06

    How environmental change affects species abundances depends on both the food web within which species interact and their potential to evolve. Using field experiments, we investigated both ecological and evolutionary responses of pea aphids (Acyrthosiphon pisum), a common agricultural pest, to increased frequency of episodic heat shocks. One predator species ameliorated the decrease in aphid population growth with increasing heat shocks, whereas a second predator did not, with this contrast caused by behavioral differences between predators. We also compared aphid strains with stably inherited differences in heat tolerance caused by bacterial endosymbionts and showed the potential for rapid evolution for heat-shock tolerance. Our results illustrate how ecological and evolutionary complexities should be incorporated into predictions of the consequences of environmental change for species' populations.

  15. Rapid evolution buffers ecosystem impacts of viruses in a microbial food web.

    Science.gov (United States)

    Lennon, Jay T; Martiny, Jennifer B H

    2008-11-01

    Predation and parasitism often regulate population dynamics, community interactions, and ecosystem functioning. The strength of these top-down pressures is variable, however, and may be influenced by both ecological and evolutionary processes. We conducted a chemostat experiment to assess the direct and indirect effects of viruses on a marine microbial food web comprised of an autotrophic host (Synechococcus) and non-target heterotrophic bacteria. Viruses dramatically altered the host population dynamics, which in turn influenced phosphorus resource availability and the stoichiometric allocation of nutrients into microbial biomass. These virus effects diminished with time, but could not be attributed to changes in the abundance or composition of heterotrophic bacteria. Instead, attenuation of the virus effects coincided with the detection of resistant host phenotypes, suggesting that rapid evolution buffered the effect of viruses on nutrient cycling. Our results demonstrate that evolutionary processes are important for community dynamics and ecosystem processes on ecologically relevant time scales.

  16. Assimilation of old carbon by stream food webs in arctic Alaska

    Science.gov (United States)

    O'Donnell, J. A.; Carey, M.; Xu, X.; Koch, J. C.; Walker, J. C.; Zimmerman, C. E.

    2017-12-01

    Permafrost thaw in arctic and sub-arctic region is mobilizing old carbon (C) from perennially frozen soils, driving the release of old C to the atmosphere and to aquatic ecosystems. Much research has focused on the transport and lability of old dissolved organic C (DOC) as a possible feedback to the climate system following thaw. However, little is known about the role of old C as a source to aquatic food webs in watersheds underlain by thawing permafrost. To quantify the contributions of old C to Arctic stream food-webs, we measured the radiocarbon (Δ14C) and stable isotope (δ13C, δ15N) contents of periphyton, macroinvertebrates, and resident fish species (Arctic Grayling (Thymallus arcticus) and Dolly Varden (Salvelinus malma)). We also characterized the isotopic composition of possible C sources, including DOC, dissolved inorganic carbon (DIC), and soil organic matter. Samples were collected across 10 streams in Arctic Alaska, draining watersheds underlain by varying parent material and ground-ice content, from ice-poor bedrock to ice-rich loess (i.e. Yedoma). Fraction modern (FM) values for Arctic Grayling and Dolly Varden ranged from 0.6720 to 1.0101 (3195 years BP to modern) across all streams, and closely tracked spatial variation in Δ14C content of periphyton. Parent material and ground-ice content appear to govern the age and form of dissolved C sources to stream biota. For instance, in watersheds underlain by ice-poor bedrock, old DIC (delivery of aged C to surface waters. Given the large stores Pleistocene-aged organic C in Yedoma deposits, we hypothesize that older C may become a more important contribution to stream biota under warmer conditions that promote thaw.

  17. Food web structure and vulnerability of a deep-sea ecosystem in the NW Mediterranean Sea

    Science.gov (United States)

    Tecchio, Samuele; Coll, Marta; Christensen, Villy; Company, Joan B.; Ramírez-Llodra, Eva; Sardà, Francisco

    2013-05-01

    There is increasing fishing pressure on the continental margins of the oceans, and this raises concerns about the vulnerability of the ecosystems thriving there. The current knowledge of the biology of deep-water fish species identifies potential reduced resilience to anthropogenic disturbance. However, there are extreme difficulties in sampling the deep sea, resulting in poorly resolved and indirectly obtained food-web relationships. Here, we modelled the flows and biomasses of a Mediterranean deep-sea ecosystem, the Catalan Sea continental slope at depths of 1000-1400 m. This is the first model of a deep-water ecosystem in the Mediterranean Sea. The objectives were to (a) quantitatively describe the food web structure of the ecosystem, (b) examine the role of key species in the ecosystem, and (c) explore the vulnerability of this deep-sea ecosystem to potential future fishing exploitation. We used the Ecopath with Ecosim (EwE) modelling approach and software to model the ecosystem. The trophic model included 18 consumers, a marine snow group, and a sediment detritus group. Trophic network analysis identified low levels of consumer biomass cycling and low system omnivory index when compared with expected values of marine ecosystems, and higher cycling and omnivory when compared with available EwE models of shallower areas of the Mediterranean Sea. The majority of flows in the ecosystem were concentrated at the trophic level of first-order consumers (TL 2). Benthic invertebrates and demersal sharks were identified to have key ecological roles in the ecosystem. We used the dynamic temporal model Ecosim to simulate expansion of the red-shrimp benthic trawl fishery that currently operates at shallower depths, down to 800 m depth. The simulations showed reductions in fish biomass and that the state of the deep continental slope ecosystem in the western Mediterranean seems to be the result of a long-term succession process, which has reached ecological stability, and is

  18. Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web.

    Science.gov (United States)

    Niiranen, Susa; Yletyinen, Johanna; Tomczak, Maciej T; Blenckner, Thorsten; Hjerne, Olle; Mackenzie, Brian R; Müller-Karulis, Bärbel; Neumann, Thomas; Meier, H E Markus

    2013-11-01

    Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multimodel approach to project how the interaction of climate, nutrient loads, and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, whereas low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, nonlinearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context. © 2013 John Wiley & Sons Ltd.

  19. Fate and Trophic Transfer of Rare Earth Elements in Temperate Lake Food Webs.

    Science.gov (United States)

    Amyot, Marc; Clayden, Meredith G; MacMillan, Gwyneth A; Perron, Tania; Arscott-Gauvin, Alexandre

    2017-06-06

    Many mining projects targeting rare earth elements (REE) are in development in North America, but the background concentrations and trophic transfer of these elements in natural environments have not been well characterized. We sampled abiotic and food web components in 14 Canadian temperate lakes unaffected by mines to assess the natural ecosystem fate of REE. Individual REE and total REE concentrations (sum of individual element concentrations, ΣREE) were strongly related with each other throughout different components of lake food webs. Dissolved organic carbon and dissolved oxygen in the water column, as well as ΣREE in sediments, were identified as potential drivers of aqueous ΣREE. Log 10 of median bioaccumulation factors ranged from 1.3, 3.7, 4.0, and 4.4 L/kg (wet weight) for fish muscle, zooplankton, predatory invertebrates, and nonpredatory invertebrates, respectively. [ΣREE] in fish, benthic macroinvertebrates, and zooplankton declined as a function of their trophic position, as determined by functional feeding groups and isotopic signatures of nitrogen (δ 15 N), indicating that REE were subject to trophic dilution. Low concentrations of REE in freshwater fish muscle compared to their potential invertebrate prey suggest that fish fillet consumption is unlikely to be a significant source of REE to humans in areas unperturbed by mining activities. However, other fish predators (e.g., piscivorous birds and mammals) may accumulate REE from whole fish as they are more concentrated than muscle. Overall, this study provides key information on the baseline concentrations and trophic patterns for REE in freshwater temperate lakes in Quebec, Canada.

  20. A comparison of PCB bioaccumulation factors between an arctic and a temperate marine food web

    International Nuclear Information System (INIS)

    Sobek, Anna; McLachlan, Michael S.; Borga, Katrine; Asplund, Lillemor; Lundstedt-Enkel, Katrin; Polder, Anuschka; Gustafsson, Orjan

    2010-01-01

    To test how environmental conditions in the Arctic and the resulting ecological adaptations affect accumulation of persistent organic pollutants (POPs) in the marine food web, bioaccumulation of four polychlorinated biphenyls (PCBs) in an arctic (Barents Sea 77 o N-82 o N) and a temperate marine (Baltic Sea 54 o N-62 o N) food web were compared. Three different trophic levels were studied (zooplankton, fish, and seal), representing the span from first-level consumer to top predator. Previously published high-quality data on PCB water concentrations in the two areas were used for calculation of bioaccumulation factors (BAF). BAF was calculated as the ratio of the PCB concentration in the organism ([PCB] org ; pg/kg lipid) to the dissolved water concentration (C w ; pg/L). The BAF Arctic :BAF Temperate ratios were above 1 for all four PCB congeners in zooplankton (6.4-13.8) and planktivorous fish (2.9-5.0)), whereas the ratios were below 1 in seal. The mean ratio between arctic and temperate BAFs for all trophic levels and congeners (BAF Arcti :BAF Temperate ) was 4.8. When the data were corrected for the seawater temperature difference between the two ecosystems, the ratio was 2.0. We conclude that bioaccumulation differences caused by ecological or physiological adaptations of organisms between the two ecosystems were well within a water concentration variability of 50%. Further, our data support the hypothesis that lower seawater temperature lead to a thermodynamically favoured passive partitioning to organic matrices and thus elevated ambient BAFs in the Arctic compared to the Baltic Sea. This would imply that bioaccumulation in the Arctic may be described in the same way as bioaccumulation in temperate regions, e.g. by the use of mechanistic models parameterised for the Arctic.

  1. Fukushima 137Cs at the base of planktonic food webs off Japan

    Science.gov (United States)

    Baumann, Z.; Fisher, N. S.; Gobler, C. J.; Buesseler, K. O.; George, J. A.; Breier, C. F.; Nishikawa, J.

    2015-12-01

    The potential bioaccumulation of 137Cs in marine food webs off Japan became a concern following the release of radioactive contaminants from the damaged Fukushima nuclear power plant into the coastal ocean. Previous studies suggest that 137Cs activities increase with trophic level in pelagic food webs, however, the bioaccumulation of 137Cs from seawater to primary producers, to zooplankton has not been evaluated in the field. Since phytoplankton are frequently the largest component of suspended particulate matter (SPM) we used SPM concentrations and particle-associated 137Cs to understand bioaccumulation of 137Cs in through trophic pathways in the field. We determined particle-associated 137Cs for samples collected at 20 m depth from six stations off Japan three months after the initial release from the Fukushima nuclear power plant. At 20 m SPM ranged from 0.65 to 1.60 mg L-1 and rapidly declined with depth. The ratios of particulate organic carbon to chlorophyll a suggested that phytoplankton comprised much of the SPM in these samples. 137Cs activities on particles accounted for on average 0.04% of the total 137Cs in seawater samples, and measured concentration factors of 137Cs on small suspended particles were comparatively low (∼102). However, when 137Cs in crustacean zooplankton was derived based only on modeling dietary 137Cs uptake, we found predicted and measured 137Cs concentrations in good agreement. We therefore postulate the possibility that the dietary route of 137Cs bioaccumulation (i.e., phytoplankton ingestion) could be largely responsible for the measured levels in the copepod-dominated (%) zooplankton assemblages in Japanese coastal waters. Finally, our data did not support the notion that zooplankton grazing on phytoplankton results in a biomagnification of 137Cs.

  2. Reciprocal diversification in a complex plant-herbivore-parasitoid food web

    Directory of Open Access Journals (Sweden)

    Bokma Folmer

    2007-11-01

    Full Text Available Abstract Background Plants, plant-feeding insects, and insect parasitoids form some of the most complex and species-rich food webs. According to the classic escape-and-radiate (EAR hypothesis, these hyperdiverse communities result from coevolutionary arms races consisting of successive cycles of enemy escape, radiation, and colonization by new enemy lineages. It has also been suggested that "enemy-free space" provided by novel host plants could promote host shifts by herbivores, and that parasitoids could similarly drive diversification of gall form in insects that induce galls on plants. Because these central coevolutionary hypotheses have never been tested in a phylogenetic framework, we combined phylogenetic information on willow-galling sawflies with data on their host plants, gall types, and enemy communities. Results We found that evolutionary shifts in host plant use and habitat have led to dramatic prunings of parasitoid communities, and that changes in gall phenotype can provide "enemy-free morphospace" for millions of years even in the absence of host plant shifts. Some parasites have nevertheless managed to colonize recently-evolved gall types, and this has apparently led to adaptive speciation in several enemy groups. However, having fewer enemies does not in itself increase speciation probabilities in individual sawfly lineages, partly because the high diversity of the enemy community facilitates compensatory attack by remaining parasite taxa. Conclusion Taken together, our results indicate that niche-dependent parasitism is a major force promoting ecological divergence in herbivorous insects, and that prey divergence can cause speciation in parasite lineages. However, the results also show that the EAR hypothesis is too simplistic for species-rich food webs: instead, diversification seems to be spurred by a continuous stepwise process, in which ecological and phenotypic shifts in prey lineages are followed by a lagged evolutionary

  3. A comparison of PCB bioaccumulation factors between an arctic and a temperate marine food web

    Energy Technology Data Exchange (ETDEWEB)

    Sobek, Anna; McLachlan, Michael S. [Department of Applied Environmental Science (ITM), Stockholm University, Svante Arrhenius Vaeg 8c, 10691 Stockholm (Sweden); Borga, Katrine [Norwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo (Norway); Asplund, Lillemor [Department of Applied Environmental Science (ITM), Stockholm University, Svante Arrhenius Vaeg 8c, 10691 Stockholm (Sweden); Lundstedt-Enkel, Katrin [Environmental Toxicology, Evolutionary Biology Centre, Uppsala University, 75236 Sweden (Sweden); Polder, Anuschka [Norwegian School of Veterinary Science, POB 8146, 0033 Oslo (Norway); Gustafsson, Orjan, E-mail: orjan.gustafsson@itm.su.se [Department of Applied Environmental Science (ITM), Stockholm University, Svante Arrhenius Vaeg 8c, 10691 Stockholm (Sweden)

    2010-06-01

    To test how environmental conditions in the Arctic and the resulting ecological adaptations affect accumulation of persistent organic pollutants (POPs) in the marine food web, bioaccumulation of four polychlorinated biphenyls (PCBs) in an arctic (Barents Sea 77 {sup o}N-82 {sup o}N) and a temperate marine (Baltic Sea 54 {sup o}N-62 {sup o}N) food web were compared. Three different trophic levels were studied (zooplankton, fish, and seal), representing the span from first-level consumer to top predator. Previously published high-quality data on PCB water concentrations in the two areas were used for calculation of bioaccumulation factors (BAF). BAF was calculated as the ratio of the PCB concentration in the organism ([PCB]{sub org}; pg/kg lipid) to the dissolved water concentration (C{sub w}; pg/L). The BAF{sub Arctic}:BAF{sub Temperate} ratios were above 1 for all four PCB congeners in zooplankton (6.4-13.8) and planktivorous fish (2.9-5.0)), whereas the ratios were below 1 in seal. The mean ratio between arctic and temperate BAFs for all trophic levels and congeners (BAF{sub Arcti}:BAF{sub Temperate}) was 4.8. When the data were corrected for the seawater temperature difference between the two ecosystems, the ratio was 2.0. We conclude that bioaccumulation differences caused by ecological or physiological adaptations of organisms between the two ecosystems were well within a water concentration variability of 50%. Further, our data support the hypothesis that lower seawater temperature lead to a thermodynamically favoured passive partitioning to organic matrices and thus elevated ambient BAFs in the Arctic compared to the Baltic Sea. This would imply that bioaccumulation in the Arctic may be described in the same way as bioaccumulation in temperate regions, e.g. by the use of mechanistic models parameterised for the Arctic.

