Prey responses to predator chemical cues: disentangling the importance of the number and biomass of prey consumed.

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Michael W McCoy

Full Text Available To effectively balance investment in predator defenses versus other traits, organisms must accurately assess predation risk. Chemical cues caused by predation events are indicators of risk for prey in a wide variety of systems, but the relationship between how prey perceive risk in relation to the amount of prey consumed by predators is poorly understood. While per capita predation rate is often used as the metric of relative risk, studies aimed at quantifying predator-induced defenses commonly control biomass of prey consumed as the metric of risk. However, biomass consumed can change by altering either the number or size of prey consumed. In this study we determine whether phenotypic plasticity to predator chemical cues depends upon prey biomass consumed, prey number consumed, or both. We examine the growth response of red-eyed treefrog tadpoles (Agalychnis callidryas to cues from a larval dragonfly (Anax amazili. Biomass consumed was manipulated by either increasing the number of prey while holding individual prey size constant, or by holding the number of prey constant and varying individual prey size. We address two questions. (i Do prey reduce growth rate in response to chemical cues in a dose dependent manner? (ii Does the magnitude of the response depend on whether prey consumption increases via number or size of prey? We find that the phenotypic response of prey is an asymptotic function of prey biomass consumed. However, the asymptotic response is higher when more prey are consumed. Our findings have important implications for evaluating past studies and how future experiments should be designed. A stronger response to predation cues generated by more individual prey deaths is consistent with models that predict prey sensitivity to per capita risk, providing a more direct link between empirical and theoretical studies which are often focused on changes in population sizes not individual biomass.

Estimation of feeding patterns for piscivorous fish using individual prey data from stomach contents

DEFF Research Database (Denmark)

Berg, Casper Willestofte; Temming, Axel

2011-01-01

The problem of estimating temporal feeding patterns using stomach data is considered, where the time of ingestion for each prey item can be predicted through a gastric evacuation model. The arrival of prey is modelled as a nonhomogeneous Poisson process with known periodic intensity. A maximum...

Influence of primary prey on home-range size and habitat-use patterns of northern spotted owls (Strix occidentalis caurina)

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Cynthia J. Zabel; Kevin S. McKelvey; James P. Ward

1995-01-01

Correlations between the home-range size of northern spotted owls (Strix occidentalis caurina) and proportion of their range in old-growth forest have been reported, but there are few data on the relationship between their home-range size and prey. The primary prey of spotted owls are wood rats and northern flying squirrels (Glaucomys sabrinus). Wood...

Using accelerometry to quantify prey attack and handling behaviours in piscivorous pike Esox lucius

DEFF Research Database (Denmark)

Deurs, Mikael van; Andersson, A.; Vinterstare, J.

2017-01-01

Accelerometer technology was used to evaluate behaviours in the teleost ambush predator pike Esox lucius foraging on crucian carp Carassius carassius. Automated rule-based estimates of prey-size determined handling time were obtained and are compared with video-recorded behaviours. Solutions to t...... attachment and the limitations imposed by battery-time and data-logging capacities are evaluated......Accelerometer technology was used to evaluate behaviours in the teleost ambush predator pike Esox lucius foraging on crucian carp Carassius carassius. Automated rule-based estimates of prey-size determined handling time were obtained and are compared with video-recorded behaviours. Solutions to tag...

Predatory functional morphology in raptors: interdigital variation in talon size is related to prey restraint and immobilisation technique.

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Fowler, Denver W; Freedman, Elizabeth A; Scannella, John B

2009-11-25

Despite the ubiquity of raptors in terrestrial ecosystems, many aspects of their predatory behaviour remain poorly understood. Surprisingly little is known about the morphology of raptor talons and how they are employed during feeding behaviour. Talon size variation among digits can be used to distinguish families of raptors and is related to different techniques of prey restraint and immobilisation. The hypertrophied talons on digits (D) I and II in Accipitridae have evolved primarily to restrain large struggling prey while they are immobilised by dismemberment. Falconidae have only modest talons on each digit and only slightly enlarged D-I and II. For immobilisation, Falconini rely more strongly on strike impact and breaking the necks of their prey, having evolved a 'tooth' on the beak to aid in doing so. Pandionidae have enlarged, highly recurved talons on each digit, an adaptation for piscivory, convergently seen to a lesser extent in fishing eagles. Strigiformes bear enlarged talons with comparatively low curvature on each digit, part of a suite of adaptations to increase constriction efficiency by maximising grip strength, indicative of specialisation on small prey. Restraint and immobilisation strategy change as prey increase in size. Small prey are restrained by containment within the foot and immobilised by constriction and beak attacks. Large prey are restrained by pinning under the bodyweight of the raptor, maintaining grip with the talons, and immobilised by dismemberment (Accipitridae), or severing the spinal cord (Falconini). Within all raptors, physical attributes of the feet trade off against each other to attain great strength, but it is the variable means by which this is achieved that distinguishes them ecologically. Our findings show that interdigital talon morphology varies consistently among raptor families, and that this is directly correlative with variation in their typical prey capture and restraint strategy.

Prey availability affects territory size, but not territorial display behavior, in green anole lizards

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Stehle, Chelsea M.; Battles, Andrew C.; Sparks, Michelle N.; Johnson, Michele A.

2017-10-01

The availability of food resources can affect the size and shape of territories, as well as the behaviors used to defend territories, in a variety of animal taxa. However, individuals within a population may respond differently to variation in food availability if the benefits of territoriality vary among those individuals. For example, benefits to territoriality may differ for animals of differing sizes, because larger individuals may require greater territory size to acquire required resources, or territorial behavior may differ between the sexes if males and females defend different resources in their territories. In this study, we tested whether arthropod abundance and biomass were associated with natural variation in territory size and defense in insectivorous green anole lizards, Anolis carolinensis. Our results showed that both male and female lizards had smaller territories in a habitat with greater prey biomass than lizards in habitats with less available prey, but the rates of aggressive behaviors used to defend territories did not differ among these habitats. Further, we did not find a relationship between body size and territory size, and the sexes did not differ in their relationships between food availability and territory size or behavioral defense. Together, these results suggest that differences in food availability influenced male and female territorial strategies similarly, and that territory size may be more strongly associated with variation in food resources than social display behavior. Thus, anole investment in the behavioral defense of a territory may not vary with territory quality.

Beak measurements of octopus ( Octopus variabilis) in Jiaozhou Bay and their use in size and biomass estimation

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Xue, Ying; Ren, Yiping; Meng, Wenrong; Li, Long; Mao, Xia; Han, Dongyan; Ma, Qiuyun

2013-09-01

Cephalopods play key roles in global marine ecosystems as both predators and preys. Regressive estimation of original size and weight of cephalopod from beak measurements is a powerful tool of interrogating the feeding ecology of predators at higher trophic levels. In this study, regressive relationships among beak measurements and body length and weight were determined for an octopus species ( Octopus variabilis), an important endemic cephalopod species in the northwest Pacific Ocean. A total of 193 individuals (63 males and 130 females) were collected at a monthly interval from Jiaozhou Bay, China. Regressive relationships among 6 beak measurements (upper hood length, UHL; upper crest length, UCL; lower hood length, LHL; lower crest length, LCL; and upper and lower beak weights) and mantle length (ML), total length (TL) and body weight (W) were determined. Results showed that the relationships between beak size and TL and beak size and ML were linearly regressive, while those between beak size and W fitted a power function model. LHL and UCL were the most useful measurements for estimating the size and biomass of O. variabilis. The relationships among beak measurements and body length (either ML or TL) were not significantly different between two sexes; while those among several beak measurements (UHL, LHL and LBW) and body weight (W) were sexually different. Since male individuals of this species have a slightly greater body weight distribution than female individuals, the body weight was not an appropriate measurement for estimating size and biomass, especially when the sex of individuals in the stomachs of predators was unknown. These relationships provided essential information for future use in size and biomass estimation of O. variabilis, as well as the estimation of predator/prey size ratios in the diet of top predators.

Sabretoothed carnivores and the killing of large prey.

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Ki Andersson

Full Text Available Sabre-like canines clearly have the potential to inflict grievous wounds leading to massive blood loss and rapid death. Hypotheses concerning sabretooth killing modes include attack to soft parts such as the belly or throat, where biting deep is essential to generate strikes reaching major blood vessels. Sabretoothed carnivorans are widely interpreted as hunters of larger and more powerful prey than that of their present-day nonsabretoothed relatives. However, the precise functional advantage of the sabretooth bite, particularly in relation to prey size, is unknown. Here, we present a new point-to-point bite model and show that, for sabretooths, depth of the killing bite decreases dramatically with increasing prey size. The extended gape of sabretooths only results in considerable increase in bite depth when biting into prey with a radius of less than ∼10 cm. For sabretooths, this size-reversed functional advantage suggests predation on species within a similar size range to those attacked by present-day carnivorans, rather than "megaherbivores" as previously believed. The development of the sabretooth condition appears to represent a shift in function and killing behaviour, rather than one in predator-prey relations. Furthermore, our results demonstrate how sabretoothed carnivorans are likely to have evolved along a functionally continuous trajectory: beginning as an extension of a jaw-powered killing bite, as adopted by present-day pantherine cats, followed by neck-powered biting and thereafter shifting to neck-powered shear-biting. We anticipate this new insight to be a starting point for detailed study of the evolution of pathways that encompass extreme specialisation, for example, understanding how neck-powered biting shifts into shear-biting and its significance for predator-prey interactions. We also expect that our model for point-to-point biting and bite depth estimations will yield new insights into the behaviours of a broad range of

When prey provide more than food: mammalian predators appropriating the refugia of their prey

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Bill Zielinski

2015-01-01

Some mammalian predators acquire both food and shelter from their prey, by eating them and using the refugia the prey construct. I searched the literature for examples of predators that exhibit this behavior and summarize their taxonomic affiliations, relative sizes, and distributions. I hypothesized that size ratios of species involved in this dynamic would be near 1....

Prey preferences of the jaguar Panthera onca reflect the post-Pleistocene demise of large prey.

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Matt W Hayward

2016-01-01

Full Text Available Documenting the impacts of the Pleistocene megafaunal extinctions on predator-prey interactions is a challenge because of the incomplete fossil record and depauperate extant community structure. We used a comparative ecological approach to investigate whether the existing prey preference patterns of jaguars Panthera onca were potentially affected by the Pleistocene extinctions in the Americas compared with large felids in Africa and Asia. We reviewed the literature and found 25 studies reporting 3214 jaguar kills recorded throughout the species’ distribution. We found that jaguars significantly preferred capybara Hydrochaeris hydrochaeris and giant anteater Myrmecophaga tridactyla, and avoided agoutis, carnivorans, primates, black-eared opossum Didelphis marsupialis and tapirs. Generalised linear models showed that jaguars select prey primarily based on socio-ecological and behavioural traits (abundance and herd size, rather than morphological characteristics (body size. Nonetheless, their accessible prey weight range was 6-60 kg, preferred prey weight range was 45-85 kg, and mean mass of significantly preferred prey was 32 ± 13 kg leading to a predator to prey body mass ratio of 1:0.53, which is much less than that of other solitary felids. Compared with other large, solitary felids, jaguars have an unusual predator to prey body mass ratio, show limited effect of prey morphology as a driver of prey selection, lack evidence of optimal foraging beyond their preferred prey, and an absence of preferentially hunting on Cetartiodactyla herbivores. These features, coupled with the reduction in jaguar body mass since the Pleistocene, suggest that the loss of larger potential prey items within the preferred and accessible weight ranges at the end-Pleistocene still affects jaguar predatory behaviour. It may be that jaguars survived this mass extinction event by preferentially preying on relatively small species.

Prey-mediated avoidance of an intraguild predator by its intraguild prey

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Wilson, R.R.; Blankenship, T.L.; Hooten, M.B.; Shivik, J.A.

2010-01-01

Intraguild (IG) predation is an important factor influencing community structure, yet factors allowing coexistence of IG predator and IG prey are not well understood. The existence of spatial refuges for IG prey has recently been noted for their importance in allowing coexistence. However, reduction in basal prey availability might lead IG prey to leave spatial refuges for greater access to prey, leading to increased IG predation and fewer opportunities for coexistence. We determined how the availability of prey affected space-use patterns of bobcats (Lynx rufus, IG prey) in relation to coyote space-use patterns (Canis latrans, IG predators). We located animals from fall 2007 to spring 2009 and estimated bobcat home ranges and core areas seasonally. For each bobcat relocation, we determined intensity of coyote use, distance to water, small mammal biomass, and mean small mammal biomass of the home range during the season the location was collected. We built generalized linear mixed models and used Akaike Information Criteria to determine which factors best predicted bobcat space use. Coyote intensity was a primary determinant of bobcat core area location. In bobcat home ranges with abundant prey, core areas occurred where coyote use was low, but shifted to areas intensively used by coyotes when prey declined. High spatial variability in basal prey abundance allowed some bobcats to avoid coyotes while at the same time others were forced into more risky areas. Our results suggest that multiple behavioral strategies associated with spatial variation in basal prey abundance likely allow IG prey and IG predators to coexist. ?? 2010 Springer-Verlag.

Examining predator–prey body size, trophic level and body mass across marine and terrestrial mammals

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Tucker, Marlee A.; Rogers, Tracey L.

2014-01-01

Predator–prey relationships and trophic levels are indicators of community structure, and are important for monitoring ecosystem changes. Mammals colonized the marine environment on seven separate occasions, which resulted in differences in species' physiology, morphology and behaviour. It is likely that these changes have had a major effect upon predator–prey relationships and trophic position; however, the effect of environment is yet to be clarified. We compiled a dataset, based on the literature, to explore the relationship between body mass, trophic level and predator–prey ratio across terrestrial (n = 51) and marine (n = 56) mammals. We did not find the expected positive relationship between trophic level and body mass, but we did find that marine carnivores sit 1.3 trophic levels higher than terrestrial carnivores. Also, marine mammals are largely carnivorous and have significantly larger predator–prey ratios compared with their terrestrial counterparts. We propose that primary productivity, and its availability, is important for mammalian trophic structure and body size. Also, energy flow and community structure in the marine environment are influenced by differences in energy efficiency and increased food web stability. Enhancing our knowledge of feeding ecology in mammals has the potential to provide insights into the structure and functioning of marine and terrestrial communities. PMID:25377460

Prey preferences and prey acceptance in juvenile Brown Treesnakes (Boiga irregularis)

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Lardner, Bjorn; Savidge, Julie A.; Rodda, Gordon H.; Reed, Robert N.

2009-01-01

On the Pacific island of Guam, control of the invasive Brown Treesnake (Boiga irregularis) relies largely on methods that use mice as bait. Juvenile B. irregularis feed primarily on lizards and their eggs, but little is known about their prey preference. We conducted an experiment to investigate preferences for, and acceptance of, dead geckos, skinks, and neonatal mice, in juvenile B. irregularis ranging from 290 mm to ca. 700 mm snout-vent length (SVL). Snakes of all sizes showed a preference for geckos over skinks and neonatal mice. Geckos were the first prey chosen in 87% of 224 initial trials (56 snakes subjected to four trials each; 33% would be expected from a random choice). The smallest snakes had the most pronounced preference. Although many of the snakes accepted neonatal mice and/or skinks, some snakes of all sizes were reluctant to feed on anything but geckos, especially when well fed. We also addressed the hypothesis that repeated encounters with a particular prey type increase a snake's preference for that prey. Our study does not support this hypothesis. Our results suggest that control methods relying solely on rodent bait may be inefficient for targeting snakes < 700 mm SVL and that individual heterogeneity in prey preference may cause a significant part of this juvenile cohort to be completely refractory to capture with rodent bait, even if the bait is dead and small enough to be readily swallowed.

Examining predator-prey body size, trophic level and body mass across marine and terrestrial mammals.

Science.gov (United States)

Tucker, Marlee A; Rogers, Tracey L

2014-12-22

Predator-prey relationships and trophic levels are indicators of community structure, and are important for monitoring ecosystem changes. Mammals colonized the marine environment on seven separate occasions, which resulted in differences in species' physiology, morphology and behaviour. It is likely that these changes have had a major effect upon predator-prey relationships and trophic position; however, the effect of environment is yet to be clarified. We compiled a dataset, based on the literature, to explore the relationship between body mass, trophic level and predator-prey ratio across terrestrial (n = 51) and marine (n = 56) mammals. We did not find the expected positive relationship between trophic level and body mass, but we did find that marine carnivores sit 1.3 trophic levels higher than terrestrial carnivores. Also, marine mammals are largely carnivorous and have significantly larger predator-prey ratios compared with their terrestrial counterparts. We propose that primary productivity, and its availability, is important for mammalian trophic structure and body size. Also, energy flow and community structure in the marine environment are influenced by differences in energy efficiency and increased food web stability. Enhancing our knowledge of feeding ecology in mammals has the potential to provide insights into the structure and functioning of marine and terrestrial communities. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Prey selection by Bengal Tiger Panthera tigris tigris (Mammalia: Carnivora: Felidae of Chitwan National Park, Nepal

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Saneer Lamichhane

2015-11-01

Full Text Available Prey selection by tiger in Chitwan National Park, Nepal was studied from 77 tiger scats that contained the remains of principal prey species.  The scats were collected from January to March 2010.  Government reports on herbivore population in Chitwan provided the base data on density of principal prey species.  In order to understand prey selectivity, the observed proportion of prey species in the scats were compared with the expected proportion derived from density estimates.  The observed scat frequency of Sambar, Hog Deer and Wild Boar was found to be greater than the estimated frequency, and the reverse was true for Chital and Muntjac.  The average weight of the principal prey species killed was 84 kg. According to our results, Chital and Sambar constituted the bulk (82.07%, and Hog Deer, Wild Boar, and Muntjac constituted 17.93% of the tiger diet.  Sambar contributed the largest bulk (43.75% of prey composition, but Chital constituted the relatively most killed (50.36% prey species.  The present study makes a contribution to an understanding of the status of prey composition in tiger scat in Chitwan during the year 2010.  The study also highlights that both large and medium sized prey are important for the conservation of tiger in Chitwan National Park. 

The effects of prey size on diet differentiation of seven passerine species at two spring stopover sites

NARCIS (Netherlands)

Marchetti, C.M.; Locatelli, D.P.; Van Noordwijk, A.J.; Baldaccini, N.E.

1998-01-01

Prey size was evaluated for seven passerine trans-Saharan migrant species at two spring stopover sites in Sardinia, Italy. The species considered were Pied Flycatcher Ficedula hypoleuca, Spotted Flycatcher Muscicapa striata, Redstart Phoenicurus phoenicurus, Garden Warbler Sylvia borin, Whitethroat

A method for in situ estimation of prey selectivity and predation rate in large plankton, exemplified with the jellyfish Aurelia aurita (L.)

DEFF Research Database (Denmark)

Hansson, L.J.

2006-01-01

, predation rate can be calculated as increase in gut content over time. Clearance rates for different prey can be calculated from predation rates and prey concentrations in the water, allowing accurate estimates of prey selectivity. Thus, the problem of unknown feeding history and feeding environment, which...... of a specific individual plankton predator in situ.After prey has been evacuated from the gut of an individual predator, the predator is incubated in situ, and observed by SCUBA-divers who recapture the individual after a defined time. Given that this incubation time is shorter than prey digestion time...... among individual jellyfish and among the various oral arms and gastric pouches within individuals. Clearance rates varied strongly with prey type. The medusae selected large crustacean prey (cladocerans and copepods/copepodites) over echinoderm larvae and copepod nauplii. Prey distribution within...

Assessment of Competition between Fisheries and Steller Sea Lions in Alaska Based on Estimated Prey Biomass, Fisheries Removals and Predator Foraging Behaviour.

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Tabitha C Y Hui

Full Text Available A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estimate the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.

Predator and prey perception in copepods due to hydromechanical signals

DEFF Research Database (Denmark)

Kiørboe, Thomas; Visser, Andre

1999-01-01

of the different components of the fluid disturbance. We use this model to argue that prey perception depends on the absolute magnitude of the fluid velocity generated by the moving prey, while predator perception depends on the magnitude of one or several of the components of the fluid velocity gradients...... (deformation rate, vorticity, acceleration) generated by the predator. On the assumption that hydrodynamic disturbances are perceived through the mechanical bending of sensory setae, we estimate the magnitude of the signal strength due to each of the fluid disturbance components. We then derive equations...... for reaction distances as a function of threshold signal strength and the size and velocity of the prey or predator. We provide a conceptual framework for quantifying threshold signal strengths and, hence, perception distances. The model is illustrated by several examples, and we demonstrate, for example, (1...

Laboratory investigations of the effects of predator sex and size on prey selection by the Asian crab, Hemigrapsus sanguineus.

Science.gov (United States)

Brousseau, D J.; Filipowicz, A; Baglivo, J A.

2001-07-30

Laboratory studies have shown that the nonindigenous Asian shore crab, Hemigrapsus sanguineus, readily consumes three species of commercial bivalves: blue mussels, Mytilus edulis, soft-shell clams, Mya arenaria, and oysters, Crassostrea virginica. Although crabs can eat bivalves of a wide size range, they preferred the smaller prey (Hemigrapsus that occur in the wild, their effectiveness as predators of juvenile bivalves and their large appetites suggest an important role for these predators in restructuring the prey communities in habitats into which they have been introduced.

Selective Predation of a Stalking Predator on Ungulate Prey.

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Marco Heurich

Full Text Available Prey selection is a key factor shaping animal populations and evolutionary dynamics. An optimal forager should target prey that offers the highest benefits in terms of energy content at the lowest costs. Predators are therefore expected to select for prey of optimal size. Stalking predators do not pursue their prey long, which may lead to a more random choice of prey individuals. Due to difficulties in assessing the composition of available prey populations, data on prey selection of stalking carnivores are still scarce. We show how the stalking predator Eurasian lynx (Lynx lynx selects prey individuals based on species identity, age, sex and individual behaviour. To address the difficulties in assessing prey population structure, we confirm inferred selection patterns by using two independent data sets: (1 data of 387 documented kills of radio-collared lynx were compared to the prey population structure retrieved from systematic camera trapping using Manly's standardized selection ratio alpha and (2 data on 120 radio-collared roe deer were analysed using a Cox proportional hazards model. Among the larger red deer prey, lynx selected against adult males-the largest and potentially most dangerous prey individuals. In roe deer lynx preyed selectively on males and did not select for a specific age class. Activity during high risk periods reduced the risk of falling victim to a lynx attack. Our results suggest that the stalking predator lynx actively selects for size, while prey behaviour induces selection by encounter and stalking success rates.

Prey perception in feeding-current feeding copepods

DEFF Research Database (Denmark)

Kiørboe, Thomas; Goncalves, Rodrigo J.; Florian Couespel, Damien

2016-01-01

We reply to the comments of Paffenhöfer and Jiang () who argues that remote chemical prey perception is necessary for feeding-current feeding copepods to fulfill their nutritional requirements in a dilute ocean, that remote chemical prey detection may only be observed at very low prey concentrati......We reply to the comments of Paffenhöfer and Jiang () who argues that remote chemical prey perception is necessary for feeding-current feeding copepods to fulfill their nutritional requirements in a dilute ocean, that remote chemical prey detection may only be observed at very low prey...... cells have short intense leakage burst, only a very small fraction of prey cells would be available to the copepod at any instance in time and, thus would be inefficient at low prey concentration. Finally, we report a few new observations of prey capture in two species of copepods, Temora longicornis...... and Centropages hamatus, offered a 45-μm sized dinoflagellate at very low concentration. The observed short prey detection distances, up to a few prey cell radii, are consistent with mechanoreception and we argue briefly that near-field mechanoreception is the most likely and common prey perception mechanism...

Prey Selection of Scandinavian Wolves: Single Large or Several Small?

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Sand, Håkan; Eklund, Ann; Zimmermann, Barbara; Wikenros, Camilla; Wabakken, Petter

2016-01-01

Research on large predator-prey interactions are often limited to the predators' primary prey, with the potential for prey switching in systems with multiple ungulate species rarely investigated. We evaluated wolf (Canis lupus) prey selection at two different spatial scales, i.e., inter- and intra-territorial, using data from 409 ungulate wolf-kills in an expanding wolf population in Scandinavia. This expansion includes a change from a one-prey into a two-prey system with variable densities of one large-sized ungulate; moose (Alces alces) and one small-sized ungulate; roe deer (Capreolus capreolus). Among wolf territories, the proportion of roe deer in wolf kills was related to both pack size and roe deer density, but not to moose density. Pairs of wolves killed a higher proportion of roe deer than did packs, and wolves switched to kill more roe deer as their density increased above a 1:1 ratio in relation to the availability of the two species. At the intra-territorial level, wolves again responded to changes in roe deer density in their prey selection whereas we found no effect of snow depth, time during winter, or other predator-related factors on the wolves' choice to kill moose or roe deer. Moose population density was only weakly related to intra-territorial prey selection. Our results show that the functional response of wolves on moose, the species hitherto considered as the main prey, was strongly dependent on the density of a smaller, alternative, ungulate prey. The impact of wolf predation on the prey species community is therefore likely to change with the composition of the multi-prey species community along with the geographical expansion of the wolf population.

Fear on the move: predator hunting mode predicts variation in prey mortality and plasticity in prey spatial response.

Science.gov (United States)

Miller, Jennifer R B; Ament, Judith M; Schmitz, Oswald J

2014-01-01

Ecologists have long searched for a framework of a priori species traits to help predict predator-prey interactions in food webs. Empirical evidence has shown that predator hunting mode and predator and prey habitat domain are useful traits for explaining predator-prey interactions. Yet, individual experiments have yet to replicate predator hunting mode, calling into question whether predator impacts can be attributed to hunting mode or merely species identity. We tested the effects of spider predators with sit-and-wait, sit-and-pursue and active hunting modes on grasshopper habitat domain, activity and mortality in a grassland system. We replicated hunting mode by testing two spider predator species of each hunting mode on the same grasshopper prey species. We observed grasshoppers with and without each spider species in behavioural cages and measured their mortality rates, movements and habitat domains. We likewise measured the movements and habitat domains of spiders to characterize hunting modes. We found that predator hunting mode explained grasshopper mortality and spider and grasshopper movement activity and habitat domain size. Sit-and-wait spider predators covered small distances over a narrow domain space and killed fewer grasshoppers than sit-and-pursue and active predators, which ranged farther distances across broader domains and killed more grasshoppers, respectively. Prey adjusted their activity levels and horizontal habitat domains in response to predator presence and hunting mode: sedentary sit-and-wait predators with narrow domains caused grasshoppers to reduce activity in the same-sized domain space; more mobile sit-and-pursue predators with broader domains caused prey to reduce their activity within a contracted horizontal (but not vertical) domain space; and highly mobile active spiders led grasshoppers to increase their activity across the same domain area. All predators impacted prey activity, and sit-and-pursue predators generated strong

Prey Selection of Scandinavian Wolves: Single Large or Several Small?

Directory of Open Access Journals (Sweden)

Håkan Sand

Full Text Available Research on large predator-prey interactions are often limited to the predators' primary prey, with the potential for prey switching in systems with multiple ungulate species rarely investigated. We evaluated wolf (Canis lupus prey selection at two different spatial scales, i.e., inter- and intra-territorial, using data from 409 ungulate wolf-kills in an expanding wolf population in Scandinavia. This expansion includes a change from a one-prey into a two-prey system with variable densities of one large-sized ungulate; moose (Alces alces and one small-sized ungulate; roe deer (Capreolus capreolus. Among wolf territories, the proportion of roe deer in wolf kills was related to both pack size and roe deer density, but not to moose density. Pairs of wolves killed a higher proportion of roe deer than did packs, and wolves switched to kill more roe deer as their density increased above a 1:1 ratio in relation to the availability of the two species. At the intra-territorial level, wolves again responded to changes in roe deer density in their prey selection whereas we found no effect of snow depth, time during winter, or other predator-related factors on the wolves' choice to kill moose or roe deer. Moose population density was only weakly related to intra-territorial prey selection. Our results show that the functional response of wolves on moose, the species hitherto considered as the main prey, was strongly dependent on the density of a smaller, alternative, ungulate prey. The impact of wolf predation on the prey species community is therefore likely to change with the composition of the multi-prey species community along with the geographical expansion of the wolf population.

Prey Selection of Scandinavian Wolves: Single Large or Several Small?

Science.gov (United States)

Eklund, Ann; Zimmermann, Barbara; Wikenros, Camilla; Wabakken, Petter

2016-01-01

Research on large predator-prey interactions are often limited to the predators’ primary prey, with the potential for prey switching in systems with multiple ungulate species rarely investigated. We evaluated wolf (Canis lupus) prey selection at two different spatial scales, i.e., inter- and intra-territorial, using data from 409 ungulate wolf-kills in an expanding wolf population in Scandinavia. This expansion includes a change from a one-prey into a two-prey system with variable densities of one large-sized ungulate; moose (Alces alces) and one small-sized ungulate; roe deer (Capreolus capreolus). Among wolf territories, the proportion of roe deer in wolf kills was related to both pack size and roe deer density, but not to moose density. Pairs of wolves killed a higher proportion of roe deer than did packs, and wolves switched to kill more roe deer as their density increased above a 1:1 ratio in relation to the availability of the two species. At the intra-territorial level, wolves again responded to changes in roe deer density in their prey selection whereas we found no effect of snow depth, time during winter, or other predator-related factors on the wolves’ choice to kill moose or roe deer. Moose population density was only weakly related to intra-territorial prey selection. Our results show that the functional response of wolves on moose, the species hitherto considered as the main prey, was strongly dependent on the density of a smaller, alternative, ungulate prey. The impact of wolf predation on the prey species community is therefore likely to change with the composition of the multi-prey species community along with the geographical expansion of the wolf population. PMID:28030549

Predator cannibalism can intensify negative impacts on heterospecific prey.

Science.gov (United States)

Takatsu, Kunio; Kishida, Osamu

2015-07-01

Although natural populations consist of individuals with different traits, and the degree of phenotypic variation varies among populations, the impact of phenotypic variation on ecological interactions has received little attention, because traditional approaches to community ecology assume homogeneity of individuals within a population. Stage structure, which is a common way of generating size and developmental variation within predator populations, can drive cannibalistic interactions, which can affect the strength of predatory effects on the predator's heterospecific prey. Studies have shown that predator cannibalism weakens predatory effects on heterospecific prey by reducing the size of the predator population and by inducing less feeding activity of noncannibal predators. We predict, however, that predator cannibalism, by promoting rapid growth of the cannibals, can also intensify predation pressure on heterospecific prey, because large predators have large resource requirements and may utilize a wider variety of prey species. To test this hypothesis, we conducted an experiment in which we created carnivorous salamander (Hynobius retardatus) populations with different stage structures by manipulating the salamander's hatch timing (i.e., populations with large or small variation in the timing of hatching), and explored the resultant impacts on the abundance, behavior, morphology, and life history of the salamander's large heterospecific prey, Rana pirica frog tadpoles. Cannibalism was rare in salamander populations having small hatch-timing variation, but was frequent in those having large hatch-timing variation. Thus, giant salamander cannibals occurred only in the latter. We clearly showed that salamander giants exerted strong predation pressure on frog tadpoles, which induced large behavioral and morphological defenses in the tadpoles and caused them to metamorphose late at large size. Hence, predator cannibalism arising from large variation in the timing

Zooplankton predators and prey: body size and stable isotope to investigate the pelagic food web in a deep lake (Lake Iseo, Northern Italy

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Barbara Leoni

2016-09-01

Full Text Available Seasonal changes in trophic position and food sources of deep subalpine lake (Lake Iseo, Northern Italy zooplankton taxa were investigated during the year 2011. Furthermore, it's combined carbon and nitrogen Stable Isotope Analysis (SIA with size-specific analyses of both, the major predatory cladoceran (Leptodora kindtii, Focke and two potential preys (Daphnia longispina complex and Eubosmina longicornis. SIA studies have been extremely useful to track the energy flow through complex trophic network, however, if it is applied to analyze relation between two/few species may lead to misleading interpretations. In fact, integrating size-specificity allowed for understanding why L. kindtii nitrogen isotopic fingerprint fully overlapped with Daphnia, in spring. By investigating changes in L. kindtii's feeding basket, we found that in spring, L. kindtii mainly relied upon E. longicornis as prey, Daphnia being of too large body size for being captured by L. kindtii. Among preys encountered directly in front by a free-swimming Leptodora, only those able to fit into basket opening can be captured. As basket diameter increases with animal body length, size selection of prey depends on L. kindtii body length. As in other deep, subalpine lakes, E. longicornis was less 15N-enriched than Daphnia, most likely because of exploiting nitrogen fixing, cyanobacteria colonies, commonly detected in Lake Iseo with the onset of thermal stratification. Cyclopoid adults were at the top of zooplankton food chain and they could potentially be feeding on Daphnia. They, however, likely fed in a different habitat (>20 m deep water, as suggested by a rather than negligible carbon fractionation. The results overall suggest that size-specificity is crucial for addressing space and time changes in trophic links between organisms composing the two hierarchical levels within open water zooplankton community. 