  4. A comparison of PCB bioaccumulation factors between an arctic and a temperate marine food web.

    Science.gov (United States)

    Sobek, Anna; McLachlan, Michael S; Borgå, Katrine; Asplund, Lillemor; Lundstedt-Enkel, Katrin; Polder, Anuschka; Gustafsson, Orjan

    2010-06-01

    To test how environmental conditions in the Arctic and the resulting ecological adaptations affect accumulation of persistent organic pollutants (POPs) in the marine food web, bioaccumulation of four polychlorinated biphenyls (PCBs) in an arctic (Barents Sea 77 degrees N-82 degrees N) and a temperate marine (Baltic Sea 54 degrees N-62 degrees N) food web were compared. Three different trophic levels were studied (zooplankton, fish, and seal), representing the span from first-level consumer to top predator. Previously published high-quality data on PCB water concentrations in the two areas were used for calculation of bioaccumulation factors (BAF). BAF was calculated as the ratio of the PCB concentration in the organism ([PCB](org); pg/kg lipid) to the dissolved water concentration (C(w); pg/L). The BAF(Arctic):BAF(Temperate) ratios were above 1 for all four PCB congeners in zooplankton (6.4-13.8) and planktivorous fish (2.9-5.0)), whereas the ratios were below 1 in seal. The mean ratio between arctic and temperate BAFs for all trophic levels and congeners (BAF(Arcti):BAF(Temperate)) was 4.8. When the data were corrected for the seawater temperature difference between the two ecosystems, the ratio was 2.0. We conclude that bioaccumulation differences caused by ecological or physiological adaptations of organisms between the two ecosystems were well within a water concentration variability of 50%. Further, our data support the hypothesis that lower seawater temperature lead to a thermodynamically favoured passive partitioning to organic matrices and thus elevated ambient BAFs in the Arctic compared to the Baltic Sea. This would imply that bioaccumulation in the Arctic may be described in the same way as bioaccumulation in temperate regions, e.g. by the use of mechanistic models parameterised for the Arctic. Copyright (c) 2010. Published by Elsevier B.V.

  5. Tracing carbon flow through coral reef food webs using a compound-specific stable isotope approach.

    Science.gov (United States)

    McMahon, Kelton W; Thorrold, Simon R; Houghton, Leah A; Berumen, Michael L

    2016-03-01

    Coral reefs support spectacularly productive and diverse communities in tropical and sub-tropical waters throughout the world's oceans. Debate continues, however, on the degree to which reef biomass is supported by new water column production, benthic primary production, and recycled detrital carbon (C). We coupled compound-specific stable C isotope ratio (δ(13)C) analyses with Bayesian mixing models to quantify C flow from primary producers to coral reef fishes across multiple feeding guilds and trophic positions in the Red Sea. Analyses of reef fishes with putative diets composed primarily of zooplankton (Amblyglyphidodon indicus), benthic macroalgae (Stegastes nigricans), reef-associated detritus (Ctenochaetus striatus), and coral tissue (Chaetodon trifascialis) confirmed that δ(13)C values of essential amino acids from all baseline C sources were both isotopically diagnostic and accurately recorded in consumer tissues. While all four source end-members contributed to the production of coral reef fishes in our study, a single-source end-member often dominated dietary C assimilation of a given species, even for highly mobile, generalist top predators. Microbially reworked detritus was an important secondary C source for most species. Seascape configuration played an important role in structuring resource utilization patterns. For instance, Lutjanus ehrenbergii showed a significant shift from a benthic macroalgal food web on shelf reefs (71 ± 13 % of dietary C) to a phytoplankton-based food web (72 ± 11 %) on oceanic reefs. Our work provides insights into the roles that diverse C sources play in the structure and function of coral reef ecosystems and illustrates a powerful fingerprinting method to develop and test nutritional frameworks for understanding resource utilization.

  6. Methanogenic food web in the gut contents of methane-emitting earthworm Eudrilus eugeniae from Brazil.

    Science.gov (United States)

    Schulz, Kristin; Hunger, Sindy; Brown, George G; Tsai, Siu M; Cerri, Carlos C; Conrad, Ralf; Drake, Harold L

    2015-08-01

    The anoxic saccharide-rich conditions of the earthworm gut provide an ideal transient habitat for ingested microbes capable of anaerobiosis. It was recently discovered that the earthworm Eudrilus eugeniae from Brazil can emit methane (CH4) and that ingested methanogens might be associated with this emission. The objective of this study was to resolve trophic interactions of bacteria and methanogens in the methanogenic food web in the gut contents of E. eugeniae. RNA-based stable isotope probing of bacterial 16S rRNA as well as mcrA and mrtA (the alpha subunit of methyl-CoM reductase and its isoenzyme, respectively) of methanogens was performed with [(13)C]-glucose as a model saccharide in the gut contents. Concomitant fermentations were augmented by the rapid consumption of glucose, yielding numerous products, including molecular hydrogen (H2), carbon dioxide (CO2), formate, acetate, ethanol, lactate, succinate and propionate. Aeromonadaceae-affiliated facultative aerobes, and obligate anaerobes affiliated to Lachnospiraceae, Veillonellaceae and Ruminococcaceae were associated with the diverse fermentations. Methanogenesis was ongoing during incubations, and (13)C-labeling of CH4 verified that supplemental [(13)C]-glucose derived carbon was dissimilated to CH4. Hydrogenotrophic methanogens affiliated with Methanobacteriaceae and Methanoregulaceae were linked to methanogenesis, and acetogens related to Peptostreptoccocaceae were likewise found to be participants in the methanogenic food web. H2 rather than acetate stimulated methanogenesis in the methanogenic gut content enrichments, and acetogens appeared to dissimilate supplemental H2 to acetate in methanogenic enrichments. These findings provide insight on the processes and associated taxa potentially linked to methanogenesis and the turnover of organic carbon in the alimentary canal of methane-emitting E. eugeniae.

  7. Tracing carbon flow through coral reef food webs using a compound-specific stable isotope approach

    KAUST Repository

    McMahon, Kelton

    2015-11-21

    Coral reefs support spectacularly productive and diverse communities in tropical and sub-tropical waters throughout the world’s oceans. Debate continues, however, on the degree to which reef biomass is supported by new water column production, benthic primary production, and recycled detrital carbon (C). We coupled compound-specific stable C isotope ratio (δ13C) analyses with Bayesian mixing models to quantify C flow from primary producers to coral reef fishes across multiple feeding guilds and trophic positions in the Red Sea. Analyses of reef fishes with putative diets composed primarily of zooplankton (Amblyglyphidodon indicus), benthic macroalgae (Stegastes nigricans), reef-associated detritus (Ctenochaetus striatus), and coral tissue (Chaetodon trifascialis) confirmed that δ13C values of essential amino acids from all baseline C sources were both isotopically diagnostic and accurately recorded in consumer tissues. While all four source end-members contributed to the production of coral reef fishes in our study, a single-source end-member often dominated dietary C assimilation of a given species, even for highly mobile, generalist top predators. Microbially reworked detritus was an important secondary C source for most species. Seascape configuration played an important role in structuring resource utilization patterns. For instance, Lutjanus ehrenbergii showed a significant shift from a benthic macroalgal food web on shelf reefs (71 ± 13 % of dietary C) to a phytoplankton-based food web (72 ± 11 %) on oceanic reefs. Our work provides insights into the roles that diverse C sources play in the structure and function of coral reef ecosystems and illustrates a powerful fingerprinting method to develop and test nutritional frameworks for understanding resource utilization.

  8. Ethnic/racial disparities in adolescents' home food environments and linkages to dietary intake and weight status.

    Science.gov (United States)

    Larson, Nicole; Eisenberg, Marla E; Berge, Jerica M; Arcan, Chrisa; Neumark-Sztainer, Dianne

    2015-01-01

    Research is needed to confirm that public health recommendations for home/family food environments are equally relevant for diverse populations. This study examined ethnic/racial differences in the home/family environments of adolescents and associations with dietary intake and weight status. The sample included 2374 ethnically/racially diverse adolescents and their parents enrolled in coordinated studies, EAT 2010 (Eating and Activity in Teens) and Project F-EAT (Families and Eating and Activity in Teens), in the Minneapolis/St. Paul metropolitan area. Adolescents and parents completed surveys and adolescents completed anthropometric measurements in 2009-2010. Nearly all home/family environment variables (n=7 of 8 examined) were found to vary significantly across the ethnic/racial groups. Several of the home/family food environment variables were significantly associated with one or more adolescent outcome in expected directions. For example, parental modeling of healthy food choices was inversely associated with BMI z-score (p=0.03) and positively associated with fruit/vegetable consumption (peating was associated with lower intake of sugar-sweetened beverages only among youth representing the White, African American, Asian, and mixed/other ethnic/racial groups and was unrelated to intake among East African, Hispanic, and Native American youth. Food and nutrition professionals along with other providers of health programs and services for adolescents should encourage ethnically/racially diverse parents to follow existing recommendations to promote healthy eating such as modeling nutrient-dense food choices, but also recognize the need for cultural sensitivity in providing such guidance. Copyright © 2014 Elsevier Ltd. All rights reserved.

  9. Ethnic/racial disparities in adolescents' home food environments and linkages to dietary intake and weight status

    OpenAIRE

    Larson, Nicole; Eisenberg, Marla E.; Berge, Jerica M.; Arcan, Chrisa; Neumark-Sztainer, Dianne

    2014-01-01

    Research is needed to confirm that public health recommendations for home/family food environments are equally relevant for diverse populations. This study examined ethnic/racial differences in the home/family environments of adolescents and associations with dietary intake and weight status. The sample included 2,382 ethnically/racially diverse adolescents and their parents enrolled in coordinated studies, EAT 2010 (Eating and Activity in Teens) and Project F-EAT (Families and Eating and Act...

  10. Bioaccumulation and trophic transfer of polybrominated diphenyl ethers (PBDEs) in a marine food web from Liaodong Bay, North China

    International Nuclear Information System (INIS)

    Ma, Xindong; Zhang, Haijun; Yao, Ziwei; Zhao, Xiaofeng; Wang, Longxing; Wang, Zhen; Chen, Jiping; Chen, Jingwen

    2013-01-01

    Highlights: • BDE-47 was the dominating congener in organisms of the Liaodong Bay. • The length of food chain played an important role on the TMFs. • PBDEs were steadily metabolized in the trophic transfer process along the food chain. -- Abstract: The concentrations of 21 polybrominated diphenyl ethers (PBDEs) congeners were analyzed in organisms within a marine food web collected from the Liaodong Bay, North China. The total concentrations of PBDEs in all samples ranged from 0.87 to 91.4 ng g −1 lipid weight (lw). BDE-47 was the predominant congener and had a concentration ranging from 0.30 to 36.1 ng g −1 lw. The trophic magnification factors (TMF) of the PBDEs were calculated using the trophic levels obtained from the stable nitrogen isotope ratios. The TMF value of ∑PBDEs was 3.50 for the entire food web and 2.21 for the food web excluding seabirds. Four concentration ratios, BDE-99/BDE-100, BDE-99/BDE-47, BDE-153/BDE-154 and BDE-183/BDE-154, decreased linearly with the increase of the trophic levels in the invertebrates and the fishes (p < 0.01). The results suggested that the PBDEs were steadily metabolized in the trophic transfer process along the food chain

  11. Ecosystem differences in the trophic enrichment of 13C in aquatic food webs

    International Nuclear Information System (INIS)

    France, R.L.; Peters, R.H.

    1997-01-01

    Data from 35 published studies were collated to examine patterns in the trophic enrichment of 13 C of consumers. Because both δ 13 C and δ 14 N vary systematically across ecosystems, it was necessary to standardize for such differences before combining data from numerous sources. Relationships of these measures of ecosystem-standardized δ 13 C to ecosystem-standardized trophic position (Δδ 15 N) for freshwater, estuarine, coastal, and open-ocean and for all aquatic ecosystems yielded regression equations of low predictive capability (average of 20% explained variance in δ 13 C). However, differences were observed in the slopes between δ 13 C and standardized trophic position when data were examined study-specifically: the average trophic fractionation of 13 C was found to increase from +0.2micron for freshwater to +0.5micron for estuarine to +0.8micron for coastal, and to +1.1micron for open-ocean food webs. This ecosystem-specific gradient in 13 C enrichment for consumers supports previous findings of a similar continuum existing for zooplankton - particulate organic matter differences in δ 13 C. Possible mechanisms to explain these ecosystem-specific patterns in 13 C enrichment may be related to the relative importance of detritus, heterotrophic respiration, partial reliance on alternative food sources, and lipid influences in the different ecosystems. (author)

  12. Trophic structure in a seabird host-parasite food web: insights from stable isotope analyses.

    Directory of Open Access Journals (Sweden)

    Elena Gómez-Díaz

    2010-05-01

    Full Text Available Ecological studies on food webs rarely include parasites, partly due to the complexity and dimensionality of host-parasite interaction networks. Multiple co-occurring parasites can show different feeding strategies and thus lead to complex and cryptic trophic relationships, which are often difficult to disentangle by traditional methods. We analyzed stable isotope ratios of C ((13C/(12C, delta(13C and N ((15N/(14N, delta(15N of host and ectoparasite tissues to investigate trophic structure in 4 co-occurring ectoparasites: three lice and one flea species, on two closely related and spatially segregated seabird hosts (Calonectris shearwaters. delta(13C isotopic signatures confirmed feathers as the main food resource for the three lice species and blood for the flea species. All ectoparasite species showed a significant enrichment in delta(15N relatively to the host tissue consumed (discrimination factors ranged from 2 to 5 per thousand depending on the species. Isotopic differences were consistent across multiple host-ectoparasite locations, despite of some geographic variability in baseline isotopic levels. Our findings illustrate the influence of both ectoparasite and host trophic ecology in the isotopic structuring of the Calonectris ectoparasite community. This study highlights the potential of stable isotope analyses in disentangling the nature and complexity of trophic relationships in symbiotic systems.

  13. Dynamic Mental Representations of Habitual Behaviours: Food Choice on a Web-Based Environment

    Directory of Open Access Journals (Sweden)

    Rui Gaspar

    2016-08-01

    Full Text Available AimRather than being rigid, habitual behaviours may be determined by dynamic mental representations that can adapt to context changes. This adaptive potential may result from particular conditions dependent on the interaction between two sources of mental constructs activation: perceived context applicability and cognitive accessibility.MethodTwo web-shopping simulations offering the choice between habitually chosen and non-habitually chosen food products were presented to participants. This considered two choice contexts differing in the habitual behaviour perceived applicability (low vs. high and a measure of habitual behaviour chronicity.ResultsStudy 1 demonstrated a perceived applicability effect, with more habitual (non-organic than non-habitual (organic food products chosen in a high perceived applicability (familiar than in a low perceived applicability (new context. The adaptive potential of habitual behaviour was evident in the habitual products choice consistency across three successive choices, despite the decrease in perceived applicability. Study 2 evidenced the adaptive potential in strong habitual behaviour participants – high chronic accessibility – who chose a habitual product (milk more than a non-habitual product (orange juice, even when perceived applicability was reduced (new context.ConclusionResults portray consumers as adaptive decision makers that can flexibly cope with changes in their (inner and outer choice contexts.

  14. A spatial theory for emergent multiple predator-prey interactions in food webs.

    Science.gov (United States)

    Northfield, Tobin D; Barton, Brandon T; Schmitz, Oswald J

    2017-09-01

    Predator-prey interaction is inherently spatial because animals move through landscapes to search for and consume food resources and to avoid being consumed by other species. The spatial nature of species interactions necessitates integrating spatial processes into food web theory and evaluating how predators combine to impact their prey. Here, we present a spatial modeling approach that examines emergent multiple predator effects on prey within landscapes. The modeling is inspired by the habitat domain concept derived from empirical synthesis of spatial movement and interactions studies. Because these principles are motivated by synthesis of short-term experiments, it remains uncertain whether spatial contingency principles hold in dynamical systems. We address this uncertainty by formulating dynamical systems models, guided by core habitat domain principles, to examine long-term multiple predator-prey spatial dynamics. To describe habitat domains, we use classical niche concepts describing resource utilization distributions, and assume species interactions emerge from the degree of overlap between species. The analytical results generally align with those from empirical synthesis and present a theoretical framework capable of demonstrating multiple predator effects that does not depend on the small spatial or temporal scales typical of mesocosm experiments, and help bridge between empirical experiments and long-term dynamics in natural systems.

  15. Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web

    Science.gov (United States)

    Dang, V.D.; Walters, D.M.; Lee, C.M.

    2010-01-01

    The enantiomeric composition of chiral PCB congeners was determined in Twelvemile Creek (Clemson, SC) to examine potential mechanisms of biotransformation in a stream food web. We measured enantiomeric fractions (EFs) of six PCB atropisomers (PCBs 84, 91, 95, 136, 149, and 174) in surface sediment, fine benthic organic matter (FBOM), coarse particulate organic matter (CPOM), periphyton, Asian clam, mayflies, yellowfin shiner, and semipermeable membrane devices (SPMDs) using gas chromatography (GC-ECD). Nonracemic EFs of PCBs 91, 95, 136, and 149 were measured in almost all samples. Enantiomeric compositions of PCBs 84 and 174 were infrequently detected with racemic EFs measured in samples except for a nonracemic EF of PCB 84 in clams. Nonracemic EFs of PCBs 91, 136, and 149 in SPMDs may be due to desorption of nonracemic residues from FBOM. EFs for some atropisomers were significantly different among FBOM, CPOM, and periphyton, suggesting that their microbial communities have different biotransformation processes. Nonracemic EFs in clams and fish suggest both in vivo biotransformation and uptake of nonracemic residues from their food sources. Longitudinal variability in EFs was generally low among congeners observed in matrices. ?? 2010 American Chemical Society.

  16. Dangerous relations in the Arctic marine food web: Interactions between toxin producing Pseudo-nitzschia diatoms and Calanus copepodites

    DEFF Research Database (Denmark)

    Hardardottir, Sara; Pancic, Marina; Tammilehto, Anna

    2015-01-01

    Diatoms of the genus Pseudo-nitzschia produce domoic acid (DA), a toxin that is vectored in the marine food web, thus causing serious problems for marine organisms and humans. In spite of this, knowledge of interactions between grazing zooplankton and diatoms is restricted. In this study, we...

  17. The relative importance of herbivory and carnivory on the distribution of energy in a stochastic tri-trophic food web.

    Science.gov (United States)

    Ballantyne, Ford

    2004-02-07

    A three-state, discrete-time Markov chain is used to model the dynamics of energy flow in a tri-trophic food web. The distribution of energy in the three trophic levels is related to the rates of flow between the trophic levels and calculated for the entire range of possible flow values. These distributions are then analysed for stability and used to test the idea that plants are resource-limited and herbivores are predation-limited. Low rates of death and decomposition, when coupled with low rates of herbivory and carnivory, tend to destabilize this food web. Food webs with higher rates of death and decomposition are relatively more stable regardless of rates of herbivory and carnivory. Plants are more prone to resource-limitation and herbivores are, in general, limited by their predators, which supports Hairston et al. (Am. Nat. 94 (1960) 421). The rate of decomposition often mediates the roles of top-down and bottom-up control of energy flow in the food web.

  18. Bacterial traits, organism mass, and numerical abundance in the detrital soil food web of Dutch agricultural grasslands

    NARCIS (Netherlands)

    Mulder, C.; Cohen, J.E.; Setälä, H.; Bloem, J.; Breure, A.M.

    2005-01-01

    This paper compares responses to environmental stress of the ecophysiological traits of organisms in the detrital soil food webs of grasslands in the Netherlands, using the relationship between average body mass M and numerical abundance N. The microbial biomass and biodiversity of belowground fauna

  19. A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

    DEFF Research Database (Denmark)

    Weitz, Joshua S.; Stock, Charles A.; Wilhelm, Steven W.

    2015-01-01

    that viruses can have significant stimulatory effects across whole-ecosystem scales. We suggest that existing efforts to predict carbon and nutrient cycling without considering virus effects are likely to miss essential features of marine food webs that regulate global biogeochemical cycles.The ISME Journal...

  20. Medium-sized exotic prey create novel food webs: the case of predators and scavengers consuming lagomorphs.

    Science.gov (United States)

    Barbar, Facundo; Hiraldo, Fernando; Lambertucci, Sergio A

    2016-01-01

    Food web interactions are key to community structure. The introduction of species can be seen as an uncontrolled experiment of the addition of species. Introduced species lead to multiple changes, frequently threatening the native biodiversity. However, little is known about their direct effect on the upper level of the food web. In this study we review empirical data on the predator-prey relationship between the introduced lagomorphs and their consumers, and use meta-analytical tools to quantify the strength of their interactions. We expect that exotic lagomorphs will destabilize food webs, affect ecological processes and compromise the conservation of the invaded regions. We found 156 studies on the diet of 43 species of predators that consume lagomorphs as exotic preys in South America and Oceania. We found an average exotic lagomorphs-predator link of 20% which indicates a strong interaction, given that the average for the strongest links with native prey (when lagomorphs are not included in the predator diet) is about 24%. Additionally, this last link decreases to 17% when lagomorphs are present. When lagomorphs arrive in a new environment they may become the most important resource for predators, producing an unstable equilibrium in the novel food web. Any disruption of this interaction could have catastrophic consequences for the native diversity by directly impacting predators or indirectly impacting native preys by apparent competition. Eradication or any change in their abundances should be carefully considered in conservation actions since those will have great impacts on predator populations and ultimately in the whole communities.

  1. Effects of fish and nutrient additions on food-web stability in a charophyte-dominated lake

    NARCIS (Netherlands)

    van de Bund, W.; Van Donk, E.

    2004-01-01

    1. The response of major food-web constituents to combinations of nutrient addition and zooplanktivorous fish abundance was tested during two subsequent years in the shallow charophyte-dominated lake Naardermeer in the Netherlands, using in situ enclosures. 2. Treatment effects differed sharply

  2. Selective alteration of soil food web components by invasive giant goldenrod Solidago gigantea in two distinct habitat types

    NARCIS (Netherlands)

    Quist, C.W.; Vervoort, M.T.W.; Van Megen, H.; Gort, G.; Bakker, J.; Van der Putten, W.H.; Helder, J.

    2014-01-01

    Apart from relatively well-studied aboveground effects, invasive plant species will also impact the soil food web. So far, most research has been focusing on primary decomposers, while studies on effects at higher trophic levels are relatively scarce. Giant goldenrod Solidago gigantea, native to

  3. Selective alteration of soil food web components by invasive Giant goldenrod (Solidago gigantea) in two distinct habitat types

    NARCIS (Netherlands)

    Quist, C.W.; Vervoort, M.T.W.; Megen, van H.H.B.; Gort, G.; Bakker, J.; Putten, van der W.H.; Helder, J.

    2014-01-01

    Apart from relatively well-studied aboveground effects, invasive plant species will also impact the soil food web. So far, most research has been focusing on primary decomposers, while studies on effects at higher trophic levels are relatively scarce. Giant goldenrod Solidago gigantea, native to

  4. Risk assessment of bioaccumulation in the food webs of two marine AMOEBE species: common tern and harbor seal

    NARCIS (Netherlands)

    Jongbloed RH; Mensink BJWG; Vethaak AD; Luttik R; Rijksinstituut voor Kust en Zee; ACT; RIKZ

    1995-01-01

    A model has been developed for calculating Maximum Permissible Concentrations (MPCs) in water for chemicals accumulating in food webs of sea birds and mammals. Calculations are carried out for two marine AMOEBE species: common tern (Sterna hirundo) and harbor seal (Phoca vitulina), and five

  5. Bioaccumulation of per- and polyfluorinated alkyl substances (PFAS) in selected species from the Barents Sea food web

    International Nuclear Information System (INIS)

    Haukas, Marianne; Berger, Urs; Hop, Haakon; Gulliksen, Bjorn; Gabrielsen, Geir W.

    2007-01-01

    The present study reports concentrations and biomagnification potential of per- and polyfluorinated alkyl substances (PFAS) in species from the Barents Sea food web. The examined species included sea ice amphipod (Gammarus wilkitzkii), polar cod (Boreogadus saida), black guillemot (Cepphus grylle) and glaucous gull (Larus hyperboreus). These were analyzed for PFAS, polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs) and polybrominated diphenyl ethers (PBDEs). Perfluorooctane sulfonate (PFOS) was the predominant of the detected PFAS. Trophic levels and food web transfer of PFAS were determined using stable nitrogen isotopes (δ 15 N). No correlation was found between PFOS concentrations and trophic level within species. However, a non-linear relationship was established when the entire food web was analyzed. Biomagnification factors displayed values >1 for perfluorohexane sulfonate (PFHxS), perfluorononanoic acid (PFNA), PFOS and ΣPFAS(7). Multivariate analyses showed that the degree of trophic transfer of PFAS is similar to that of PCB, DDT and PBDE, despite their accumulation through different pathways. - The first comprehensive survey of fluoroorganic contamination in an European Arctic marine food web

  6. Bioaccumulation of per- and polyfluorinated alkyl substances (PFAS) in selected species from the Barents Sea food web

    Energy Technology Data Exchange (ETDEWEB)

    Haukas, Marianne [Norwegian Polar Institute, NO-9296 Tromso (Norway) and Norwegian College of Fishery Science, University of Tromso, NO-9037 Tromso (Norway)]. E-mail: m.haukaas@nilu.no; Berger, Urs [Norwegian Institute for Air Research, NO-9296 Tromso (Norway); Department of Applied Environmental Science (ITM), Stockholm University, SE-10691 Stockholm (Sweden); Hop, Haakon [Norwegian Polar Institute, NO-9296 Tromso (Norway); Gulliksen, Bjorn [Norwegian College of Fishery Science, University of Tromso, NO-9037 Tromso (Norway); Gabrielsen, Geir W. [Norwegian Polar Institute, NO-9296 Tromso (Norway)

    2007-07-15

    The present study reports concentrations and biomagnification potential of per- and polyfluorinated alkyl substances (PFAS) in species from the Barents Sea food web. The examined species included sea ice amphipod (Gammarus wilkitzkii), polar cod (Boreogadus saida), black guillemot (Cepphus grylle) and glaucous gull (Larus hyperboreus). These were analyzed for PFAS, polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs) and polybrominated diphenyl ethers (PBDEs). Perfluorooctane sulfonate (PFOS) was the predominant of the detected PFAS. Trophic levels and food web transfer of PFAS were determined using stable nitrogen isotopes ({delta} {sup 15}N). No correlation was found between PFOS concentrations and trophic level within species. However, a non-linear relationship was established when the entire food web was analyzed. Biomagnification factors displayed values >1 for perfluorohexane sulfonate (PFHxS), perfluorononanoic acid (PFNA), PFOS and {sigma}PFAS(7). Multivariate analyses showed that the degree of trophic transfer of PFAS is similar to that of PCB, DDT and PBDE, despite their accumulation through different pathways. - The first comprehensive survey of fluoroorganic contamination in an European Arctic marine food web.

  7. Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

    NARCIS (Netherlands)

    Bezemer, T.M.; Fountain, T.; Barea, J.M.; Christensen, S.; Dekker, S.C.; Duyts, H.; Hal, van R.; Harvey, J.A.; Hedlund, K.; Maraun, M.; Mikola, J.; Mladenov, A.G.; Robin, C.; Ruiter, de P.C.; Scheu, H.; Setälä, S.; šmilauer, P.; Putten, van der W.H.

    2010-01-01

    Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and

  8. Impact of the blue mussel Mytilus edulis on the microbial food web in the western Wadden Sea, The Netherlands.

    NARCIS (Netherlands)

    Jacobs, P.; Riegman, R.; van der Meer, J.

    2015-01-01

    To study the impact of juvenile blue mussels Mytilus edulis on the microbial food web in the Dutch Wadden Sea, natural sea water was first exposed to mussel filtration. Subsequently, filtered plankton communities were used in a dilution experiment to establish mussel-induced changes in bacterial,

  9. Impact of the blue mussel Mytilus edulis on the microbial food web in the western Wadden Sea, the Netherlands

    NARCIS (Netherlands)

    Jacobs, P.; Riegman, R.; Meer, van der J.

    2015-01-01

    To study the impact of juvenile blue mussels Mytilus edulis on the microbial food web in the Dutch Wadden Sea, natural sea water was first exposed to mussel filtration. Subsequently, filtered plankton communities were used in a dilution experiment to establish mussel-induced changes in bacterial,

  10. A finely tuned symphony of factors modulates the microbial food web of a freshwater reservoir in spring

    Czech Academy of Sciences Publication Activity Database

    Šimek, Karel; Nedoma, Jiří; Znachor, Petr; Kasalický, Vojtěch; Jezbera, Jan; Horňák, Karel; Seďa, Jaromír

    2014-01-01

    Roč. 59, č. 5 (2014), s. 1477-1492 ISSN 0024-3590 R&D Projects: GA ČR(CZ) GA13-00243S Institutional support: RVO:60077344 Keywords : microbial food web * freshwater reservoir * limnology Subject RIV: EE - Microbiology, Virology Impact factor: 3.794, year: 2014

  11. Trophic efficiency of plankton food webs: Observations from the Gulf of Mannar and the Palk Bay, Southeast Coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Anjusha, A.; Jyothibabu, R.; Jagadeesan, L.; Mohan, A.P.; Sudheesh, K.; Krishna, K.; Ullas, N.; Deepak, M.P.

    This paper introduces the structure and trophic efficiency of plankton food webs in the Gulf of Mannar (GoM) and the Palk Bay (PB) - two least studied marine environments located between India and Sri Lanka. The study is based on the results...