Prey interception drives web invasion and spider size determines successful web takeover in nocturnal orb-web spiders.

Science.gov (United States)

Gan, Wenjin; Liu, Shengjie; Yang, Xiaodong; Li, Daiqin; Lei, Chaoliang

2015-09-24

A striking feature of web-building spiders is the use of silk to make webs, mainly for prey capture. However, building a web is energetically expensive and increases the risk of predation. To reduce such costs and still have access to abundant prey, some web-building spiders have evolved web invasion behaviour. In general, no consistent patterns of web invasion have emerged and the factors determining web invasion remain largely unexplored. Here we report web invasion among conspecifics in seven nocturnal species of orb-web spiders, and examined the factors determining the probability of webs that could be invaded and taken over by conspecifics. About 36% of webs were invaded by conspecifics, and 25% of invaded webs were taken over by the invaders. A web that was built higher and intercepted more prey was more likely to be invaded. Once a web was invaded, the smaller the size of the resident spider, the more likely its web would be taken over by the invader. This study suggests that web invasion, as a possible way of reducing costs, may be widespread in nocturnal orb-web spiders. © 2015. Published by The Company of Biologists Ltd.

Prey interception drives web invasion and spider size determines successful web takeover in nocturnal orb-web spiders

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Wenjin Gan

2015-10-01

Full Text Available A striking feature of web-building spiders is the use of silk to make webs, mainly for prey capture. However, building a web is energetically expensive and increases the risk of predation. To reduce such costs and still have access to abundant prey, some web-building spiders have evolved web invasion behaviour. In general, no consistent patterns of web invasion have emerged and the factors determining web invasion remain largely unexplored. Here we report web invasion among conspecifics in seven nocturnal species of orb-web spiders, and examined the factors determining the probability of webs that could be invaded and taken over by conspecifics. About 36% of webs were invaded by conspecifics, and 25% of invaded webs were taken over by the invaders. A web that was built higher and intercepted more prey was more likely to be invaded. Once a web was invaded, the smaller the size of the resident spider, the more likely its web would be taken over by the invader. This study suggests that web invasion, as a possible way of reducing costs, may be widespread in nocturnal orb-web spiders.

Population and prey of the Bengal Tiger Panthera tigris tigris (Linnaeus, 1758 (Carnivora: Felidae in the Sundarbans, Bangladesh

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M.M.H. Khan

2012-02-01

Full Text Available The results from intensive small scale surveys are often difficult to extrapolate to wider spatial scales, yet an understanding at such scales is critical for assessing the minimum densities and populations of rare and wide ranging species. In this paper, the minimum size of population and minimum density estimates of Bengal Tigers Panthera tigris tigris and its prey were conducted from 2005 to 2007 using camera traps for 90 days and using distance sampling surveys for over 200 days, respectively. The results were extrapolated from the core study area in Katka-Kochikhali, southeastern Sundarbans, to five additional sites using indices of abundance. With the use of 10 camera-traps at 15 trap-points, field data provided a total of 829 photos, including seven photos of five individual tigers. A total of 5.0 (SE = 0.98 tigers (adults and sub-adults are thus estimated in the core area with an estimated density of 4.8 tigers/100km2. Distance sampling surveys conducted on large mammalian prey species obtained an overall density estimate of 27.9 individuals/km2 and a biomass density of 1,037kg/km2. Indices of abundance were obtained by using tiger track sighting rates (number of tracks/km of riverbank and the sighting rates of the prey species (number of prey/km of riverbank in the core area and in five additional sites across the region. The densities of tiger tracks and sighting rates of prey were strongly correlated suggesting a wide scale relationship between predator and prey in the region. By combining the estimates of absolute density with indices of abundance, an average of 3.7 tigers/100km2 across the region is estimated, which given an area of 5,770km2, predicts a minimum of approximately 200 tigers in the Bangladesh Sundarbans.

Are owl pellets good estimators of prey abundance?

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Analia Andrade

2016-07-01

Full Text Available Some ecologists have been skeptics about the use of owl pellets to estimate small mammal’s fauna. This is due to the assumptions required by this method: (a that owls hunt at random, and (b that pellets represent a random sample from the environment. We performed statistical analysis to test these assumptions and to assess the effectiveness of Barn owl pellets as a useful estimator of field abundances of its preys. We used samples collected in the arid Extra-Andean Patagonia along an altitudinal environmental gradient from lower Monte ecoregion to upper Patagonian steppe ecoregion, with a mid-elevation ecotone. To test if owls hunt at random, we estimated expected pellet frequency by creating a distribution of random pellets, which we compared with data using a simulated chi-square. To test if pellets represent a random sample from the environment, differences between ecoregions were evaluated by PERMANOVAs with Bray–Curtis dissimilarities. We did not find evidence that owls foraged non-randomly. Therefore, we can assume that the proportions of the small mammal’s species in the diet are representative of the proportions of the species in their communities. Only Monte is different from other ecoregions. The ecotone samples are grouped with those of Patagonian steppes. There are no real differences between localities in the small mammal’s abundances in each of these ecoregions and/or Barn owl pellets cannot detect patterns at a smaller spatial scale. Therefore, we have no evidence to invalidate the use of owl pellets at an ecoregional scale.

Optimal intermittent search strategies: smelling the prey

International Nuclear Information System (INIS)

Revelli, J A; Wio, H S; Rojo, F; Budde, C E

2010-01-01

We study the kinetics of the search of a single fixed target by a searcher/walker that performs an intermittent random walk, characterized by different states of motion. In addition, we assume that the walker has the ability to detect the scent left by the prey/target in its surroundings. Our results, in agreement with intuition, indicate that the prey's survival probability could be strongly reduced (increased) if the predator is attracted (or repelled) by the trace left by the prey. We have also found that, for a positive trace (the predator is guided towards the prey), increasing the inhomogeneity's size reduces the prey's survival probability, while the optimal value of α (the parameter that regulates intermittency) ceases to exist. The agreement between theory and numerical simulations is excellent.

Optimal intermittent search strategies: smelling the prey

Energy Technology Data Exchange (ETDEWEB)

Revelli, J A; Wio, H S [Instituto de Fisica de Cantabria, Universidad de Cantabria and CSIC, E-39005 Santander (Spain); Rojo, F; Budde, C E [Fa.M.A.F., Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina)

2010-05-14

We study the kinetics of the search of a single fixed target by a searcher/walker that performs an intermittent random walk, characterized by different states of motion. In addition, we assume that the walker has the ability to detect the scent left by the prey/target in its surroundings. Our results, in agreement with intuition, indicate that the prey's survival probability could be strongly reduced (increased) if the predator is attracted (or repelled) by the trace left by the prey. We have also found that, for a positive trace (the predator is guided towards the prey), increasing the inhomogeneity's size reduces the prey's survival probability, while the optimal value of {alpha} (the parameter that regulates intermittency) ceases to exist. The agreement between theory and numerical simulations is excellent.

Influence of prey dispersion on territory and group size of African lions: a test of the resource dispersion hypothesis.

Science.gov (United States)

Valeix, Marion; Loveridge, Andrew J; MacDonald, David W

2012-11-01

Empirical tests of the resource dispersion hypothesis (RDH), a theory to explain group living based on resource heterogeneity, have been complicated by the fact that resource patch dispersion and richness have proved difficult to define and measure in natural systems. Here, we studied the ecology of African lions Panthera leo in Hwange National Park, Zimbabwe, where waterholes are prey hotspots, and where dispersion of water sources and abundance of prey at these water sources are quantifiable. We combined a 10-year data set from GPS-collared lions for which information of group composition was available concurrently with data for herbivore abundance at waterholes. The distance between two neighboring waterholes was a strong determinant of lion home range size, which provides strong support for the RDH prediction that territory size increases as resource patches are more dispersed in the landscape. The mean number of herbivore herds using a waterhole, a good proxy of patch richness, determined the maximum lion group biomass an area can support. This finding suggests that patch richness sets a maximum ceiling on lion group size. This study demonstrates that landscape ecology is a major driver of ranging behavior and suggests that aspects of resource dispersion limit group sizes.

Functional responses of human hunters to their prey - why harvest statistics may not always reflect changes in prey population abundance

DEFF Research Database (Denmark)

Kahlert, Johnny Abildgaard; Fox, Anthony David; Heldbjerg, Henning

pigeon Columba palumbus, coot Fulica atra, grey partridge Perdix perdix, roe deer Capreolus capreolus and brown hare Lepus europaeus in Denmark. If we consider hunting a form of predator-prey interaction, the annual kill can be viewed as a predator functional response to prey population size. Convergence...

Prey detection and prey capture in copepod nauplii.

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Eleonora Bruno

Full Text Available Copepod nauplii are either ambush feeders that feed on motile prey or they produce a feeding current that entrains prey cells. It is unclear how ambush and feeding-current feeding nauplii perceive and capture prey. Attack jumps in ambush feeding nauplii should not be feasible at low Reynolds numbers due to the thick viscous boundary layer surrounding the attacking nauplius. We use high-speed video to describe the detection and capture of phytoplankton prey by the nauplii of two ambush feeding species (Acartia tonsa and Oithona davisae and by the nauplii of one feeding-current feeding species (Temora longicornis. We demonstrate that the ambush feeders both detect motile prey remotely. Prey detection elicits an attack jump, but the jump is not directly towards the prey, such as has been described for adult copepods. Rather, the nauplius jumps past the prey and sets up an intermittent feeding current that pulls in the prey from behind towards the mouth. The feeding-current feeding nauplius detects prey arriving in the feeding current but only when the prey is intercepted by the setae on the feeding appendages. This elicits an altered motion pattern of the feeding appendages that draws in the prey.

Prey detection and prey capture in copepod nauplii

DEFF Research Database (Denmark)

Bruno, Eleonora; Borg, Marc Andersen; Kiørboe, Thomas

2012-01-01

Copepod nauplii are either ambush feeders that feed on motile prey or they produce a feeding current that entrains prey cells. It is unclear how ambush and feeding-current feeding nauplii perceive and capture prey. Attack jumps in ambush feeding nauplii should not be feasible at low Reynolds...... (Temora longicornis). We demonstrate that the ambush feeders both detect motile prey remotely. Prey detection elicits an attack jump, but the jump is not directly towards the prey, such as has been described for adult copepods. Rather, the nauplius jumps past the prey and sets up an intermittent feeding...

Predator size and the suitability of a common prey.

Science.gov (United States)

Erickson, Kristin S; Morse, D H

1997-02-01

 Although a predator's mass should influence the suitability of its prey, this subject has received little direct attention. We studied the capture and processing of an abundant syrphid fly Toxomerus marginatus (c. 4 mg) by 0.6- to 40-mg juvenile crab spiders Misumena vatia (Thomisidae) to determine how profitability, relative profitability (profitability/predator mass), overall gain in mass, and relative gain in mass differed with predator mass, and whether foraging changed concurrently. In multi-prey experiments, the smallest successful spiders (0.6-3.0 mg) extracted less mass from flies, and did so more slowly, than large spiders. This gain was proportionately similar to that of 10- to 40-mg spiders with access to many Toxomerus. However, many small spiders failed to capture flies. When we gave spiders only a single Toxomerus, the smallest ones again extracted mass more slowly than the large ones and increased in mass less than the large ones, but increased in mass proportionately more than large ones. Relative gain in mass from a single prey decreased with increasing spider mass. Spiders larger than 10 mg all extracted similar amounts of mass from a single Toxomerus at similar rates, but varied in time spent between captures. Thus, Toxomerus changes with spider mass from a large, hard-to-capture bonanza to a small, easy-to-capture item of low per capita value. However, Toxomerus is common enough that large spiders can capture it en masse, thereby compensating for its decline in per capita value.

Echolocating bats cry out loud to detect their prey.

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Annemarie Surlykke

Full Text Available Echolocating bats have successfully exploited a broad range of habitats and prey. Much research has demonstrated how time-frequency structure of echolocation calls of different species is adapted to acoustic constraints of habitats and foraging behaviors. However, the intensity of bat calls has been largely neglected although intensity is a key factor determining echolocation range and interactions with other bats and prey. Differences in detection range, in turn, are thought to constitute a mechanism promoting resource partitioning among bats, which might be particularly important for the species-rich bat assemblages in the tropics. Here we present data on emitted intensities for 11 species from 5 families of insectivorous bats from Panamá hunting in open or background cluttered space or over water. We recorded all bats in their natural habitat in the field using a multi-microphone array coupled with photographic methods to assess the bats' position in space to estimate emitted call intensities. All species emitted intense search signals. Output intensity was reduced when closing in on background by 4-7 dB per halving of distance. Source levels of open space and edge space foragers (Emballonuridae, Mormoopidae, Molossidae, and Vespertilionidae ranged between 122-134 dB SPL. The two Noctilionidae species hunting over water emitted the loudest signals recorded so far for any bat with average source levels of ca. 137 dB SPL and maximum levels above 140 dB SPL. In spite of this ten-fold variation in emitted intensity, estimates indicated, surprisingly, that detection distances for prey varied far less; bats emitting the highest intensities also emitted the highest frequencies, which are severely attenuated in air. Thus, our results suggest that bats within a local assemblage compensate for frequency dependent attenuation by adjusting the emitted intensity to achieve comparable detection distances for prey across species. We conclude that for bats

Mechanical work as a determinant of prey-handling behavior in the tokay gecko (Gekko gecko).

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Andrews, C; Bertram, J E

1997-01-01

In this study an in vitro analysis of the force and mechanical work required to bite prey items of different size and physical character is combined with an in vivo analysis of prey-handling behavior in the tokay gecko (Gekko gecko). The force required to bite and the work of biting increase with prey size, but the rate of increase is prey specific, with crickets (Acheta domestica) requiring substantially more force and work per bite than larvae (Galleria mellonella and Manduca sexta) for all but the smallest prey. Prey-handling behavior is also prey specific. Geckos exert more bites per feeding event on small crickets than on small insect larvae, but the number of bites increases faster with prey mass for larvae than for crickets. Combination of the in vitro mechanical measurements with the in vivo behavior analysis allows the calculation of total mechanical work per feeding event and indicates that total work increases with prey size but that the difference between prey types is far less than predicted from the differences in structural properties of the prey. This occurs because the number of bites and work per bite relationships tend to cancel the differences in the total work necessary to process each prey type. Thus, when considering the effect of prey size, a 13-fold greater rate of increase in bite force and an 18-fold greater rate of increase of work per bit for crickets over larvae was partially compensated for by a threefold increase in the number of bites used on larvae relative to crickets. These results can be interpreted in two ways. The effect of mechanical work in feeding behavior suggests that the energetics of jaw adductor musculature could play a greater role in governing the feeding behavior of this lizard than has previously been expected. Alternatively, the scaling of work in feeding over a range of prey sizes suggests distinct differences in the geometric features of the prey that determine how they are processed.

Putting prey and predator into the CO2 equation--qualitative and quantitative effects of ocean acidification on predator-prey interactions.

Science.gov (United States)

Ferrari, Maud C O; McCormick, Mark I; Munday, Philip L; Meekan, Mark G; Dixson, Danielle L; Lonnstedt, Öona; Chivers, Douglas P

2011-11-01

Little is known about the impact of ocean acidification on predator-prey dynamics. Herein, we examined the effect of carbon dioxide (CO(2)) on both prey and predator by letting one predatory reef fish interact for 24 h with eight small or large juvenile damselfishes from four congeneric species. Both prey and predator were exposed to control or elevated levels of CO(2). Mortality rate and predator selectivity were compared across CO(2) treatments, prey size and species. Small juveniles of all species sustained greater mortality at high CO(2) levels, while large recruits were not affected. For large prey, the pattern of prey selectivity by predators was reversed under elevated CO(2). Our results demonstrate both quantitative and qualitative consumptive effects of CO(2) on small and larger damselfish recruits respectively, resulting from CO(2)-induced behavioural changes likely mediated by impaired neurological function. This study highlights the complexity of predicting the effects of climate change on coral reef ecosystems. © 2011 Blackwell Publishing Ltd/CNRS.

Predator-induced flow disturbances alert prey, from the onset of an attack

Science.gov (United States)

Casas, Jérôme; Steinmann, Thomas

2014-01-01

Many prey species, from soil arthropods to fish, perceive the approach of predators, allowing them to escape just in time. Thus, prey capture is as important to predators as prey finding. We extend an existing framework for understanding the conjoint trajectories of predator and prey after encounters, by estimating the ratio of predator attack and prey danger perception distances, and apply it to wolf spiders attacking wood crickets. Disturbances to air flow upstream from running spiders, which are sensed by crickets, were assessed by computational fluid dynamics with the finite-elements method for a much simplified spider model: body size, speed and ground effect were all required to obtain a faithful representation of the aerodynamic signature of the spider, with the legs making only a minor contribution. The relationship between attack speed and the maximal distance at which the cricket can perceive the danger is parabolic; it splits the space defined by these two variables into regions differing in their values for this ratio. For this biological interaction, the ratio is no greater than one, implying immediate perception of the danger, from the onset of attack. Particular attention should be paid to the ecomechanical aspects of interactions with such small ratio, because of the high degree of bidirectional coupling of the behaviour of the two protagonists. This conclusion applies to several other predator–prey systems with sensory ecologies based on flow sensing, in air and water. PMID:25030986

SRKW summer prey - Prey species and stock specific consumption estimates for SRKW in their summer range

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Southern Resident Killer Whales (SRKW) are listed as a Distinct Population Segment under the Endangered Species Act. Data concerning their prey species and stock...

The effects of meal size, body size and temperature on gastric evacuation in pikeperch

DEFF Research Database (Denmark)

Koed, Anders

2001-01-01

Prey size had no effect on the gastric evacuation rate of pikeperch Stizostedion lucioperca. The gastric evacuation was adequately described applying an exponent of 0.5 in the power model. Applying length instead of weight of pikeperch in the gastric evacuation model resulted in a change of estim...

Effects of insecticide exposure on movement and population size estimates of predatory ground beetles (Coleoptera: Carabidae).

Science.gov (United States)

Prasifka, Jarrad R; Lopez, Miriam D; Hellmich, Richard L; Prasifka, Patricia L

2008-01-01

Estimates of arthropod population size may paradoxically increase following insecticide applications. Research with ground beetles (Coleoptera: Carabidae) suggests that such unusual results reflect increased arthropod movement and capture in traps rather than real changes in population size. However, it is unclear whether direct (hyperactivity) or indirect (prey-mediated) mechanisms produce increased movement. Video tracking of Scarites quadriceps Chaudior indicated that brief exposure to lambda-cyhalothrin or tefluthrin increased total distance moved, maximum velocity and percentage of time moving. Repeated measurements on individual beetles indicated that movement decreased 240 min after initial lambda-cyhalothrin exposure, but increased again following a second exposure, suggesting hyperactivity could lead to increased trap captures in the field. Two field experiments in which ground beetles were collected after lambda-cyhalothrin or permethrin application attempted to detect increases in population size estimates as a result of hyperactivity. Field trials used mark-release-recapture methods in small plots and natural carabid populations in larger plots, but found no significant short-term (<6 day) increases in beetle trap captures. The disagreement between laboratory and field results suggests mechanisms other than hyperactivity may better explain unusual changes in population size estimates. When traps are used as a primary sampling tool, unexpected population-level effects should be interpreted carefully or with additional data less influenced by arthropod activity.

The diets of Hispaniolan colubrid snakes : I. Introduction and prey genera.

Science.gov (United States)

Henderson, Robert W

1984-05-01

Approximately 1590 Hispaniolan colubrid snakes representing six genera and eight species were examined for prey remains (Alsophis cantherigerus, Antillophis parvifrons, Darlingtonia haetiana, Hypsirhynchus ferox, Ialtris dorsalis, Uromacer catesbyi, U. frenatus, and U. oxyrhynchus). The snakes were collected at many localities over a span of 80 years.Of 426 prey items, 77.9% were lizards (of which 69.6% were anoles), 19% frogs, 2.6% birds and mammals, and 0.5% other snakes. Darlingtonia was the only snake that did not exploit lizards; it fed exclusively on Eleutherodactylus frogs, including egg clutches. Disregarding Darlingtonia, there is no size class of Hispaniolan colubrids between 20-90 cm SVL that does not prey primarily on Anolis. Certain prey genera are added to, or deleted from, diets depending on snake size, but the data suggest that snake SVL alone does little to dictate what prey genera (or groups) are eaten. Shannon-Wiener values (H') indicate that Darlingtonia has the narrowest trophic niche, while Alsophis and Ialtris have the widest. Values of H' are not correlated with snake SVL, but highly significant (Peats diurnally active (anoles) and diurnally quiescent (hylid frogs) prey with almost equal frequency.Within Maglio's cantherigerus species assemblage, in which an Alsophis cantherigerus-like snake was ancestral to the other species, and in which longsnouted Uromacer are the most morphologically derived, there is an obvious trend toward trophic specialization on Hispaniola. The West Indies have provided an ideal natural laboratory for the investigation of many aspects of vertebrate ecology, and an arena in which to test theories of island biogeography. The most extensively studied West Indian vertebrates have been the lizards of the iguanid genus Anolis. Conversely, the ecology of West Indian snakes has been largely ignored. This is surprising in light of the fact that much has been written about Anolis predation, but little has been written about

Turbulence-enhanced prey encounter rates in larval fish : Effects of spatial scale, larval behaviour and size

DEFF Research Database (Denmark)

Kiørboe, Thomas; MacKenzie, Brian

1995-01-01

Turbulent water motion has several effects on the feeding ecology of larval fish and other planktivorous predators. In this paper, we consider the appropriate spatial scales for estimating relative velocities between larval fish predators and their prey, and the effect that different choices of s...... in the range in which turbulent intensity has an overall positive effect on larval fish ingestion rate probability. However, experimental data to test the model predictions are lacking. We suggest that the model inputs require further empirical study....

Prey selection by the Barn Owl Tyto alba (Scopoli, 1769 in captivity

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V. Vanitha

2009-07-01

Full Text Available We investigated prey selection of the Barn Owl Tyto alba under captive conditions where birds were allowed to choose among individuals of varying size from four field rodent species: Bandicota bengalensis, Millardia meltada, Tatera indica and Mus booduga. Owls showed little species preference and a tendency to favour the medium weight class in all prey species except M. booduga. Preference for body parts consumed varied according to prey size, ranging from the head alone in the large weight class to the entire body in the small weight class. Biochemical measurements showed that protein, carbohydrate and lipid levels were higher respectively in the brain, liver and muscles of all three species and weight classes studied. The preference for medium weight prey despite a lower nutrient content compared to large weight prey is attributed to a greater ease of capture.

Production of live prey for marine fish larvae

OpenAIRE

Kraul, S

1989-01-01

Tropical marine fish larvae vary in their requirements for live planktonic food. Selection of live prey species for culture depends on larval size and larval tolerance of water quality. This report describes some of the cultured prey species, and their uses and limits as effective food for fish larvae. Methods are presented for the culture of phytoplankton, rotifers, copepods, and other live feeds.

Nephila clavipes spiders (Araneae: Nephilidae) keep track of captured prey counts: testing for a sense of numerosity in an orb-weaver.

Science.gov (United States)

Rodríguez, Rafael L; Briceño, R D; Briceño-Aguilar, Eduardo; Höbel, Gerlinde

2015-01-01

Nephila clavipes golden orb-web spiders accumulate prey larders on their webs and search for them if they are removed from their web. Spiders that lose larger larders (i.e., spiders that lose larders consisting of more prey items) search for longer intervals, indicating that the spiders form memories of the size of the prey larders they have accumulated, and use those memories to regulate recovery efforts when the larders are pilfered. Here, we ask whether the spiders represent prey counts (i.e., numerosity) or a continuous integration of prey quantity (mass) in their memories. We manipulated larder sizes in treatments that varied in either prey size or prey numbers but were equivalent in total prey quantity (mass). We then removed the larders to elicit searching and used the spiders' searching behavior as an assay of their representations in memory. Searching increased with prey quantity (larder size) and did so more steeply with higher prey counts than with single prey of larger sizes. Thus, Nephila spiders seem to track prey quantity in two ways, but to attend more to prey numerosity. We discuss alternatives for continuous accumulator mechanisms that remain to be tested against the numerosity hypothesis, and the evolutionary and adaptive significance of evidence suggestive of numerosity in a sit-and-wait invertebrate predator.

Disturbed flow in an aquatic environment may create a sensory refuge for aggregated prey

Directory of Open Access Journals (Sweden)

Asa Johannesen

2017-03-01

Full Text Available Predators use olfactory cues moved within water and air to locate prey. Because prey aggregations may produce more cue and be easier to detect, predation could limit aggregation size. However, disturbance in the flow may diminish the reliability of odour as a prey cue, impeding predator foraging success and efficiency. We explore how different cue concentrations (as a proxy for prey group size affect risk to prey by fish predators in disturbed (more turbulent or mixed and non-disturbed (less mixed flowing water. We find that increasing odour cue concentration increases predation risk and disturbing the flow reduces predation risk. At high cue concentration fish were able to locate the cue source in both disturbed and non-disturbed flow, but at medium concentrations, predators only located the cue source more often than expected by chance in non-disturbed flow. This suggests that objects disturbing flow provide a sensory refuge allowing prey to form larger groups, but that group sizes may be limited by level of disturbance to the flow.

Wild North Island Robins (Petroica longipes respond to Prey Animacy

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Alexis Garland

2014-08-01

Full Text Available North Island robins of New Zealand are a food hoarding species, which is unique in that they almost exclusively cache highly perishable hunted insects for later retrieval. In order to do so, they either kill and dismember or paralyze their prey for caching, depending on the prey size and kind. The present study comprises two experiments, using a Violation of Expectancy (VoE paradigm to examine variation in search behavior response to different prey conditions. The first experiment presents three different types of prey (mealworms, earthworms and locusts in expected (present and unexpected (absent conditions. The second experiment presents prey in varying states of animacy (alive and whole, dead and whole, dead and halved, and an inanimate stick and reveals prey in expected (same state or unexpected (differing state conditions. While robins did not respond with differential search times to different types of unexpectedly missing prey in Experiment 1, in Experiment 2 robins searched longer in conditions where prey was found in a differing state of animacy than initially shown. Robins also searched longer for prey when immediately consuming retrieved prey than when caching retrieved prey. Results indicate that North Island robins may be sensitive to prey animacy upon storage and retrieval of insect prey; such information could play a role in storage, pilfering and retrieval strategies of such a perishable food source.

Modelling prey consumption and switching by UK grey seals

DEFF Research Database (Denmark)

Smout, Sophie; Rindorf, Anna; Hammond, Philip S.

2014-01-01

Grey seals (Halichoerus grypus) are adaptable generalist predatorswhose diet includes commercial fish species such as cod. Consumption by the seals may reduce the size of some fish stocks or have an adverse effect on stock recovery programmes, especially because predation may trap sparse prey...... populations in a “predator pit”. To assess the likely impact of such effects, it is important to know how consumption and consequent predation mortality respond to the changing availability of prey.Wepresent a model of grey seal consumption as a function of the availability of multiple prey types [a Multi...

A comparison of food habits and prey preference of Amur tiger (Panthera tigris altaica) at three sites in the Russian Far East.

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Kerley, Linda L; Mukhacheva, Anna S; Matyukhina, Dina S; Salmanova, Elena; Salkina, Galina P; Miquelle, Dale G

2015-07-01

Prey availability is one of the principal drivers of tiger distribution and abundance. Therefore, formulating effective conservation strategies requires a clear understanding of tiger diet. We used scat analysis in combination with data on the abundance of several prey species to estimate Amur tiger diet and preference at 3 sites in the Russian Far East. We also examined the effect of pseudoreplication on estimates of tiger diet. We collected 770 scats across the 3 sites. Similar to previous studies, we found that tigers primarily preyed on medium to large ungulates, with wild boar, roe, sika and red deer collectively comprising 86.7% of total biomass consumed on average. According to Jacobs' index, tigers preferred wild boar, and avoided sika deer. Variation in preference indices derived from these scat analyses compared to indices derived from kill data appear to be due to adjustments in biomass intake when sex-age of a killed individual is known: a component missing from scat data. Pseudoreplication (multiple samples collected from a single kill site) also skewed results derived from scat analyses. Scat analysis still appears useful in providing insight into the diets of carnivores when the full spectrum of prey species needs to be identified, or when sample sizes from kill data are not sufficient. When sample sizes of kill data are large (as is now possible with GPS-collared animals), kill data adjusted by sex-age categories probably provides the most accurate estimates of prey biomass composition. Our results provide further confirmation of the centrality of medium ungulates, in particular wild boar, to Amur tiger diet, and suggest that the protection of this group of species is critical to Amur tiger conservation. © 2015 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd.

Comparing prey composition and prey size delivered to nestlings by great tits, Parus major, and blue tits, Cyanistes caeruleus, in a Mediterranean sclerophyllous mixed forest

International Nuclear Information System (INIS)

Navalpotro, H.; Pagani-Nuñez, E.; Hernandez-Gomez, S.; Senar, J.C.

2016-01-01

Resource partitioning is a central issue in ecology because it can establish to which point similar species can coexist in the same habitat. Great tits and blue tits have been classical model species in studies of trophic competence. However, most studies on the topic have been conducted at localities where caterpillars are by far the most relevant prey brought to the nestlings. In Mediterranean mixed forests, nevertheless, the abundance of caterpillars is relatively low and it is spiders that play a key role in the diet of great tits, at least for nestlings. The aim of this paper was to study nest food provisioning to establish the degree of diet overlap of these two tit species in a Mediterranean forest. Our results showed that blue tit feeding rates were higher than those of great tits, probably to compensate for the smaller prey delivered to nestlings by blue tits. Blue tits brought more spiders than great tits, while grey tits brought larger prey and more caterpillars. This may be because larger great tits can prey upon larger prey items than blue tits. As a main result, this study supports the view of resource partitioning by great and blue tits in sclerophyllous Mediterranean forest ecosystem. (Author)

Comparing prey composition and prey size delivered to nestlings by great tits, Parus major, and blue tits, Cyanistes caeruleus, in a Mediterranean sclerophyllous mixed forest

Directory of Open Access Journals (Sweden)

Navalpotro, H.