  12. The importance of landscape and spatial structure for hymenopteran-based food webs in an agro-ecosystem.

    Science.gov (United States)

    Fabian, Yvonne; Sandau, Nadine; Bruggisser, Odile T; Aebi, Alex; Kehrli, Patrik; Rohr, Rudolf P; Naisbit, Russell E; Bersier, Louis-Félix

    2013-11-01

    1. Understanding the environmental factors that structure biodiversity and food webs among communities is central to assess and mitigate the impact of landscape changes. 2. Wildflower strips are ecological compensation areas established in farmland to increase pollination services and biological control of crop pests and to conserve insect diversity. They are arranged in networks in order to favour high species richness and abundance of the fauna. 3. We describe results from experimental wildflower strips in a fragmented agricultural landscape, comparing the importance of landscape, of spatial arrangement and of vegetation on the diversity and abundance of trap-nesting bees, wasps and their enemies, and the structure of their food webs. 4. The proportion of forest cover close to the wildflower strips and the landscape heterogeneity stood out as the most influential landscape elements, resulting in a more complex trap-nest community with higher abundance and richness of hosts, and with more links between species in the food webs and a higher diversity of interactions. We disentangled the underlying mechanisms for variation in these quantitative food web metrics. 5. We conclude that in order to increase the diversity and abundance of pollinators and biological control agents and to favour a potentially stable community of cavity-nesting hymenoptera in wildflower strips, more investment is needed in the conservation and establishment of forest habitats within agro-ecosystems, as a reservoir of beneficial insect populations. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

  13. Exposure and food web transfer of pharmaceuticals in ospreys (Pandion haliaetus): Predictive model and empirical data.

    Science.gov (United States)

    Lazarus, Rebecca S; Rattner, Barnett A; Brooks, Bryan W; Du, Bowen; McGowan, Peter C; Blazer, Vicki S; Ottinger, Mary Ann

    2015-01-01

    The osprey (Pandion haliaetus) is a well-known sentinel of environmental contamination, yet no studies have traced pharmaceuticals through the water-fish-osprey food web. A screening-level exposure assessment was used to evaluate the bioaccumulation potential of 113 pharmaceuticals and metabolites, and an artificial sweetener in this food web. Hypothetical concentrations in water reflecting "wastewater effluent dominated" or "dilution dominated" scenarios were combined with pH-specific bioconcentration factors (BCFs) to predict uptake in fish. Residues in fish and osprey food intake rate were used to calculate the daily intake (DI) of compounds by an adult female osprey. Fourteen pharmaceuticals and a drug metabolite with a BCF greater than 100 and a DI greater than 20 µg/kg were identified as being most likely to exceed the adult human therapeutic dose (HTD). These 15 compounds were also evaluated in a 40 day cumulative dose exposure scenario using first-order kinetics to account for uptake and elimination. Assuming comparable absorption to humans, the half-lives (t1/2 ) for an adult osprey to reach the HTD within 40 days were calculated. For 3 of these pharmaceuticals, the estimated t1/2 in ospreys was less than that for humans, and thus an osprey might theoretically reach or exceed the HTD in 3 to 7 days. To complement the exposure model, 24 compounds were quantified in water, fish plasma, and osprey nestling plasma from 7 potentially impaired locations in Chesapeake Bay. Of the 18 analytes detected in water, 8 were found in fish plasma, but only 1 in osprey plasma (the antihypertensive diltiazem). Compared to diltiazem detection rate and concentrations in water (10/12 detects, osprey plasma samples (540-8630 ng/L), with 41% of these samples exceeding maximum concentrations found in fish. Diltiazem levels in fish and osprey plasma were below the human therapeutic plasma concentration (30000 ng/L). Effect thresholds for diltiazem are unknown in ospreys at this

  14. Effects of Didymosphenia geminata massive growth on stream communities: Smaller organisms and simplified food web structure.

    Science.gov (United States)

    Ladrera, Rubén; Gomà, Joan; Prat, Narcís

    2018-01-01

    This study aims to contribute to the understanding of the impact of Didymosphenia geminata massive growths upon river ecosystem communities' composition and functioning. This is the first study to jointly consider the taxonomic composition and functional structure of diatom and macroinvertebrate assemblages in order to determine changes in community structure, and the food web alterations associated with this invasive alga. This study was carried out in the Lumbreras River (Ebro Basin, La Rioja, Northern Spain), which has been affected by a considerable massive growth of D. geminata since 2011. The study shows a profound alteration in both the river community composition and in the food web structure at the sites affected by the massive growth, which is primarily due to the alteration of the environmental conditions, thus demonstrating that D. geminata has an important role as an ecosystem engineer in the river. Thick filamentous mats impede the movement of large invertebrates-especially those that move and feed up on it-and favor small, opportunistic, herbivorous organisms, mainly chironomids, that are capable of moving between filaments and are aided by the absence of large trophic competitors and predators -prey release effect-. Only small predators, such as hydra, are capable of surviving in the new environment, as they are favored by the increase in chironomids, a source of food, and by the reduction in both their own predators and other midge predators -mesopredator release-. This change in the top-down control affects the diatom community, since chironomids may feed on large diatoms, increasing the proportion of small diatoms in the substrate. The survival of small and fast-growing pioneer diatoms is also favored by the mesh of filaments, which offers them a new habitat for colonization. Simultaneously, D. geminata causes a significant reduction in the number of diatoms with similar ecological requirements (those attached to the substrate). Overall, D

  15. Water quality management in Lake Kinneret (Israel: hydrological and food web perspectives

    Directory of Open Access Journals (Sweden)

    Moshe GOPHEN

    2003-09-01

    Full Text Available Long term (1969-2001 data record of nutrient and plankton temporal distribution, and hydrological parameters in Lake Kinneret, combined with metabolic parameters of zooplankton, which were experimentally measured, were statistically (ANOVA analyzed. Trophic relations between food web compartments were quantitatively considered to evaluate directional combination of ecological forces. Monthly data of inflow discharges, and lake volume were used to calculate residence time values and the data were incorporated into the ecological analysis. The seasonal fluctuations of the hydrological parameters, nutrients, and plankton inventories represent typical subtropical climate conditions: high level in winter and low in summer months. It was found that nitrogen inventories in the lake declined and the biomass of grazable phytoplankton was enhanced since early 1980’s. Dissolved phosphorus was decreased mostly in summer months when the lake is nutrient limited, as a result of phytoplankton uptake. Zooplankton was declined until 1993 and increased later. Zooplankton preferably feed on chlorophytes and diatoms with supplemental resources of detritus, bacteria and protozoa. The most abundant zooplanktivorous fish, Lavnun (Bleak, Acanthobrama spp. populated the lake very densely during 1993-95 and biomanipulation management of subsidized fishery caused lowering of predation pressure resulted in zooplankton enhancement and suppression of additional primary produced matter. It is concluded that zooplankton in Lake Kinneret is not food limited and fishery management (Lavnun removal might be efficient to enhance zooplankton grazing capacity and algal suppression if phosphorus flux is reduced. Long term changes of nano-phytoplankton are affected by both phosphorus availability and zooplankton grazing and fish predation has a significant impact on zooplankton density. Fishery management aimed at algal suppression might be efficient if phosphorus supply is reduced

  16. Carbon transfer in herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer

    NARCIS (Netherlands)

    De Laender, F.; Oevelen, D. van; Soetaert, K.; Middelburg, J.J.

    2010-01-01

    We compared carbon budgets between a herbivore-dominated and a microbial loopdominated food web and examined the implications of food web structure for fish production. We used the southern Barents Sea as a case study and inverse modelling as an analysis method. In spring, when the system was

  17. Carbon transfer in a herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer

    NARCIS (Netherlands)

    De Laender, F.; Van Oevelen, D.; Soetaert, K.E.R.; Middelburg, J.J.

    2010-01-01

    We compare carbon budgets between a herbivore-dominated and a microbial loop-dominated food web and examine the implications of food web structure for fish production. We use the southern Barents Sea as a case study and inverse modelling as an analysis method. In spring, when the system was

  18. Changes in food web structure and ecosystem functioning of a large, shallow Chinese lake during the 1950s, 1980s and 2000s

    NARCIS (Netherlands)

    Kong, X.; He, Wei; Liu, W.; Yang, B.; Xu, F.; Jørgensen, S.E.; Mooij, W.M.

    2016-01-01

    Food web structure dynamics and ecosystem functioning are strongly linked, and both are indispensable in evaluating ecosystem development in lakes under multiple anthropogenic stressors. However, model-based approaches concerning the changes in food web structure and ecosystem functioning in a

  19. Plankton food-web functioning in anthropogenically impacted coastal waters (SW Mediterranean Sea): An ecological network analysis

    Science.gov (United States)

    Meddeb, Marouan; Grami, Boutheïna; Chaalali, Aurélie; Haraldsson, Matilda; Niquil, Nathalie; Pringault, Olivier; Sakka Hlaili, Asma

    2018-03-01

    The study is the first attempt to (i) model spring food webs in three SW Mediterranean ecosystems which are under different anthropogenic pressures and (ii) to project the consequence of this stress on their function. Linear inverse models were built using the Monte Carlo method coupled with Markov Chains to characterize the food-web status of the Lagoon, the Channel (inshore waters under high eutrophication and chemical contamination) and the Bay of Bizerte (offshore waters under less anthropogenic pressure). Ecological network analysis was used for the description of structural and functional properties of each food web and for inter-ecosystem comparisons. Our results showed that more carbon was produced by phytoplankton in the inshore waters (966-1234 mg C m-2 d-1) compared to the Bay (727 mg C m-2 d-1). The total ecosystem carbon inputs into the three food webs was supported by high primary production, which was mainly due to >10 μm algae. However, the three carbon pathways were characterized by low detritivory and a high herbivory which was mainly assigned to protozooplankton. This latter was efficient in channelling biogenic carbon. In the Lagoon and the Channel, foods webs acted almost as a multivorous structure with a tendency towards herbivorous one, whereas in the Bay the herbivorous pathway was more dominant. Ecological indices revealed that the Lagoon and the Channel food webs/systems had high total system throughput and thus were more active than the Bay. The Bay food web, which had a high relative ascendency value, was more organized and specialized. This inter-ecosystem difference could be due to the varying levels of anthropogenic impact among sites. Indeed, the low value of Finn's cycling index indicated that the three systems are disturbed, but the Lagoon and the Channel, with low average path lengths, appeared to be more stressed, as both sites have undergone higher chemical pollution and nutrient loading. This study shows that ecosystem models

  20. Linkage of food consumption and export to ammonia emissions in Canada and the overriding implications for mitigation

    Science.gov (United States)

    Sheppard, S. C.; Bittman, S.

    2015-02-01

    Ammonia (NH3) emissions from agriculture to the atmosphere, along with emissions of other pollutants from a variety of sources, are of concern to agriculture worldwide. National emissions from agricultural sources in Canada are linked to domestic consumption and export demand for agricultural products. The onus to limit emissions is often directed to the producers, but the marketplace and consumer are also responsible for the environmental impact of their choices. This objective of this study was to quantitatively link agricultural NH3 emissions to per person consumption of food and protein and to agricultural exports from Canada. There are substantial differences in the NH3 emissions per unit consumed protein among the various food types. As a result, shifts in the Canadian diet have had a large impact on relative per person NH3 emissions. From 1981 to 2006, the total per person protein intake in the Canadian diet increased about 5%, but NH3 emission related to that diet decreased 20%. This is largely related to consumption of less beef, which has a high emission per unit of meat or protein, and more poultry and cereals which have much lower emissions. Although these changes in diet were not because of environmental concerns by the consumers, they had substantial effects on national-level emissions. These consumer driven effects may well exceed the possible effects of best management practices intended to address NH3 emissions at the producer level. Note that the Canadian population has increased 50% from 1981 to 2006 and meat and egg exports increased 570%, so that total emissions from food production in Canada have increased. Our results imply there will be further effects on national NH3 emissions because of dietary and export drivers that are generally outside the scope of agro-environmental policy.

  1. Bioaccumulation and trophic transfer of mercury and selenium in african sub-tropical fluvial reservoirs food webs (Burkina Faso.

    Directory of Open Access Journals (Sweden)

    Ousséni Ouédraogo

    Full Text Available The bioaccumulation and biomagnification of mercury (Hg and selenium (Se were investigated in sub-tropical freshwater food webs from Burkina Faso, West Africa, a region where very few ecosystem studies on contaminants have been performed. During the 2010 rainy season, samples of water, sediment, fish, zooplankton, and mollusks were collected from three water reservoirs and analysed for total Hg (THg, methylmercury (MeHg, and total Se (TSe. Ratios of δ13C and δ15N were measured to determine food web structures and patterns of contaminant accumulation and transfer to fish. Food chain lengths (FCLs were calculated using mean δ15N of all primary consumer taxa collected as the site-specific baseline. We report relatively low concentrations of THg and TSe in most fish. We also found in all studied reservoirs short food chain lengths, ranging from 3.3 to 3.7, with most fish relying on a mixture of pelagic and littoral sources for their diet. Mercury was biomagnified in fish food webs with an enrichment factor ranging from 2.9 to 6.5 for THg and from 2.9 to 6.6 for MeHg. However, there was no evidence of selenium biomagnification in these food webs. An inverse relationship was observed between adjusted δ15N and log-transformed Se:Hg ratios, indicating that Se has a lesser protective effect in top predators, which are also the most contaminated animals with respect to MeHg. Trophic position, carbon source, and fish total length were the factors best explaining Hg concentration in fish. In a broader comparison of our study sites with literature data for other African lakes, the THg biomagnification rate was positively correlated with FCL. We conclude that these reservoir systems from tropical Western Africa have low Hg biomagnification associated with short food chains. This finding may partly explain low concentrations of Hg commonly reported in fish from this area.

  2. Role of small-sized copepods in the lipid-driven Arctic marine food web

    Science.gov (United States)

    Daase, M.; Boissonnot, L.; Graeve, M.; Søreide, J.; Niehoff, B.

    2016-02-01

    Despite of the low individual biomass of small-sized copepods such as the calanoid Pseudocalanus minutus and the cyclopoid Oithona similis, they are extremely numerous which make them an important trophic component in Arctic marine ecosystems. Due to the strong seasonality in light and thus primary production and food availability, the accumulation of lipid reserves is a key feature in Arctic marine ecosystems. However, very few studies exist on the lipid biochemistry of small copepods such as P. minutus and O. similis. In order to investigate the importance of these species in terms of transfer of lipids from primary production to higher trophic levels, feeding experiments were conducted, based on animals from Billefjorden, a high-Arctic fjord in Svalbard, Norway. A mixture of 13C labeled flagellates and diatoms was fed to the animals and the transfer and assimilation of lipid carbon, fatty acids and fatty alcohols was analyzed with gas chromatography-IRMS technique (CSIA). The results revealed that both species were incorporating dietary lipids in high quantities. The highest accumulation occurred in P. minutus in which 54.4% of the lipids were exchanged after 21 days, whereas 9.4% were assimilated in O. similis. Hence, at least this amount of carbon was used for metabolism and replaced by feeding. The lipid composition of the copepods did not reflect exactly the algal lipids, and differed between P. minutus and O. similis. Our results suggested intrinsic preferences in the accumulation of particular fatty acids, probably related to species-specific body requirements. This emphasizes the importance of also food quality in Arctic marine systems. Due to the relatively high lipid turnover rates in particularly in P. minutus, also small copepods are important drivers of the lipid-driven Arctic marine food web.

  3. Trophic transfer of persistent organochlorine contaminants (OCs) within an Arctic marine food web from the southern Beaufort-Chukchi Seas

    International Nuclear Information System (INIS)

    Hoekstra, P.F.; O'Hara, T.M.; Fisk, A.T.; Borgaa, K.; Solomon, K.R.; Muir, D.C.G.

    2003-01-01

    The trophic status and biomagnification of persistent OCs within the near-shore Beaufort-Chukchi Seas food web from Barrow, AK is discussed. - Stable isotope values (δ 13 C, δ 15 N) and concentrations of persistent organochlorine contaminants (OCs) were determined to evaluate the near-shore marine trophic status of biota and biomagnification of OCs from the southern Beaufort-Chukchi Seas (1999-2000) near Barrow, AK. The biota examined included zooplankton (Calanus spp.), fish species such as arctic cod (Boreogadus saida), arctic char (Salvelinus alpinus), pink salmon (Oncorhynchus gorbuscha), and fourhorn sculpin (Myoxocephalus quadricornis), along with marine mammals, including bowhead whales (Balaena mysticetus), beluga whales (Delphinapterus leucas), ringed seals (Phoca hispida) and bearded seals (Erignathus barbatus). The isotopically derived trophic position of biota from the Beaufort-Chukchi Seas marine food web, avian fauna excluded, is similar to other coastal food webs in the Arctic. Concentrations of OCs in marine mammals were significantly greater than in fish and corresponded with determined trophic level. In general, OCs with the greatest food web magnification factors (FWMFs) were those either formed due to biotransformation (e.g. p,p'-DDE, oxychlordane) or considered recalcitrant (e.g. β-HCH, 2,4,5-Cl substituted PCBs) in most biota, whereas concentrations of OCs that are considered to be readily eliminated (e.g. γ-HCH) did not correlate with trophic level. Differences in physical-chemical properties of OCs, feeding strategy and possible biotransformation were reflected in the variable biomagnification between fish and marine mammals. The FWMFs in the Beaufort-Chukchi Seas region were consistent with reported values in the Canadian Arctic and temperate food webs, but were statistically different than FWMFs from the Barents and White Seas, indicating that the spatial variability of OC contamination in top-level marine Arctic predators is

  4. Simulating climate change-induced alterations in bioaccumulation of organic contaminants in an Arctic marine food web.

    Science.gov (United States)

    Borgå, Katrine; Saloranta, Tuomo M; Ruus, Anders

    2010-06-01

    Climate change is expected to alter environmental distribution of contaminants and their bioaccumulation due to changes in transport, partitioning, carbon pathways, and bioaccumulation process rates. Magnitude and direction of these changes and resulting overall bioaccumulation in food webs is currently not known. The present study investigates and quantifies the effect of climate change in terms of increased temperature and primary production (i.e., concentrations of particulate organic carbon, C(POC)), on bioaccumulation of organic contaminants in biota at various trophic levels. The present study covers only parts of the contaminant behavior that is influenced by climate change, and it was assumed that there were no changes in food web structure and in total air and water concentrations of organic contaminants. Therefore, other climate change-induced effects on net bioaccumulation, such as altered contaminant transport and food web structure, should be addressed in future studies. To determine the effect of climate change, a bioaccumulation model was used on the pelagic marine food web of the Arctic, where climate change is expected to occur fastest and to the largest magnitude. The effect of climate change on model parameters and processes, and on net bioaccumulation, were quantified for three modeling substances (gamma-hexachlorocyclohexane [HCH], polychlorinated biphenyl [PCB]-52, and PCB-153) for two possible climate scenarios. In conclusion, increased temperature and C(POC) reduced the overall bioaccumulation of organic contaminants in the Arctic marine food web, with the largest change being for PCB-52 and PCB-153. Reduced bioavailability, due to increased C(POC), was the most influential parameter for the less water soluble compounds. Increase in temperature resulted in an overall reduction in net bioaccumulation. Copyright 2010 SETAC.

  5. Trophodynamics of Organic Pollutants in Pelagic and Benthic Food Webs of Lake Dianchi: Importance of Ingested Sediment As Uptake Route.

    Science.gov (United States)

    Fan, Senrong; Wang, Beili; Liu, Hang; Gao, Shixiong; Li, Tong; Wang, Shuran; Liu, Yong; Liu, Xueqin; Wan, Yi

    2017-12-19

    Habitat is of great importance in determining the trophic transfer of pollutants in freshwater ecosystems; however, the major factors influencing chemical trophodynamics in pelagic and benthic food webs remain unclear. This study investigated the levels of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), polycyclic aromatic hydrocarbons (PAHs), and substituted PAHs (s-PAHs) in 2 plankton species, 6 invertebrate species, and 10 fish species collected from Lake Dianchi in southern China. Relatively high concentrations of PAHs and s-PAHs were detected with total concentrations of 11.4-1400 ng/g wet weight (ww) and 5.3-115 ng/g ww, respectively. Stable isotope analysis and stomach content analysis were applied to quantitatively determine the trophic level of individual organisms and discriminate between pelagic and benthic pathways, and the trophodynamics of the detected compounds in the two food webs were assessed. P,p'-DDE was found to exhibit relatively higher trophic magnification rate in the pelagic food web than in the benthic food web. In contrast, PAHs and s-PAHs exhibited greater dilution rates along the trophic levels in the pelagic food web. The lower species differences of pollutants accumulated in benthic organisms compared to pelagic organisms is attributable to extra uptake via ingested sediment in benthos. The average uptake proportions of PAHs and s-PAHs via ingested sediment in benthic biotas were estimated to be 31-77%, and that of p,p'-DDE was 46%. The uptake routes are of importance for assessing the trophic magnification potentials of organic pollutants, especially in eutrophic freshwater ecosystems.

  6. Identification of trophic interactions within an estuarine food web (northern New Zealand) using fatty acid biomarkers and stable isotopes

    Science.gov (United States)

    Alfaro, Andrea C.; Thomas, François; Sergent, Luce; Duxbury, Mark

    2006-10-01

    Fatty acid biomarkers and stable isotope signatures were used to identify the trophic dynamics of a mangrove/seagrass estuarine food web at Matapouri, northern New Zealand. Specific fatty acids were used to identify the preferred food sources (i.e., mangroves, seagrass, phytoplankton, macroalgae, bacteria, and zooplankton) of dominant fauna (i.e., filter feeders, grazing snails, scavenger/predatory snails, shrimp, crabs, and fish), and their presence in water and sediment samples throughout the estuary. The diets of filter feeders were found to be dominated by dinoflagellates, whereas grazers showed a higher diatom contribution. Bacteria associated with organic debris on surface sediments and brown algal ( Hormosira banksii) material in the form of suspended organic matter also accounted for a high proportion of most animal diets. Animals within higher trophic levels had diverse fatty acid profiles, revealing their varied feeding strategies and carbon sources. The stable isotope (δ 13C and δ 15N) analyses of major primary producers and consumers/predators revealed a trend of 15N enrichment with increasing trophic level, while δ 13C values provided a generally good description of carbon flow through the food web. Overall results from both fatty acid profiles and stable isotopes indicate that a variety of carbon sources with a range of trophic pathways typify this food web. Moreover, none of the animals studied was dependent on a single food source. This study is the first to use a comprehensive fatty acid biomarker and stable isotope approach to investigate the food web dynamics within a New Zealand temperate mangrove/seagrass estuary. This quantitative research may contribute to the currently developing management strategies for estuaries in northern New Zealand, especially for those perceived to have expanding mangrove fringes.

  7. Linking functional response and bioenergetics to estimate juvenile salmon growth in a reservoir food web

    Science.gov (United States)

    Haskell, Craig A.; Beauchamp, David A.; Bollens, Stephen M.

    2017-01-01

    Juvenile salmon (Oncorhynchus spp.) use of reservoir food webs is understudied. We examined the feeding behavior of subyearling Chinook salmon (O. tshawytscha) and its relation to growth by estimating the functional response of juvenile salmon to changes in the density of Daphnia, an important component of reservoir food webs. We then estimated salmon growth across a broad range of water temperatures and daily rations of two primary prey, Daphnia and juvenile American shad (Alosa sapidissima) using a bioenergetics model. Laboratory feeding experiments yielded a Type-II functional response curve: C = 29.858 P *(4.271 + P)-1 indicating that salmon consumption (C) of Daphnia was not affected until Daphnia densities (P) were < 30 · L-1. Past field studies documented Daphnia densities in lower Columbia River reservoirs of < 3 · L-1 in July but as high as 40 · L-1 in August. Bioenergetics modeling indicated that subyearlings could not achieve positive growth above 22°C regardless of prey type or consumption rate. When feeding on Daphnia, subyearlings could not achieve positive growth above 20°C (water temperatures they commonly encounter in the lower Columbia River during summer). At 16–18°C, subyearlings had to consume about 27,000 Daphnia · day-1 to achieve positive growth. However, when feeding on juvenile American shad, subyearlings had to consume 20 shad · day-1 at 16–18°C, or at least 25 shad · day-1 at 20°C to achieve positive growth. Using empirical consumption rates and water temperatures from summer 2013, subyearlings exhibited negative growth during July (-0.23 to -0.29 g · d-1) and August (-0.05 to -0.07 g · d-1). By switching prey from Daphnia to juvenile shad which have a higher energy density, subyearlings can partially compensate for the effects of higher water temperatures they experience in the lower Columbia River during summer. However, achieving positive growth as piscivores requires subyearlings to feed at

  8. Mercury Dynamics in Aquatic Food Webs of the Finger Lakes, New York

    Science.gov (United States)

    Cleckner, L.; Razavi, N. R.; Halfman, J. D.; Cushman, S. F.; Foust, J.; Gilman, B.

    2016-12-01

    Mercury (Hg) contamination of fish is a global concern due to the deleterious health effects in humans and wildlife associated with ingesting fish with elevated concentrations. A key to understanding elevated fish Hg concentrations is to examine methyl Hg dynamics at the base of food webs, including algae and zooplankton. Predicting determinants of methyl Hg concentrations in lower trophic level biota remains an active area of research. This study was conducted to assess Hg concentrations in biota of the Finger Lakes (New York, USA), a region where fisheries are an important economic driver, but where no comprehensive assessment of food web Hg dynamics has been completed to date. Sources of Hg in the region include atmospheric pollution from an active coal-fired power plant. The objectives of this study were to: 1) determine if fish Hg concentrations were of concern, 2) assess differences in Hg accumulation among lakes and determine predictors of fish Hg concentrations, and 3) evaluate the predictive power of monthly zooplankton methyl Hg concentrations on fish Hg concentrations. From May - October 2015, suspended particulate matter, zooplankton, and benthos were sampled monthly in five of the Finger Lakes (Honeoye, Canandaigua, Seneca, Cayuga, and Owasco Lakes). Fish were sampled once over the same study period and species were targeted from all trophic levels. Results for top predatory fish including Lake Trout (Salvelinus namaycush), Largemouth Bass (Micropterus salmoides), and Walleye (Sander vitreus) showed significant differences among lakes, and elevated concentrations are above US Environmental Protection Agency's screening value (300 ng/g wet weight). No clear pattern in Hg levels among lakes was evident in lower trophic level fishes such as Yellow Perch (Perca flavescens) and Golden Shiner (Notemigonus crysoleucas), but concentrations were low. Benthivorous Brown Bullhead (Ameiurus nebulosus) exhibited significant differences in Hg among lakes with

  9. Isotopic study of mercury sources and transfer between a freshwater lake and adjacent forest food web

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Sae Yun, E-mail: saeyunk@umich.edu [Department of Earth and Environmental Sciences, University of Michigan, 1100 N. University Ave, Ann Arbor, MI 48109 (United States); Blum, Joel D. [Department of Earth and Environmental Sciences, University of Michigan, 1100 N. University Ave, Ann Arbor, MI 48109 (United States); Department of Ecology and Evolutionary Biology, University of Michigan, 830 N. University Ave, Ann Arbor, MI 48109 (United States); Nadelhoffer, Knute J. [Department of Ecology and Evolutionary Biology, University of Michigan, 830 N. University Ave, Ann Arbor, MI 48109 (United States); Timothy Dvonch, J. [Department of Environmental Health Sciences, University of Michigan, 1415 Washington Heights, Ann Arbor, MI 48109 (United States); Tsui, Martin Tsz-Ki [Department of Biology, University of North Carolina at Greensboro, 321 McIver Street, Greensboro, NC 27402 (United States)

    2015-11-01

    Studies of monomethylmercury (MMHg) sources and biogeochemical pathways have been extensive in aquatic ecosystems, but limited in forest ecosystems. Increasing evidence suggests that there is significant mercury (Hg) exchange between aquatic and forest ecosystems. We use Hg stable isotope ratios (δ{sup 202}Hg and Δ{sup 199}Hg) to investigate the relative importance of MMHg sources and assess Hg transfer pathways between Douglas Lake and adjacent forests located at the University of Michigan Biological Station, USA. We characterize Hg isotopic compositions of basal resources and use linear regression of % MMHg versus δ{sup 202}Hg and Δ{sup 199}Hg to estimate Hg isotope values for inorganic mercury (IHg) and MMHg in the aquatic and adjacent forest food webs. In the aquatic ecosystem, we found that lake sediment represents a mixture of IHg pools deposited via watershed runoff and precipitation. The δ{sup 202}Hg and Δ{sup 199}Hg values estimated for IHg are consistent with other studies that measured forest floor in temperate forests. The Δ{sup 199}Hg value estimated for MMHg in the aquatic food web indicates that MMHg is subjected to ~ 20% photochemical degradation prior to bioaccumulation. In the forest ecosystem, we found a significant negative relationship between total Hg and δ{sup 202}Hg and Δ{sup 199}Hg of soil collected at multiple distances from the lakeshore and lake sediment. This suggests that IHg input from watershed runoff provides an important Hg transfer pathway between the forest and aquatic ecosystems. We measured Δ{sup 199}Hg values for high trophic level insects and compared these insects at multiple distances perpendicular to the lake shoreline. The Δ{sup 199}Hg values correspond to the % canopy cover suggesting that forest MMHg is subjected to varying extents of photochemical degradation and the extent may be controlled by sunlight. Our study demonstrates that the use of Hg isotopes adds important new insight into the relative

  10. Bridging Food Webs, Ecosystem Metabolism, and Biogeochemistry Using Ecological Stoichiometry Theory

    Science.gov (United States)

    Welti, Nina; Striebel, Maren; Ulseth, Amber J.; Cross, Wyatt F.; DeVilbiss, Stephen; Glibert, Patricia M.; Guo, Laodong; Hirst, Andrew G.; Hood, Jim; Kominoski, John S.; MacNeill, Keeley L.; Mehring, Andrew S.; Welter, Jill R.; Hillebrand, Helmut

    2017-01-01

    Although aquatic ecologists and biogeochemists are well aware of the crucial importance of ecosystem functions, i.e., how biota drive biogeochemical processes and vice-versa, linking these fields in conceptual models is still uncommon. Attempts to explain the variability in elemental cycling consequently miss an important biological component and thereby impede a comprehensive understanding of the underlying processes governing energy and matter flow and transformation. The fate of multiple chemical elements in ecosystems is strongly linked by biotic demand and uptake; thus, considering elemental stoichiometry is important for both biogeochemical and ecological research. Nonetheless, assessments of ecological stoichiometry (ES) often focus on the elemental content of biota rather than taking a more holistic view by examining both elemental pools and fluxes (e.g., organismal stoichiometry and ecosystem process rates). ES theory holds the promise to be a unifying concept to link across hierarchical scales of patterns and processes in ecology, but this has not been fully achieved. Therefore, we propose connecting the expertise of aquatic ecologists and biogeochemists with ES theory as a common currency to connect food webs, ecosystem metabolism, and biogeochemistry, as they are inherently concatenated by the transfer of carbon, nitrogen, and phosphorous through biotic and abiotic nutrient transformation and fluxes. Several new studies exist that demonstrate the connections between food web ecology, biogeochemistry, and ecosystem metabolism. In addition to a general introduction into the topic, this paper presents examples of how these fields can be combined with a focus on ES. In this review, a series of concepts have guided the discussion: (1) changing biogeochemistry affects trophic interactions and ecosystem processes by altering the elemental ratios of key species and assemblages; (2) changing trophic dynamics influences the transformation and fluxes of matter

  11. How Stress Treatments Influence the Performance of Biodegradable Poly(Butylene Succinate-Based Copolymers with Thioether Linkages for Food Packaging Applications

    Directory of Open Access Journals (Sweden)

    Valentina Siracusa

    2017-08-01

    Full Text Available Biodegradable poly(butylene succinate (PBS-based random copolymers containing thioether linkages (P(BSxTDGSy of various compositions have been investigated and characterized from the gas barrier, thermal, and mechanical point of view, after food contact simulants or thermal and photoaging processes. Each stress treatment was performed on thin films and the results obtained have been compared to the same untreated film, used as a standard. Barrier properties with different gases (O2 and CO2 were evaluated, showing that the polymer chemical composition strongly influenced the permeability behavior. The relationships between the diffusion coefficients (D and solubility (S with polymer composition were also investigated. The results highlighted a correlation between polymer chemical structure and treatment. Gas transmission rate (GTR mainly depending on the performed treatment, as GTR increased with the increase of TDGS co-unit amount. Thermal and mechanical tests allowed for the recording of variations in the degree of crystallinity and in the tensile properties. An increase in the crystallinity degree was recorded after contact with simulant liquids and aging treatments, together with a molecular weight decrease, a slight enhancement of the elastic modulus and a decrement of the elongation at break, proportional to the TDGS co-unit content.