2016-04-01

Full Text Available Resource partitioning is a central issue in ecology because it can establish to which point similar species can coexist in the same habitat. Great tits and blue tits have been classical model species in studies of trophic competence. However, most studies on the topic have been conducted at localities where caterpillars are by far the most relevant prey brought to the nestlings. In Mediterranean mixed forests, nevertheless, the abundance of caterpillars is relatively low and it is spiders that play a key role in the diet of great tits, at least for nestlings. The aim of this paper was to study nest food provisioning to establish the degree of diet overlap of these two tit species in a Mediterranean forest. Our results showed that blue tit feeding rates were higher than those of great tits, probably to compensate for the smaller prey delivered to nestlings by blue tits. Blue tits brought more spiders than great tits, while grey tits brought larger prey and more caterpillars. This may be because larger great tits can prey upon larger prey items than blue tits. As a main result, this study supports the view of resource partitioning by great and blue tits in sclerophyllous Mediterranean forest ecosystem.

Comparing prey composition and prey size delivered to nestlings by great tits, Parus major, and blue tits, Cyanistes caeruleus, in a Mediterranean sclerophyllous mixed forest

Energy Technology Data Exchange (ETDEWEB)

Navalpotro, H.; Pagani-Nuñez, E.; Hernandez-Gomez, S.; Senar, J.C.

2016-07-01

Resource partitioning is a central issue in ecology because it can establish to which point similar species can coexist in the same habitat. Great tits and blue tits have been classical model species in studies of trophic competence. However, most studies on the topic have been conducted at localities where caterpillars are by far the most relevant prey brought to the nestlings. In Mediterranean mixed forests, nevertheless, the abundance of caterpillars is relatively low and it is spiders that play a key role in the diet of great tits, at least for nestlings. The aim of this paper was to study nest food provisioning to establish the degree of diet overlap of these two tit species in a Mediterranean forest. Our results showed that blue tit feeding rates were higher than those of great tits, probably to compensate for the smaller prey delivered to nestlings by blue tits. Blue tits brought more spiders than great tits, while grey tits brought larger prey and more caterpillars. This may be because larger great tits can prey upon larger prey items than blue tits. As a main result, this study supports the view of resource partitioning by great and blue tits in sclerophyllous Mediterranean forest ecosystem. (Author)

Size-density scaling in protists and the links between consumer-resource interaction parameters.

Science.gov (United States)

DeLong, John P; Vasseur, David A

2012-11-01

Recent work indicates that the interaction between body-size-dependent demographic processes can generate macroecological patterns such as the scaling of population density with body size. In this study, we evaluate this possibility for grazing protists and also test whether demographic parameters in these models are correlated after controlling for body size. We compiled data on the body-size dependence of consumer-resource interactions and population density for heterotrophic protists grazing algae in laboratory studies. We then used nested dynamic models to predict both the height and slope of the scaling relationship between population density and body size for these protists. We also controlled for consumer size and assessed links between model parameters. Finally, we used the models and the parameter estimates to assess the individual- and population-level dependence of resource use on body-size and prey-size selection. The predicted size-density scaling for all models matched closely to the observed scaling, and the simplest model was sufficient to predict the pattern. Variation around the mean size-density scaling relationship may be generated by variation in prey productivity and area of capture, but residuals are relatively insensitive to variation in prey size selection. After controlling for body size, many consumer-resource interaction parameters were correlated, and a positive correlation between residual prey size selection and conversion efficiency neutralizes the apparent fitness advantage of taking large prey. Our results indicate that widespread community-level patterns can be explained with simple population models that apply consistently across a range of sizes. They also indicate that the parameter space governing the dynamics and the steady states in these systems is structured such that some parts of the parameter space are unlikely to represent real systems. Finally, predator-prey size ratios represent a kind of conundrum, because they are

Red fox prey demands and implications to prairie duck production

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Sargeant, A.B.

1978-01-01

Experiments were conducted during spring and summer with 33 red foxes (Vulpes vulpes) to determine prey demands, feeding characteristics, and growth rates using natural foods. Pups began eating prey the 4th week after birth. Then, prey consumption averaged 1.38 and 1.90 kg/pup/week for weeks 5-8 and 9-12 of the denning season respectively, and 2.54 kg/pup/week for the postdenning period. Feeding by adults averaged 2.25 kg/adult/week. Free water was not needed by either pups or adults. About 90 percent of the prey offered to pups on simulated natural diets was consumed, remains varied with prey availability and prey type. Prey biomass required by a typical fox family was estimated at 18.5 kg/km2 for the 12-week denning season and 2.4 kg/km2/week for the postdenning period. Because of the large prey demands, ducks could represent a small part of the foxes' diet and yet be of consequence to the productivity of particular species. An example is provided for the mallard (Anas platyrhynchos).

Evaluating prey switching in wolf-ungulate systems.

Science.gov (United States)

Garrott, Robert A; Bruggeman, Jason E; Becker, Matthew S; Kalinowski, Steven T; White, P J

2007-09-01

Wolf restoration has become a widely accepted conservation and management practice throughout North America and Europe, though the ecosystem effects of returning top carnivores remain both scientific and societal controversies. Mathematical models predicting and describing wolf-ungulate interactions are typically limited to the wolves' primary prey, with the potential for prey switching in wolf-multiple-ungulate systems only suggested or assumed by a number of investigators. We used insights gained from experiments on small taxa and field data from ongoing wolf-ungulate studies to construct a model of predator diet composition for a wolf-elk-bison system in Yellowstone National Park, Wyoming, USA. The model explicitly incorporates differential vulnerability of the ungulate prey types to predation, predator preference, differences in prey biomass, and the possibility of prey switching. Our model demonstrates wolf diet shifts with changes in relative abundance of the two prey, with the dynamics of this shift dependent on the combined influences of preference, differential vulnerability, relative abundances of prey, and whether or not switching occurs. Differences in vulnerability between elk and bison, and strong wolf preference for elk, result in an abrupt dietary shift occurring only when elk are very rare relative to bison, whereas incorporating switching initiates the dietary shift more gradually and at higher bison-elk ratios. We demonstrate how researchers can apply these equations in newly restored wolf-two-prey systems to empirically evaluate whether prey switching is occurring. Each coefficient in the model has a biological interpretation, and most can be directly estimated from empirical data collected from field studies. Given the potential for switching to dramatically influence predator-prey dynamics and the wide range of expected prey types and abundances in some systems where wolves are present and/or being restored, we suggest that this is an

A community-level evaluation of the impact of prey behavioural and ecological characteristics on predator diet composition.

Science.gov (United States)

Shultz, Susanne; Noë, Ronald; McGraw, W Scott; Dunbar, R I M

2004-04-07

Although predation avoidance is the most commonly invoked explanation for vertebrate social evolution, there is little evidence that individuals in larger groups experience lower predation rates than those in small groups. We compare the morphological and behavioural traits of mammal prey species in the Taï forest, Ivory Coast, with the diet preferences of three of their non-human predators: leopards, chimpanzees and African crowned eagles. Individual predators show marked differences in their predation rates on prey species of different body sizes, but clear patterns with prey behaviour were apparent only when differences in prey habitat use were incorporated into the analyses. Leopard predation rates are highest for terrestrial species living in smaller groups, whereas eagle predation rates are negatively correlated with group size only among arboreal prey. When prey predation rates are summed over all three predators, terrestrial species incur higher predation rates than arboreal species and, within both categories, predation rates decline with increasing prey group size and decreasing density of groups in the habitat. These results reveal that it is necessary to consider anti-predator strategies in the context of a dynamic behavioural interaction between predators and prey.

A tiger beetle’s pursuit of prey depends on distance

Science.gov (United States)

Noest, R. M.; Wang, Z. Jane

2017-04-01

Tiger beetles pursue prey by adjusting their heading according to a time-delayed proportional control law that minimizes the error angle (Haselsteiner et al 2014 J. R. Soc. Interface 11 20140216). This control law can be further interpreted in terms of mechanical actuation: to catch prey, tiger beetles exert a sideways force by biasing their tripod gait in proportion to the error angle measured half a stride earlier. The proportional gain was found to be nearly optimal in the sense that it minimizes the time to point directly toward the prey. For a time-delayed linear proportional controller, the optimal gain, k, is inversely proportional to the time delay, τ, and satisfies kτ =1/e . Here we present evidence that tiger beetles adjust their control gain during their pursuit of prey. Our analysis shows two critical distances: one corresponding to the beetle’s final approach to the prey, and the second, less expected, occurring at a distance around 10 cm for a prey size of 4.5 mm. The beetle initiates its chase using a sub-critical gain and increases the gain to the optimal value once the prey is within this critical distance. Insects use a variety of methods to detect distance, often involving different visual cues. Here we examine two such methods: one based on motion parallax and the other based on the prey’s elevation angle. We show that, in order for the motion parallax method to explain the observed data, the beetle needs to correct for the ratio of the prey’s sideways velocity relative to its own. On the other hand, the simpler method based on the elevation angle can detect both the distance and the prey’s size. Moreover we find that the transition distance corresponds to the accuracy required to distinguish small prey from large predators.

Predator-Prey Dynamics in the Mesopelagic: Odontocete Foraging Ecology and Anti-predator Behavior of Prey

Science.gov (United States)

Benoit-Bird, K. J.

2016-02-01

We explored the behavior of Risso's dolphins foraging in scattering layers off California using an integrated approach comprising echosounders deployed in a deep-diving autonomous underwater vehicle, ship based acoustics, visual observations, direct prey sampling, and animal-borne tags on deep-diving predators. We identified three distinct prey layers: a persistent layer around 425 m, a vertically migrating layer around 300 m, and a layer intermittently present near 50 m, all of which were used by individual tagged animals. Active acoustic measurements demonstrated that Risso's dolphins dove to discrete prey layers throughout the day and night with only slightly higher detection rates at night. Dolphins were detected in all three layers during the day with over half of detections in the middle layer, 20% of detections in the deepest layer, and 10% falling outside the main layers. Dolphins were found less frequently in areas where the shallow, intermittent layer was absent, suggesting that this layer, while containing the smallest prey and the lowest densities of squid, was an important component of their foraging strategy. The deepest layer was targeted equally both during the day and at night. Using acoustic data collected from the AUV, we found layers were made up of distinct, small patches of animals of similar size and taxonomy adjacent to contrasting patches. Squid made up over 70% of the patches in which dolphins were found and more than 95% of those in deep water. Squid targeted by dolphins in deep water were also relatively large, indicating significant benefit from these relatively rare, physically demanding dives. Within these patches, prey formed tighter aggregations when Risso's dolphins were present. Careful integration of a suite of traditional and novel tools is providing insight into the ecology and dynamics of predator and prey in the mesopelagic.

Sequential assessment of prey through the use of multiple sensory cues by an eavesdropping bat

Science.gov (United States)

Page, Rachel A.; Schnelle, Tanja; Kalko, Elisabeth K. V.; Bunge, Thomas; Bernal, Ximena E.

2012-06-01

Predators are often confronted with a broad diversity of potential prey. They rely on cues associated with prey quality and palatability to optimize their hunting success and to avoid consuming toxic prey. Here, we investigate a predator's ability to assess prey cues during capture, handling, and consumption when confronted with conflicting information about prey quality. We used advertisement calls of a preferred prey item (the túngara frog) to attract fringe-lipped bats, Trachops cirrhosus, then offered palatable, poisonous, and chemically manipulated anurans as prey. Advertisement calls elicited an attack response, but as bats approached, they used additional sensory cues in a sequential manner to update their information about prey size and palatability. While both palatable and poisonous small anurans were readily captured, large poisonous toads were approached but not contacted suggesting the use of echolocation for assessment of prey size at close range. Once prey was captured, bats used chemical cues to make final, post-capture decisions about whether to consume the prey. Bats dropped small, poisonous toads as well as palatable frogs coated in toad toxins either immediately or shortly after capture. Our study suggests that echolocation and chemical cues obtained at close range supplement information obtained from acoustic cues at long range. Updating information about prey quality minimizes the occurrence of costly errors and may be advantageous in tracking temporal and spatial fluctuations of prey and exploiting novel food sources. These findings emphasize the sequential, complex nature of prey assessment that may allow exploratory and flexible hunting behaviors.

A modified Leslie-Gower predator-prey interaction model and parameter identifiability

Science.gov (United States)

Tripathi, Jai Prakash; Meghwani, Suraj S.; Thakur, Manoj; Abbas, Syed

2018-01-01

In this work, bifurcation and a systematic approach for estimation of identifiable parameters of a modified Leslie-Gower predator-prey system with Crowley-Martin functional response and prey refuge is discussed. Global asymptotic stability is discussed by applying fluctuation lemma. The system undergoes into Hopf bifurcation with respect to parameters intrinsic growth rate of predators (s) and prey reserve (m). The stability of Hopf bifurcation is also discussed by calculating Lyapunov number. The sensitivity analysis of the considered model system with respect to all variables is performed which also supports our theoretical study. To estimate the unknown parameter from the data, an optimization procedure (pseudo-random search algorithm) is adopted. System responses and phase plots for estimated parameters are also compared with true noise free data. It is found that the system dynamics with true set of parametric values is similar to the estimated parametric values. Numerical simulations are presented to substantiate the analytical findings.

Feeding, prey selection and prey encounter mechanisms in the heterotrophic dinoflagellate Noctiluca scintillans

DEFF Research Database (Denmark)

Kiørboe, Thomas; Titelman, J.

1998-01-01

/or that microscale shear brings it into contact with prey. Noctiluca scintillans has a specific carbon content 1-2 orders of magnitude less than that typical for protists and, thus, an inflated volume. It also has a density slightly less than that of the ambient water and therefore ascends at high velocities...... (similar to 1 m h(- 1)). In stagnant water, clearance rates of latex spheres (5-80 mu m) increased approximately with prey particle size squared. This scaling is consistent with N.scintillans being an interception feeder. However, absolute clearance rates were substantially lower than those predicted...... higher rates than latex beads and other phytoplankters, particularly dinoflagellates. We propose that diatoms stick more efficiently than latex beads to the mucus of N.scintillans and that dinoflagellates reduce fatal contact behaviorally. We conclude that N.scintillans is an interception feeder...

Prey and mound disassembly, manipulation and transport by fire ant collectives

Science.gov (United States)

Dutta, Bahnisikha; Monaenkova, Daria; Goodisman, Michael A.; Goldman, Daniel

Fire ants inhabit subterranean nests covered by a hemispherical mound of soil permeated by narrow ( 1 body length diameter) tunnels. Fire ants can use their mound for long-term food storage [Gayahan &Tschinkel, J. Insect Sci.,2008]. Since mound tunnels are narrow, we expect that in addition to prey manipulation, mound reconfiguration could also be an important aspect of the food storage strategy. Ant colonies collected from wild were allowed to build nests in containers filled with clay soil in the laboratory. These colonies were offered diverse prey embedded with lead markers, including mealworms, crickets and shrimp. Ant-prey-soil interactions on the nest surface were recorded using overhead video and subsurface using x-ray imaging. Individual ants involved in prey storage exhibited three distinct behaviors: prey maneuvering, prey dissection and mound reconfiguration. Small prey (e.g. mealworms) were collectively carried intact into the mound through a tunnel, and then disassembled within the mound. Larger prey (e.g. shrimp) were dismantled into small pieces above the surface and carried to mound tunnels. The bodies of hard medium-sized prey (e.g. crickets) were buried after limb removal and then disassembled and moved into tunnels. Soil reconfiguration occurred in all cases.

Modelling landscape-level numerical responses of predators to prey: the case of cats and rabbits.

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Jennyffer Cruz

Full Text Available Predator-prey systems can extend over large geographical areas but empirical modelling of predator-prey dynamics has been largely limited to localised scales. This is due partly to difficulties in estimating predator and prey abundances over large areas. Collection of data at suitably large scales has been a major problem in previous studies of European rabbits (Oryctolagus cuniculus and their predators. This applies in Western Europe, where conserving rabbits and predators such as Iberian lynx (Lynx pardinus is important, and in other parts of the world where rabbits are an invasive species supporting populations of introduced, and sometimes native, predators. In pastoral regions of New Zealand, rabbits are the primary prey of feral cats (Felis catus that threaten native fauna. We estimate the seasonal numerical response of cats to fluctuations in rabbit numbers in grassland-shrubland habitat across the Otago and Mackenzie regions of the South Island of New Zealand. We use spotlight counts over 1645 km of transects to estimate rabbit and cat abundances with a novel modelling approach that accounts simultaneously for environmental stochasticity, density dependence and varying detection probability. Our model suggests that cat abundance is related consistently to rabbit abundance in spring and summer, possibly through increased rabbit numbers improving the fecundity and juvenile survival of cats. Maintaining rabbits at low abundance should therefore suppress cat numbers, relieving predation pressure on native prey. Our approach provided estimates of the abundance of cats and rabbits over a large geographical area. This was made possible by repeated sampling within each season, which allows estimation of detection probabilities. A similar approach could be applied to predator-prey systems elsewhere, and could be adapted to any method of direct observation in which there is no double-counting of individuals. Reliable estimates of numerical

Challenges to a molecular approach to prey identification in the Burmese python, Python molurus bivittatus

Science.gov (United States)

Falk, Bryan; Reed, Robert N.

2015-01-01

Molecular approaches to prey identification are increasingly useful in elucidating predator–prey relationships, and we aimed to investigate the feasibility of these methods to document the species identities of prey consumed by invasive Burmese pythons in Florida. We were particularly interested in the diet of young snakes, because visual identification of prey from this size class has proven difficult. We successfully extracted DNA from the gastrointestinal contents of 43 young pythons, as well as from several control samples, and attempted amplification of DNA mini-barcodes, a 130-bp region of COX1. Using a PNA clamp to exclude python DNA, we found that prey DNA was not present in sufficient quality for amplification of this locus in 86% of our samples. All samples from the GI tracts of young pythons contained only hair, and the six samples we were able to identify to species were hispid cotton rats. This suggests that young Burmese pythons prey predominantly on small mammals and that prey diversity among snakes of this size class is low. We discuss prolonged gastrointestinal transit times and extreme gastric breakdown as possible causes of DNA degradation that limit the success of a molecular approach to prey identification in Burmese pythons

Body size and predatory performance in wolves: is bigger better?

Science.gov (United States)

MacNulty, Daniel R; Smith, Douglas W; Mech, L David; Eberly, Lynn E

2009-05-01

1. Large body size hinders locomotor performance in ways that may lead to trade-offs in predator foraging ability that limit the net predatory benefit of larger size. For example, size-related improvements in handling prey may come at the expense of pursuing prey and thus negate any enhancement in overall predatory performance due to increasing size. 2. This hypothesis was tested with longitudinal data from repeated observations of 94 individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park, USA. Wolf size was estimated from an individually based sex-specific growth model derived from body mass measurements of 304 wolves. 3. Larger size granted individual wolves a net predatory advantage despite substantial variation in its effect on the performance of different predatory tasks; larger size improved performance of a strength-related task (grappling and subduing elk) but failed to improve performance of a locomotor-related task (selecting an elk from a group) for wolves > 39 kg. 4. Sexual dimorphism in wolf size also explained why males outperformed females in each of the three tasks considered (attacking, selecting, and killing). 5. These findings support the generalization that bigger predators are overall better hunters, but they also indicate that increasing size ultimately limits elements of predatory behaviour that require superior locomotor performance. We argue that this could potentially narrow the dietary niche of larger carnivores as well as limit the evolution of larger size if prey are substantially more difficult to pursue than to handle.

Is the red spotted green frog Hypsiboas punctatus (Anura: Hylidae) selecting its preys? The importance of prey availability.

Science.gov (United States)

López, Javier A; Scarabotti, Pablo A; Medrano, María C; Ghirardi, Romina

2009-09-01

The study of the feeding ecology of amphibians is an old issue in herpetology. Notwithstanding, the lack of food resources data in many studies of amphibians feeding has lead to partial understanding of frog feeding strategies. In this study we evaluate the trophic selectivity of a red spotted green frog (Hypsiboas punctatus) population from a Middle Paraná River floodplain pond in Argentina, and discuss the importance of prey availability data when interpreting results from diet analysis. We analyzed the gut contents of 47 H. punctatus adults and compared frog's diet with the environmental food resources. Prey availability was estimated by systematically seep-netting the microhabitat where anurans were localized foraging. We identified 33 taxonomic categories from gastrointestinal contents. Numerically, the most important prey categories were dipterans, followed by hemipterans, homopterans and coleopterans. The diet similarity between males and females was high and no statistical differences in diet composition were found. The most abundant food resources in the environment were dipterans, coleopterans, homopterans and collembolans. In order to assess whether frogs were selecting their preys, we calculated Pianka's niche overlap index and Jacobs' electivity index comparing gut contents to prey availability data. Trophic niche overlap was medium but significantly higher than expected by chance. The electivity index indicated that H. punctatus foraged dipterans slightly above their environmental abundance. Among the secondary preys, hemipterans were foraged selectively, homopterans were consumed in the same proportion to their occurrence in the environment, coleopterans were foraged quite under their availability and collembolans were practically ignored by frogs. Without food resources data, H. punctatus could be classified as a specialist feeder, but dipterans also were quite abundant in the environment. Our results show that H. punctatus fit better as a

Comparative growth and development of spiders reared on live and dead prey.

Science.gov (United States)

Peng, Yu; Zhang, Fan; Gui, Shaolan; Qiao, Huping; Hose, Grant C

2013-01-01

Scavenging (feeding on dead prey) has been demonstrated across a number of spider families, yet the implications of feeding on dead prey for the growth and development of individuals and population is unknown. In this study we compare the growth, development, and predatory activity of two species of spiders that were fed on live and dead prey. Pardosa astrigera (Lycosidae) and Hylyphantes graminicola (Lyniphiidae) were fed live or dead fruit flies, Drosophila melanogaster. The survival of P. astrigera and H. graminicola was not affected by prey type. The duration of late instars of P. astrigera fed dead prey were longer and mature spiders had less protein content than those fed live prey, whereas there were no differences in the rate of H. graminicola development, but the mass of mature spiders fed dead prey was greater than those fed live prey. Predation rates by P. astrigera did not differ between the two prey types, but H. graminicola had a higher rate of predation on dead than alive prey, presumably because the dead flies were easier to catch and handle. Overall, the growth, development and reproduction of H. graminicola reared with dead flies was better than those reared on live flies, yet for the larger P. astrigera, dead prey may suit smaller instars but mature spiders may be best maintained with live prey. We have clearly demonstrated that dead prey may be suitable for rearing spiders, although the success of the spiders fed such prey appears size- and species specific.

Noise-induced extinction for a ratio-dependent predator-prey model with strong Allee effect in prey

Science.gov (United States)

Mandal, Partha Sarathi

2018-04-01

In this paper, we study a stochastically forced ratio-dependent predator-prey model with strong Allee effect in prey population. In the deterministic case, we show that the model exhibits the stable interior equilibrium point or limit cycle corresponding to the co-existence of both species. We investigate a probabilistic mechanism of the noise-induced extinction in a zone of stable interior equilibrium point. Computational methods based on the stochastic sensitivity function technique are applied for the analysis of the dispersion of random states near stable interior equilibrium point. This method allows to construct a confidence domain and estimate the threshold value of the noise intensity for a transition from the coexistence to the extinction.

Estimating Search Engine Index Size Variability

DEFF Research Database (Denmark)

Van den Bosch, Antal; Bogers, Toine; De Kunder, Maurice

2016-01-01

One of the determining factors of the quality of Web search engines is the size of their index. In addition to its influence on search result quality, the size of the indexed Web can also tell us something about which parts of the WWW are directly accessible to the everyday user. We propose a novel...... method of estimating the size of a Web search engine’s index by extrapolating from document frequencies of words observed in a large static corpus of Web pages. In addition, we provide a unique longitudinal perspective on the size of Google and Bing’s indices over a nine-year period, from March 2006...... until January 2015. We find that index size estimates of these two search engines tend to vary dramatically over time, with Google generally possessing a larger index than Bing. This result raises doubts about the reliability of previous one-off estimates of the size of the indexed Web. We find...

Foraging behavior of larval cod ( Gadus morhua ) influenced by prey density and hunger

DEFF Research Database (Denmark)

Munk, Peter

1995-01-01

activity, prey selectivity, and hunger in a variable prey environment. Gadus morhua eggs were collected in March 1992 and 1993 from the Kattegat area, Denmark, fertilised and incubated in the laboratory. After hatching, the larvae were transferred to rearing tanks of 172 litres. The behaviour of larvae (6...... their prey size selectivity. Behavioural response was to a large degree determined by the level of hunger, represented by the number of newly ingested prey in the gut. The findings show that cod larvae have a flexible response to changes in feeding conditions and imply that larvae can grow and survive even...

Disentangling mite predator-prey relationships by multiplex PCR.

Science.gov (United States)

Pérez-Sayas, Consuelo; Pina, Tatiana; Gómez-Martínez, María A; Camañes, Gemma; Ibáñez-Gual, María V; Jaques, Josep A; Hurtado, Mónica A

2015-11-01

Gut content analysis using molecular techniques can help elucidate predator-prey relationships in situations in which other methodologies are not feasible, such as in the case of trophic interactions between minute species such as mites. We designed species-specific primers for a mite community occurring in Spanish citrus orchards comprising two herbivores, the Tetranychidae Tetranychus urticae and Panonychus citri, and six predatory mites belonging to the Phytoseiidae family; these predatory mites are considered to be these herbivores' main biological control agents. These primers were successfully multiplexed in a single PCR to test the range of predators feeding on each of the two prey species. We estimated prey DNA detectability success over time (DS50), which depended on the predator-prey combination and ranged from 0.2 to 18 h. These values were further used to weight prey detection in field samples to disentangle the predatory role played by the most abundant predators (i.e. Euseius stipulatus and Phytoseiulus persimilis). The corrected predation value for E. stipulatus was significantly higher than for P. persimilis. However, because this 1.5-fold difference was less than that observed regarding their sevenfold difference in abundance, we conclude that P. persimilis is the most effective predator in the system; it preyed on tetranychids almost five times more frequently than E. stipulatus did. The present results demonstrate that molecular tools are appropriate to unravel predator-prey interactions in tiny species such as mites, which include important agricultural pests and their predators. © 2015 John Wiley & Sons Ltd.

Impact of marine reserve on maximum sustainable yield in a traditional prey-predator system

Science.gov (United States)

Paul, Prosenjit; Kar, T. K.; Ghorai, Abhijit

2018-01-01

Multispecies fisheries management requires managers to consider the impact of fishing activities on several species as fishing impacts both targeted and non-targeted species directly or indirectly in several ways. The intended goal of traditional fisheries management is to achieve maximum sustainable yield (MSY) from the targeted species, which on many occasions affect the targeted species as well as the entire ecosystem. Marine reserves are often acclaimed as the marine ecosystem management tool. Few attempts have been made to generalize the ecological effects of marine reserve on MSY policy. We examine here how MSY and population level in a prey-predator system are affected by the low, medium and high reserve size under different possible scenarios. Our simulation works shows that low reserve area, the value of MSY for prey exploitation is maximum when both prey and predator species have fast movement rate. For medium reserve size, our analysis revealed that the maximum value of MSY for prey exploitation is obtained when prey population has fast movement rate and predator population has slow movement rate. For high reserve area, the maximum value of MSY for prey's exploitation is very low compared to the maximum value of MSY for prey's exploitation in case of low and medium reserve. On the other hand, for low and medium reserve area, MSY for predator exploitation is maximum when both the species have fast movement rate.

Dynamics analysis of a predator-prey system with harvesting prey and disease in prey species.

Science.gov (United States)

Meng, Xin-You; Qin, Ni-Ni; Huo, Hai-Feng

2018-12-01

In this paper, a predator-prey system with harvesting prey and disease in prey species is given. In the absence of time delay, the existence and stability of all equilibria are investigated. In the presence of time delay, some sufficient conditions of the local stability of the positive equilibrium and the existence of Hopf bifurcation are obtained by analysing the corresponding characteristic equation, and the properties of Hopf bifurcation are given by using the normal form theory and centre manifold theorem. Furthermore, an optimal harvesting policy is investigated by applying the Pontryagin's Maximum Principle. Numerical simulations are performed to support our analytic results.

Aspects of the winter predator--prey relationship between sauger and threadfin shad in Watts Bar Reservoir, Tennessee

International Nuclear Information System (INIS)

McGee, M.V.; Griffith, J.S.; McLean, R.B.

1978-01-01

This study sought to determine the impact of cold-induced mortality and impingement of threadfin shad (Dorsoma petenense) on the food consumption and prey selection of sauger (Stizostedion canadense), and to estimate the ability of sauger to digest meals consumed at low temperatures in winter. Prey selection of sauger was monitored from November 1976 through April 1977. Stomach contents of 536 sauger indicated threadfin provided the entire forage base for sauger through January. Food consumption of sauger was reduced and prey selection shifted to other species after January due to the combined effects of predation, impingement, and natural mortality of cold-stressed threadfin. Threadfin shad of a size available to most sauger were virtually eliminated by February. From February through April some sauger utilized alternate prey species. Laboratory digestion rate studies of sauger indicated digestion of force-fed meals of 4 to 7 g fathead minnows (Pimephales promelas) could proceed to 90 percent completion in 54 h at 5 C, 47 hr at 10 C, and 25 hr at 15 C. Conclusions of this study are: (1) that threadfin shad were the most abundant and vulnerable prey species available to and utilized by sauger during the late fall and winter months; (2) extensive mortalities of threadfin due to cold-stress increased sauger predation on four alternate prey species; (3) sauger continued feeding and digesting meals at temperatures between 5 and 15 C every 1 to 3 days; (4) sauger stored excess energy available from threadfin early in the winter as visceral fat which was available later when food consumption was reduced

Aspects of the winter predator--prey relationship between sauger and threadfin shad in Watts Bar Reservoir, Tennessee

Energy Technology Data Exchange (ETDEWEB)

McGee, M.V.; Griffith, J.S.; McLean, R.B.

1978-04-01

This study sought to determine the impact of cold-induced mortality and impingement of threadfin shad (Dorsoma petenense) on the food consumption and prey selection of sauger (Stizostedion canadense), and to estimate the ability of sauger to digest meals consumed at low temperatures in winter. Prey selection of sauger was monitored from November 1976 through April 1977. Stomach contents of 536 sauger indicated threadfin provided the entire forage base for sauger through January. Food consumption of sauger was reduced and prey selection shifted to other species after January due to the combined effects of predation, impingement, and natural mortality of cold-stressed threadfin. Threadfin shad of a size available to most sauger were virtually eliminated by February. From February through April some sauger utilized alternate prey species. Laboratory digestion rate studies of sauger indicated digestion of force-fed meals of 4 to 7 g fathead minnows (Pimephales promelas) could proceed to 90 percent completion in 54 h at 5 C, 47 hr at 10 C, and 25 hr at 15 C. Conclusions of this study are: (1) that threadfin shad were the most abundant and vulnerable prey species available to and utilized by sauger during the late fall and winter months; (2) extensive mortalities of threadfin due to cold-stress increased sauger predation on four alternate prey species; (3) sauger continued feeding and digesting meals at temperatures between 5 and 15 C every 1 to 3 days; (4) sauger stored excess energy available from threadfin early in the winter as visceral fat which was available later when food consumption was reduced.