  12. Phytoplankton chytridiomycosis: fungal parasites of phytoplankton and their imprints on the food web dynamics

    Directory of Open Access Journals (Sweden)

    Télesphore eSIME - NGANDO

    2012-10-01

    Full Text Available Parasitism is one of the earlier and common ecological interactions in the nature, occurring in almost all environments. Microbial parasites typically are characterized by their small size, short generation time, and high rates of reproduction, with simple life cycle occurring generally within a single host. They are diverse and ubiquitous in aquatic ecosystems, comprising viruses, prokaryotes and eukaryotes. Recently, environmental 18S-rDNA surveys of microbial eukaryotes have unveiled major infecting agents in pelagic systems, consisting primarily of the fungal order of Chytridiales (chytrids. Chytrids are considered the earlier branch of the Eumycetes and produce motile, flagellated zoospores, characterized by a small size (2-6 µm and a single, posterior flagellum. The existence of these dispersal propagules includes chytrids within the so-called group of zoosporic fungi, which are particularly adapted to the plankton lifestyle where they infect a wide variety of hosts, including fishes, eggs, zooplankton, algae, and other aquatic fungi but primarily freshwater phytoplankton. Related ecological implications are huge because chytrids can killed their hosts, release substrates for microbial processes, and provide nutrient-rich particles as zoospores and short fragments of filamentous inedible hosts for the grazer food chain. Furthermore, based on the observation that phytoplankton chytridiomycosis preferentially impacts the larger size species, blooms of such species (e.g. filamentous cyanobacteria may not totally represent trophic bottlenecks. Besides, chytrid epidemics represent an important driving factor in phytoplankton seasonal successions. In this review, I summarize the knowledge on the diversity, community structure, quantitative importance, and functional roles of fungal chytrids, primarily those who are parasites of phytoplankton, and infer the ecological implications and potentials for the food web dynamics and properties.

  13. Effect of substrate on periphyton communities and relationships among food web components in shallow hypertrophic lake

    Directory of Open Access Journals (Sweden)

    Tomasz Mieczan

    2012-07-01

    Full Text Available We studied the role of natural (common reed and artificial substrata (bamboo in structuring the abundance and taxonomic composition of periphyton assemblages. Investigations were conducted in a shallow, hypertrophic lake situated in the area of Polesie Lubelskie (Eastern Poland. Periphyton communities (algae, ciliates, small metazoa and chironomids on both types of substratum were sampled monthly, from May to November of 2007. Water samples for chemical analysis were collected together with biological samples. We selected the group of ten environmental variables which are the most important in determining the habitat conditions in highly eutrophic lakes: temperature, Secchi disc visibility, conductivity, dissolved oxygen, periphytic chlorophyll-a, N-NO3, N-NH4, TP, P-PO4 and total organic carbon (TOC. The abundances of periphytic algae, ciliates, metazoa and chironomids were significantly affected by season and substrate. On natural substrata, in all studied months, periphyton communities showed higher abundances. The results of PCA analysis confirmed the distinction between periphyton communities on natural and artificial substrata. The Monte Carlo permutation test showed that the periphyton communities on common reed were the most significantly affected by temperature, N-NO3, Secchi disc visibility and TOC. The communities on artificial substrata were significantly influenced by temperature, P-PO4 and TOC. On natural substrata biomass of periphytic algae was significantly negatively correlated with abundances of all groups of potential grazers (ciliates, metazoa, chironomids. On artificial substrata the relations between components of periphytic food web were stronger; correlation coefficients between algae, protists and chironomids were significant at P<0.01. The results of analysis indicate that periphytic algae can play an important role as food source for higher trophic levels. These interactions are less significant on natural (reed

  14. Trophodynamics of the Hanna Shoal Ecosystem (Chukchi Sea, Alaska): Connecting multiple end-members to a rich food web

    Science.gov (United States)

    McTigue, N. D.; Dunton, K. H.

    2017-10-01

    Predicting how alterations in sea ice-mediated primary production will impact Arctic food webs remains a challenge in forecasting ecological responses to climate change. One top-down approach to this challenge is to elucidate trophic roles of consumers as either specialists (i.e., consumers of predominantly one food resource) or generalists (i.e., consumers of multiple food resources) to categorize the dependence of consumers on each primary producer. At Hanna Shoal in the Chukchi Sea, Alaska, we used stable carbon and nitrogen isotope data to quantify trophic redundancy with standard ellipse areas at both the species and trophic guild levels. We also investigated species-level trophic plasticity by analyzing the varying extents that three end-members were assimilated by the food web using the mixing model simmr (Stable Isotope Mixing Model in R). Our results showed that ice algae, a combined phytoplankton and sediment organic matter composite (PSOM), and a hypothesized microphytobenthos (MPB) component were incorporated by consumers in the benthic food web, but their importance varied by species. Some primary consumers relied heavily on PSOM (e.g, the amphipods Ampelisca sp. and Byblis sp.; the copepod Calanus sp.), while others exhibited generalist feeding and obtained nutrition from multiple sources (e.g., the holothuroidean Ocnus glacialis, the gastropod Tachyrhynchus sp., the sipunculid Golfingia margaritacea, and the bivalves Ennucula tenuis, Nuculana pernula, Macoma sp., and Yoldia hyperborea). Most higher trophic level benthic predators, including the gastropods Buccinum sp., Cryptonatica affinis, and Neptunea sp, the seastar Leptasterias groenlandica, and the amphipod Anonyx sp. also exhibited trophic plasticity by coupling energy pathways from multiple primary producers including PSOM, ice algae, and MPB. Our stable isotope data indicate that consumers in the Hanna Shoal food web exhibit considerable trophic redundancy, while few species were specialists

  15. Invasive plants have different effects on trophic structure of green and brown food webs in terrestrial ecosystems: a meta-analysis.

    Science.gov (United States)

    McCary, Matthew A; Mores, Robin; Farfan, Monica A; Wise, David H

    2016-03-01

    Although invasive plants are a major source of terrestrial ecosystem degradation worldwide, it remains unclear which trophic levels above the base of the food web are most vulnerable to plant invasions. We performed a meta-analysis of 38 independent studies from 32 papers to examine how invasive plants alter major groupings of primary and secondary consumers in three globally distributed ecosystems: wetlands, woodlands and grasslands. Within each ecosystem we examined if green (grazing) food webs are more sensitive to plant invasions compared to brown (detrital) food webs. Invasive plants have strong negative effects on primary consumers (detritivores, bacterivores, fungivores, and/or herbivores) in woodlands and wetlands, which become less abundant in both green and brown food webs in woodlands and green webs in wetlands. Plant invasions increased abundances of secondary consumers (predators and/or parasitoids) only in woodland brown food webs and green webs in wetlands. Effects of invasive plants on grazing and detrital food webs clearly differed between ecosystems. Overall, invasive plants had the most pronounced effects on the trophic structure of wetlands and woodlands, but caused no detectable changes to grassland trophic structure. © 2016 John Wiley & Sons Ltd/CNRS.

  16. Food web analysis reveals effects of pH on mercury bioaccumulation at multiple trophic levels in streams

    International Nuclear Information System (INIS)

    Jardine, Timothy D.; Kidd, Karen A.; O’ Driscoll, Nelson

    2013-01-01

    Highlights: ► We examine biomagnification of Hg through stream food webs using δ15 N. ► Slopes of methyl Hg vs. trophic level were higher than total Hg vs. trophic level. ► Biomagnification from predatory insects to fish was related to pH of the water. ► Biomagnification at lower trophic levels was related to dietary concentrations. ► These trends can explain variation in field-measured Hg in food webs. -- Abstract: Biomagnification processes and the factors that govern them, including those for mercury (Hg), are poorly understood in streams. Total and methyl Hg concentrations and relative trophic position (using δ 15 N) were analyzed in biofilm and invertebrates from 21 streams in New Brunswick, Canada to assess food web biomagnification leading to the common minnow blacknose dace (Rhinichthys atratulus), a species known to have Hg concentrations that are higher in low pH waters. Biomagnification slopes within stream food webs measured using Hg vs. δ 15 N or corresponding trophic levels (TL) differed depending on the chemical species analyzed, with total Hg exhibiting increases of 1.3–2.5 per TL (mean slope of total Hg vs. δ 15 N = 0.14 ± 0.06 S.D., range = 0.06–0.20) and methyl Hg showing a more pronounced increase of 2.8 to 6.0 per TL (mean slope of methyl Hg vs. δ 15 N = 0.30 ± 0.08 S.D., range = 0.22–0.39). While Hg biomagnification slopes through the entire food web (Trophic Magnification Factors, TMFs) were not influenced by water chemistry (pH), dietary concentrations of methyl Hg strongly influenced biomagnification factors (BMFs) for consumer-diet pairs within the food web at lower trophic levels, and BMFs between dace and predatory invertebrates were significantly higher in low pH waters. These analyses, coupled with observations of higher Hg in primary producers in streams with low pH, suggest that pH influences both baseline concentrations and biomagnification of Hg in these systems. Because higher Hg concentrations in the diets

  17. Differential mercury transfer in the aquatic food web of a double basined lake associated with selenium and habitat

    Energy Technology Data Exchange (ETDEWEB)

    Arcagni, Marina [Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, CNEA, Av. Bustillo km 9.5, 8400 Bariloche (Argentina); Campbell, Linda [Faculty of Science, Saint Mary' s University, 923 Robie Street, Halifax, Nova Scotia B3H 3C3 (Canada); Arribére, María A. [Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, CNEA, Av. Bustillo km 9.5, 8400 Bariloche (Argentina); Instituto Balseiro, Universidad Nacional de Cuyo and Comisión Nacional de Energía Atómica (Argentina); Marvin-DiPasquale, Mark [U.S. Geological Survey, 345 Middlefield Rd./MS 480, Menlo Park, CA 94025 (United States); Rizzo, Andrea [Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, CNEA, Av. Bustillo km 9.5, 8400 Bariloche (Argentina); CONICET (Argentina); Ribeiro Guevara, Sergio, E-mail: ribeiro@cab.cnea.gov.ar [Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, CNEA, Av. Bustillo km 9.5, 8400 Bariloche (Argentina)

    2013-06-01

    Food web trophodynamics of total mercury (THg) and selenium (Se) were assessed for the double-basined ultraoligotrophic system of Lake Moreno, Patagonia. Each basin has differing proportions of littoral and pelagic habitats, thereby providing an opportunity to assess the importance of habitat (e.g. food web structure or benthic MeHg production) in the transfer of Hg and Se to top trophic fish species. Pelagic plankton, analyzed in three size classes (10–53, 53–200, and > 200 μm), had very high [THg], exceeding 200 μg g{sup −1} dry weight (DW) in the smallest, and a low ratio of MeHg to THg (0.1 to 3%). In contrast, [THg] in littoral macroinvertebrates showed lower values (0.3 to 1.8 μg g{sup −1} DW). Juvenile and small fish species feeding upon plankton had higher [THg] (0.2 to 8 μg g{sup −1} muscle DW) compared to large piscivore fish species (0.1 to 1.6 μg g{sup −1} muscle DW). Selenium concentrations exhibited a much narrower variation range than THg in the food web, varying from 0.5 to 2.7 μg g{sup −1} DW. Molar Se:Hg ratios exceeded 1 for the majority of organisms in both basins, with most ratios exceeding 10. Using stable nitrogen isotopes as indicator of trophic level, no significant correlations were found with [THg], [Se] or Se:Hg. The apparent lack of biomagnification trends was attributed to elevated [THg] in plankton in the inorganic form mostly, as well as the possibility of consistent Se supply reducing the biomagnification in the food web of the organic portion of THg. Highlights: • Mercury was studied in the food web of Lake Moreno, Nahuel Huapi National Park. • Mercury trophic transfer was assessed by nitrogen stable isotope (δ{sup 15}N) analysis. • Selenium was determined showing consistent source in pelagic and littoral organisms. • High mercury concentrations, mostly inorganic, were determined in plankton. • No mercury biomagnification was observed in Lake Moreno food web.

  18. Biomagnification of mercury through lake trout (Salvelinus namaycush) food webs of lakes with different physical, chemical and biological characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Kidd, Karen A., E-mail: kiddk@unbsj.ca [Canadian Rivers Institute and Biology Department, University of New Brunswick, Saint John, NB, Canada E2L 4L5 (Canada); Muir, Derek C.G., E-mail: derek.muir@ec.gc.ca [Aquatic Contaminants Research Division, Environment Canada, Burlington, ON, Canada L7R 4A6 (Canada); Evans, Marlene S., E-mail: marlene.evans@ec.gc.ca [Aquatic Contaminants Research Division, Environment Canada, Saskatoon, SK, Canada S7N 3H5 (Canada); Wang, Xioawa, E-mail: xiaowa.wang@ec.gc.ca [Aquatic Contaminants Research Division, Environment Canada, Burlington, ON, Canada L7R 4A6 (Canada); Whittle, Mike [Aquatic Contaminants Research Division, Environment Canada, Burlington, ON, Canada L7R 4A6 (Canada); Swanson, Heidi K., E-mail: heidikswanson@yahoo.ca [Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9 (Canada); Johnston, Tom, E-mail: tjohnston@laurentian.ca [Cooperative Freshwater Ecology Unit, Ontario Ministry of Natural Resources, and Biology Department, Laurentian University, Sudbury, ON, Canada P3E 2C6 (Canada); Guildford, Stephanie, E-mail: sguildfo@d.umn.edu [Department of Biology and Large Lakes Observatory, University of Minnesota Duluth, 2205 5th St., Duluth, MN, 55812 (United States)

    2012-11-01

    Mercury (Hg) biomagnification in aquatic ecosystems remains a concern because this pollutant is known to affect the health of fish-eating wildlife and humans, and the fish themselves. The 'rate' of mercury biomagnification is being assessed more frequently using stable nitrogen isotope ratios ({delta}{sup 15}N), a measure of relative trophic position of biota within a food web. Within food webs and across diverse systems, log-transformed Hg concentrations are significantly and positively related to {delta}{sup 15}N and the slopes of these models vary from one study to another for reasons that are not yet understood. Here we compared the rates of Hg biomagnification in 14 lake trout lakes from three provinces in Canada to understand whether any characteristics of the ecosystems explained this among-system variability. Several fish species, zooplankton and benthic invertebrates were collected from these lakes and analyzed for total Hg (fish only), methyl Hg (invertebrates) and stable isotopes ({delta}{sup 15}N; {delta}{sup 13}C to assess energy sources). Mercury biomagnification rates varied significantly across systems and were higher for food webs of larger (surface area), higher nutrient lakes. However, the slopes were not predictive of among-lake differences in Hg in the lake trout. Results indicate that among-system differences in the rates of Hg biomagnification seen in the literature may be due, in part, to differences in ecosystem characteristics although the mechanisms for this variability are not yet understood. -- Highlights: Black-Right-Pointing-Pointer Mercury biomagnifies through aquatic food webs to toxic levels in top predator fishes. Black-Right-Pointing-Pointer Among-system differences in mercury transfer through food webs occur but have not been explained. Black-Right-Pointing-Pointer Diverse lakes supporting lake trout were compared to understand the ecosystem processes that affect mercury biomagnification. Black

  19. Contrasting time trends of organic contaminants in Antarctic pelagic and benthic food webs.

    Science.gov (United States)

    van den Brink, Nico W; Riddle, Martin J; van den Heuvel-Greve, Martine; van Franeker, Jan Andries

    2011-01-01

    We demonstrate that pelagic Antarctic seabirds show significant decreases in concentrations of some persistent organic pollutants. Trends in Adélie penguins and Southern fulmars fit in a general pattern revealed by a broad literature review. Downward trends are also visible in pelagic fish, contrasting sharply with steady or increasing concentrations in Antarctic benthic organisms. Transfer of contaminants between Antarctic pelagic and benthic food webs is associated with seasonal sea-ice dynamics which may influence the balance between the final receptors of contaminants under different climatic conditions. This complicates the predictability of future trends of emerging compounds in the Antarctic ecosystem, such as of the brominated compounds that we detected in Antarctic petrels. The discrepancy in trends between pelagic and benthic organisms shows that Antarctic biota are still final receptors of globally released organic contaminants and it remains questionable whether the total environmental burden of contaminants in the Antarctic ecosystem is declining. Copyright © 2010 Elsevier Ltd. All rights reserved.

  20. Food-web dynamics and trophic-level interactions in a multispecies community of freshwater unionids

    Science.gov (United States)

    Nichols, S.J.; Garling, D.

    2000-01-01

    We compared feeding habits and trophic-level relationships of unionid species in a detritus-dominated river and an alga-dominated lake using biochemical analyses, gut contents, and stable-isotope ratios. The δ13C ratios for algae and other food-web components show that all unionids from both the river and the lake used bacterial carbons, not algal carbons, as their main dietary source, in spite of positive selection and concentration of diatoms and green algae from the water column in the gut and mantle cavity. Algae did provide key nutrients such as vitamins A and D and phytosterols that were bioaccumulated in the tissues of all species. The δ15N ratios for the multispecies unionid community in the Huron River indicated some differences in nitrogen enrichment between species, the greatest enrichment being found in Pyganadon grandis. These δ15N ratios indicate that unionids may not always feed as primary consumers or omnivores. Stable-isotope data were critical for delineating diets and trophic-level interactions of this group of filter-feeders. Further refinements in identifying bacterial and picoplankton components of the fine particulate organic matter are needed to complete our understanding of resource partitioning between multispecies unionid populations.

  1. Network structure beyond food webs: mapping non-trophic and trophic interactions on Chilean rocky shores.

    Science.gov (United States)

    Sonia Kéfi; Berlow, Eric L; Wieters, Evie A; Joppa, Lucas N; Wood, Spencer A; Brose, Ulrich; Navarrete, Sergio A

    2015-01-01

    How multiple types of non-trophic interactions map onto trophic networks in real communities remains largely unknown. We present the first effort, to our knowledge, describing a comprehensive ecological network that includes all known trophic and diverse non-trophic links among >100 coexisting species for the marine rocky intertidal community of the central Chilean coast. Our results suggest that non-trophic interactions exhibit highly nonrandom structures both alone and with respect to food web structure. The occurrence of different types of interactions, relative to all possible links, was well predicted by trophic structure and simple traits of the source and target species. In this community, competition for space and positive interactions related to habitat/refuge provisioning by sessile and/or basal species were by far the most abundant non-trophic interactions. If these patterns are orroborated in other ecosystems, they may suggest potentially important dynamic constraints on the combined architecture of trophic and non-trophic interactions. The nonrandom patterning of non-trophic interactions suggests a path forward for developing a more comprehensive ecological network theory to predict the functioning and resilience of ecological communities.

  2. Extinction cascades partially estimate herbivore losses in a complete Lepidoptera--plant food web.

    Science.gov (United States)

    Pearse, Ian S; Altermatt, Florian

    2013-08-01

    The loss of species from an ecological community can have cascading effects leading to the extinction of other species. Specialist herbivores are highly diverse and may be particularly susceptible to extinction due to host plant loss. We used a bipartite food web of 900 Lepidoptera (butterfly and moth) herbivores and 2403 plant species from Central Europe to simulate the cascading effect of plant extinctions on Lepidoptera extinctions. Realistic extinction sequences of plants, incorporating red-list status, range size, and native status, altered subsequent Lepidoptera extinctions. We compared simulated Lepidoptera extinctions to the number of actual regional Lepidoptera extinctions and found that all predicted scenarios underestimated total observed extinctions but accurately predicted observed extinctions attributed to host loss (n = 8, 14%). Likely, many regional Lepidoptera extinctions occurred for reasons other than loss of host plant alone, such as climate change and habitat loss. Ecological networks can be useful in assessing a component of extinction risk to herbivores based on host loss, but further factors may be equally important.

  3. Ecotracer: analyzing concentration of contaminants and radioisotopes in an aquatic spatial-dynamic food web model.

    Science.gov (United States)

    Walters, William J; Christensen, Villy

    2018-01-01

    Ecotracer is a tool in the Ecopath with Ecosim (EwE) software package used to simulate and analyze the transport of contaminants such as methylmercury or radiocesium through aquatic food webs. Ecotracer solves the contaminant dynamic equations simultaneously with the biomass dynamic equations in Ecosim/Ecospace. In this paper, we give a detailed description of the Ecotracer module and analyze the performance on two problems of differing complexity. Ecotracer was modified from previous versions to more accurately model contaminant excretion, and new numerical integration algorithms were implemented to increase accuracy and robustness. To test the mathematical robustness of the computational algorithm, Ecotracer was tested on a simple problem for which we know an analytical solution. These results demonstrated the effectiveness of the program numerics. A much more complex model, the release of the cesium radionuclide 137 Cs from the Fukushima Dai-ichi nuclear accident, was also modeled and analyzed. A comparison of the Ecotracer results to sampled 137 Cs measurements in the coastal ocean area around Fukushima show the promise of the tool but also highlight some important limitations. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Lake Michigan offshore ecosystem structure and food web changes from 1987 to 2008

    Science.gov (United States)

    Rogers, Mark W.; Bunnell, David B.; Madenjian, Charles P.; Warner, David M.

    2014-01-01

    Ecosystems undergo dynamic changes owing to species invasions, fisheries management decisions, landscape modifications, and nutrient inputs. At Lake Michigan, new invaders (e.g., dreissenid mussels (Dreissena spp.), spiny water flea (Bythotrephes longimanus), round goby (Neogobius melanostomus)) have proliferated and altered energy transfer pathways, while nutrient concentrations and stocking rates to support fisheries have changed. We developed an ecosystem model to describe food web structure in 1987 and ran simulations through 2008 to evaluate changes in biomass of functional groups, predator consumption, and effects of recently invading species. Keystone functional groups from 1987 were identified as Mysis, burbot (Lota lota), phytoplankton, alewife (Alosa pseudoharengus), nonpredatory cladocerans, and Chinook salmon (Oncorhynchus tshawytscha). Simulations predicted biomass reductions across all trophic levels and predicted biomasses fit observed trends for most functional groups. The effects of invasive species (e.g., dreissenid grazing) increased across simulation years, but were difficult to disentangle from other changes (e.g., declining offshore nutrient concentrations). In total, our model effectively represented recent changes to the Lake Michigan ecosystem and provides an ecosystem-based tool for exploring future resource management scenarios.

  5. Species invasion history influences community evolution in a tri-trophic food web model.

    Directory of Open Access Journals (Sweden)

    Akihiko Mougi

    2009-08-01

    Full Text Available Recent experimental studies have demonstrated the importance of invasion history for evolutionary formation of community. However, only few theoretical studies on community evolution have focused on such views.We used a tri-trophic food web model to analyze the coevolutionary effects of ecological invasions by a mutant and by a predator and/or resource species of a native consumer species community and found that ecological invasions can lead to various evolutionary histories. The invasion of a predator makes multiple evolutionary community histories possible, and the evolutionary history followed can determine both the invasion success of the predator into the native community and the fate of the community. A slight difference in the timing of an ecological invasion can lead to a greatly different fate. In addition, even greatly different community histories can converge as a result of environmental changes such as a predator trait shift or a productivity change. Furthermore, the changes to the evolutionary history may be irreversible.Our modeling results suggest that the timing of ecological invasion of a species into a focal community can largely change the evolutionary consequences of the community. Our approach based on adaptive dynamics will be a useful tool to understand the effect of invasion history on evolutionary formation of community.

  6. The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe.

    Science.gov (United States)

    Yeakel, Justin D; Guimarães, Paulo R; Bocherens, Hervé; Koch, Paul L

    2013-07-07

    Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before--and possibly after--the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities.

  7. Microbial food webs and metabolic state across oligotrophic waters of the Mediterranean Sea during summer

    Directory of Open Access Journals (Sweden)

    U. Christaki

    2011-07-01

    Full Text Available The abundance and activity of the major members of the heterotrophic microbial community – from viruses to ciliates – were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to-east gradient of deepening of DCM (deep chlorophyll maximum and increasing oligotrophy reflected in gradients of biomass and production. However, within this well documented longitudinal trend, hydrological mesoscale features exist and likely influence microbial dynamics. Here we present data from a W-E transect of 17 stations during the period of summer stratification. Along the transect the production and fate of organic matter was investigated at three selected sites each one located in the centre of an anticyclonic eddy: in the Algero-Provencal Basin (St. A, the Ionian Basin (St. B, and the Levantine Basin (St. C. The 3 geographically distant eddies showed low values of the different heterotrophic compartments of the microbial food web, and except for viruses in site C, all integrated (0–150 m stocks were higher in reference stations located in the same basin outside the eddies. During our study the 3 eddies showed equilibrium between GPP (Gross Primary Production and DCR (Dark Community Respiration. Integrated PPp (Particulate Primary Production values at A, B and C varied from ~140 to ~190 mg C m−2.

  8. Top-down control in a detritus-based food web: fish, shredders, and leaf breakdown.

    Science.gov (United States)

    Ruetz, Carl R; Newman, Raymond M; Vondracek, Bruce

    2002-07-01

    We tested the hypothesis that fish decrease shredder abundance in leaf packs, thereby reducing leaf breakdown rates. Our goal was to test for the occurrence of a trophic cascade in a detritus-based food web. Willow leaves (Salix spp.) were fastened into leaf packs and placed into cages (13×13×13 cm) in Valley Creek, Minnesota, USA. Fish were excluded from leaf packs that were placed in cages with mesh on all sides, whereas open control cages allowed fish access to leaf packs. We collected leaf packs from two replicate cages 0, 14, 31, 55, and 112 days after placement in each of three riffles (n=6 per collection). Total abundance of invertebrates and shredders inhabiting leaf packs was significantly higher in exclosures than controls (Pshredder taxa had significantly higher biomass in exclosures than controls (PLeaf breakdown rates differed significantly between exclosures and controls (P=0.003), but the direction of effects varied among riffles. When shredder density was analyzed separately for each riffle, we found that shredder density may explain differences in leaf breakdown rates between exclosures and controls. The differential responses of shredder taxa to predators may explain variability in fish effects on leaf breakdown. In conclusion, leaf packs did not provide invertebrates refuge from fish predation and fish reduced the densities of most shredders. Fish can indirectly affect leaf breakdown rates, but different responses to predation among taxa within the shredder guild can cause interactions that contradict trophic cascade predictions.

  9. Flow management for hydropower extirpates aquatic insects, undermining river food webs

    Science.gov (United States)

    Kennedy, Theodore A.; Muehlbauer, Jeffrey D.; Yackulic, Charles B.; Lytle, D.A.; Miller, S.A.; Dibble, Kimberly L.; Kortenhoeven, Eric W.; Metcalfe, Anya; Baxter, Colden V.

    2016-01-01

    Dams impound the majority of rivers and provide important societal benefits, especially daily water releases that enable on-peak hydroelectricity generation. Such “hydropeaking” is common worldwide, but its downstream impacts remain unclear. We evaluated the response of aquatic insects, a cornerstone of river food webs, to hydropeaking using a life history–hydrodynamic model. Our model predicts that aquatic-insect abundance will depend on a basic life-history trait—adult egg-laying behavior—such that open-water layers will be unaffected by hydropeaking, whereas ecologically important and widespread river-edge layers, such as mayflies, will be extirpated. These predictions are supported by a more-than-2500-sample, citizen-science data set of aquatic insects from the Colorado River in the Grand Canyon and by a survey of insect diversity and hydropeaking intensity across dammed rivers of the Western United States. Our study reveals a hydropeaking-related life history bottleneck that precludes viable populations of many aquatic insects from inhabiting regulated rivers.

  10. Local food web management increases resilience and buffers against global change effects on freshwaters

    Science.gov (United States)

    Urrutia-Cordero, Pablo; Ekvall, Mattias K.; Hansson, Lars-Anders

    2016-07-01

    A major challenge for ecological research is to identify ways to improve resilience to climate-induced changes in order to secure the ecosystem functions of natural systems, as well as ecosystem services for human welfare. With respect to aquatic ecosystems, interactions between climate warming and the elevated runoff of humic substances (brownification) may strongly affect ecosystem functions and services. However, we hitherto lack the adaptive management tools needed to counteract such global-scale effects on freshwater ecosystems. Here we show, both experimentally and using monitoring data, that predicted climatic warming and brownification will reduce freshwater quality by exacerbating cyanobacterial growth and toxin levels. Furthermore, in a model based on long-term data from a natural system, we demonstrate that food web management has the potential to increase the resilience of freshwater systems against the growth of harmful cyanobacteria, and thereby that local efforts offer an opportunity to secure our water resources against some of the negative impacts of climate warming and brownification. This allows for novel policy action at a local scale to counteract effects of global-scale environmental change, thereby providing a buffer period and a safer operating space until climate mitigation strategies are effectively established.