Piscivorous fish exhibit temperature-influenced binge feeding during an annual prey pulse.

Science.gov (United States)

Furey, Nathan B; Hinch, Scott G; Mesa, Matthew G; Beauchamp, David A

2016-09-01

Understanding the limits of consumption is important for determining trophic influences on ecosystems and predator adaptations to inconsistent prey availability. Fishes have been observed to consume beyond what is sustainable (i.e. digested on a daily basis), but this phenomenon of hyperphagia (or binge-feeding) is largely overlooked. We expect hyperphagia to be a short-term (1-day) event that is facilitated by gut volume providing capacity to store consumed food during periods of high prey availability to be later digested. We define how temperature, body size and food availability influence the degree of binge-feeding by comparing field observations with laboratory experiments of bull trout (Salvelinus confluentus), a large freshwater piscivore that experiences highly variable prey pulses. We also simulated bull trout consumption and growth during salmon smolt outmigrations under two scenarios: 1) daily consumption being dependent upon bioenergetically sustainable rates and 2) daily consumption being dependent upon available gut volume (i.e. consumption is equal to gut volume when empty and otherwise 'topping off' based on sustainable digestion rates). One-day consumption by laboratory-held bull trout during the first day of feeding experiments after fasting exceeded bioenergetically sustainable rates by 12- to 87-fold at low temperatures (3 °C) and by  ˜1·3-fold at 20 °C. The degree of binge-feeding by bull trout in the field was slightly reduced but largely in agreement with laboratory estimates, especially when prey availability was extremely high [during a sockeye salmon (Oncorhynchus nerka) smolt outmigration and at a counting fence where smolts are funnelled into high densities]. Consumption by bull trout at other settings were lower and more variable, but still regularly hyperphagic. Simulations demonstrated the ability to binge-feed increased cumulative consumption (16-32%) and cumulative growth (19-110%) relative to only feeding at

Stomach fullness shapes prey choice decisions in crab plovers (Dromas ardeola)

Science.gov (United States)

Bom, Roeland A.; Fijen, Thijs P. M.; van Gils, Jan A.

2018-01-01

Foragers whose energy intake rate is constrained by search and handling time should, according to the contingency model (CM), select prey items whose profitability exceeds or equals the forager’s long-term average energy intake rate. This rule does not apply when prey items are found and ingested at a higher rate than the digestive system can process them. According to the digestive rate model (DRM), foragers in such situations should prefer prey with the highest digestive quality, instead of the highest profitability. As the digestive system fills up, the limiting constraint switches from ingestion rate to digestion rate, and prey choice is expected to change accordingly for foragers making decisions over a relative short time window. We use these models to understand prey choice in crab plovers (Dromas ardeola), preying on either small burrowing crabs that are swallowed whole (high profitability, but potentially inducing a digestive constraint) or on larger swimming crabs that are opened to consume only the flesh (low profitability, but easier to digest). To parameterize the CM and DRM, we measured energy content, ballast mass and handling times for different sized prey, and the birds’ digestive capacity in three captive individuals. Subsequently, these birds were used in ad libitum experiments to test if they obeyed the rules of the CM or DRM. We found that crab plovers with an empty stomach mainly chose the most profitable prey, matching the CM. When stomach fullness increased, the birds switched their preference from the most profitable prey to the highest-quality prey, matching the predictions of the DRM. This shows that prey choice is context dependent, affected by the stomach fullness of an animal. Our results suggest that prey choice experiments should be carefully interpreted, especially under captive conditions as foragers often ‘fill up’ in the course of feeding trials. PMID:29641542

Body size and predatory performance in wolves: Is bigger better?

Science.gov (United States)

MacNulty, D.R.; Smith, D.W.; Mech, L.D.; Eberly, L.E.

2009-01-01

Large body size hinders locomotor performance in ways that may lead to trade-offs in predator foraging ability that limit the net predatory benefit of larger size. For example, size-related improvements in handling prey may come at the expense of pursuing prey and thus negate any enhancement in overall predatory performance due to increasing size. 2. This hypothesis was tested with longitudinal data from repeated observations of 94 individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park, USA. Wolf size was estimated from an individually based sex-specific growth model derived from body mass measurements of 304 wolves. 3. Larger size granted individual wolves a net predatory advantage despite substantial variation in its effect on the performance of different predatory tasks; larger size improved performance of a strength-related task (grappling and subduing elk) but failed to improve performance of a locomotor-related task (selecting an elk from a group) for wolves > 39 kg. 4. Sexual dimorphism in wolf size also explained why males outperformed females in each of the three tasks considered (attacking, selecting, and killing). 5. These findings support the generalization that bigger predators are overall better hunters, but they also indicate that increasing size ultimately limits elements of predatory behaviour that require superior locomotor performance. We argue that this could potentially narrow the dietary niche of larger carnivores as well as limit the evolution of larger size if prey are substantially more difficult to pursue than to handle. ?? 2009 British Ecological Society.

Cheetahs, Acinonyx jubatus, balance turn capacity with pace when chasing prey

Science.gov (United States)

Wilson, John W.; Mills, Michael G. L.; Wilson, Rory P.; Peters, Gerrit; Mills, Margaret E. J.; Speakman, John R.; Durant, Sarah M.; Bennett, Nigel C.; Marks, Nikki J.; Scantlebury, Michael

2013-01-01

Predator–prey interactions are fundamental in the evolution and structure of ecological communities. Our understanding, however, of the strategies used in pursuit and evasion remains limited. Here, we report on the hunting dynamics of the world's fastest land animal, the cheetah, Acinonyx jubatus. Using miniaturized data loggers, we recorded fine-scale movement, speed and acceleration of free-ranging cheetahs to measure how hunting dynamics relate to chasing different sized prey. Cheetahs attained hunting speeds of up to 18.94 m s−1 and accelerated up to 7.5 m s−2 with greatest angular velocities achieved during the terminal phase of the hunt. The interplay between forward and lateral acceleration during chases showed that the total forces involved in speed changes and turning were approximately constant over time but varied with prey type. Thus, rather than a simple maximum speed chase, cheetahs first accelerate to decrease the distance to their prey, before reducing speed 5–8 s from the end of the hunt, so as to facilitate rapid turns to match prey escape tactics, varying the precise strategy according to prey species. Predator and prey thus pit a fine balance of speed against manoeuvring capability in a race for survival. PMID:24004493

Cheetahs, Acinonyx jubatus, balance turn capacity with pace when chasing prey.

Science.gov (United States)

Wilson, John W; Mills, Michael G L; Wilson, Rory P; Peters, Gerrit; Mills, Margaret E J; Speakman, John R; Durant, Sarah M; Bennett, Nigel C; Marks, Nikki J; Scantlebury, Michael

2013-10-23

Predator-prey interactions are fundamental in the evolution and structure of ecological communities. Our understanding, however, of the strategies used in pursuit and evasion remains limited. Here, we report on the hunting dynamics of the world's fastest land animal, the cheetah, Acinonyx jubatus. Using miniaturized data loggers, we recorded fine-scale movement, speed and acceleration of free-ranging cheetahs to measure how hunting dynamics relate to chasing different sized prey. Cheetahs attained hunting speeds of up to 18.94 m s(-1) and accelerated up to 7.5 m s(-2) with greatest angular velocities achieved during the terminal phase of the hunt. The interplay between forward and lateral acceleration during chases showed that the total forces involved in speed changes and turning were approximately constant over time but varied with prey type. Thus, rather than a simple maximum speed chase, cheetahs first accelerate to decrease the distance to their prey, before reducing speed 5-8 s from the end of the hunt, so as to facilitate rapid turns to match prey escape tactics, varying the precise strategy according to prey species. Predator and prey thus pit a fine balance of speed against manoeuvring capability in a race for survival.

Making inference from wildlife collision data: inferring predator absence from prey strikes

Directory of Open Access Journals (Sweden)

Peter Caley

2017-02-01

Full Text Available Wildlife collision data are ubiquitous, though challenging for making ecological inference due to typically irreducible uncertainty relating to the sampling process. We illustrate a new approach that is useful for generating inference from predator data arising from wildlife collisions. By simply conditioning on a second prey species sampled via the same collision process, and by using a biologically realistic numerical response functions, we can produce a coherent numerical response relationship between predator and prey. This relationship can then be used to make inference on the population size of the predator species, including the probability of extinction. The statistical conditioning enables us to account for unmeasured variation in factors influencing the runway strike incidence for individual airports and to enable valid comparisons. A practical application of the approach for testing hypotheses about the distribution and abundance of a predator species is illustrated using the hypothesized red fox incursion into Tasmania, Australia. We estimate that conditional on the numerical response between fox and lagomorph runway strikes on mainland Australia, the predictive probability of observing no runway strikes of foxes in Tasmania after observing 15 lagomorph strikes is 0.001. We conclude there is enough evidence to safely reject the null hypothesis that there is a widespread red fox population in Tasmania at a population density consistent with prey availability. The method is novel and has potential wider application.

Making inference from wildlife collision data: inferring predator absence from prey strikes.

Science.gov (United States)

Caley, Peter; Hosack, Geoffrey R; Barry, Simon C

2017-01-01

Wildlife collision data are ubiquitous, though challenging for making ecological inference due to typically irreducible uncertainty relating to the sampling process. We illustrate a new approach that is useful for generating inference from predator data arising from wildlife collisions. By simply conditioning on a second prey species sampled via the same collision process, and by using a biologically realistic numerical response functions, we can produce a coherent numerical response relationship between predator and prey. This relationship can then be used to make inference on the population size of the predator species, including the probability of extinction. The statistical conditioning enables us to account for unmeasured variation in factors influencing the runway strike incidence for individual airports and to enable valid comparisons. A practical application of the approach for testing hypotheses about the distribution and abundance of a predator species is illustrated using the hypothesized red fox incursion into Tasmania, Australia. We estimate that conditional on the numerical response between fox and lagomorph runway strikes on mainland Australia, the predictive probability of observing no runway strikes of foxes in Tasmania after observing 15 lagomorph strikes is 0.001. We conclude there is enough evidence to safely reject the null hypothesis that there is a widespread red fox population in Tasmania at a population density consistent with prey availability. The method is novel and has potential wider application.

Fine-scale spatio-temporal variation in tiger Panthera tigris diet: Effect of study duration and extent on estimates of tiger diet in Chitwan National Park, Nepal

Science.gov (United States)

Kapfer, Paul M.; Streby, Henry M.; Gurung, B.; Simcharoen, A.; McDougal, C.C.; Smith, J.L.D.

2011-01-01

Attempts to conserve declining tiger Panthera tigris populations and distributions have experienced limited success. The poaching of tiger prey is a key threat to tiger persistence; a clear understanding of tiger diet is a prerequisite to conserve dwindling populations. We used unpublished data on tiger diet in combination with two previously published studies to examine fine-scale spatio-temporal changes in tiger diet relative to prey abundance in Chitwan National Park, Nepal, and aggregated data from the three studies to examine the effect that study duration and the size of the study area have on estimates of tiger diet. Our results correspond with those of previous studies: in all three studies, tiger diet was dominated by members of Cervidae; small to medium-sized prey was important in one study. Tiger diet was unrelated to prey abundance, and the aggregation of studies indicates that increasing study duration and study area size both result in increased dietary diversity in terms of prey categories consumed, and increasing study duration changed which prey species contributed most to tiger diet. Based on our results, we suggest that managers focus their efforts on minimizing the poaching of all tiger prey, and that future studies of tiger diet be of long duration and large spatial extent to improve our understanding of spatio-temporal variation in estimates of tiger diet. ?? 2011 Wildlife Biology, NKV.

Energetic solutions of Rock Sandpipers to harsh winter conditions rely on prey quality

Science.gov (United States)

Ruthrauff, Daniel R.; Dekinga, Anne; Gill, Robert E.; Piersma, Theunis

2018-01-01

Rock Sandpipers Calidris ptilocnemis have the most northerly non-breeding distribution of any shorebird in the Pacific Basin (upper Cook Inlet, Alaska; 61°N, 151°W). In terms of freezing temperatures, persistent winds and pervasive ice, this site is the harshest used by shorebirds during winter. We integrated physiological, metabolic, behavioural and environmental aspects of the non-breeding ecology of Rock Sandpipers at the northern extent of their range to determine the relative importance of these factors in facilitating their unique non-breeding ecology. Not surprisingly, estimated daily energetic demands were greatest during January, the coldest period of winter. These estimates were greatest for foraging birds, and exceeded basal metabolic rates by a factor of 6.5, a scope of increase that approaches the maximum sustained rate of energetic output by shorebirds during periods of migration, but far exceeds these periods in duration. We assessed the quality of their primary prey, the bivalve Macoma balthica, to determine the daily foraging duration required by Rock Sandpipers to satisfy such energetic demands. Based on size-specific estimates of M. balthica quality, Rock Sandpipers require over 13 h/day of foraging time in upper Cook Inlet in January, even when feeding on the highest quality prey. This range approaches the average daily duration of mudflat availability in this region (c. 18 h), a maximum value that annually decreases due to the accumulation of shore-fast ice. Rock Sandpipers are likely to maximize access to foraging sites by following the exposure of ice-free mudflats across the upper Cook Inlet region and by selecting smaller, higher quality M. balthica to minimize foraging times. Ultimately, this unusual non-breeding ecology relies on the high quality of their prey resources. Compared with other sites across their range, M. balthica from upper Cook Inlet have relatively light shells, potentially the result of the region

Prey preferences of aquatic insects: potential implications for the regulation of wetland mosquitoes.

Science.gov (United States)

Saha, N; Aditya, G; Saha, G K

2014-03-01

Wetlands are potential sites for mosquito breeding and are thus important in the context of public health. The use of chemical and microbial controls is constrained in wetlands in view of their potential impact on the diverse biota. Biological control using generalist aquatic insects can be effective, provided a preference for mosquito larvae is exhibited. The mosquito prey preferences of water bugs and larvae of odonate species were evaluated using chironomid larvae, fish fingerlings and tadpoles as alternative prey. Manly's selectivity (αi ) values with 95% confidence intervals (CIs) were estimated to judge prey preference patterns. Multivariate analysis of variance (manova) and standardized canonical coefficients were used to test the effects of density on prey selectivity. The αi values indicated a significant preference (P insect predators tested for mosquito larvae over the alternative prey as a density-dependent function. On a comparative scale, chironomid larvae had the highest impact as alternative prey. In a multiple-prey experiment, predators showed a similar pattern of preference for mosquito larvae over alternative prey, reflecting a significant (P insect predators can effectively reduce mosquito density in the presence of multiple alternative prey. © 2013 The Royal Entomological Society.

Prey-Predator Model with a Nonlocal Bistable Dynamics of Prey

Directory of Open Access Journals (Sweden)

Malay Banerjee

2018-03-01

Full Text Available Spatiotemporal pattern formation in integro-differential equation models of interacting populations is an active area of research, which has emerged through the introduction of nonlocal intra- and inter-specific interactions. Stationary patterns are reported for nonlocal interactions in prey and predator populations for models with prey-dependent functional response, specialist predator and linear intrinsic death rate for predator species. The primary goal of our present work is to consider nonlocal consumption of resources in a spatiotemporal prey-predator model with bistable reaction kinetics for prey growth in the absence of predators. We derive the conditions of the Turing and of the spatial Hopf bifurcation around the coexisting homogeneous steady-state and verify the analytical results through extensive numerical simulations. Bifurcations of spatial patterns are also explored numerically.

Models of prey capture in larval fish

NARCIS (Netherlands)

Drost, M.R.

1986-01-01

The food uptake of larval carp and pike is described from high speed movies with synchronous lateral and ventral views.

During prey intake by larval fishes the velocities of the created suction flow are high relative to their own size: 0.3 m/s for carp larvae of 6

Prey and plastic ingestion of Pacific Northern Fulmars (Fulmarus glacialis rogersii) from Monterey Bay, California.

Science.gov (United States)

Donnelly-Greenan, Erica L; Harvey, James T; Nevins, Hannahrose M; Hester, Michelle M; Walker, William A

2014-08-15

Marine plastic pollution affects seabirds, including Pacific Northern Fulmars (Fulmarus glacialis rodgersii), that feed at the surface and mistake plastic for prey or incidentally ingest it. Direct and indirect health issues can result, including satiety and possibly leading to inefficient foraging. Our objective was to examine fulmar body condition, identify cephalopod diet to species, enumerate and weigh ingested plastic, and determine if prey number and size were correlated with ingested plastics in beach-cast fulmars wintering in Monterey Bay California (2003, n=178: 2007, n=185). Fulmars consumed mostly Gonatus pyros, G. onyx, and G. californiensis of similar size for both years. We found a significant negative correlation between pectoral muscle index and average size of cephalopod beaks per stomach; a significant increase in plastic categories between 2003 and 2007; and no significant correlation between number and mass of plastic compared with number and size of prey for either year. Copyright © 2014 Elsevier Ltd. All rights reserved.

Cost of living dictates what whales, dolphins and porpoises eat: the importance of prey quality on predator foraging strategies.

Directory of Open Access Journals (Sweden)

Jérôme Spitz

Full Text Available Understanding the mechanisms that drive prey selection is a major challenge in foraging ecology. Most studies of foraging strategies have focused on behavioural costs, and have generally failed to recognize that differences in the quality of prey may be as important to predators as the costs of acquisition. Here, we tested whether there is a relationship between the quality of diets (kJ · g(-1 consumed by cetaceans in the North Atlantic and their metabolic costs of living as estimated by indicators of muscle performance (mitochondrial density, n = 60, and lipid content, n = 37. We found that the cost of living of 11 cetacean species is tightly coupled with the quality of prey they consume. This relationship between diet quality and cost of living appears to be independent of phylogeny and body size, and runs counter to predictions that stem from the well-known scaling relationships between mass and metabolic rates. Our finding suggests that the quality of prey rather than the sheer quantity of food is a major determinant of foraging strategies employed by predators to meet their specific energy requirements. This predator-specific dependence on food quality appears to reflect the evolution of ecological strategies at a species level, and has implications for risk assessment associated with the consequences of changing the quality and quantities of prey available to top predators in marine ecosystems.

Interactive effects of prey refuge and additional food for predator in a diffusive predator-prey system

DEFF Research Database (Denmark)

Chakraborty, Subhendu; Tiwari, P. K.; Sasmal, S.K.

2017-01-01

a predator-prey system with prey refuge and additional food for predator apart from the focal prey in the presence of diffusion. Our main aim is to study the interactive effects of prey refuge and additional food on the system dynamics and especially on the controllability of prey (pest). Different types......Additional food for predators has been considered as one of the best established techniques in integrated pest management and biological conservation programs. In natural systems, there are several other factors, e.g., prey refuge, affect the success of pest control. In this paper, we analyze...... of Turing patterns such as stripes, spots, holes, and mixtures of them are obtained. It is found that the supply of additional food to the predator is unable to control the prey (pest) population when prey refuge is high. Moreover, when both prey refuge and additional food are low, spatial distribution...

Tadpoles of three common anuran species from Thailand do not prey on mosquito larvae.

Science.gov (United States)

Weterings, Robbie

2015-12-01

Tadpoles are often considered to be predators of mosquito larvae and are therefore beneficial for the control of certain disease vectors. Nevertheless, only a few species have actually been recorded to prey on mosquito larvae. The mosquito larvae predation rates of tadpoles of three common Thai anuran species (Bufo melanostictus, Kaloula pulchra and Hylarana raniceps) were experimentally tested. Tadpoles in varying developmental stages were used to assess a size/age effect on the predation rate. In addition, different instars of Culex quinquefasciatus were used in order to assess a prey size effect on the predation rates. All three species failed to show any evidence of mosquito larvae predation. Neither small nor large tadpoles fed on mosquito larvae. Prey size also did not affect predation. Although tadpoles do not feed on mosquito larvae, there may be other direct or indirect inter-specific interactions that adversely impact the development of larvae in shared habitats with tadpoles. © 2015 The Society for Vector Ecology.

Effect size estimates: current use, calculations, and interpretation.

Science.gov (United States)

Fritz, Catherine O; Morris, Peter E; Richler, Jennifer J

2012-02-01

The Publication Manual of the American Psychological Association (American Psychological Association, 2001, American Psychological Association, 2010) calls for the reporting of effect sizes and their confidence intervals. Estimates of effect size are useful for determining the practical or theoretical importance of an effect, the relative contributions of factors, and the power of an analysis. We surveyed articles published in 2009 and 2010 in the Journal of Experimental Psychology: General, noting the statistical analyses reported and the associated reporting of effect size estimates. Effect sizes were reported for fewer than half of the analyses; no article reported a confidence interval for an effect size. The most often reported analysis was analysis of variance, and almost half of these reports were not accompanied by effect sizes. Partial η2 was the most commonly reported effect size estimate for analysis of variance. For t tests, 2/3 of the articles did not report an associated effect size estimate; Cohen's d was the most often reported. We provide a straightforward guide to understanding, selecting, calculating, and interpreting effect sizes for many types of data and to methods for calculating effect size confidence intervals and power analysis.

Plant architecture and prey distribution influence foraging behavior of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae).

Science.gov (United States)

Gontijo, Lessando M; Nechols, James R; Margolies, David C; Cloyd, Raymond A

2012-01-01

The arrangement, number, and size of plant parts may influence predator foraging behavior, either directly, by altering the rate or pattern of predator movement, or, indirectly, by affecting the distribution and abundance of prey. We report on the effects of both plant architecture and prey distribution on foraging by the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), on cucumber (Cucumis sativus L.). Plants differed in leaf number (2- or 6-leafed), and there were associated differences in leaf size, plant height, and relative proportions of plant parts; but all had the same total surface area. The prey, the twospotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), were distributed either on the basal leaf or on all leaves. The effect of plant architecture on predator foraging behavior varied depending on prey distribution. The dimensions of individual plant parts affected time allocated to moving and feeding, but they did not appear to influence the frequency with which predators moved among different plant parts. Overall, P. persimilis moved less, and fed upon prey longer, on 6-leafed plants with prey on all leaves than on plants representing other treatment combinations. Our findings suggest that both plant architecture and pattern of prey distribution should be considered, along with other factors such as herbivore-induced plant volatiles, in augmentative biological control programs.

The Dynamics of a Nonautonomous Predator-Prey Model with Infertility Control in the Prey

Directory of Open Access Journals (Sweden)

Xiaomei Feng

2014-01-01

Full Text Available A nonautonomous predator-prey model with infertility control in the prey is formulated and investigated. Threshold conditions for the permanence and extinction of fertility prey and infertility prey are established. Some new threshold values of integral form are obtained. For the periodic cases, these threshold conditions act as sharp threshold values for the permanence and extinction of fertility prey and infertility prey. There are also mounting concerns that the quantity of biological sterile drug is obtained in the process of the prevention and control of pest in the grasslands and farmland. Finally, two examples are given to illustrate the main results of this paper. The numerical simulations shown that, when the pest population is permanet, different dynamic behaviors may be found in this model, such as the global attractivity and the chaotic attractor.

Can species-specific prey responses to chemical cues explain prey susceptibility to predation?

Science.gov (United States)

Šmejkal, Marek; Ricard, Daniel; Sajdlová, Zuzana; Čech, Martin; Vejřík, Lukáš; Blabolil, Petr; Vejříková, Ivana; Prchalová, Marie; Vašek, Mojmír; Souza, Allan T; Brönmark, Christer; Peterka, Jiří

2018-05-01

The perception of danger represents an essential ability of prey for gaining an informational advantage over their natural enemies. Especially in complex environments or at night, animals strongly rely on chemoreception to avoid predators. The ability to recognize danger by chemical cues and subsequent adaptive responses to predation threats should generally increase prey survival. Recent findings suggest that European catfish ( Silurus glanis ) introduction induce changes in fish community and we tested whether the direction of change can be attributed to differences in chemical cue perception. We tested behavioral response to chemical cues using three species of freshwater fish common in European water: rudd ( Scardinius erythrophthalmus ), roach ( Rutilus rutilus ), and perch ( Perca fluviatilis ). Further, we conducted a prey selectivity experiment to evaluate the prey preferences of the European catfish. Roach exhibited the strongest reaction to chemical cues, rudd decreased use of refuge and perch did not alter any behavior in the experiment. These findings suggest that chemical cue perception might be behind community data change and we encourage collecting more community data of tested prey species before and after European catfish introduction to test the hypothesis. We conclude that used prey species can be used as a model species to verify whether chemical cue perception enhances prey survival.

How much is too much? Assessment of prey consumption by Magellanic penguins in Patagonian colonies.

Directory of Open Access Journals (Sweden)

Juan E Sala

Full Text Available Penguins are major consumers in the southern oceans although quantification of this has been problematic. One suggestion proposes the use of points of inflection in diving profiles ('wiggles' for this, a method that has been validated for the estimation of prey consumption by Magellanic penguins (Spheniscus magellanicus by Simeone and Wilson (2003. Following them, we used wiggles from 31 depth logger-equipped Magellanic penguins foraging from four Patagonian colonies; Punta Norte (PN, Bahía Bustamente (BB, Puerto Deseado (PD and Puerto San Julián (PSJ, all located in Argentina between 42-49° S, to estimate the prey captured and calculate the catch per unit time (CPUT for birds foraging during the early chick-rearing period. Numbers of prey caught and CPUT were significantly different between colonies. Birds from PD caught the highest number of prey per foraging trip, with CPUT values of 68±19 prey per hour underwater (almost two times greater than for the three remaining colonies. We modeled consumption from these data and calculate that the world Magellanic penguin population consumes about 2 million tons of prey per year. Possible errors in this calculation are discussed. Despite this, the analysis of wiggles seems a powerful and simple tool to begin to quantify prey consumption by Magellanic penguins, allowing comparison between different breeding sites. The total number of wiggles and/or CPUT do not reflect, by themselves, the availability of food for each colony, as the number of prey consumed by foraging trip is strongly associated with the energy content and wet mass of each colony-specific 'prey type'. Individuals consuming more profitable prey could be optimizing the time spent underwater, thereby optimizing the energy expenditure associated with the dives.

Sub-indicator: Prey fish

Science.gov (United States)

Weidel, Brian C.; Dunlop, Erin

2017-01-01

Prey fish communities across the Great Lakes continue to change, although the direction and magnitude of those changes are not consistent across the lakes. The metrics used to categorize prey fish status in this and previous periods are based on elements that are common among each of the lake’s Fish Community Objectives and include diversity and the relative role of native species in the prey fish communities. The diversity index categorized three of lakes as ‘fair’, while Superior and Erie were ‘good’ (Table 1). The short term trend, from the previous period (2008-2010) to the current period (2011-2014) found diversity in Erie and Superior to be unchanging, but the other three lakes to be ‘deteriorating’, resulting in an overall trend categorization of ‘undetermined’ (Table 1). The long term diversity trend suggested Lakes Superior and Erie have the most diverse prey communities although the index for those prey fish have been quite variable over time (Figure 1). In Lake Huron, where non-native alewife have substantially declined, the diversity index has also declined. The continued dominance of alewife in Lake Ontario (96% of the prey fish biomass) resulted in the lowest diversity index value (Figure 1). The proportion of native species within the community was judged as ‘good’ in Lakes Superior and Huron, ‘fair’ in Michigan and Erie and ‘poor’ in Ontario (Table 2). The short term trend was improving in in all lakes except Michigan (‘deteriorating’) and Ontario (‘unchanging’), resulting in an overall short term trend of ‘undetermined’ (Table 2). Over the current period, Lake Superior consistently had the highest proportion native prey fish (87%) while Lake Ontario had the lowest (1%) (Figure 2). Lake Michigan’s percent native has declined as round goby increase and comprises a greater proportion of the community. Native prey fish make up 51% of Lake Erie, although basin-specific values differed (Figure 2). Most notably

Sperm whale predator-prey interactions involve chasing and buzzing, but no acoustic stunning

DEFF Research Database (Denmark)

Fais, Andrea; Johnson, M.; Wilson, Maria

2016-01-01

The sperm whale carries a hypertrophied nose that generates powerful clicks for long-range echolocation. However, it remains a conundrum how this bizarrely shaped apex predator catches its prey. Several hypotheses have been advanced to propose both active and passive means to acquire prey......, including acoustic debilitation of prey with very powerful clicks. Here we test these hypotheses by using sound and movement recording tags in a fine-scale study of buzz sequences to relate the acoustic behaviour of sperm whales with changes in acceleration in their head region during prey capture attempts....... We show that in the terminal buzz phase, sperm whales reduce inter-click intervals and estimated source levels by 1-2 orders of magnitude. As a result, received levels at the prey are more than an order of magnitude below levels required for debilitation, precluding acoustic stunning to facilitate...

Are all prey created equal? A review and synthesis of differential predation on prey in substandard condition

Science.gov (United States)

Mesa, Matthew G.; Poe, Thomas P.; Gadomski, Dena M.; Petersen, James H.

1994-01-01

Our understanding of predator-prey interactions in fishes has been influenced largely by research assuming that the condition of the participants is normal. However, fish populations today often reside in anthropogenically altered environments and are subjected to many kinds of stressors, which may reduce their ecological performance by adversely affecting their morphology, physiology, or behaviour. One consequence is that either the predator or prey, or both, may be in a substandard condition at the time of an interaction. We reviewed the literature on predator-prey interactions in fishes where substandard prey were used as experimental groups. Although most of this research indicates that such prey are significantly more vulnerable to predation, prey condition has rarely been considered in ecological theory regarding predator-prey interactions. The causal mechanisms for increased vulnerability of substandard prey to predation include a failure to detect predators, lapses in decision-making, poor fast-start performance, inability to shoal effectively, and increased prey conspicuousness. Despite some problems associated with empirical predator-prey studies using substandard prey, their results can have theoretical and applied uses, such as in ecological modelling or justification of corrective measures to be implemented in the wild. There is a need for more corroborative field experimentation, a better understanding of the causal mechanisms behind differential predation, and increased incorporation of prey condition into the research of predator-prey modellers and theoreticians. If the concept of prey condition is considered in predator-prey interactions, our understanding of how such interactions influence the structure and dynamics of fish communities is likely to change, which should prove beneficial to aquatic ecosystems.

Influence of prey body characteristics and performance on predator selection.

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Holmes, Thomas H; McCormick, Mark I

2009-03-01

At the time of settlement to the reef environment, coral reef fishes differ in a number of characteristics that may influence their survival during a predatory encounter. This study investigated the selective nature of predation by both a multi-species predator pool, and a single common predator (Pseudochromis fuscus), on the reef fish, Pomacentrus amboinensis. The study focused on the early post-settlement period of P. amboinensis, when mortality, and hence selection, is known to be highest. Correlations between nine different measures of body condition/performance were examined at the time of settlement, in order to elucidate the relationships between different traits. Single-predator (P. fuscus) choice trials were conducted in 57.4-l aquaria with respect to three different prey characteristics [standard length (SL), body weight and burst swimming speed], whilst multi-species trials were conducted on open patch reefs, manipulating prey body weight only. Relationships between the nine measures of condition/performance were generally poor, with the strongest correlations occurring between the morphological measures and within the performance measures. During aquaria trials, P. fuscus was found to be selective with respect to prey SL only, with larger individuals being selected significantly more often. Multi-species predator communities, however, were selective with respect to prey body weight, with heavier individuals being selected significantly more often than their lighter counterparts. Our results suggest that under controlled conditions, body length may be the most important prey characteristic influencing prey survival during predatory encounters with P. fuscus. In such cases, larger prey size may actually be a distinct disadvantage to survival. However, these relationships appear to be more complex under natural conditions, where the expression of prey characteristics, the selectivity fields of a number of different predators, their relative abundance, and

Not So Fast: Swimming Behavior of Sailfish during Predator-Prey Interactions using High-Speed Video and Accelerometry.

Science.gov (United States)

Marras, Stefano; Noda, Takuji; Steffensen, John F; Svendsen, Morten B S; Krause, Jens; Wilson, Alexander D M; Kurvers, Ralf H J M; Herbert-Read, James; Boswell, Kevin M; Domenici, Paolo

2015-10-01

Billfishes are considered among the fastest swimmers in the oceans. Despite early estimates of extremely high speeds, more recent work showed that these predators (e.g., blue marlin) spend most of their time swimming slowly, rarely exceeding 2 m s(-1). Predator-prey interactions provide a context within which one may expect maximal speeds both by predators and prey. Beyond speed, however, an important component determining the outcome of predator-prey encounters is unsteady swimming (i.e., turning and accelerating). Although large predators are faster than their small prey, the latter show higher performance in unsteady swimming. To contrast the evading behaviors of their highly maneuverable prey, sailfish and other large aquatic predators possess morphological adaptations, such as elongated bills, which can be moved more rapidly than the whole body itself, facilitating capture of the prey. Therefore, it is an open question whether such supposedly very fast swimmers do use high-speed bursts when feeding on evasive prey, in addition to using their bill for slashing prey. Here, we measured the swimming behavior of sailfish by using high-frequency accelerometry and high-speed video observations during predator-prey interactions. These measurements allowed analyses of tail beat frequencies to estimate swimming speeds. Our results suggest that sailfish burst at speeds of about 7 m s(-1) and do not exceed swimming speeds of 10 m s(-1) during predator-prey interactions. These speeds are much lower than previous estimates. In addition, the oscillations of the bill during swimming with, and without, extension of the dorsal fin (i.e., the sail) were measured. We suggest that extension of the dorsal fin may allow sailfish to improve the control of the bill and minimize its yaw, hence preventing disturbance of the prey. Therefore, sailfish, like other large predators, may rely mainly on accuracy of movement and the use of the extensions of their bodies, rather than resorting

"Prey Play": Learning about Predators and Prey through an Interactive, Role-Play Game

Science.gov (United States)

Deaton, Cynthia C. M.; Dodd, Kristen; Drennon, Katherine; Nagle, Jack

2012-01-01

"Prey Play" is an interactive role-play activity that provides fifth-grade students with opportunities to examine predator-prey interactions. This four-part, role-play activity allows students to take on the role of a predator and prey as they reflect on the behaviors animals exhibit as they collect food and interact with one another, as well as…

Prey-predator dynamics with prey refuge providing additional food to predator

International Nuclear Information System (INIS)

Ghosh, Joydev; Sahoo, Banshidhar; Poria, Swarup

2017-01-01

Highlights: • The effects of interplay between prey refugia and additional food are reported. • Hopf bifurcation conditions are derived analytically. • Existence of unique limit cycle is shown analytically. • Predator extinction may be possible at very high prey refuge ecological systems. - Abstract: The impacts of additional food for predator on the dynamics of a prey-predator model with prey refuge are investigated. The equilibrium points and their stability behaviours are determined. Hopf bifurcation conditions are derived analytically. Most significantly, existence conditions for unique stable limit cycle in the phase plane are shown analytically. The analytical results are in well agreement with the numerical simulation results. Effects of variation of refuge level as well as the variation of quality and quantity of additional food on the dynamics are reported with the help of bifurcation diagrams. It is found that high quality and high quantity of additional food supports oscillatory coexistence of species. It is observed that predator extinction possibility in high prey refuge ecological systems may be removed by supplying additional food to predator population. The reported theoretical results may be useful to conservation biologist for species conservation in real world ecological systems.

Asymptotic size determines species abundance in the marine size spectrum

DEFF Research Database (Denmark)

Andersen, Ken Haste; Beyer, Jan

2006-01-01

The majority of higher organisms in the marine environment display indeterminate growth; that is, they continue to grow throughout their life, limited by an asymptotic size. We derive the abundance of species as a function of their asymptotic size. The derivation is based on size-spectrum theory......, where population structure is derived from physiology and simple arguments regarding the predator-prey interaction. Using a hypothesis of constant satiation, which states that the average degree of satiation is independent of the size of an organism, the number of individuals with a given size is found...... to be proportional to the weight raised to the power -2.05, independent of the predator/prey size ratio. This is the first time the spectrum exponent has been derived solely on the basis of processes at the individual level. The theory furthermore predicts that the parameters in the von Bertalanffy growth function...

Photometric estimation of defect size in radiation direction

International Nuclear Information System (INIS)

Zuev, V.M.

1993-01-01

Factors, affecting accuracy of photometric estimation of defect size in radiation transmission direction, are analyzed. Experimentally obtained dependences of contrast of defect image on its size in radiation transmission direction are presented. Practical recommendations on improving accuracy of photometric estimation of defect size in radiation transmission direction, are developed

Sample Size Calculations for Population Size Estimation Studies Using Multiplier Methods With Respondent-Driven Sampling Surveys.

Science.gov (United States)

Fearon, Elizabeth; Chabata, Sungai T; Thompson, Jennifer A; Cowan, Frances M; Hargreaves, James R

2017-09-14

While guidance exists for obtaining population size estimates using multiplier methods with respondent-driven sampling surveys, we lack specific guidance for making sample size decisions. To guide the design of multiplier method population size estimation studies using respondent-driven sampling surveys to reduce the random error around the estimate obtained. The population size estimate is obtained by dividing the number of individuals receiving a service or the number of unique objects distributed (M) by the proportion of individuals in a representative survey who report receipt of the service or object (P). We have developed an approach to sample size calculation, interpreting methods to estimate the variance around estimates obtained using multiplier methods in conjunction with research into design effects and respondent-driven sampling. We describe an application to estimate the number of female sex workers in Harare, Zimbabwe. There is high variance in estimates. Random error around the size estimate reflects uncertainty from M and P, particularly when the estimate of P in the respondent-driven sampling survey is low. As expected, sample size requirements are higher when the design effect of the survey is assumed to be greater. We suggest a method for investigating the effects of sample size on the precision of a population size estimate obtained using multipler methods and respondent-driven sampling. Uncertainty in the size estimate is high, particularly when P is small, so balancing against other potential sources of bias, we advise researchers to consider longer service attendance reference periods and to distribute more unique objects, which is likely to result in a higher estimate of P in the respondent-driven sampling survey. ©Elizabeth Fearon, Sungai T Chabata, Jennifer A Thompson, Frances M Cowan, James R Hargreaves. Originally published in JMIR Public Health and Surveillance (http://publichealth.jmir.org), 14.09.2017.

New insights in insect prey choice by chimpanzees and gorillas in southeast Cameroon: the role of nutritional value.

Science.gov (United States)

Deblauwe, Isra; Janssens, Geert P J

2008-01-01

The insect diet of chimpanzees and gorillas living at the northern periphery of the Dja Biosphere Reserve in southeast Cameroon and its nutritional contribution is described. We analyzed fecal samples and recorded additional evidence of insectivory. A detailed prey species list is presented for both apes. We carried out nutritional analyses (macronutrients, macro- and micro-minerals) on 11 important and eight nonimportant, but accessible, ant and termite prey species, and estimated the average nutrient intake/day through insects. Although gorillas ate insects more frequently, the average prey biomass intake/day by chimpanzees was twice that by gorillas. The lack of tool-use by gorillas cannot be the main reason for the small overlap of important prey species. Both apes did not seem to consume ant prey for one or more specific nutrients. Also other factors, such as medicinal use, should be considered. Termites, on the other hand, seemed to be selected for particular nutrients. Gorilla intake of the important termite prey, Cubitermes and Thoracotermes, met with estimated iron requirements. Their potential role as antidiarrheal treatment is as yet unclear. Chimpanzee intake of the important termite prey, Macrotermes spp., met with estimated manganese requirements and the protein intake/day (mean: 2 g/d) reached significant values (>20 g/d). To fully understand the importance of nutritional contributions of insects to ape diets in Cameroon, the chemical composition and nutrient intake of fruit and foliage in their diets should be investigated. (c) 2007 Wiley-Liss, Inc.

On population size estimators in the Poisson mixture model.

Science.gov (United States)

Mao, Chang Xuan; Yang, Nan; Zhong, Jinhua

2013-09-01

Estimating population sizes via capture-recapture experiments has enormous applications. The Poisson mixture model can be adopted for those applications with a single list in which individuals appear one or more times. We compare several nonparametric estimators, including the Chao estimator, the Zelterman estimator, two jackknife estimators and the bootstrap estimator. The target parameter of the Chao estimator is a lower bound of the population size. Those of the other four estimators are not lower bounds, and they may produce lower confidence limits for the population size with poor coverage probabilities. A simulation study is reported and two examples are investigated. © 2013, The International Biometric Society.

Coexistence for an Almost Periodic Predator-Prey Model with Intermittent Predation Driven by Discontinuous Prey Dispersal

Directory of Open Access Journals (Sweden)

Yantao Luo

2017-01-01

Full Text Available An almost periodic predator-prey model with intermittent predation and prey discontinuous dispersal is studied in this paper, which differs from the classical continuous and impulsive dispersal predator-prey models. The intermittent predation behavior of the predator species only happens in the channels between two patches where the discontinuous migration movement of the prey species occurs. Using analytic approaches and comparison theorems of the impulsive differential equations, sufficient criteria on the boundedness, permanence, and coexistence for this system are established. Finally, numerical simulations demonstrate that, for an intermittent predator-prey model, both the intermittent predation and intrinsic growth rates of the prey and predator species can greatly impact the permanence, extinction, and coexistence of the population.

The effect of wounds on desiccation of prey: implications for a predator with extra-oral digestion.

Science.gov (United States)

Morse, Douglass H

1998-06-01

Predators that inject prey with proteolytic enzymes, thereby breaking down their tissues for subsequent ingestion, run the risk that desiccation will hinder eventual retrieval of resources from these prey. Wounds made in capture might exacerbate this problem. However, desiccation rates of small syrphid flies Toxomerusmarginatus (Diptera: Syrphidae) killed by juvenile crab spiders Misumena vatia (Araneae: Thomisidae) and intact dead syrphid flies did not differ over the normal period of feeding, though desiccation rates in shade and sun differed several-fold. Neither the size of the spider (and presumably the size of the wounds it inflicted) nor the location of the wounds on the flies' bodies affected desiccation rates. Thus, this tactic of prey handling does not exact an added processing cost on Misumena.

Parasites as prey

NARCIS (Netherlands)

Goedknegt, M.A.; Welsh, J.E.; Thieltges, D.W.

2012-01-01

Parasites are usually considered to use their hosts as a resource for energy. However, there is increasing awareness that parasites can also become a resource themselves and serve as prey for other organisms. Here we describe various types of predation in which parasites act as prey for other

Assessing breeding potential of peregrine falcons based on chlorinated hydrocarbon concentrations in prey

Energy Technology Data Exchange (ETDEWEB)

Elliott, J.E. [Canadian Wildlife Service, Pacific Wildlife Research Centre, 5421 Robertson Rd., RR no. 1, Delta, British Columbia, V4K 3N2 (Canada)]. E-mail: john.elliott@ec.gc.ca; Miller, M.J. [Iolaire Ecological Consulting, 7899 Thrasher St., Mission, British Columbia, V2V 5H3 (Canada); Wilson, L.K. [Canadian Wildlife Service, Pacific Wildlife Research Centre, 5421 Robertson Rd., RR no. 1, Delta, British Columbia, V4K 3N2 (Canada)

2005-03-01

Peregrine falcons (Falco peregrinus) now breed successfully in most areas of North America from which they were previously extirpated. The loss during the mid-part of the last century of many of the world's peregrine populations was largely a consequence of impaired reproduction caused by the effects of DDE on eggshell quality and embryo hatchability. Population recovery has been attributed to re-introduction efforts, coupled with regulatory restrictions on the use of organochlorine pesticides. Peregrines have not returned to breed in some areas, such as the Okanagan Valley of British Columbia. That region has been extensively planted in fruit orchards which were treated annually with DDT during the early 1950s to the 1970s. Ongoing contamination of avian species, including potential peregrine prey, inhabiting orchards has been documented. In response to an initiative to release peregrines around the city of Kelowna in the Okanagan Valley, we collected potential peregrine prey species and analyzed whole bodies for chlorinated hydrocarbon residues. We used a simple bioaccumulation model to predict concentrations of DDE in peregrine eggs using concentrations in prey and estimates of dietary makeup as input. Peregrines would be expected to breed successfully only if they fed on a diet primarily of doves. Feeding on as little as 10% of other species such as starlings, robins, gulls and magpies would produce DDE concentrations in peregrine eggs greater than the threshold of 15 mg/kg. We also estimated the critical concentration of DDE in total prey to be about 0.5 mg/kg, one half of the previous most conservative criterion for peregrine prey. Concentrations of dieldrin and PCBs in peregrine prey are less than suggested critical levels. - Based on the level of DDE contamination of prey items, it seems unlikely that peregrine falcons could breed successfully throughout most of the Okanagan Valley of British Columbia.

Clay Caterpillar Whodunit: A Customizable Method for Studying Predator-Prey Interactions in the Field

Science.gov (United States)

Curtis, Rachel; Klemens, Jeffrey A.; Agosta, Salvatore J.; Bartlow, Andrew W.; Wood, Steve; Carlson, Jason A.; Stratford, Jeffrey A.; Steele, Michael A.

2013-01-01

Predator-prey dynamics are an important concept in ecology, often serving as an introduction to the field of community ecology. However, these dynamics are difficult for students to observe directly. We describe a methodology that employs model caterpillars made of clay to estimate rates of predator attack on a prey species. This approach can be…

The diet of otters ( Lutra lutra L.) in Danish freshwater habitats : comparisons of prey fish populations

DEFF Research Database (Denmark)

Taastrom, H.M.; Jacobsen, Lene

1999-01-01

Otter spraints from five Danish freshwater localities were analysed. In all localities fish was the main prey (76-99% of estimated bulk), especially in winter. Depending on locality, the prey fish mainly consisted of cyprinids (Cyprinidae), percids (Percidae) or salmonids (Salmonidae). Seasonal v...

Changes in Alaskan soft-bottom prey communities along a gradient in sea otter predation

Science.gov (United States)

Kvitek, R.G.; Oliver, J.S.; DeGange, A.R.; Anderson, B.S.

1992-01-01

Sea Otter (Enhydra lutris), well documented as "keystone" predators in rocky marine communities, were found to exert a strong influence on infaunal prey communities in soft-sediment habitats. Direct and indirect effects of sea otter predation on subtidal soft-bottom prey communities were evaluated along a temporal gradient of sea otter occupancy around the Kodiak Archipelago. The results indicate that Kodiak otters forage primarily on bivalve prey and dramatically reduce infaunal bivalve and green sea urchin (Strongylocentrotus droebachiensis) prey populations. Bivalve prey abundance, biomass, and size were inversely related to duration of sea otter occupancy. The relative conditions of shells discarded by otters in shallow ( 20 m) water at the same sites indicate that otters first exploited Saxidomus in shallow-water feeding areas, and later switched to Macoma spp. in deeper water. Otter-cracked shells of the deep-burrowing clam Tresus capax were rarely found, even at otter foraging sites where the clam accounted for the majority of available prey biomass, suggesting that it has a partial depth refuge from otter predation. The indirect effects of otter predation included substratum disturbance and the facilitation of sea star predation on infaunal prey. Sea stars, Pycnopodia helianthoides, were attracted to experimentally dug excavations as well as natural sea otter foraging pits, where the sea stars foraged on smaller size classes of infaunal bivalves than those eaten by otters. Otters also discard clam shells on the sediment surface and expose old, buried shells during excavation. Surface shells were found to provide attachment sites for large anemones and kelp. Our study shows that sea otters can affect soft-sediment communities, not only through predation, as in rocky habitats, but also through disturbance, and thus retain a high degree of influence in two very different habitat types.

Encounter success of free-ranging marine predator movements across a dynamic prey landscape.

Science.gov (United States)

Sims, David W; Witt, Matthew J; Richardson, Anthony J; Southall, Emily J; Metcalfe, Julian D

2006-05-22

Movements of wide-ranging top predators can now be studied effectively using satellite and archival telemetry. However, the motivations underlying movements remain difficult to determine because trajectories are seldom related to key biological gradients, such as changing prey distributions. Here, we use a dynamic prey landscape of zooplankton biomass in the north-east Atlantic Ocean to examine active habitat selection in the plankton-feeding basking shark Cetorhinus maximus. The relative success of shark searches across this landscape was examined by comparing prey biomass encountered by sharks with encounters by random-walk simulations of 'model' sharks. Movements of transmitter-tagged sharks monitored for 964 days (16754 km estimated minimum distance) were concentrated on the European continental shelf in areas characterized by high seasonal productivity and complex prey distributions. We show movements by adult and sub-adult sharks yielded consistently higher prey encounter rates than 90% of random-walk simulations. Behavioural patterns were consistent with basking sharks using search tactics structured across multiple scales to exploit the richest prey areas available in preferred habitats. Simple behavioural rules based on learned responses to previously encountered prey distributions may explain the high performances. This study highlights how dynamic prey landscapes enable active habitat selection in large predators to be investigated from a trophic perspective, an approach that may inform conservation by identifying critical habitat of vulnerable species.

Penguin head movement detected using small accelerometers: a proxy of prey encounter rate.

Science.gov (United States)

Kokubun, Nobuo; Kim, Jeong-Hoon; Shin, Hyoung-Chul; Naito, Yasuhiko; Takahashi, Akinori

2011-11-15

Determining temporal and spatial variation in feeding rates is essential for understanding the relationship between habitat features and the foraging behavior of top predators. In this study we examined the utility of head movement as a proxy of prey encounter rates in medium-sized Antarctic penguins, under the presumption that the birds should move their heads actively when they encounter and peck prey. A field study of free-ranging chinstrap and gentoo penguins was conducted at King George Island, Antarctica. Head movement was recorded using small accelerometers attached to the head, with simultaneous monitoring for prey encounter or body angle. The main prey was Antarctic krill (>99% in wet mass) for both species. Penguin head movement coincided with a slow change in body angle during dives. Active head movements were extracted using a high-pass filter (5 Hz acceleration signals) and the remaining acceleration peaks (higher than a threshold acceleration of 1.0 g) were counted. The timing of head movements coincided well with images of prey taken from the back-mounted cameras: head movement was recorded within ±2.5 s of a prey image on 89.1±16.1% (N=7 trips) of images. The number of head movements varied largely among dive bouts, suggesting large temporal variations in prey encounter rates. Our results show that head movement is an effective proxy of prey encounter, and we suggest that the method will be widely applicable for a variety of predators.

An objective approach to determining the weight ranges of prey preferred by and accessible to the five large African carnivores.

Directory of Open Access Journals (Sweden)

Hayley S Clements

Full Text Available Broad-scale models describing predator prey preferences serve as useful departure points for understanding predator-prey interactions at finer scales. Previous analyses used a subjective approach to identify prey weight preferences of the five large African carnivores, hence their accuracy is questionable. This study uses a segmented model of prey weight versus prey preference to objectively quantify the prey weight preferences of the five large African carnivores. Based on simulations of known predator prey preference, for prey species sample sizes above 32 the segmented model approach detects up to four known changes in prey weight preference (represented by model break-points with high rates of detection (75% to 100% of simulations, depending on number of break-points and accuracy (within 1.3±4.0 to 2.7±4.4 of known break-point. When applied to the five large African carnivores, using carnivore diet information from across Africa, the model detected weight ranges of prey that are preferred, killed relative to their abundance, and avoided by each carnivore. Prey in the weight ranges preferred and killed relative to their abundance are together termed "accessible prey". Accessible prey weight ranges were found to be 14-135 kg for cheetah Acinonyx jubatus, 1-45 kg for leopard Panthera pardus, 32-632 kg for lion Panthera leo, 15-1600 kg for spotted hyaena Crocuta crocuta and 10-289 kg for wild dog Lycaon pictus. An assessment of carnivore diets throughout Africa found these accessible prey weight ranges include 88±2% (cheetah, 82±3% (leopard, 81±2% (lion, 97±2% (spotted hyaena and 96±2% (wild dog of kills. These descriptions of prey weight preferences therefore contribute to our understanding of the diet spectrum of the five large African carnivores. Where datasets meet the minimum sample size requirements, the segmented model approach provides a means of determining, and comparing, the prey weight range preferences of any carnivore

An objective approach to determining the weight ranges of prey preferred by and accessible to the five large African carnivores.

Science.gov (United States)

Clements, Hayley S; Tambling, Craig J; Hayward, Matt W; Kerley, Graham I H

2014-01-01

Broad-scale models describing predator prey preferences serve as useful departure points for understanding predator-prey interactions at finer scales. Previous analyses used a subjective approach to identify prey weight preferences of the five large African carnivores, hence their accuracy is questionable. This study uses a segmented model of prey weight versus prey preference to objectively quantify the prey weight preferences of the five large African carnivores. Based on simulations of known predator prey preference, for prey species sample sizes above 32 the segmented model approach detects up to four known changes in prey weight preference (represented by model break-points) with high rates of detection (75% to 100% of simulations, depending on number of break-points) and accuracy (within 1.3±4.0 to 2.7±4.4 of known break-point). When applied to the five large African carnivores, using carnivore diet information from across Africa, the model detected weight ranges of prey that are preferred, killed relative to their abundance, and avoided by each carnivore. Prey in the weight ranges preferred and killed relative to their abundance are together termed "accessible prey". Accessible prey weight ranges were found to be 14-135 kg for cheetah Acinonyx jubatus, 1-45 kg for leopard Panthera pardus, 32-632 kg for lion Panthera leo, 15-1600 kg for spotted hyaena Crocuta crocuta and 10-289 kg for wild dog Lycaon pictus. An assessment of carnivore diets throughout Africa found these accessible prey weight ranges include 88±2% (cheetah), 82±3% (leopard), 81±2% (lion), 97±2% (spotted hyaena) and 96±2% (wild dog) of kills. These descriptions of prey weight preferences therefore contribute to our understanding of the diet spectrum of the five large African carnivores. Where datasets meet the minimum sample size requirements, the segmented model approach provides a means of determining, and comparing, the prey weight range preferences of any carnivore species.

Trophic feasibility of reintroducing anadromous salmonids in three reservoirs on the north fork Lewis River, Washington: Prey supply and consumption demand of resident fishes

Science.gov (United States)

Sorel, Mark H.; Hansen, Adam G.; Connelly, Kristin A.; Beauchamp, David A.

2016-01-01

The reintroduction of anadromous salmonids in reservoirs is being proposed with increasing frequency, requiring baseline studies to evaluate feasibility and estimate the capacity of reservoir food webs to support reintroduced populations. Using three reservoirs on the north fork Lewis River as a case study, we demonstrate a method to determine juvenile salmonid smolt rearing capacities for lakes and reservoirs. To determine if the Lewis River reservoirs can support reintroduced populations of juvenile stream-type Chinook Salmon Oncorhynchus tshawytscha, we evaluated the monthly production of daphniaDaphnia spp. (the primary zooplankton consumed by resident salmonids in the system) and used bioenergetics to model the consumption demand of resident fishes in each reservoir. To estimate the surplus of Daphnia prey available for reintroduced salmonids, we assumed a maximum sustainable exploitation rate and accounted for the consumption demand of resident fishes. The number of smolts that could have been supported was estimated by dividing any surplus Daphnia production by the simulated consumption demand of an individual Chinook Salmon fry rearing in the reservoir to successful smolt size. In all three reservoirs, densities of Daphnia were highest in the epilimnion, but warm epilimnetic temperatures and the vertical distribution of planktivores suggested that access to abundant epilimnetic prey was limited. By comparing accessible prey supply and demand on a monthly basis, we were able to identify potential prey supply bottlenecks that could limit smolt production and growth. These results demonstrate that a bioenergetics approach can be a valuable method of examining constraints on lake and reservoir rearing capacity, such as thermal structure and temporal food supply. This method enables numerical estimation of rearing capacity, which is a useful metric for managers evaluating the feasibility of reintroducing Pacific salmon Oncorhynchus spp. in lentic systems.

Two-prey one-predator model

International Nuclear Information System (INIS)

Elettreby, M.F.

2009-01-01

In this paper we propose a new multi-team prey-predator model, in which the prey teams help each other. We study its local stability. In the absence of predator, there is no help between the prey teams. So, we study the global stability and persistence of the model without help.

Estimation of sample size and testing power (Part 4).

Science.gov (United States)

Hu, Liang-ping; Bao, Xiao-lei; Guan, Xue; Zhou, Shi-guo

2012-01-01

Sample size estimation is necessary for any experimental or survey research. An appropriate estimation of sample size based on known information and statistical knowledge is of great significance. This article introduces methods of sample size estimation of difference test for data with the design of one factor with two levels, including sample size estimation formulas and realization based on the formulas and the POWER procedure of SAS software for quantitative data and qualitative data with the design of one factor with two levels. In addition, this article presents examples for analysis, which will play a leading role for researchers to implement the repetition principle during the research design phase.

Modulation of shark prey capture kinematics in response to sensory deprivation.

Science.gov (United States)

Gardiner, Jayne M; Atema, Jelle; Hueter, Robert E; Motta, Philip J

2017-02-01

The ability of predators to modulate prey capture in response to the size, location, and behavior of prey is critical to successful feeding on a variety of prey types. Modulating in response to changes in sensory information may be critical to successful foraging in a variety of environments. Three shark species with different feeding morphologies and behaviors were filmed using high-speed videography while capturing live prey: the ram-feeding blacktip shark, the ram-biting bonnethead, and the suction-feeding nurse shark. Sharks were examined intact and after sensory information was blocked (olfaction, vision, mechanoreception, and electroreception, alone and in combination), to elucidate the contribution of the senses to the kinematics of prey capture. In response to sensory deprivation, the blacktip shark demonstrated the greatest amount of modulation, followed by the nurse shark. In the absence of olfaction, blacktip sharks open the jaws slowly, suggestive of less motivation. Without lateral line cues, blacktip sharks capture prey from greater horizontal angles using increased ram. When visual cues are absent, blacktip sharks elevate the head earlier and to a greater degree, allowing them to overcome imprecise position of the prey relative to the mouth, and capture prey using decreased ram, while suction remains unchanged. When visual cues are absent, nurse sharks open the mouth wider, extend the labial cartilages further, and increase suction while simultaneously decreasing ram. Unlike some bony fish, neither species switches feeding modalities (i.e. from ram to suction or vice versa). Bonnetheads failed to open the mouth when electrosensory cues were blocked, but otherwise little to no modulation was found in this species. These results suggest that prey capture may be less plastic in elasmobranchs than in bony fishes, possibly due to anatomical differences, and that the ability to modulate feeding kinematics in response to available sensory information varies

Harvesting policy for a delayed stage-structured Holling II predator-prey model with impulsive stocking prey

International Nuclear Information System (INIS)

Jiao Jianjun; Meng Xinzhu; Chen Lansun

2009-01-01

A predator-prey model with a stage structure for the predator, which improves the assumption that each individual predator has the same ability to capture prey, is proposed by Wang et al. [Wang W, Mulone G, Salemi F, Salone V. Permanence and stability of a stage-structured predator-prey model. J Math Anal Appl 2001;262:499-528]. It is assumed that immature individuals and mature individuals of the predator are divided by a fixed age and that immature predators do not have the ability to attack prey. We do economic management behavior for Wang model [Wang et al., 2001] by continuous harvesting on predator and impulsive stocking on prey. Then, a delayed stage-structured Holling type II predator-prey model with impulsive stocking prey and continuous harvesting predator is established. It is also assumed that the predating products of the predator is only to increase its bearing ability. We obtain the sufficient conditions of the global attractivity of predator-extinction boundary periodic solution and the permanence of the system. Our results show that the behavior of impulsive stocking prey plays an important role for the permanence of the system, and provide tactical basis for the biological resource management. Further, the numerical analysis is also inserted to illuminate the dynamics of the system.

Estimating software development project size, using probabilistic ...

African Journals Online (AJOL)

Estimating software development project size, using probabilistic techniques. ... of managing the size of software development projects by Purchasers (Clients) and Vendors (Development ... EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT

Effect of sociality and season on gray wolf (Canis lupus) foraging behavior: implications for estimating summer kill rate.

Science.gov (United States)

Metz, Matthew C; Vucetich, John A; Smith, Douglas W; Stahler, Daniel R; Peterson, Rolf O

2011-03-01

Understanding how kill rates vary among seasons is required to understand predation by vertebrate species living in temperate climates. Unfortunately, kill rates are only rarely estimated during summer. For several wolf packs in Yellowstone National Park, we used pairs of collared wolves living in the same pack and the double-count method to estimate the probability of attendance (PA) for an individual wolf at a carcass. PA quantifies an important aspect of social foraging behavior (i.e., the cohesiveness of foraging). We used PA to estimate summer kill rates for packs containing GPS-collared wolves between 2004 and 2009. Estimated rates of daily prey acquisition (edible biomass per wolf) decreased from 8.4±0.9 kg (mean ± SE) in May to 4.1±0.4 kg in July. Failure to account for PA would have resulted in underestimating kill rate by 32%. PA was 0.72±0.05 for large ungulate prey and 0.46±0.04 for small ungulate prey. To assess seasonal differences in social foraging behavior, we also evaluated PA during winter for VHF-collared wolves between 1997 and 2009. During winter, PA was 0.95±0.01. PA was not influenced by prey size but was influenced by wolf age and pack size. Our results demonstrate that seasonal patterns in the foraging behavior of social carnivores have important implications for understanding their social behavior and estimating kill rates. Synthesizing our findings with previous insights suggests that there is important seasonal variation in how and why social carnivores live in groups. Our findings are also important for applications of GPS collars to estimate kill rates. Specifically, because the factors affecting the PA of social carnivores likely differ between seasons, kill rates estimated through GPS collars should account for seasonal differences in social foraging behavior.

Comparing fishers' and scientific estimates of size at maturity and maximum body size as indicators for overfishing.

Science.gov (United States)

Mclean, Elizabeth L; Forrester, Graham E

2018-04-01

We tested whether fishers' local ecological knowledge (LEK) of two fish life-history parameters, size at maturity (SAM) at maximum body size (MS), was comparable to scientific estimates (SEK) of the same parameters, and whether LEK influenced fishers' perceptions of sustainability. Local ecological knowledge was documented for 82 fishers from a small-scale fishery in Samaná Bay, Dominican Republic, whereas SEK was compiled from the scientific literature. Size at maturity estimates derived from LEK and SEK overlapped for most of the 15 commonly harvested species (10 of 15). In contrast, fishers' maximum size estimates were usually lower than (eight species), or overlapped with (five species) scientific estimates. Fishers' size-based estimates of catch composition indicate greater potential for overfishing than estimates based on SEK. Fishers' estimates of size at capture relative to size at maturity suggest routine inclusion of juveniles in the catch (9 of 15 species), and fishers' estimates suggest that harvested fish are substantially smaller than maximum body size for most species (11 of 15 species). Scientific estimates also suggest that harvested fish are generally smaller than maximum body size (13 of 15), but suggest that the catch is dominated by adults for most species (9 of 15 species), and that juveniles are present in the catch for fewer species (6 of 15). Most Samaná fishers characterized the current state of their fishery as poor (73%) and as having changed for the worse over the past 20 yr (60%). Fishers stated that concern about overfishing, catching small fish, and catching immature fish contributed to these perceptions, indicating a possible influence of catch-size composition on their perceptions. Future work should test this link more explicitly because we found no evidence that the minority of fishers with more positive perceptions of their fishery reported systematically different estimates of catch-size composition than those with the more

Estimating spatio-temporal dynamics of size-structured populations

DEFF Research Database (Denmark)

Kristensen, Kasper; Thygesen, Uffe Høgsbro; Andersen, Ken Haste

2014-01-01

with simple stock dynamics, to estimate simultaneously how size distributions and spatial distributions develop in time. We demonstrate the method for a cod population sampled by trawl surveys. Particular attention is paid to correlation between size classes within each trawl haul due to clustering...... of individuals with similar size. The model estimates growth, mortality and reproduction, after which any aspect of size-structure, spatio-temporal population dynamics, as well as the sampling process can be probed. This is illustrated by two applications: 1) tracking the spatial movements of a single cohort...