  11. Foraging mode affects the evolution of egg size in generalist predators embedded in complex food webs.

    Science.gov (United States)

    Verdeny-Vilalta, O; Fox, C W; Wise, D H; Moya-Laraño, J

    2015-06-01

    Ecological networks incorporate myriad biotic interactions that determine the selection pressures experienced by the embedded populations. We argue that within food webs, the negative scaling of abundance with body mass and foraging theory predict that the selective advantages of larger egg size should be smaller for sit-and-wait than active-hunting generalist predators, leading to the evolution of a difference in egg size between them. Because body mass usually scales negatively with predator abundance and constrains predation rate, slightly increasing egg mass should simultaneously allow offspring to feed on more prey and escape from more predators. However, the benefits of larger offspring would be relatively smaller for sit-and-wait predators because (i) due to their lower mobility, encounters with other predators are less common, and (ii) they usually employ a set of alternative hunting strategies that help to subdue relatively larger prey. On the other hand, for active predators, which need to confront prey as they find them, body-size differences may be more important in subduing prey. This difference in benefits should lead to the evolution of larger egg sizes in active-hunting relative to sit-and-wait predators. This prediction was confirmed by a phylogenetically controlled analysis of 268 spider species, supporting the view that the structure of ecological networks may serve to predict relevant selective pressures acting on key life history traits. © 2015 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2015 European Society For Evolutionary Biology.

  12. Species invasion history influences community evolution in a tri-trophic food web model.

    Science.gov (United States)

    Mougi, Akihiko; Nishimura, Kinya

    2009-08-24

    Recent experimental studies have demonstrated the importance of invasion history for evolutionary formation of community. However, only few theoretical studies on community evolution have focused on such views. We used a tri-trophic food web model to analyze the coevolutionary effects of ecological invasions by a mutant and by a predator and/or resource species of a native consumer species community and found that ecological invasions can lead to various evolutionary histories. The invasion of a predator makes multiple evolutionary community histories possible, and the evolutionary history followed can determine both the invasion success of the predator into the native community and the fate of the community. A slight difference in the timing of an ecological invasion can lead to a greatly different fate. In addition, even greatly different community histories can converge as a result of environmental changes such as a predator trait shift or a productivity change. Furthermore, the changes to the evolutionary history may be irreversible. Our modeling results suggest that the timing of ecological invasion of a species into a focal community can largely change the evolutionary consequences of the community. Our approach based on adaptive dynamics will be a useful tool to understand the effect of invasion history on evolutionary formation of community.

  13. Compound-specific amino acid isotopic analyses of invertebrates in the Chukchi Sea: New insights on food web dynamics

    Science.gov (United States)

    Zhang, M.; Cooper, L. W.; Biasatti, D. M.; Kedra, M.; Grebmeier, J. M.

    2016-02-01

    Food web dynamics in the Chukchi Sea have been previously evaluated using bulk analysis of stable carbon and nitrogen isotopes of organisms. However, recent advances in compound-specific stable isotope analysis of amino acids indicate the potential to better identify the contributions of different dietary sources (e.g., pelagic vs. benthic, ice algae vs. phytoplankton) and to resolve complexities of food web structure that are difficult to address with bulk isotope analysis. Here we combine amino acid δ13C and δ15N data measured from primary producers and tissues of bivalves, polychaetes and other benthic invertebrates collected during two cruises in the summer of 2013 and 2015 in the Pacific Arctic. The results showed spatial variation of carbon isotope values in amino acids with difference up to 6 per mil for each individual species or taxa studied, indicating a shift in the food-web baseline geographically. Furthermore, the spatial variation in isotopic values was related to environmental factors, specifically sea ice extent, and total organic carbon, total organic nitrogen and the carbon/nitrogen ratio of the organic fractions of surface sediments. Results also indicated that trophic levels, as estimated by differences in the nitrogen isotope composition of glutamic acid and phenylalanine [Δ15Nglu-phe (δ15Nglu - δ15Nphe)], varied spatially by 0.5 to 1.5 trophic levels for certain species or taxa such as Macoma calcarea, Maldanidae and Ampelisca, indicating trophic level shifts that were associated with the food quality of organic matter in the organic fraction of the sediments. These results can be potentially used to predict future food web change in this high latitude marine system that is known for its ecological importance and on-going environmental changes, including warming and sea ice decline.

  14. A Web-Based Graphical Food Frequency Assessment System: Design, Development and Usability Metrics.

    Science.gov (United States)

    Franco, Rodrigo Zenun; Alawadhi, Balqees; Fallaize, Rosalind; Lovegrove, Julie A; Hwang, Faustina

    2017-05-08

    Food frequency questionnaires (FFQs) are well established in the nutrition field, but there remain important questions around how to develop online tools in a way that can facilitate wider uptake. Also, FFQ user acceptance and evaluation have not been investigated extensively. This paper presents a Web-based graphical food frequency assessment system that addresses challenges of reproducibility, scalability, mobile friendliness, security, and usability and also presents the utilization metrics and user feedback from a deployment study. The application design employs a single-page application Web architecture with back-end services (database, authentication, and authorization) provided by Google Firebase's free plan. Its design and responsiveness take advantage of the Bootstrap framework. The FFQ was deployed in Kuwait as part of the EatWellQ8 study during 2016. The EatWellQ8 FFQ contains 146 food items (including drinks). Participants were recruited in Kuwait without financial incentive. Completion time was based on browser timestamps and usability was measured using the System Usability Scale (SUS), scoring between 0 and 100. Products with a SUS higher than 70 are considered to be good. A total of 235 participants created accounts in the system, and 163 completed the FFQ. Of those 163 participants, 142 reported their gender (93 female, 49 male) and 144 reported their date of birth (mean age of 35 years, range from 18-65 years). The mean completion time for all FFQs (n=163), excluding periods of interruption, was 14.2 minutes (95% CI 13.3-15.1 minutes). Female participants (n=93) completed in 14.1 minutes (95% CI 12.9-15.3 minutes) and male participants (n=49) completed in 14.3 minutes (95% CI 12.6-15.9 minutes). Participants using laptops or desktops (n=69) completed the FFQ in an average of 13.9 minutes (95% CI 12.6-15.1 minutes) and participants using smartphones or tablets (n=91) completed in an average of 14.5 minutes (95% CI 13.2-15.8 minutes). The median SUS

  15. Analysis and prediction of agricultural pest dynamics with Tiko'n, a generic tool to develop agroecological food web models

    Science.gov (United States)

    Malard, J. J.; Rojas, M.; Adamowski, J. F.; Anandaraja, N.; Tuy, H.; Melgar-Quiñonez, H.

    2016-12-01

    While several well-validated crop growth models are currently widely used, very few crop pest models of the same caliber have been developed or applied, and pest models that take trophic interactions into account are even rarer. This may be due to several factors, including 1) the difficulty of representing complex agroecological food webs in a quantifiable model, and 2) the general belief that pesticides effectively remove insect pests from immediate concern. However, pests currently claim a substantial amount of harvests every year (and account for additional control costs), and the impact of insects and of their trophic interactions on agricultural crops cannot be ignored, especially in the context of changing climates and increasing pressures on crops across the globe. Unfortunately, most integrated pest management frameworks rely on very simple models (if at all), and most examples of successful agroecological management remain more anecdotal than scientifically replicable. In light of this, there is a need for validated and robust agroecological food web models that allow users to predict the response of these webs to changes in management, crops or climate, both in order to predict future pest problems under a changing climate as well as to develop effective integrated management plans. Here we present Tiko'n, a Python-based software whose API allows users to rapidly build and validate trophic web agroecological models that predict pest dynamics in the field. The programme uses a Bayesian inference approach to calibrate the models according to field data, allowing for the reuse of literature data from various sources and reducing the need for extensive field data collection. We apply the model to the cononut black-headed caterpillar (Opisina arenosella) and associated parasitoid data from Sri Lanka, showing how the modeling framework can be used to rapidly develop, calibrate and validate models that elucidate how the internal structures of food webs

  16. Web page of the Ibero-American laboratories network of radioactivity analysis in foods: a tool for inter regional diffusion

    International Nuclear Information System (INIS)

    Melo Ferreira, Ana C. de; Osores, Jose M.; Fernandez Gomez, Isis M.; Iglicki, Flora A.; Vazquez Bolanos, Luis R.; Romero, Maria de L.; Aguirre Gomez, Jaime; Flores, Yasmine

    2008-01-01

    One objective of the thematic networks is the exchanges of knowledge among participants, for this reason, actions focused to the diffusion of their respective work are prioritized, evidencing the result of the cooperation among the participant groups and also among different networks. The Ibero-American Laboratories Network of Radioactivity Analysis in Foods (RILARA) was constituted in 2007, and one of the first actions carried out in this framework, was the design and conformation of a web page. The web pages have become a powerful means for diffusion of specialized information. Their power, as well as their continuous upgrading and the specificity of the topics that can develop, allow the user to obtain fast information on a wide range of products, services and organizations at local and world level. The main objective of the RILARA web page is to provide updated relevant information to interested specialists in the subject and also to public in general, about the work developed by the network laboratories regarding the control of radioactive pollutants in foods and related scientific issues. This web has been developed based on a Content Management Systems that helps to eliminate potential barriers to the communication web, reducing the creation costs, contribution and maintenance of the content. The tool used for its design is very effective to be used in the process of teaching, learning and for the organization of the information. This paper describes how was conceived the design of this web page, the information that contains and how can be accessed and/or to include any contribution, the value of this page depends directly on the grade of updating of the available contents so that it can be useful and attractive to the users. (author)

  17. Fatty acid composition at the base of aquatic food webs is influenced by habitat type and watershed land use

    Science.gov (United States)

    Larson, James H.; Richardson, William B.; Knights, Brent C.; Bartsch, Lynn; Bartsch, Michelle; Nelson, J. C.; Veldboom, Jason A.; Vallazza, Jonathan M.

    2013-01-01

    Spatial variation in food resources strongly influences many aspects of aquatic consumer ecology. Although large-scale controls over spatial variation in many aspects of food resources are well known, others have received little study. Here we investigated variation in the fatty acid (FA) composition of seston and primary consumers within (i.e., among habitats) and among tributary systems of Lake Michigan, USA. FA composition of food is important because all metazoans require certain FAs for proper growth and development that cannot be produced de novo, including many polyunsaturated fatty acids (PUFAs). Here we sampled three habitat types (river, rivermouth and nearshore zone) in 11 tributaries of Lake Michigan to assess the amount of FA in seston and primary consumers of seston. We hypothesize that among-system and among-habitat variation in FAs at the base of food webs would be related to algal production, which in turn is influenced by three land cover characteristics: 1) combined agriculture and urban lands (an indication of anthropogenic nutrient inputs that fuel algal production), 2) the proportion of surface waters (an indication of water residence times that allow algal producers to accumulate) and 3) the extent of riparian forested buffers (an indication of stream shading that reduces algal production). Of these three land cover characteristics, only intense land use appeared to strongly related to seston and consumer FA and this effect was only strong in rivermouth and nearshore lake sites. River seston and consumer FA composition was highly variable, but that variation does not appear to be driven by the watershed land cover characteristics investigated here. Whether the spatial variation in FA content at the base of these food webs significantly influences the production of economically important species higher in the food web should be a focus of future research.

  18. Zinc isotope ratios of bones and teeth as new dietary indicators: results from a modern food web (Koobi Fora, Kenya)

    Science.gov (United States)

    Jaouen, Klervia; Beasley, Melanie; Schoeninger, Margaret; Hublin, Jean-Jacques; Richards, Michael P.

    2016-05-01

    In order to explore the possibilities of using zinc (Zn) stable isotope ratios as dietary indicators, we report here on the measurements of the ratio of stable isotopes of zinc (66Zn/64Zn, expressed here as δ66Zn) in bioapatite (bone and dental enamel) of animals from a modern food web in the Koobi Fora region of the Turkana Basin in Kenya. We demonstrate that δ66Zn values in both bone and enamel allow a clear distinction between carnivores and herbivores from this food web. Differences were also observed between browsers and grazers as well as between carnivores that consumed bone (i.e. hyenas) compared to those that largely consume flesh (i.e. lions). We conclude that Zn isotope ratio measurements of bone and teeth are a new and promising dietary indicator.

  19. How does litter quality and site heterogeneity interact on decomposer food webs of a semi-natural forest?

    DEFF Research Database (Denmark)

    Strandmark, Lisa Bjørnlund; Christensen, Søren

    2005-01-01

    The relative importance of litter quality and site heterogeneity on population dynamics of decomposer food webs was investigated in a semi-natural mixed deciduous forest in Denmark. Litterbags containing beech or ash leaves were placed in four plots. Plots were located within gaps and under closed...... at the end of the study period. At the first sampling, where bacterial activity prevailed, the relative abundance of the two dominant bacterial-feeders, Rhabditidae (fast growing) and Plectus spp. (slower growing), depended more on site than litter type. At the second sampling where fungal activity became...... in the decomposer food web, site effects were also detected and nematode functional groups responded more to site than to litter quality early on in the decomposition process....

  20. The Spider and the Sea : Effects of marine subsidies on the role of spiders in terrestrial food webs

    OpenAIRE

    Mellbrand, Kajsa

    2009-01-01

    The purpose of this study was to identify if terrestrial arthropod predators on Baltic Sea shores vary in their use of marine versus terrestrial food items, and to construct a bottom-up food web for Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g. phantom midges, Chironomidae). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis, and a two source mixing model was us...

  1. Root-derived carbon and nitrogen from beech and ash trees differentially fuel soil animal food webs of deciduous forests.

    Directory of Open Access Journals (Sweden)

    Sarah L Zieger

    Full Text Available Evidence is increasing that soil animal food webs are fueled by root-derived carbon (C and also by root-derived nitrogen (N. Functioning as link between the above- and belowground system, trees and their species identity are important drivers structuring soil animal communities. A pulse labeling experiment using 15N and 13C was conducted by exposing beech (Fagus sylvatica and ash (Fraxinus excelsior seedlings to 13CO2 enriched atmosphere and tree leaves to 15N ammonium chloride solution in a plant growth chamber under controlled conditions for 72 h. C and N fluxes into the soil animal food web of beech, associated with ectomycorrhizal fungi (EMF, and ash, associated with arbuscular mycorrhizal fungi (AMF, were investigated at two sampling dates (5 and 20 days after labeling. All of the soil animal taxa studied incorporated root-derived C, while root-derived N was only incorporated into certain taxa. Tree species identity strongly affected C and N incorporation with the incorporation in the beech rhizosphere generally exceeding that in the ash rhizosphere. Incorporation differed little between 5 and 20 days after labeling indicating that both C and N are incorporated quickly into soil animals and are used for tissue formation. Our results suggest that energy and nutrient fluxes in soil food webs depend on the identity of tree species with the differences being associated with different types of mycorrhiza. Further research is needed to prove the generality of these findings and to quantify the flux of plant C and N into soil food webs of forests and other terrestrial ecosystems.

  2. Medium-sized exotic prey create novel food webs: the case of predators and scavengers consuming lagomorphs

    Directory of Open Access Journals (Sweden)

    Facundo Barbar

    2016-0