Turing-Hopf bifurcations in a predator-prey model with herd behavior, quadratic mortality and prey-taxis

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Liu, Xia; Zhang, Tonghua; Meng, Xinzhu; Zhang, Tongqian

2018-04-01

In this paper, we propose a predator-prey model with herd behavior and prey-taxis. Then, we analyze the stability and bifurcation of the positive equilibrium of the model subject to the homogeneous Neumann boundary condition. By using an abstract bifurcation theory and taking prey-tactic sensitivity coefficient as the bifurcation parameter, we obtain a branch of stable nonconstant solutions bifurcating from the positive equilibrium. Our results show that prey-taxis can yield the occurrence of spatial patterns.

Modelling size-dependent cannibalism in barramundi Lates calcarifer: cannibalistic polyphenism and its implication to aquaculture.

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Flavio F Ribeiro

Full Text Available This study quantified size-dependent cannibalism in barramundi Lates calcarifer through coupling a range of prey-predator pairs in a different range of fish sizes. Predictive models were developed using morphological traits with the alterative assumption of cannibalistic polyphenism. Predictive models were validated with the data from trials where cannibals were challenged with progressing increments of prey sizes. The experimental observations showed that cannibals of 25-131 mm total length could ingest the conspecific prey of 78-72% cannibal length. In the validation test, all predictive models underestimate the maximum ingestible prey size for cannibals of a similar size range. However, the model based on the maximal mouth width at opening closely matched the empirical observations, suggesting a certain degree of phenotypic plasticity of mouth size among cannibalistic individuals. Mouth size showed allometric growth comparing with body depth, resulting in a decreasing trend on the maximum size of ingestible prey as cannibals grow larger, which in parts explains why cannibalism in barramundi is frequently observed in the early developmental stage. Any barramundi has the potential to become a cannibal when the initial prey size was 58% of their size, suggesting that 50% of size difference can be the threshold to initiate intracohort cannibalism in a barramundi population. Cannibalistic polyphenism was likely to occur in barramundi that had a cannibalistic history. An experienced cannibal would have a greater ability to stretch its mouth size to capture a much larger prey than the models predict. The awareness of cannibalistic polyphenism has important application in fish farming management to reduce cannibalism.

Size dimorphism, molt status, and body mass variation of Prairie Falcons nesting in the Snake River Birds of Prey National Conservation Area

Science.gov (United States)

Steenhof, Karen; McKinley, James O.

2006-01-01

Birds face challenges in how they allocate energy during the reproductive season. Most temperate zone species do not breed and molt at the same time, presumably because of the high energy demands of these two activities (Espie et al. 1996 and citations therein). However, representatives of at least four raptor genera are known to molt during the nesting season (Schmutz and Schmutz 1975, Newton and Marquiss 1982, Schmutz 1992, Espie et al. 1996). Molt strategies vary among raptor species depending on prey abundance, migration strategies, and the relative costs of reproduction. Sexually-dimorphic raptors typically have different roles in parenting, which result in different strategies for energy allocation. Male and female Eurasian Kestrels (Falco tinnunculus), for example, exhibit different molt patterns and mass changes during the breeding season (Village 1990). Prairie Falcons (Falco mexicanus) are similar to Eurasian Kestrels in that males provide most of the prey to females and young during the first part of the nesting season (Holthuijzen 1990), but no published data exist on molt patterns or mass changes in Prairie Falcons. Reliable information about raptor molt and morphometrics has important implications for modeling energetics and for understanding the role of sexes in raising young. Such knowledge also has practical application for distinguishing sexes of raptors and for determining appropriate size limits of transmitters used for telemetry studies. In this paper, we report on morphometric characteristics useful in distinguishing sexes of Prairie Falcons captured during several breeding seasons in the Snake River Birds of Prey National Conservation Area (NCA), and we assess changes in mass and molt status through the nesting season.

Effects of dams on downstream molluscan predator-prey interactions in the Colorado River estuary.

Science.gov (United States)

Smith, Jansen A; Handley, John C; Dietl, Gregory P

2018-05-30

River systems worldwide have been modified for human use and the downstream ecological consequences are often poorly understood. In the Colorado River estuary, where upstream water diversions have limited freshwater input during the last century, mollusc remains from the last several hundred years suggest widespread ecological change. The once abundant clam Mulinia modesta has undergone population declines of approximately 94% and populations of predators relying on this species as a food source have probably declined, switched to alternative prey species or both. We distinguish between the first two hypotheses using a null model of predation preference to test whether M. modesta was preyed upon selectively by the naticid snail, Neverita reclusiana , along the estuary's past salinity gradient. To evaluate the third hypothesis, we estimate available prey biomass today and in the past, assuming prey were a limiting resource. Data on the frequency of drill holes-identifiable traces of naticid predation on prey shells-showed several species, including M. modesta , were preferred prey. Neverita reclusiana was probably able to switch prey. Available prey biomass also declined, suggesting the N. reclusiana population probably also declined. These results indicate a substantial change to the structure of the benthic food web. Given the global scale of water management, such changes have probably also occurred in many of the world's estuaries. © 2018 The Author(s).

Trophic dynamics of few selected nearshore coastal finfishes with emphasis on prawns as prey item

Science.gov (United States)

Velip, Dinesh T.; Rivonker, Chandrashekher U.

2018-06-01

A trophic dynamic study of marine finfishes was undertaken based on stomach content analysis of twenty four species (N = 1742) collected from the nearshore coastal waters off Goa, west coast of India (15°29‧07.6″ N to 15°34‧44.3″ N, and 73°38‧10.5″ E to 73°46‧03.1″ E) during November 2010 to May 2013. This study aimed to thoroughly understand the feeding attributes of finfishes, and comprehend the possible effects of bycatch-related loss of biomass on trophic ecology. The study assessed diet preferences of the finfishes, their feeding guilds, significance of prawns as prey items, and the influence of mouth parts in prey selection. Altogether 84 prey taxa were identified from the stomach contents. Percentage Index of Relative Importance (IRI) values revealed that zooplankton (34.74), prawns (21.71), phytoplankton (19.80), and teleosts (18.62) were the major prey categories, and, among prawns, Metapenaeus dobsoni (%IRI = 19.34) was the single-most important prey item. Cluster analysis revealed three major trophic guilds namely 'teleost feeders' (mean Trophic Level (TrL) = 4.06 ± 0.42; mean B = 0.46 ± 0.24), 'zooplankton feeders' (mean TrL = 3.43 ± 0.29; mean B = 0.23 ± 0.13), and 'prawn feeders' (mean TrL = 3.86 ± 0.25; mean B = 0.48 ± 0.32), with low diet overlap among them. Principal Component Analysis of prey categories and mouth parts of finfishes suggested that zooplanktivory is associated with gill raker density as well as number of gill arches bearing rakers, whereas gape height determined the size of large-sized prey (fish and invertebrates). The study identified M. dobsoni, mysis and teleosts as highly influential prey for predatory finfishes. The present results could be useful to resolve broader issues in fisheries management.

Non-webbuilding spiders: prey specialists or generalists?

Science.gov (United States)

Nentwig, Wolfgang

1986-07-01

Feeding experiments were performed with seven species of non-webbuilding spiders and a variety of prey taxa. Some species were generally polyphagous whereas other spiders restricted their prey to a few groups. At one end of the spectrum of prey specialization the thomisid Misumena vatia is limited to a few taxa of possible prey (Table 1). The literature of prey records of non-webbuilding spiders is reviewed (Table 2) with special emphasis on oligophagous or monophagous spiders. Monophagous spiders are generally rare and have specialized on only a few prey taxa: social insects (ants, bees, termites) and spiders.

Laboratory estimation of net trophic transfer efficiencies of PCB congeners to lake trout (Salvelinus namaycush) from its prey

Science.gov (United States)

Madenjian, Charles P.; Rediske, Richard R.; O'Keefe, James P.; David, Solomon R.

2014-01-01

A technique for laboratory estimation of net trophic transfer efficiency (γ) of polychlorinated biphenyl (PCB) congeners to piscivorous fish from their prey is described herein. During a 135-day laboratory experiment, we fed bloater (Coregonus hoyi) that had been caught in Lake Michigan to lake trout (Salvelinus namaycush) kept in eight laboratory tanks. Bloater is a natural prey for lake trout. In four of the tanks, a relatively high flow rate was used to ensure relatively high activity by the lake trout, whereas a low flow rate was used in the other four tanks, allowing for low lake trout activity. On a tank-by-tank basis, the amount of food eaten by the lake trout on each day of the experiment was recorded. Each lake trout was weighed at the start and end of the experiment. Four to nine lake trout from each of the eight tanks were sacrificed at the start of the experiment, and all 10 lake trout remaining in each of the tanks were euthanized at the end of the experiment. We determined concentrations of 75 PCB congeners in the lake trout at the start of the experiment, in the lake trout at the end of the experiment, and in bloaters fed to the lake trout during the experiment. Based on these measurements, γ was calculated for each of 75 PCB congeners in each of the eight tanks. Mean γ was calculated for each of the 75 PCB congeners for both active and inactive lake trout. Because the experiment was replicated in eight tanks, the standard error about mean γ could be estimated. Results from this type of experiment are useful in risk assessment models to predict future risk to humans and wildlife eating contaminated fish under various scenarios of environmental contamination.

Environmental fluctuations restrict eco-evolutionary dynamics in predator-prey system.

Science.gov (United States)

Hiltunen, Teppo; Ayan, Gökçe B; Becks, Lutz

2015-06-07

Environmental fluctuations, species interactions and rapid evolution are all predicted to affect community structure and their temporal dynamics. Although the effects of the abiotic environment and prey evolution on ecological community dynamics have been studied separately, these factors can also have interactive effects. Here we used bacteria-ciliate microcosm experiments to test for eco-evolutionary dynamics in fluctuating environments. Specifically, we followed population dynamics and a prey defence trait over time when populations were exposed to regular changes of bottom-up or top-down stressors, or combinations of these. We found that the rate of evolution of a defence trait was significantly lower in fluctuating compared with stable environments, and that the defence trait evolved to lower levels when two environmental stressors changed recurrently. The latter suggests that top-down and bottom-up changes can have additive effects constraining evolutionary response within populations. The differences in evolutionary trajectories are explained by fluctuations in population sizes of the prey and the predator, which continuously alter the supply of mutations in the prey and strength of selection through predation. Thus, it may be necessary to adopt an eco-evolutionary perspective on studies concerning the evolution of traits mediating species interactions. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Characterizing a novel predator–prey relationship between native Diplonychus esakii (Heteroptera: Belostomatidae and invasive Gambusia affinis (Teleostei: Poeciliidae in central China

Directory of Open Access Journals (Sweden)

Xu Ouyang

2017-04-01

Full Text Available Abstract A considerable body of the literature considers the potential impact of exotic predators on native prey organisms, while comparatively, few studies have asked whether and how native predators include novel prey types into their diet spectrum. Here, we asked whether the native aquatic heteropteran Diplonychus esakii preys on the highly invasive western mosquitofish (Gambusia affinis, which has been introduced to southern China and threatens native fish species through competition and predation on their fry. We conducted 48-h prey choice experiments under semi-natural conditions. In a ‘no-choice’ experiment (one predator and one potential prey; n = 200, we found the heteropterans to prey more on large-bodied fish, a pattern that was also described for other belostomatids, while prey sex had no effect on capture rates. Moreover, large-bodied heteropterans caught more fish than small-bodied individuals. However, overall capture rates in our study were low (11.5–30% compared to studies on other belostomatids, which explains why subsequent binary prey choice experiments using one predator and two prey—either large and small females or male and female (with smaller sample sizes of n = 20 and 30, respectively—did not confirm the results of our first experiment. Our study exemplifies how a pattern of body size-dependent predation can arise in a novel (not coevolved predator–prey interaction. We tentatively argue that the observed pattern could be driven by intrinsic features of the predator, namely, altered prey preferences with increasing age coupled with a general preference for large-bodied prey, or changing nutritional needs at different developmental stages.

Inferring predator behavior from attack rates on prey-replicas that differ in conspicuousness.

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Yoel E Stuart

Full Text Available Behavioral ecologists and evolutionary biologists have long studied how predators respond to prey items novel in color and pattern. Because a predatory response is influenced by both the predator's ability to detect the prey and a post-detection behavioral response, variation among prey types in conspicuousness may confound inference about post-prey-detection predator behavior. That is, a relatively high attack rate on a given prey type may result primarily from enhanced conspicuousness and not predators' direct preference for that prey. Few studies, however, account for such variation in conspicuousness. In a field experiment, we measured predation rates on clay replicas of two aposematic forms of the poison dart frog Dendrobates pumilio, one novel and one familiar, and two cryptic controls. To ask whether predators prefer or avoid a novel aposematic prey form independently of conspicuousness differences among replicas, we first modeled the visual system of a typical avian predator. Then, we used this model to estimate replica contrast against a leaf litter background to test whether variation in contrast alone could explain variation in predator attack rate. We found that absolute predation rates did not differ among color forms. Predation rates relative to conspicuousness did, however, deviate significantly from expectation, suggesting that predators do make post-detection decisions to avoid or attack a given prey type. The direction of this deviation from expectation, though, depended on assumptions we made about how avian predators discriminate objects from the visual background. Our results show that it is important to account for prey conspicuousness when investigating predator behavior and also that existing models of predator visual systems need to be refined.

Population estimates of extended family structure and size.

Science.gov (United States)

Garceau, Anne; Wideroff, Louise; McNeel, Timothy; Dunn, Marsha; Graubard, Barry I

2008-01-01

Population-based estimates of biological family size can be useful for planning genetic studies, assessing how distributions of relatives affect disease associations with family history and estimating prevalence of potential family support. Mean family size per person is estimated from a population-based telephone survey (n = 1,019). After multivariate adjustment for demographic variables, older and non-White respondents reported greater mean numbers of total, first- and second-degree relatives. Females reported more total and first-degree relatives, while less educated respondents reported more second-degree relatives. Demographic differences in family size have implications for genetic research. Therefore, periodic collection of family structure data in representative populations would be useful. Copyright 2008 S. Karger AG, Basel.

Status and trends of prey fish populations in Lake Michigan, 2013

Science.gov (United States)

Madenjian, Charles P.; Bunnell, David B.; Desorcie, Timothy J.; Kostich, Melissa Jean; Armenio, Patricia M.; Adams, Jean V.

2015-01-01

The U.S. Geological Survey Great Lakes Science Center has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size and age structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2013. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels. Lake-wide biomass of alewives in 2013 was estimated at 29 kilotonnes (kt, 1 kt = 1000 metric tonnes), which was more than three times the 2012 estimate. However, the unusually high standard error associated with the 2013 estimate indicated no significant increase in lake-wide biomass between 2012 and 2013. Moreover, the age distribution of alewives remained truncated with no alewife exceeding an age of 5. The population of age-1 and older alewives was dominated (i.e., 88%) by the 2010 and 2012 year-classes. Record low biomass was observed for deepwater sculpin (1.3 kt) and ninespine stickleback (0.004 kt) in 2013, while bloater (1.6 kt) and rainbow smelt (0.2 kt) biomasses remained at low levels. Slimy sculpin lake-wide biomass was 0.32 kt in 2013, marking the fourth consecutive year of a decline. The 2013 biomass of round goby was estimated at 10.9 kt, which represented the peak estimate to date. Burbot lake-wide biomass (0.4 kt in 2013) has remained below 3 kt since 2001. Numeric density of age-0 yellow perch (i.e., fish per ha, which is indicative of a relatively poor year-class. Lake-wide biomass estimate of dreissenid mussels in 2013 was 23.2 kt. Overall, the total

Resource partitioning between sympatric starfish from tropical unconsolidated substrate: Implications for coexistence and top-down control on benthic prey

Science.gov (United States)

Fernandez, Wellington S.; Dias, Gustavo M.; Majer, Alessandra P.; Delboni, Cynthia G.; Denadai, Marcia R.; Turra, Alexander

2017-09-01

Starfish are important predators that may shape rocky shore communities, but their ecological role in unconsolidated substrate communities is still poorly known. We assessed the feeding niche overlap of two sympatric starfish, Astropecten marginatus and Luidia senegalensis, from the shallow subtidal zone in southeastern Brazil. During one year, we conducted monthly samples to compare diet composition, abundance and frequency of occurrence of each food item between species. With 24 of the 34 food items identified in this study consumed by both species, they exhibited generalist behaviors, with a more diverse diet during the warm periods, when the main prey items were abundant. However, A. marginatus showed more variation in abundance of prey consumed over time than L. senegalensis. The diet of A. marginatus consisted primarily of the bivalve Tivela mactroides and L. senegalensis of the bivalve Mulinia cleryana. The size of T. mactroides was positively correlated to the size of A. marginatus, while only small-sized individuals of L. senegalensis consumed this item, the most abundant prey in the area and an important food resource for local the community. The large quantity and variety of items consumed by both species support the structuring role of starfish in subtidal unconsolidated substrate communities, exerting a generalist top-down control, primarily on dominant bivalve populations. Temporal variation in the availability of the main prey may change how selective are both species. The differences in prey composition between species and the ontogenetic differences in prey selectivity by L. senegalensis may attenuate interspecific competition, facilitating their coexistence.

Prey risk allocation in a grazing ecosystem.

Science.gov (United States)

Gude, Justin A; Garrott, Robert A; Borkowski, John J; King, Fred

2006-02-01

Understanding the behaviorally mediated indirect effects of predators in ecosystems requires knowledge of predator-prey behavioral interactions. In predator-ungulate-plant systems, empirical research quantifying how predators affect ungulate group sizes and distribution, in the context of other influential variables, is particularly needed. The risk allocation hypothesis proposes that prey behavioral responses to predation risk depend on background frequencies of exposure to risk, and it can be used to make predictions about predator-ungulate-plant interactions. We determined non-predation variables that affect elk (Cervus elaphus) group sizes and distribution on a winter range in the Greater Yellowstone Ecosystem (GYE) using logistic and log-linear regression on surveys of 513 1-km2 areas conducted over two years. Employing model selection techniques, we evaluated risk allocation and other a priori hypotheses of elk group size and distributional responses to wolf (Canis lupus) predation risk while accounting for influential non-wolf-predation variables. We found little evidence that wolves affect elk group sizes, which were strongly influenced by habitat type and hunting by humans. Following predictions from the risk allocation hypothesis, wolves likely created a more dynamic elk distribution in areas that they frequently hunted, as elk tended to move following wolf encounters in those areas. This response should dilute elk foraging pressure on plant communities in areas where they are frequently hunted by wolves. We predict that this should decrease the spatial heterogeneity of elk impacts on grasslands in areas that wolves frequently hunt. We also predict that this should decrease browsing pressure on heavily browsed woody plant stands in certain areas, which is supported by recent research in the GYE.

Estimation of grey seal (Halichoerus grypus diet composition in the Baltic Sea

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Karl Lundström

2007-01-01

Full Text Available We examined the digestive tract contents from 145 grey seals (Halichoerus grypus collected between 2001 and 2004 in the Baltic Sea. We compensated for biases introduced by erosion of otoliths, both by using additional hard-part structures other than otoliths, and species-specific size and numerical correction factors. In the absence of numerical correction factors based on feeding experiments for some species, we used correction factors based on a relationship between otolith recoveryrate and otolith width. A total of 24 prey taxa were identified but only a few species contributed substantially to the diet. The estimated diet composition was, independently of the prey number estimation method and diet composition estimation model used, dominated by herring (Clupea harengus, both by numbers and biomass. In addition to herring, common whitefish (Coregonus lavaretus and sprat (Sprattus sprattus were important prey, but cyprinids (Cyprinidae, eelpout (Zoarces viviparus, flounder (Platichtys flesus and salmon (Salmo salar also contributed significantly. Our results indicated dietary differences between grey seals of different age as well as between seals from the northern (Gulf of Bothnia and the southern (Baltic Proper Baltic Sea.

Prey detection in a cruising copepod

DEFF Research Database (Denmark)

Kjellerup, Sanne; Kiørboe, Thomas

2012-01-01

. Yet, direct interception has been proposed to explain how rapidly cruising, blind copepods feed on non-motile phytoplankton prey. Here, we demonstrate a novel mechanism for prey detection in a cruising copepod, and describe how motile and non-motile prey are discovered by hydromechanical and tactile...

Association between inaccurate estimation of body size and obesity in schoolchildren

Directory of Open Access Journals (Sweden)

Larissa da Cunha Feio Costa

2015-12-01

Full Text Available Objectives: To investigate the prevalence of inaccurate estimation of own body size among Brazilian schoolchildren of both sexes aged 7-10 years, and to test whether overweight/obesity; excess body fat and central obesity are associated with inaccuracy. Methods: Accuracy of body size estimation was assessed using the Figure Rating Scale for Brazilian Children. Multinomial logistic regression was used to analyze associations. Results: The overall prevalence of inaccurate body size estimation was 76%, with 34% of the children underestimating their body size and 42% overestimating their body size. Obesity measured by body mass index was associated with underestimation of body size in both sexes, while central obesity was only associated with overestimation of body size among girls. Conclusions: The results of this study suggest there is a high prevalence of inaccurate body size estimation and that inaccurate estimation is associated with obesity. Accurate estimation of own body size is important among obese schoolchildren because it may be the first step towards adopting healthy lifestyle behaviors.

The Dynamical Analysis of a Prey-Predator Model with a Refuge-Stage Structure Prey Population

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Raid Kamel Naji

2016-01-01

Full Text Available We proposed and analyzed a mathematical model dealing with two species of prey-predator system. It is assumed that the prey is a stage structure population consisting of two compartments known as immature prey and mature prey. It has a refuge capability as a defensive property against the predation. The existence, uniqueness, and boundedness of the solution of the proposed model are discussed. All the feasible equilibrium points are determined. The local and global stability analysis of them are investigated. The occurrence of local bifurcation (such as saddle node, transcritical, and pitchfork near each of the equilibrium points is studied. Finally, numerical simulations are given to support the analytic results.

Prey selection of corallivorous muricids at Koh Tao (Gulf of Thailand) four years after a major coral bleaching event

NARCIS (Netherlands)

Moerland, M.S.; Scott, C.M.; Hoeksema, B.W.

2016-01-01

Corallivorous Drupella (Muricidae) snails at Koh Tao are reported to have extended their range of prey species following a major coral bleaching event in 2010. Populations of their preferred Acropora prey had locally diminished in both size and abundance, and the snails had introduced free-living

Predicting prey population dynamics from kill rate, predation rate and predator-prey ratios in three wolf-ungulate systems.

Science.gov (United States)

Vucetich, John A; Hebblewhite, Mark; Smith, Douglas W; Peterson, Rolf O

2011-11-01

1. Predation rate (PR) and kill rate are both fundamental statistics for understanding predation. However, relatively little is known about how these statistics relate to one another and how they relate to prey population dynamics. We assess these relationships across three systems where wolf-prey dynamics have been observed for 41 years (Isle Royale), 19 years (Banff) and 12 years (Yellowstone). 2. To provide context for this empirical assessment, we developed theoretical predictions of the relationship between kill rate and PR under a broad range of predator-prey models including predator-dependent, ratio-dependent and Lotka-Volterra dynamics. 3. The theoretical predictions indicate that kill rate can be related to PR in a variety of diverse ways (e.g. positive, negative, unrelated) that depend on the nature of predator-prey dynamics (e.g. structure of the functional response). These simulations also suggested that the ratio of predator-to-prey is a good predictor of prey growth rate. That result motivated us to assess the empirical relationship between the ratio and prey growth rate for each of the three study sites. 4. The empirical relationships indicate that PR is not well predicted by kill rate, but is better predicted by the ratio of predator-to-prey. Kill rate is also a poor predictor of prey growth rate. However, PR and ratio of predator-to-prey each explained significant portions of variation in prey growth rate for two of the three study sites. 5. Our analyses offer two general insights. First, Isle Royale, Banff and Yellowstone are similar insomuch as they all include wolves preying on large ungulates. However, they also differ in species diversity of predator and prey communities, exploitation by humans and the role of dispersal. Even with the benefit of our analysis, it remains difficult to judge whether to be more impressed by the similarities or differences. This difficulty nicely illustrates a fundamental property of ecological

Do lions Panthera leo actively select prey or do prey preferences simply reflect chance responses via evolutionary adaptations to optimal foraging?

Directory of Open Access Journals (Sweden)

Matt W Hayward

Full Text Available Research on coursing predators has revealed that actions throughout the predatory behavioral sequence (using encounter rate, hunting rate, and kill rate as proxy measures of decisions drive observed prey preferences. We tested whether similar actions drive the observed prey preferences of a stalking predator, the African lion Panthera leo. We conducted two 96 hour, continuous follows of lions in Addo Elephant National Park seasonally from December 2003 until November 2005 (16 follows, and compared prey encounter rate with prey abundance, hunt rate with prey encounter rate, and kill rate with prey hunt rate for the major prey species in Addo using Jacobs' electivity index. We found that lions encountered preferred prey species far more frequently than expected based on their abundance, and they hunted these species more frequently than expected based on this higher encounter rate. Lions responded variably to non-preferred and avoided prey species throughout the predatory sequence, although they hunted avoided prey far less frequently than expected based on the number of encounters of them. We conclude that actions of lions throughout the predatory behavioural sequence, but particularly early on, drive the prey preferences that have been documented for this species. Once a hunt is initiated, evolutionary adaptations to the predator-prey interactions drive hunting success.

Do lions Panthera leo actively select prey or do prey preferences simply reflect chance responses via evolutionary adaptations to optimal foraging?

Science.gov (United States)

Hayward, Matt W; Hayward, Gina J; Tambling, Craig J; Kerley, Graham I H

2011-01-01

Research on coursing predators has revealed that actions throughout the predatory behavioral sequence (using encounter rate, hunting rate, and kill rate as proxy measures of decisions) drive observed prey preferences. We tested whether similar actions drive the observed prey preferences of a stalking predator, the African lion Panthera leo. We conducted two 96 hour, continuous follows of lions in Addo Elephant National Park seasonally from December 2003 until November 2005 (16 follows), and compared prey encounter rate with prey abundance, hunt rate with prey encounter rate, and kill rate with prey hunt rate for the major prey species in Addo using Jacobs' electivity index. We found that lions encountered preferred prey species far more frequently than expected based on their abundance, and they hunted these species more frequently than expected based on this higher encounter rate. Lions responded variably to non-preferred and avoided prey species throughout the predatory sequence, although they hunted avoided prey far less frequently than expected based on the number of encounters of them. We conclude that actions of lions throughout the predatory behavioural sequence, but particularly early on, drive the prey preferences that have been documented for this species. Once a hunt is initiated, evolutionary adaptations to the predator-prey interactions drive hunting success.

A Size-based Ecosystem Model

DEFF Research Database (Denmark)

Ravn-Jonsen, Lars

 Ecosystem Management requires models that can link the ecosystem level to the operation level. This link can be created by an ecosystem production model. Because the function of the individual fish in the marine ecosystem, seen in trophic context, is closely related to its size, the model groups...... fish according to size. The model summarises individual predation events into ecosystem level properties, and thereby uses the law of conversation of mass as a framework. This paper provides the background, the conceptual model, basic assumptions, integration of fishing activities, mathematical...... the predator--prey interaction, (ii) mass balance in the predator--prey allocation, and (iii) mortality and somatic growth as a consequence of the predator--prey allocation. By incorporating additional assumptions, the model can be extended to other dimensions of the ecosystem, for example, space or species...

When attempts at robbing prey turn fatal

Science.gov (United States)

Dejean, Alain; Corbara, Bruno; Azémar, Frédéric; Carpenter, James M.

2012-07-01

Because group-hunting arboreal ants spread-eagle insect prey for a long time before retrieving them, these prey can be coveted by predatory flying insects. Yet, attempting to rob these prey is risky if the ant species is also an effective predator. Here, we show that trying to rob prey from Azteca andreae workers is a fatal error as 268 out of 276 potential cleptobionts (97.1 %) were captured in turn. The ant workers hunt in a group and use the "Velcro®" principle to cling firmly to the leaves of their host tree, permitting them to capture very large prey. Exceptions were one social wasp, plus some Trigona spp. workers and flies that landed directly on the prey and were able to take off immediately when attacked. We conclude that in this situation, previously captured prey attract potential cleptobionts that are captured in turn in most of the cases.

Preliminarily study on the maximum handling size, prey size and species selectivity of growth hormone transgenic and non-transgenic common carp Cyprinus carpio when foraging on gastropods

Science.gov (United States)

Zhu, Tingbing; Zhang, Lihong; Zhang, Tanglin; Wang, Yaping; Hu, Wei; Olsen, Rolf Eric; Zhu, Zuoyan

2017-10-01

The present study preliminarily examined the differences in maximum handling size, prey size and species selectivity of growth hormone transgenic and non-transgenic common carp Cyprinus carpio when foraging on four gastropods species (Bellamya aeruginosa, Radix auricularia, Parafossarulus sinensis and Alocinma longicornis) under laboratory conditions. In the maximum handling size trial, five fish from each age group (1-year-old and 2-year-old) and each genotype (transgenic and non-transgenic) of common carp were individually allowed to feed on B. aeruginosa with wide shell height range. The results showed that maximum handling size increased linearly with fish length, and there was no significant difference in maximum handling size between the two genotypes. In the size selection trial, three pairs of 2-year-old transgenic and non-transgenic carp were individually allowed to feed on three size groups of B. aeruginosa. The results show that the two genotypes of C. carpio favored the small-sized group over the large-sized group. In the species selection trial, three pairs of 2-year-old transgenic and non-transgenic carp were individually allowed to feed on thin-shelled B. aeruginosa and thick-shelled R. auricularia, and five pairs of 2-year-old transgenic and non-transgenic carp were individually allowed to feed on two gastropods species (P. sinensis and A. longicornis) with similar size and shell strength. The results showed that both genotypes preferred thin-shelled Radix auricularia rather than thick-shelled B. aeruginosa, but there were no significant difference in selectivity between the two genotypes when fed on P. sinensis and A. longicornis. The present study indicates that transgenic and non-transgenic C. carpio show similar selectivity of predation on the size- and species-limited gastropods. While this information may be useful for assessing the environmental risk of transgenic carp, it does not necessarily demonstrate that transgenic common carp might

Behavioral response races, predator-prey shell games, ecology of fear, and patch use of pumas and their ungulate prey.

Science.gov (United States)

Laundré, John W

2010-10-01

The predator-prey shell game predicts random movement of prey across the landscape, whereas the behavioral response race and landscape of fear models predict that there should be a negative relationship between the spatial distribution of a predator and its behaviorally active prey. Additionally, prey have imperfect information on the whereabouts of their predator, which the predator should incorporate in its patch use strategy. I used a one-predator-one-prey system, puma (Puma concolor)-mule deer (Odocoileus hemionus) to test the following predictions regarding predator-prey distribution and patch use by the predator. (1) Pumas will spend more time in high prey risk/low prey use habitat types, while deer will spend their time in low-risk habitats. Pumas should (2) select large forage patches more often, (3) remain in large patches longer, and (4) revisit individual large patches more often than individual smaller ones. I tested these predictions with an extensive telemetry data set collected over 16 years in a study area of patchy forested habitat. When active, pumas spent significantly less time in open areas of low intrinsic predation risk than did deer. Pumas used large patches more than expected, revisited individual large patches significantly more often than smaller ones, and stayed significantly longer in larger patches than in smaller ones. The results supported the prediction of a negative relationship in the spatial distribution of a predator and its prey and indicated that the predator is incorporating the prey's imperfect information about its presence. These results indicate a behavioral complexity on the landscape scale that can have far-reaching impacts on predator-prey interactions.

Estimation of sample size and testing power (part 5).

Science.gov (United States)

Hu, Liang-ping; Bao, Xiao-lei; Guan, Xue; Zhou, Shi-guo

2012-02-01

Estimation of sample size and testing power is an important component of research design. This article introduced methods for sample size and testing power estimation of difference test for quantitative and qualitative data with the single-group design, the paired design or the crossover design. To be specific, this article introduced formulas for sample size and testing power estimation of difference test for quantitative and qualitative data with the above three designs, the realization based on the formulas and the POWER procedure of SAS software and elaborated it with examples, which will benefit researchers for implementing the repetition principle.

Toxoplasmosis in prey species and consequences for prevalence in feral cats: not all prey species are equal.

Science.gov (United States)

Afonso, E; Thulliez, P; Pontier, D; Gilot-Fromont, E

2007-12-01

Toxoplasma gondii is largely transmitted to definitive felid hosts through predation. Not all prey species represent identical risks of infection for cats because of differences in prey susceptibility, exposure and/or lifespan. Previously published studies have shown that prevalence in rodent and lagomorph species is positively correlated with body mass. We tested the hypothesis that different prey species have different infection risks by comparing infection dynamics of feral cats at 4 sites in the sub-Antarctic Kerguelen archipelago which differed in prey availability. Cats were trapped from 1994 to 2004 and anti-T. gondii IgG antibodies were detected using the modified agglutination test (> or =1:40). Overall seroprevalence was 51.09%. Antibody prevalence differed between sites, depending on diet and also on sex, after taking into account the effect of age. Males were more often infected than females and the difference between the sexes tended to be more pronounced in the site where more prey species were available. A difference in predation efficiency between male and female cats may explain this result. Overall, our results suggest that the composition of prey items in cat diet influences the risk of T. gondii infection. Prey compositon should therefore be considered important in any understanding of infection dynamics of T. gondii.

Relative Preference and Localized Food Affect Predator Space Use and Consumption of Incidental Prey.

Directory of Open Access Journals (Sweden)

Tyler E Schartel

Full Text Available Abundant, localized foods can concentrate predators and their foraging efforts, thus altering both the spatial distribution of predation risk and predator preferences for prey that are encountered incidentally. However, few investigations have quantified the spatial scale over which localized foods affect predator foraging behavior and consumption of incidental prey. In spring 2010, we experimentally tested how point-source foods altered how generalist predators (white-footed mice, Peromyscus leucopus utilized space and depredated two incidental prey items: almonds (Prunus dulcis; highly profitable and maple seeds (Acer saccharum; less profitable. We estimated mouse population densities with trapping webs, quantified mouse consumption rates of these incidental prey items, and measured local mouse activity with track plates. We predicted that 1 mouse activity would be elevated near full feeders, but depressed at intermediate distances from the feeder, 2 consumption of both incidental prey would be high near feeders providing less-preferred food and, 3 consumption of incidental prey would be contingent on predator preference for prey relative to feeders providing more-preferred food. Mouse densities increased significantly from pre- to post-experiment. Mean mouse activity was unexpectedly greatest in control treatments, particularly <15 m from the control (empty feeder. Feeders with highly preferred food (sunflower seeds created localized refuges for incidental prey at intermediate distances (15 to 25m from the feeder. Feeders with less-preferred food (corn generated localized high risk for highly preferred almonds <10 m of the feeder. Our findings highlight the contingent but predictable effects of locally abundant food on risk experienced by incidental prey, which can be positive or negative depending on both spatial proximity and relative preference.

Effects of allochthonous inputs in the control of infectious disease of prey

International Nuclear Information System (INIS)

Sahoo, Banshidhar; Poria, Swarup

2015-01-01

Highlights: •Infected predator–prey model with allochthonous inputs is proposed. •Stability and persistence conditions are derived. •Bifurcation is determined with respect to allochthonous inputs. •Results show that system can not be disease free without allochthonous inputs. •Hopf and its continuation bifurcation is analysed numerically. -- Abstract: Allochthonous inputs are important sources of productivity in many food webs and their influences on food chain model demand further investigations. In this paper, assuming the existence of allochthonous inputs for intermediate predator, a food chain model is formulated with disease in the prey. The stability and persistence conditions of the equilibrium points are determined. Extinction criterion for infected prey population is obtained. It is shown that suitable amount of allochthonous inputs to intermediate predator can control infectious disease of prey population, provided initial intermediate predator population is above a critical value. This critical intermediate population size increases monotonically with the increase of infection rate. It is also shown that control of infectious disease of prey is possible in some cases of seasonally varying contact rate. Dynamical behaviours of the model are investigated numerically through one and two parameter bifurcation analysis using MATCONT 2.5.1 package. The occurrence of Hopf and its continuation curves are noted with the variation of infection rate and allochthonous food availability. The continuation curves of limit point cycle and Neimark Sacker bifurcation are drawn by varying the rate of infection and allochthonous inputs. This study introduces a novel natural non-toxic method for controlling infectious disease of prey in a food chain model

Relationships of body lengths with mouth opening and prey length of nemipterid fishes (Regan, 1913 in the Gulf of Thailand

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Mithun Paul

2017-12-01

Full Text Available This study aims to investigate the relationship among total length (TL of fish with mouth opening namely horizontal opening (MH, vertical opening (VH, mouth area (MA and fork length (FL of seven sympatric nemipterid fish species and to know the relationship between total length and consumed prey length of five sympatric species sampled from the Gulf of Thailand in 2015. A total 883 fish were investigated collected from both cruise surveys and fishing port survey. TL was linearly and log-linearly related with both MV and MH for three and four species, respectively. MA’s were always the log linear relation of TL and shapes were nearly oval for all species. FL in all TL-FL relationships were proportional to the TL’s in all species (r2 = 0.94, P  .5 and in invertebrate prey items for N. tambuloides (P > .5. So, this study clearly confirms that nemipterid fishes of different sizes feed on all different specific prey items according to its own body size and feed according to size class for prey items available nearby.

The effect of structural complexity, prey density, and "predator-free space" on prey survivorship at created oyster reef mesocosms

Science.gov (United States)

Humphries, Austin T.; La Peyre, Megan K.; Decossas, Gary A.

2011-01-01

Interactions between predators and their prey are influenced by the habitat they occupy. Using created oyster (Crassostrea virginica) reef mesocosms, we conducted a series of laboratory experiments that created structure and manipulated complexity as well as prey density and “predator-free space” to examine the relationship between structural complexity and prey survivorship. Specifically, volume and spatial arrangement of oysters as well as prey density were manipulated, and the survivorship of prey (grass shrimp, Palaemonetes pugio) in the presence of a predator (wild red drum, Sciaenops ocellatus) was quantified. We found that the presence of structure increased prey survivorship, and that increasing complexity of this structure further increased survivorship, but only to a point. This agrees with the theory that structural complexity may influence predator-prey dynamics, but that a threshold exists with diminishing returns. These results held true even when prey density was scaled to structural complexity, or the amount of “predator-free space” was manipulated within our created reef mesocosms. The presence of structure and its complexity (oyster shell volume) were more important in facilitating prey survivorship than perceived refugia or density-dependent prey effects. A more accurate indicator of refugia might require “predator-free space” measures that also account for the available area within the structure itself (i.e., volume) and not just on the surface of a structure. Creating experiments that better mimic natural conditions and test a wider range of “predator-free space” are suggested to better understand the role of structural complexity in oyster reefs and other complex habitats.

Match or mismatch: the influence of phenology on size-dependent life history and divergence in population structure

Science.gov (United States)

Borcherding, Jost; Beeck, Peter; DeAngelis, Donald L.; Scharf, Werner R.

2010-01-01

Summary 1. In gape-limited predators, body size asymmetries determine the outcome of predator-prey interactions. Due to ontogenetic changes in body size, the intensity of intra- and interspecific interactions may change rapidly between the match situation of a predator-prey system and the mismatch situation in which competition, including competition with the prey, dominates. 2. Based on a physiologically structured population model using the European perch (Perca fluviatilis), analysis was performed on how prey density (bream, Abramis brama), initial size differences in the young-of-the-year (YOY) age cohort of the predator, and phenology (time-gap in hatching of predator and prey) influence the size structure of the predator cohort. 3. In relation to the seasonality of reproduction, the match situation of the predator-prey system occurred when perch hatched earlier than bream and when no gape-size limitations existed, leading to decreased size divergence in the predator age cohort. Decreased size divergence was also found when bream hatched much earlier than perch, preventing perch predation on bream occurring, which, in turn, increased the competitive interaction of the perch with bream for the common prey, zooplankton; i.e. the mismatch situation in which also the mean size of the age cohort of the predator decreased. 4. In between the total match and the mismatch, however, only the largest individuals of the perch age cohort were able to prey on the bream, while smaller conspecifics got trapped in competition with each other and with bream for zooplankton, leading to enlarged differences in growth that increased size divergence. 5. The modelling results were combined with 7 years of field data in a lake, where large differences in the length-frequency distribution of YOY perch were observed after their first summer. These field data corroborate that phenology and prey density per predator are important mechanisms in determining size differences within the YOY

Feeding opportunities of larval and juvenile cod (Gadus morhua) in a Greenlandic fjord: temporal and spatial linkages between cod and their preferred prey

DEFF Research Database (Denmark)

Swalethorp, Rasmus; Kjellerup, Sanne; Malanski, Evandro

2014-01-01

preferences of the early-life stages of Atlantic cod (Gadus morhua) to quantify the availability of prey during a spring-summer season in a West Greenlandic fjord. We hypothesized that abundances of larval and juvenile cod at size were synchronized to optimal availability of preferred prey in space and time....... These findings stress the importance of focusing on abundance of preferred prey when assessing the actual prey availability to young fish. We found a spatio-temporal overlap between cod and their preferred prey, and observations suggest that advection of both zooplankton and cod contributed to this overlap...

Effect of sociality and season on gray wolf (Canis lupus foraging behavior: implications for estimating summer kill rate.

Directory of Open Access Journals (Sweden)

Matthew C Metz

Full Text Available BACKGROUND: Understanding how kill rates vary among seasons is required to understand predation by vertebrate species living in temperate climates. Unfortunately, kill rates are only rarely estimated during summer. METHODOLOGY/PRINCIPAL FINDINGS: For several wolf packs in Yellowstone National Park, we used pairs of collared wolves living in the same pack and the double-count method to estimate the probability of attendance (PA for an individual wolf at a carcass. PA quantifies an important aspect of social foraging behavior (i.e., the cohesiveness of foraging. We used PA to estimate summer kill rates for packs containing GPS-collared wolves between 2004 and 2009. Estimated rates of daily prey acquisition (edible biomass per wolf decreased from 8.4±0.9 kg (mean ± SE in May to 4.1±0.4 kg in July. Failure to account for PA would have resulted in underestimating kill rate by 32%. PA was 0.72±0.05 for large ungulate prey and 0.46±0.04 for small ungulate prey. To assess seasonal differences in social foraging behavior, we also evaluated PA during winter for VHF-collared wolves between 1997 and 2009. During winter, PA was 0.95±0.01. PA was not influenced by prey size but was influenced by wolf age and pack size. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that seasonal patterns in the foraging behavior of social carnivores have important implications for understanding their social behavior and estimating kill rates. Synthesizing our findings with previous insights suggests that there is important seasonal variation in how and why social carnivores live in groups. Our findings are also important for applications of GPS collars to estimate kill rates. Specifically, because the factors affecting the PA of social carnivores likely differ between seasons, kill rates estimated through GPS collars should account for seasonal differences in social foraging behavior.

Tigers and Their Prey in Bukit Rimbang Bukit Baling: Abundance Baseline for Effective Wildlife Reserve Management

Directory of Open Access Journals (Sweden)

Febri Anggriawan Widodo

2017-07-01

Full Text Available Managing the critically endangered Sumatran tiger (Panthera tigris sumatrae needs accurate information on its abundance and availability of prey at the landscape level. Bukit Rimbang Bukit Baling Wildlife Reserve in central Sumatra represents an important area for tigers at local, regional and global levels. The area has been recognized as a long-term priority Tiger Conservation Landscape. Solid baseline information on tigers and prey is fundamentally needed for the management. The objective of this study was to produce robust estimate of tiger density and prey a vailability in the reserve. We used camera traps to systematically collecting photographic samples of tigers and prey using Spatial Capture Recapture (SCR framework. We estimated density for tigers and calculated trap success rate (TSR; independent pictures/100 trap nights for main prey species. Three blocks in the reserve were sampled from 2012 to 2015 accumulating a total of 8,125 effective trap nights. We captured 14 tiger individuals including three cubs. We documented the highest density of tigers (individuals/100 km2 in southern sampling block (based on traditional capture recapture (TCR : 1.52 ± SE 0.55; based on Maximum Likelihood (ML SCR:0.51 ± SE 0.22 and the lowest in northeastern sampling block (TCR: 0.77 ±SE 0.39; ML SCR: 0.19 ± SE 0.16. The highest TSR of main prey (large ungulates and primates was in northeastern block (35.01 ± SD 8.67 and the lowest was in southern block (12.42 ± SD 2.91. The highest level of disturbance, as indicated by TSR of people, was in northeastern sampling block (5.45 ± SD 5.64 and the lowest in southern (1.26 ± SD 2.41. The results suggested that human disturbance strongly determine the density of tigers in the area, more than prey availability. To recover tigers, suggested strategies include controlling human disturbance and poaching to the lowest possible level in addition to maintaining main prey availability.

Diversity in thermal affinity among key piscivores buffers impacts of ocean warming on predator-prey interactions.

Science.gov (United States)

Selden, Rebecca L; Batt, Ryan D; Saba, Vincent S; Pinsky, Malin L

2018-01-01

Asymmetries in responses to climate change have the potential to alter important predator-prey interactions, in part by altering the location and size of spatial refugia for prey. We evaluated the effect of ocean warming on interactions between four important piscivores and four of their prey in the U.S. Northeast Shelf by examining species overlap under historical conditions (1968-2014) and with a doubling in CO 2 . Because both predator and prey shift their distributions in response to changing ocean conditions, the net impact of warming or cooling on predator-prey interactions was not determined a priori from the range extent of either predator or prey alone. For Atlantic cod, an historically dominant piscivore in the region, we found that both historical and future warming led to a decline in the proportion of prey species' range it occupied and caused a potential reduction in its ability to exert top-down control on these prey. In contrast, the potential for overlap of spiny dogfish with prey species was enhanced by warming, expanding their importance as predators in this system. In sum, the decline in the ecological role for cod that began with overfishing in this ecosystem will likely be exacerbated by warming, but this loss may be counteracted by the rise in dominance of other piscivores with contrasting thermal preferences. Functional diversity in thermal affinity within the piscivore guild may therefore buffer against the impact of warming on marine ecosystems, suggesting a novel mechanism by which diversity confers resilience. © 2017 John Wiley & Sons Ltd.

The threshold of coexistence and critical behaviour of a predator-prey cellular automaton

International Nuclear Information System (INIS)

Arashiro, Everaldo; Tome, Tania

2007-01-01

We study a probabilistic cellular automaton to describe two population biology problems: the threshold of species coexistence in a predator-prey system and the spreading of an epidemic in a population. By carrying out mean-field approximations and numerical simulations we obtain the phase boundaries (thresholds) related to the transition between an active state, where prey and predators present a stable coexistence, and a prey absorbing state. The numerical estimates for the critical exponents show that the transition belongs to the directed percolation universality class. In the limit where the cellular automaton maps into a model for the spreading of an epidemic with immunization we observe a crossover from directed percolation class to the dynamic percolation class. Patterns of growing clusters related to species coexistence and spreading of epidemic are shown and discussed

Prey selection of a captive Oystercatcher Haematopus ostralegus hammering Mussels Mytilus edulis from the ventral side

NARCIS (Netherlands)

Ens, Bruno J.; Alting, D

1996-01-01

We studied prey choice of a captive Oystercatcher:hat hammered Mussels from the ventral side. The results replicate previous findings that ventral hammerers select Mussels of intermediate size, select against thick-shelled Mussels, abandon an increasing proportion of Mussels with increasing size and

Competition and Dispersal in Predator-Prey Waves

NARCIS (Netherlands)

Savill, N.J.; Hogeweg, P.

1998-01-01

Dispersing predators and prey can exhibit complex spatio-temporal wave-like patterns if the interactions between them cause oscillatory dynamics. We study the effect of these predator- prey density waves on the competition between prey populations and between predator popu- lations with different

How to Estimate and Interpret Various Effect Sizes

Science.gov (United States)

Vacha-Haase, Tammi; Thompson, Bruce

2004-01-01

The present article presents a tutorial on how to estimate and interpret various effect sizes. The 5th edition of the Publication Manual of the American Psychological Association (2001) described the failure to report effect sizes as a "defect" (p. 5), and 23 journals have published author guidelines requiring effect size reporting. Although…

Indirect Allee effect, bistability and chaotic oscillations in a predator-prey discrete model of logistic type

International Nuclear Information System (INIS)

Lopez-Ruiz, Ricardo; Fournier-Prunaret, Daniele

2005-01-01

A cubic discrete coupled logistic equation is proposed to model the predator-prey problem. The coupling depends on the population size of both species and on a positive constant λ, which could depend on the prey reproduction rate and on the predator hunting strategy. Different dynamical regimes are obtained when λ is modified. For small λ, the species become extinct. For a bigger λ, the preys survive but the predators extinguish. Only when the prey population reaches a critical value then predators can coexist with preys. For increasing λ, a bistable regime appears where the populations apart of being stabilized in fixed quantities can present periodic, quasiperiodic and chaotic oscillations. Finally, bistability is lost and the system settles down in a steady state, or, for the biggest permitted λ, in an invariant curve. We also present the basins for the different regimes. The use of the critical curves lets us determine the influence of the zones with different number of first rank preimages in the bifurcation mechanisms of those basins

What enables size-selective trophy hunting of wildlife?

Directory of Open Access Journals (Sweden)

Chris T Darimont

Full Text Available Although rarely considered predators, wildlife hunters can function as important ecological and evolutionary agents. In part, their influence relates to targeting of large reproductive adults within prey populations. Despite known impacts of size-selective harvests, however, we know little about what enables hunters to kill these older, rarer, and presumably more wary individuals. In other mammalian predators, predatory performance varies with knowledge and physical condition, which accumulates and declines, respectively, with age. Moreover, some species evolved camouflage as a physical trait to aid in predatory performance. In this work, we tested whether knowledge-based faculty (use of a hunting guide with accumulated experience in specific areas, physical traits (relative body mass [RBM] and camouflage clothing, and age can predict predatory performance. We measured performance as do many hunters: size of killed cervid prey, using the number of antler tines as a proxy. Examining ∼ 4300 online photographs of hunters posing with carcasses, we found that only the presence of guides increased the odds of killing larger prey. Accounting for this effect, modest evidence suggested that unguided hunters presumably handicapped with the highest RBM actually had greater odds of killing large prey. There was no association with hunter age, perhaps because of our coarse measure (presence of grey hair and the performance trade-offs between knowledge accumulation and physical deterioration with age. Despite its prevalence among sampled hunters (80%, camouflage had no influence on size of killed prey. Should these patterns be representative of other areas and prey, and our interpretations correct, evolutionarily-enlightened harvest management might benefit from regulatory scrutiny on guided hunting. More broadly, we suggest that by being nutritionally and demographically de-coupled from prey and aided by efficient killing technology and road access

Food photographs in portion size estimation among adolescent Mozambican girls.

Science.gov (United States)

Korkalo, Liisa; Erkkola, Maijaliisa; Fidalgo, Lourdes; Nevalainen, Jaakko; Mutanen, Marja

2013-09-01

To assess the validity of food photographs in portion size estimation among adolescent girls in Mozambique. The study was carried out in preparation for the larger ZANE study, which used the 24 h dietary recall method. Life-sized photographs of three portion sizes of two staple foods and three sauces were produced. Participants ate weighed portions of one staple food and one sauce. After the meal, they were asked to estimate the amount of food with the aid of the food photographs. Zambezia Province, Mozambique. Ninety-nine girls aged 13–18 years. The mean differences between estimated and actual portion sizes relative to the actual portion size ranged from 219% to 8% for different foods. The respective mean difference for all foods combined was 25% (95% CI 212, 2 %). Especially larger portions of the staple foods were often underestimated. For the staple foods, between 62% and 64% of the participants were classified into the same thirds of the distribution of estimated and actual food consumption and for sauces, the percentages ranged from 38% to 63%. Bland–Altman plots showed wide limits of agreement. Using life-sized food photographs among adolescent Mozambican girls resulted in a rather large variation in the accuracy of individuals’ estimates. The ability to rank individuals according to their consumption was, however, satisfactory for most foods. There seems to be a need to further develop and test food photographs used in different populations in Sub-Saharan Africa to improve the accuracy of portion size estimates.

Prey aggregation is an effective olfactory predator avoidance strategy

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Asa Johannesen

2014-05-01

Full Text Available Predator–prey interactions have a major effect on species abundance and diversity, and aggregation is a well-known anti-predator behaviour. For immobile prey, the effectiveness of aggregation depends on two conditions: (a the inability of the predator to consume all prey in a group and (b detection of a single large group not being proportionally easier than that of several small groups. How prey aggregation influences predation rates when visual cues are restricted, such as in turbid water, has not been thoroughly investigated. We carried out foraging (predation experiments using a fish predator and (dead chironomid larvae as prey in both laboratory and field settings. In the laboratory, a reduction in visual cue availability (in turbid water led to a delay in the location of aggregated prey compared to when visual cues were available. Aggregated prey suffered high mortality once discovered, leading to better survival of dispersed prey in the longer term. We attribute this to the inability of the dead prey to take evasive action. In the field (where prey were placed in feeding stations that allowed transmission of olfactory but not visual cues, aggregated (large groups and semi-dispersed prey survived for longer than dispersed prey—including long term survival. Together, our results indicate that similar to systems where predators hunt using vision, aggregation is an effective anti-predator behaviour for prey avoiding olfactory predators.

Prey capture by harbour porpoises

DEFF Research Database (Denmark)

Verfuss, Ursula; Miller, Lee; Pilz, Peter

their ultrasonic clicks as biosonar for orientation and detection of prey (mostly smaller pelagic and bottom dwelling fish), and for communication.  For studying wild animals, hydrophone arrays [Villadsgaard et al. J.Exp.Biol. 210 (2007)] and acoustic (time/depth) tags [Akamatsu et al. Deep Sea Research II 54...... (2007)] have been used.  For studying captive animals, arrays and video techniques [Verfuß et al. J.Exp.Biol. 208 (2005)] as well as miniature acoustic-behavioral tags [Deruiter et al. JASA 123 (2008)] have been used.  While searching for prey, harbor porpoises use clicks at long intervals (>50 ms......) that progressively decrease when closing on a landmark.  The source levels of captive animals reduce by about half for each halving of the distance to the target.  After detecting the prey, the click interval first stabilizes at about 50 ms and then becomes progressively shorter while approaching the prey...

Fishing destabilizes the biomass flow in the marine size spectrum

OpenAIRE

Rochet, M.-J.; Benoît, E.

2011-01-01

Fishing impacts on marine food webs are predicted by simulations of a size spectrum community model. In this model, predation is determined by predator and prey size and abundance, and drives predator growth and prey mortality. Fishing amplifies temporal oscillations in the biomass flow. Oscillations appear at lower fishing intensity and have wider amplitude when fishing is selective (removes a narrow size range) and/or when large fish are targeted, than when fishing is more balanced (catchin...

Should fatty acid signature proportions sum to 1 for diet estimation?

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Bromaghin, Jeffrey F.; Budge, Suzanne M.; Thiemann, Gregory W.

2016-01-01

Knowledge of predator diets, including how diets might change through time or differ among predators, provides essential insights into their ecology. Diet estimation therefore remains an active area of research within quantitative ecology. Quantitative fatty acid signature analysis (QFASA) is an increasingly common method of diet estimation. QFASA is based on a data library of prey signatures, which are vectors of proportions summarizing the fatty acid composition of lipids, and diet is estimated as the mixture of prey signatures that most closely approximates a predator’s signature. Diets are typically estimated using proportions from a subset of all fatty acids that are known to be solely or largely influenced by diet. Given the subset of fatty acids selected, the current practice is to scale their proportions to sum to 1.0. However, scaling signature proportions has the potential to distort the structural relationships within a prey library and between predators and prey. To investigate that possibility, we compared the practice of scaling proportions with two alternatives and found that the traditional scaling can meaningfully bias diet estimators under some conditions. Two aspects of the prey types that contributed to a predator’s diet influenced the magnitude of the bias: the degree to which the sums of unscaled proportions differed among prey types and the identifiability of prey types within the prey library. We caution investigators against the routine scaling of signature proportions in QFASA.

Prey switching behaviour in the planktonic copepod Acartia tonsa

DEFF Research Database (Denmark)

Kiørboe, Thomas; Saiz, E.; Viitasalo, M.

1996-01-01

The copepod Acartia tonsa has 2 different prey encounter strategies. It can generate a feeding current to encounter and capture immobile prey (suspension feeding) or it can sink slowly and perceive motile prey by means of mechanoreceptors on the antennae (ambush feeding). We hypothesized that A....... tonsa adopts the feeding mode that generates the highest energy intake rate; i.e. that prey selection changes according to the relative concentrations of alternative prey (prey switching) and that the copepods spend disproportionately more time in the feeding mode that provides the greatest reward...... be captured by suspension feeding copepods. Finally, we demonstrate that turbulence favours the selection of ciliates as prey. We suggest that prey switching by copepods may provide survival windows for microzooplankters during blooms of net phytoplankton because predation pressure from the copepods...

Predatory functional response and prey choice identify predation differences between native/invasive and parasitised/unparasitised crayfish.

Science.gov (United States)

Haddaway, Neal R; Wilcox, Ruth H; Heptonstall, Rachael E A; Griffiths, Hannah M; Mortimer, Robert J G; Christmas, Martin; Dunn, Alison M

2012-01-01

Invasive predators may change the structure of invaded communities through predation and competition with native species. In Europe, the invasive signal crayfish Pacifastacus leniusculus is excluding the native white clawed crayfish Austropotamobius pallipes. This study compared the predatory functional responses and prey choice of native and invasive crayfish and measured impacts of parasitism on the predatory strength of the native species. Invasive crayfish showed a higher (>10%) prey (Gammarus pulex) intake rate than (size matched) natives, reflecting a shorter (16%) prey handling time. The native crayfish also showed greater selection for crustacean prey over molluscs and bloodworm, whereas the invasive species was a more generalist predator. A. pallipes parasitised by the microsporidian parasite Thelohania contejeani showed a 30% reduction in prey intake. We suggest that this results from parasite-induced muscle damage, and this is supported by a reduced (38%) attack rate and increased (30%) prey handling time. Our results indicate that the per capita (i.e., functional response) difference between the species may contribute to success of the invader and extinction of the native species, as well as decreased biodiversity and biomass in invaded rivers. In addition, the reduced predatory strength of parasitized natives may impair their competitive abilities, facilitating exclusion by the invader.

A snail-eating snake recognizes prey handedness.

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Danaisawadi, Patchara; Asami, Takahiro; Ota, Hidetoshi; Sutcharit, Chirasak; Panha, Somsak

2016-04-05

Specialized predator-prey interactions can be a driving force for their coevolution. Southeast Asian snail-eating snakes (Pareas) have more teeth on the right mandible and specialize in predation on the clockwise-coiled (dextral) majority in shelled snails by soft-body extraction. Snails have countered the snakes' dextral-predation by recurrent coil reversal, which generates diverse counterclockwise-coiled (sinistral) prey where Pareas snakes live. However, whether the snake predator in turn evolves any response to prey reversal is unknown. We show that Pareas carinatus living with abundant sinistrals avoids approaching or striking at a sinistral that is more difficult and costly to handle than a dextral. Whenever it strikes, however, the snake succeeds in predation by handling dextral and sinistral prey in reverse. In contrast, P. iwasakii with little access to sinistrals on small peripheral islands attempts and frequently misses capturing a given sinistral. Prey-handedness recognition should be advantageous for right-handed snail-eating snakes where frequently encountering sinistrals. Under dextral-predation by Pareas snakes, adaptive fixation of a prey population for a reversal gene instantaneously generates a sinistral species because interchiral mating is rarely possible. The novel warning, instead of sheltering, effect of sinistrality benefitting both predators and prey could further accelerate single-gene ecological speciation by left-right reversal.

Kelp Forests versus Urchin Barrens: Alternate Stable States and Their Effect on Sea Otter Prey Quality in the Aleutian Islands

Directory of Open Access Journals (Sweden)

Nathan L. Stewart

2012-01-01

Full Text Available Macroalgal and urchin barren communities are alternately stable and persist in the Aleutians due to sea otter presence and absence. In the early 1990s a rapid otter population decline released urchins from predation and caused a shift to the urchin-dominated state. Despite increases in urchin abundance, otter numbers continued to decline. Although debated, prey quality changes have been implicated in current otter population status. This study examined otter prey abundance, size, biomass, and potential energy density in remnant kelp forest and urchin-dominated communities to determine if alternate stable states affect prey quality. Findings suggest that although urchin barrens provide more abundant urchin prey, individual urchins are smaller and provide lower biomass and potential energy density compared to kelp forests. Shifts to urchin barrens do affect prey quality but changes are likely compensated by increased prey densities and are insufficient in explaining current otter population status in the Aleutians.

Body size evolution in insular speckled rattlesnakes (Viperidae: Crotalus mitchellii.

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Jesse M Meik

2010-03-01

Full Text Available Speckled rattlesnakes (Crotalus mitchellii inhabit multiple islands off the coast of Baja California, Mexico. Two of the 14 known insular populations have been recognized as subspecies based primarily on body size divergence from putative mainland ancestral populations; however, a survey of body size variation from other islands occupied by these snakes has not been previously reported. We examined body size variation between island and mainland speckled rattlesnakes, and the relationship between body size and various island physical variables among 12 island populations. We also examined relative head size among giant, dwarfed, and mainland speckled rattlesnakes to determine whether allometric differences conformed to predictions of gape size (and indirectly body size evolving in response to shifts in prey size.Insular speckled rattlesnakes show considerable variation in body size when compared to mainland source subspecies. In addition to previously known instances of gigantism on Angel de la Guarda and dwarfism on El Muerto, various degrees of body size decrease have occurred frequently in this taxon, with dwarfed rattlesnakes occurring mostly on small, recently isolated, land-bridge islands. Regression models using the Akaike information criterion (AIC showed that mean SVL of insular populations was most strongly correlated with island area, suggesting the influence of selection for different body size optima for islands of different size. Allometric differences in head size of giant and dwarf rattlesnakes revealed patterns consistent with shifts to larger and smaller prey, respectively.Our data provide the first example of a clear relationship between body size and island area in a squamate reptile species; among vertebrates this pattern has been previously documented in few insular mammals. This finding suggests that selection for body size is influenced by changes in community dynamics that are related to graded differences in area over

Recreational Fish-Finders--An Inexpensive Alternative to Scientific Echo-Sounders for Unravelling the Links between Marine Top Predators and Their Prey.

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Alistair M McInnes

Full Text Available Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R2 = 0.98 and school area (R2 = 0.70. Estimates of relative school density (mean volume backscattering strength; Sv measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions.

Recreational Fish-Finders—An Inexpensive Alternative to Scientific Echo-Sounders for Unravelling the Links between Marine Top Predators and Their Prey

Science.gov (United States)

McInnes, Alistair M.; Khoosal, Arjun; Murrell, Ben; Merkle, Dagmar; Lacerda, Miguel; Nyengera, Reason; Coetzee, Janet C.; Edwards, Loyd C.; Ryan, Peter G.; Rademan, Johan; van der Westhuizen, Jan J; Pichegru, Lorien

2015-01-01

Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF) to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES) by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R2 = 0.98) and school area (R2 = 0.70). Estimates of relative school density (mean volume backscattering strength; Sv) measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions. PMID:26600300

Impaired hand size estimation in CRPS.

Science.gov (United States)

Peltz, Elena; Seifert, Frank; Lanz, Stefan; Müller, Rüdiger; Maihöfner, Christian

2011-10-01

A triad of clinical symptoms, ie, autonomic, motor and sensory dysfunctions, characterizes complex regional pain syndromes (CRPS). Sensory dysfunction comprises sensory loss or spontaneous and stimulus-evoked pain. Furthermore, a disturbance in the body schema may occur. In the present study, patients with CRPS of the upper extremity and healthy controls estimated their hand sizes on the basis of expanded or compressed schematic drawings of hands. In patients with CRPS we found an impairment in accurate hand size estimation; patients estimated their own CRPS-affected hand to be larger than it actually was when measured objectively. Moreover, overestimation correlated significantly with disease duration, neglect score, and increase of two-point-discrimination-thresholds (TPDT) compared to the unaffected hand and to control subjects' estimations. In line with previous functional imaging studies in CRPS patients demonstrating changes in central somatotopic maps, we suggest an involvement of the central nervous system in this disruption of the body schema. Potential cortical areas may be the primary somatosensory and posterior parietal cortices, which have been proposed to play a critical role in integrating visuospatial information. CRPS patients perceive their affected hand to be bigger than it is. The magnitude of this overestimation correlates with disease duration, decreased tactile thresholds, and neglect-score. Suggesting a disrupted body schema as the source of this impairment, our findings corroborate the current assumption of a CNS involvement in CRPS. Copyright © 2011 American Pain Society. Published by Elsevier Inc. All rights reserved.

The modeling of predator-prey interactions

OpenAIRE

Muhammad Shakil; H. A. Wahab; Muhammad Naeem, et al.

2015-01-01

In this paper, we aim to study the interactions between the territorial animals like foxes and the rabbits. The territories for the foxes are considered to be the simple cells. The interactions between predator and its prey are represented by the chemical reactions which obey the mass action law. In this sense, we apply the mass action law for predator prey models and the quasi chemical approach is applied for the interactions between the predator and its prey to develop the modeled equations...

Musculoskeletal anatomy of the Eurasian lynx, Lynx lynx (Carnivora: Felidae) forelimb: Adaptations to capture large prey?

Science.gov (United States)

Viranta, Suvi; Lommi, Hanna; Holmala, Katja; Laakkonen, Juha

2016-06-01

Mammalian carnivores adhere to two different feeding strategies relative to their body masses. Large carnivores prey on animals that are the same size or larger than themselves, whereas small carnivores prey on smaller vertebrates and invertebrates. The Eurasian lynx (Lynx lynx) falls in between these two categories. Lynx descend from larger forms that were probably large prey specialists, but during the Pleistocene became predators of small prey. The modern Eurasian lynx may be an evolutionary reversal toward specializing in large prey again. We hypothesized that the musculoskeletal anatomy of lynx should show traits for catching large prey. To test our hypothesis, we dissected the forelimb muscles of six Eurasian lynx individuals and compared our findings to results published for other felids. We measured the bones and compared their dimensions to the published material. Our material displayed a well-developed pectoral girdle musculature with some uniquely extensive muscle attachments. The upper arm musculature resembled that of the pantherine felids and probably the extinct sabertooths, and also the muscles responsible for supination and pronation were similar to those in large cats. The muscles controlling the pollex were well-developed. However, skeletal indices were similar to those of small prey predators. Our findings show that lynx possess the topographic pattern of muscle origin and insertion like in large felids. J. Morphol. 277:753-765, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Body size estimation of self and others in females varying in BMI.

Directory of Open Access Journals (Sweden)

Anne Thaler

Full Text Available Previous literature suggests that a disturbed ability to accurately identify own body size may contribute to overweight. Here, we investigated the influence of personal body size, indexed by body mass index (BMI, on body size estimation in a non-clinical population of females varying in BMI. We attempted to disentangle general biases in body size estimates and attitudinal influences by manipulating whether participants believed the body stimuli (personalized avatars with realistic weight variations represented their own body or that of another person. Our results show that the accuracy of own body size estimation is predicted by personal BMI, such that participants with lower BMI underestimated their body size and participants with higher BMI overestimated their body size. Further, participants with higher BMI were less likely to notice the same percentage of weight gain than participants with lower BMI. Importantly, these results were only apparent when participants were judging a virtual body that was their own identity (Experiment 1, but not when they estimated the size of a body with another identity and the same underlying body shape (Experiment 2a. The different influences of BMI on accuracy of body size estimation and sensitivity to weight change for self and other identity suggests that effects of BMI on visual body size estimation are self-specific and not generalizable to other bodies.

Body size estimation of self and others in females varying in BMI.

Science.gov (United States)

Thaler, Anne; Geuss, Michael N; Mölbert, Simone C; Giel, Katrin E; Streuber, Stephan; Romero, Javier; Black, Michael J; Mohler, Betty J

2018-01-01

Previous literature suggests that a disturbed ability to accurately identify own body size may contribute to overweight. Here, we investigated the influence of personal body size, indexed by body mass index (BMI), on body size estimation in a non-clinical population of females varying in BMI. We attempted to disentangle general biases in body size estimates and attitudinal influences by manipulating whether participants believed the body stimuli (personalized avatars with realistic weight variations) represented their own body or that of another person. Our results show that the accuracy of own body size estimation is predicted by personal BMI, such that participants with lower BMI underestimated their body size and participants with higher BMI overestimated their body size. Further, participants with higher BMI were less likely to notice the same percentage of weight gain than participants with lower BMI. Importantly, these results were only apparent when participants were judging a virtual body that was their own identity (Experiment 1), but not when they estimated the size of a body with another identity and the same underlying body shape (Experiment 2a). The different influences of BMI on accuracy of body size estimation and sensitivity to weight change for self and other identity suggests that effects of BMI on visual body size estimation are self-specific and not generalizable to other bodies.

The Effect of Digestive Capacity on the Intake Rate of Toxic and Non-Toxic Prey in an Ecological Context.

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Thomas Oudman

Full Text Available Digestive capacity often limits food intake rate in animals. Many species can flexibly adjust digestive organ mass, enabling them to increase intake rate in times of increased energy requirement and/or scarcity of high-quality prey. However, some prey species are defended by secondary compounds, thereby forcing a toxin limitation on the forager's intake rate, a constraint that potentially cannot be alleviated by enlarging digestive capacity. Hence, physiological flexibility may have a differential effect on intake of different prey types, and consequently on dietary preferences. We tested this effect in red knots (Calidris canutus canutus, medium-sized migratory shorebirds that feed on hard-shelled, usually mollusc, prey. Because they ingest their prey whole and crush the shell in their gizzard, the intake rate of red knots is generally constrained by digestive capacity. However, one of their main prey, the bivalve Loripes lucinalis, imposes a toxin constraint due to its symbiosis with sulphide-oxidizing bacteria. We manipulated gizzard sizes of red knots through prolonged exposure to hard-shelled or soft foods. We then measured maximum intake rates of toxic Loripes versus a non-toxic bivalve, Dosinia isocardia. We found that intake of Dosinia exponentially increased with gizzard mass, confirming earlier results with non-toxic prey, whereas intake of Loripes was independent of gizzard mass. Using linear programming, we show that this leads to markedly different expected diet preferences in red knots that try to maximize energy intake rate with a small versus a large gizzard. Intra- and inter-individual variation in digestive capacity is found in many animal species. Hence, the here proposed functional link with individual differences in foraging decisions may be general. We emphasize the potential relevance of individual variation in physiology when studying trophic interactions.

Estimating particle number size distributions from multi-instrument observations with Kalman Filtering

Energy Technology Data Exchange (ETDEWEB)

Viskari, T.

2012-07-01

Atmospheric aerosol particles have several important effects on the environment and human society. The exact impact of aerosol particles is largely determined by their particle size distributions. However, no single instrument is able to measure the whole range of the particle size distribution. Estimating a particle size distribution from multiple simultaneous measurements remains a challenge in aerosol physical research. Current methods to combine different measurements require assumptions concerning the overlapping measurement ranges and have difficulties in accounting for measurement uncertainties. In this thesis, Extended Kalman Filter (EKF) is presented as a promising method to estimate particle number size distributions from multiple simultaneous measurements. The particle number size distribution estimated by EKF includes information from prior particle number size distributions as propagated by a dynamical model and is based on the reliabilities of the applied information sources. Known physical processes and dynamically evolving error covariances constrain the estimate both over time and particle size. The method was tested with measurements from Differential Mobility Particle Sizer (DMPS), Aerodynamic Particle Sizer (APS) and nephelometer. The particle number concentration was chosen as the state of interest. The initial EKF implementation presented here includes simplifications, yet the results are positive and the estimate successfully incorporated information from the chosen instruments. For particle sizes smaller than 4 micrometers, the estimate fits the available measurements and smooths the particle number size distribution over both time and particle diameter. The estimate has difficulties with particles larger than 4 micrometers due to issues with both measurements and the dynamical model in that particle size range. The EKF implementation appears to reduce the impact of measurement noise on the estimate, but has a delayed reaction to sudden

Acoustic shadows help gleaning bats find prey, but may be defeated by prey acoustic camouflage on rough surfaces.

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Clare, Elizabeth L; Holderied, Marc W

2015-09-01

Perceptual abilities of animals, like echolocating bats, are difficult to study because they challenge our understanding of non-visual senses. We used novel acoustic tomography to convert echoes into visual representations and compare these cues to traditional echo measurements. We provide a new hypothesis for the echo-acoustic basis of prey detection on surfaces. We propose that bats perceive a change in depth profile and an 'acoustic shadow' cast by prey. The shadow is more salient than prey echoes and particularly strong on smooth surfaces. This may explain why bats look for prey on flat surfaces like leaves using scanning behaviour. We propose that rather than forming search images for prey, whose characteristics are unpredictable, predators may look for disruptions to the resting surface (acoustic shadows). The fact that the acoustic shadow is much fainter on rougher resting surfaces provides the first empirical evidence for 'acoustic camouflage' as an anti-predator defence mechanism.

Improving accuracy of portion-size estimations through a stimulus equivalence paradigm.

Science.gov (United States)

Hausman, Nicole L; Borrero, John C; Fisher, Alyssa; Kahng, SungWoo

2014-01-01

The prevalence of obesity continues to increase in the United States (Gordon-Larsen, The, & Adair, 2010). Obesity can be attributed, in part, to overconsumption of energy-dense foods. Given that overeating plays a role in the development of obesity, interventions that teach individuals to identify and consume appropriate portion sizes are warranted. Specifically, interventions that teach individuals to estimate portion sizes correctly without the use of aids may be critical to the success of nutrition education programs. The current study evaluated the use of a stimulus equivalence paradigm to teach 9 undergraduate students to estimate portion size accurately. Results suggested that the stimulus equivalence paradigm was effective in teaching participants to make accurate portion size estimations without aids, and improved accuracy was observed in maintenance sessions that were conducted 1 week after training. Furthermore, 5 of 7 participants estimated the target portion size of novel foods during extension sessions. These data extend existing research on teaching accurate portion-size estimations and may be applicable to populations who seek treatment (e.g., overweight or obese children and adults) to teach healthier eating habits. © Society for the Experimental Analysis of Behavior.

Trait-based diet selection: prey behaviour and morphology predict vulnerability to predation in reef fish communities.

Science.gov (United States)

Green, Stephanie J; Côté, Isabelle M

2014-11-01

Understanding how predators select their prey can provide important insights into community structure and dynamics. However, the suite of prey species available to a predator is often spatially and temporally variable. As a result, species-specific selectivity data are of limited use for predicting novel predator-prey interactions because they are assemblage specific. We present a method for predicting diet selection that is applicable across prey assemblages, based on identifying general morphological and behavioural traits of prey that confer vulnerability to predation independent of species identity. We apply this trait-based approach to examining prey selection by Indo-Pacific lionfish (Pterois volitans and Pterois miles), invasive predators that prey upon species-rich reef fish communities and are rapidly spreading across the western Atlantic. We first generate hypotheses about morphological and behavioural traits recurring across fish species that could facilitate or deter predation by lionfish. Constructing generalized linear mixed-effects models that account for relatedness among prey taxa, we test whether these traits predict patterns of diet selection by lionfish within two independent data sets collected at different spatial scales: (i) in situ visual observations of prey consumption and availability for individual lionfish and (ii) comparisons of prey abundance in lionfish stomach contents to availability on invaded reefs at large. Both analyses reveal that a number of traits predicted to affect vulnerability to predation, including body size, body shape, position in the water column and aggregation behaviour, are important determinants of diet selection by lionfish. Small, shallow-bodied, solitary fishes found resting on or just above reefs are the most vulnerable. Fishes that exhibit parasite cleaning behaviour experience a significantly lower risk of predation than non-cleaning fishes, and fishes that are nocturnally active are at significantly

Genome size estimation: a new methodology

Science.gov (United States)

Álvarez-Borrego, Josué; Gallardo-Escárate, Crisitian; Kober, Vitaly; López-Bonilla, Oscar

2007-03-01

Recently, within the cytogenetic analysis, the evolutionary relations implied in the content of nuclear DNA in plants and animals have received a great attention. The first detailed measurements of the nuclear DNA content were made in the early 40's, several years before Watson and Crick proposed the molecular structure of the DNA. In the following years Hewson Swift developed the concept of "C-value" in reference to the haploid phase of DNA in plants. Later Mirsky and Ris carried out the first systematic study of genomic size in animals, including representatives of the five super classes of vertebrates as well as of some invertebrates. From these preliminary results it became evident that the DNA content varies enormously between the species and that this variation does not bear relation to the intuitive notion from the complexity of the organism. Later, this observation was reaffirmed in the following years as the studies increased on genomic size, thus denominating to this characteristic of the organisms like the "Paradox of the C-value". Few years later along with the no-codification discovery of DNA the paradox was solved, nevertheless, numerous questions remain until nowadays unfinished, taking to denominate this type of studies like the "C-value enigma". In this study, we reported a new method for genome size estimation by quantification of fluorescence fading. We measured the fluorescence intensity each 1600 milliseconds in DAPI-stained nuclei. The estimation of the area under the graph (integral fading) during fading period was related with the genome size.

Using radioecological data to determine prey selection by the Alaska wolf

International Nuclear Information System (INIS)

Holleman, D.F.; Luick, J.R.

1978-01-01

Recently the predation of the Alaska wolf (Canis lupus pambasileus) upon various species of big game has been the subject of considerable controversy between game management specialists and environmentalists. The basis of this controversy centers primarily on the selectivity and extent of prey utilization by the wolf. This report suggests how radioecological data can be used to assess both qualitative and quantitative aspects of wolf predation. Primary prey species of the wolf have distinctly different fallout radiocesium body burdens; e.g., reindeer/caribou have high radiocesium body burdens, whereas moose and small game have low radiocesium body burdens. Consequently, the resulting radiocesium body burden of the wolf depends upon the type and quantity of prey species consumed. Laboratory measurements for this study show a wide variation of radiocesium concentrations of skeletal muscle of wolves within Alaska. Values ranged from 263 to 17,300 pCi 137 Cs/kg of wet muscle. These data relate to known degrees of reindeer/caribou predation by the wolves. A radiocesium kinetic model was constructed from data obtained with wolves and other arctic carnivores and was used to estimate reindeer/caribou intake by wolves. Estimates ranged from 40 to 1650 g of reindeer/caribou muscle per day per wolf. Although the application has limitations, it could yield useful information for evaluating the food habits of wolves, especially in areas of the state where it is important to know the extent of reindeer/caribou utilization by the wolf

Assassin bug uses aggressive mimicry to lure spider prey.

Science.gov (United States)

Wignall, Anne E; Taylor, Phillip W

2011-05-07

Assassin bugs (Stenolemus bituberus) hunt web-building spiders by invading the web and plucking the silk to generate vibrations that lure the resident spider into striking range. To test whether vibrations generated by bugs aggressively mimic the vibrations generated by insect prey, we compared the responses of spiders to bugs with how they responded to prey, courting male spiders and leaves falling into the web. We also analysed the associated vibrations. Similar spider orientation and approach behaviours were observed in response to vibrations from bugs and prey, whereas different behaviours were observed in response to vibrations from male spiders and leaves. Peak frequency and duration of vibrations generated by bugs were similar to those generated by prey and courting males. Further, vibrations from bugs had a temporal structure and amplitude that were similar to vibrations generated by leg and body movements of prey and distinctly different to vibrations from courting males or leaves, or prey beating their wings. To be an effective predator, bugs do not need to mimic the full range of prey vibrations. Instead bugs are general mimics of a subset of prey vibrations that fall within the range of vibrations classified by spiders as 'prey'.

Demographic consequences of predators on prey: trait and density mediated effects on mosquito larvae in containers.

Directory of Open Access Journals (Sweden)

Barry W Alto

Full Text Available Predators may affect prey population growth and community diversity through density mediated lethal and trait mediated non-lethal effects that influence phenotypic traits of prey. We tested experimentally the roles of thinning the density of prey (lethality in the absence of predator cues and density and trait mediated effects (lethality + intimidation of predatory midge Corethrella appendiculata on competing native and invasive mosquito prey. Predator-mediated reductions in prey and density reductions in the absence of C. appendiculata resulted in lower percent survivorship to adulthood and estimates of the finite rate of increase (λ' for invasive mosquito Aedes albopictus relative to that of controls. In most instances, thinning the density of prey in the absence, but not in the presence, of C. appendiculata cues resulted in lower survivorship to adulthood and λ' for native mosquito Aedes triseriatus relative to that of controls. Together, these results suggested trait mediated effects of C. appendiculata specific to each species of mosquito prey. Release from intraspecific competition attributable to density reductions in the absence, but not in the presence, of C. appendiculata enhanced growth and lengthened adult lifespan relative to that of controls for A. albopictus but not A. triseriatus. These results show the importance of predator-mediated density and trait mediated effects on phenotypic traits and populations of invasive and native mosquitoes. Species-specific differences in the phenotypic responses of prey may be due, in part, to longer evolutionary history of C. appendiculata with A. triseriatus than A. albopictus.

Bottom trawl assessment of Lake Ontario prey fishes

Science.gov (United States)

Weidel, Brian C.; Connerton, Michael J.; Holden, Jeremy

2018-01-01

Managing Lake Ontario fisheries in an ecosystem-context requires prey fish community and population data. Since 1978, multiple annual bottom trawl surveys have quantified prey fish dynamics to inform management relative to published Fish Community Objectives. In 2017, two whole-lake surveys collected 341 bottom trawls (spring: 204, fall: 137), at depths from 8-225m, and captured 751,350 fish from 29 species. Alewife were 90% of the total fish catch while Deepwater Sculpin, Round Goby, and Rainbow Smelt comprised the majority of the remaining total catch (3.8, 3.1, and 1.1% respectively). The adult Alewife abundance index for US waters increased in 2017 relative to 2016, however the index for Canadian waters declined. Adult Alewife condition, assessed by the predicted weight of a 165 mm fish (6.5 inches), declined in 2017 from record high values observed in spring 2016. Spring 2017 Alewife condition was slightly less than the 10-year average, but the fall value was well below the 10-year average, likely due to increased Age-1 Alewife abundance. The Age-1 Alewife abundance index was the highest observed in 40 years, and 8-times higher than the previous year. The Age-1 index estimates Alewife reproductive success the preceding year. The warm summer and winter of 2016 likely contributed to the large year class. In contrast the relatively cool 2017 spring and cold winter may result in a lower than average 2017 year class. Abundance indices for Rainbow Smelt, Cisco, and Emerald Shiner either declined or remained at low levels in 2017. Pelagic prey fish diversity continues to be low since a single species, Alewife, dominates the catch. Deepwater Sculpin were the most abundant benthic prey fish in 2017 because Round Goby abundance declined sharply from 2016. Slimy Sculpin density continued to decline and the 2017 biomass index for US waters was the lowest ever observed. Prior to Round Goby proliferation, juvenile Slimy Sculpin comprised ~10% of the Slimy Sculpin catch, but

Predatory mites avoid ovipositing near counter-attacking prey

NARCIS (Netherlands)

Faraji, F.; Janssen, A.; Sabelis, M.W.

2001-01-01

Attacking prey is not without risk; predators may endure counterattackby the prey. Here, we study the oviposition behaviour of a predatory mite(Iphiseius degenerans) in relation to its prey, thewesternflower thrips (Frankliniella occidentalis). This thrips iscapable of killing the eggs of the

Estimating Sample Size for Usability Testing

Directory of Open Access Journals (Sweden)

Alex Cazañas

2017-02-01

Full Text Available One strategy used to assure that an interface meets user requirements is to conduct usability testing. When conducting such testing one of the unknowns is sample size. Since extensive testing is costly, minimizing the number of participants can contribute greatly to successful resource management of a project. Even though a significant number of models have been proposed to estimate sample size in usability testing, there is still not consensus on the optimal size. Several studies claim that 3 to 5 users suffice to uncover 80% of problems in a software interface. However, many other studies challenge this assertion. This study analyzed data collected from the user testing of a web application to verify the rule of thumb, commonly known as the “magic number 5”. The outcomes of the analysis showed that the 5-user rule significantly underestimates the required sample size to achieve reasonable levels of problem detection.

Prey capture behaviour evoked by simple visual stimuli in larval zebrafish

Directory of Open Access Journals (Sweden)

Isaac Henry Bianco

2011-12-01

Full Text Available Understanding how the nervous system recognises salient stimuli in the environ- ment and selects and executes the appropriate behavioural responses is a fundamen- tal question in systems neuroscience. To facilitate the neuroethological study of visually-guided behaviour in larval zebrafish, we developed virtual reality assays in which precisely controlled visual cues can be presented to larvae whilst their behaviour is automatically monitored using machine-vision algorithms. Freely swimming larvae responded to moving stimuli in a size-dependent manner: they directed multiple low amplitude orienting turns (∼ 20◦ towards small moving spots (1◦ but reacted to larger spots (10◦ with high-amplitude aversive turns (∼ 60◦. The tracking of small spots led us to examine how larvae respond to prey during hunting routines. By analysing movie sequences of larvae hunting parame- cia, we discovered that all prey capture routines commence with eye convergence and larvae maintain their eyes in a highly converged position for the duration of the prey-tracking and capture swim phases. We adapted our virtual reality assay to deliver artificial visual cues to partially restrained larvae and found that small moving spots evoked convergent eye movements and J-turns of the tail, which are defining features of natural hunting. We propose that eye convergence represents the engagement of a predatory mode of behaviour in larval fish and serves to increase the region of binocular visual space to enable stereoscopic targeting of prey.

Estimation of particle size distribution of nanoparticles from electrical ...

Indian Academy of Sciences (India)

2018-02-02

Feb 2, 2018 ... An indirect method of estimation of size distribution of nanoparticles in a nanocomposite is ... The present approach exploits DC electrical current–voltage ... the sizes of nanoparticles (NPs) by electrical characterization.

Influences of potential predictor variables on gastric evacuation in Atlantic cod Gadus morhua L. feeding on fish prey

DEFF Research Database (Denmark)

Andersen, Niels Gerner

2012-01-01

of photoperiod and pre-experimental treatment of prey were also tested. Freshly killed A. tobianus were evacuated from the stomach of G. morhua at a rate similar to the value estimated from conspecifics kept deep-frozen and subsequently thawed prior to the evacuation experiment. The evacuation rate in G. morhua...... exposed to continuous light did not differ from the rate obtained from fish maintained under a 12L:12D photoperiod. The evacuation rates estimated from the latter fish in the dark and light periods, respectively, were likewise similar. These results indicate that the resistance of prey to the digestive...

Seasonal trophic activity of the aquatic morphotype of Atelognathus patagonicus (Anura, Neobatrachia and prey availability in the littoral benthos of a permanent pond in Argentinean Patagonia

Directory of Open Access Journals (Sweden)

María Elena Cuello

2009-12-01

Full Text Available The diet of the aquatic morphotype of Atelognathus patagonicus was studied in frogs collected from the Laguna Verde pond (Laguna Blanca National Park, Neuquén, Argentina. The content of 35 gastrointestinal tracts of post-metamorphic specimens from November 2003 to April 2006 was related to the composition of the benthos in their microhabitat. Number, size, occurrence and relative importance of preys, diversity of the diet, trophic niche breadth and electivitywere estimated for each season of the year. The diet consisted of aquatic arthropods. The composition of both the benthos and the food (number and occurrence of organisms in the diet were dominated by the amphipod Hyalella sp. The relative importance (IRI of Hyalella sp. in the diet was over 99% in summer and autumn, and 100% in winter and spring. Diptera and Copepoda in summer, and Dytiscidae and Ostracoda in autumn, had seasonal IRI values ≤ 0.2%. Trophic niche breadth was very low in summer and autumn, and null (= 0 in winter and spring. The mean number of preys per individual was highest in spring (19 preys/frog and lowest in winter (4 preys/frog. Frogs continued with their trophic activity in winter, even when the surface of the pond was frozen. There is a correspondence between the frogs’ main food item and its presence in the benthos.

Spotted hyaenas Crocuta crocuta prey on new-born elephant calves in Hwange National Park, Zimbabwe

Directory of Open Access Journals (Sweden)

Julia Salnicki

2001-07-01

Full Text Available Spotted hyaena Crocuta crocuta are known to be opportunists and to have a varied diet including mammals, reptiles and birds. Prey most often hunted are medium sized ungulates but spotted hyaenas will on occasion take larger species such as giraffe Giraffa camelopardalis and zebra Equus burchellii. They are also known to hunt whichever species are most abundant and will vary their prey seasonally. In this study spotted hyaenas were observed to take an unusual prey species in the form of elephant calves (Loxodonta africana. On a number of occasions hyaenas were observed feeding on or killing newborn and very young elephant calves. These observations were made whilst the authors were conducting research on spotted hyaena ecology in the woodlands of Hwange National Park, Zimbabwe and were made during the dry season between September and November 1999.

Can rarefaction be used to estimate song repertoire size in birds?

Directory of Open Access Journals (Sweden)

Kathleen R. PESHEK, Daniel T. BLUMSTEIN

2011-06-01

Full Text Available Song repertoire size is the number of distinct syllables, phrases, or song types produced by an individual or population. Repertoire size estimation is particularly difficult for species that produce highly variable songs and those that produce many song types. Estimating repertoire size is important for ecological and evolutionary studies of speciation, studies of sexual selection, as well as studies of how species may adapt their songs to various acoustic environments. There are several methods to estimate repertoire size, however prior studies discovered that all but a full numerical count of song types might have substantial inaccuracies associated with them. We evaluated a somewhat novel approach to estimate repertoire size—rarefaction; a technique ecologists use to measure species diversity on individual and population levels. Using the syllables within American robins’ Turdus migratorius repertoire, we compared the most commonly used techniques of estimating repertoires to the results of a rarefaction analysis. American robins have elaborate and unique songs with few syllables shared between individuals, and there is no evidence that robins mimic their neighbors. Thus, they are an ideal system in which to compare techniques. We found that the rarefaction technique results resembled that of the numerical count, and were better than two alternative methods (behavioral accumulation curves, and capture-recapture to estimate syllable repertoire size. Future estimates of repertoire size, particularly in vocally complex species, may benefit from using rarefaction techniques when numerical counts are unable to be performed [Current Zoology 57 (3: 300–306, 2011].

Estimating the average grain size of metals - approved standard 1969

International Nuclear Information System (INIS)

Anon.

1975-01-01

These methods cover procedures for estimating and rules for expressing the average grain size of all metals and consisting entirely, or principally, of a single phase. The methods may also be used for any structures having appearances similar to those of the metallic structures shown in the comparison charts. The three basic procedures for grain size estimation which are discussed are comparison procedure, intercept (or Heyn) procedure, and planimetric (or Jeffries) procedure. For specimens consisting of equiaxed grains, the method of comparing the specimen with a standard chart is most convenient and is sufficiently accurate for most commercial purposes. For high degrees of accuracy in estimating grain size, the intercept or planimetric procedures may be used

Estimation of portion size in children's dietary assessment: lessons learnt.

Science.gov (United States)

Foster, E; Adamson, A J; Anderson, A S; Barton, K L; Wrieden, W L

2009-02-01

Assessing the dietary intake of young children is challenging. In any 1 day, children may have several carers responsible for providing them with their dietary requirements, and once children reach school age, traditional methods such as weighing all items consumed become impractical. As an alternative to weighed records, food portion size assessment tools are available to assist subjects in estimating the amounts of foods consumed. Existing food photographs designed for use with adults and based on adult portion sizes have been found to be inappropriate for use with children. This article presents a review and summary of a body of work carried out to improve the estimation of portion sizes consumed by children. Feasibility work was undertaken to determine the accuracy and precision of three portion size assessment tools; food photographs, food models and a computer-based Interactive Portion Size Assessment System (IPSAS). These tools were based on portion sizes served to children during the National Diet and Nutrition Survey. As children often do not consume all of the food served to them, smaller portions were included in each tool for estimation of leftovers. The tools covered 22 foods, which children commonly consume. Children were served known amounts of each food and leftovers were recorded. They were then asked to estimate both the amount of food that they were served and the amount of any food leftover. Children were found to estimate food portion size with an accuracy approaching that of adults using both the food photographs and IPSAS. Further development is underway to increase the number of food photographs and to develop IPSAS to cover a much wider range of foods and to validate the use of these tools in a 'real life' setting.

The Neuronal Control of Flying Prey Interception in Dragonflies

Science.gov (United States)

2014-08-19

Gonzalez-Bellido’s fluorescent dye ( Lucifer -yellow) injections illuminated for the first time the anatomy of the output regions of the TSDNs...out in Cape Cod (MA) to test the effect of bead size(C), and in the Olberg Laboratory (Union College, NY) to test the effect of bead speed by...AFRL-OSR-VA-TR-2014-0193 THE NEURONAL CONTROL OF FLYING PREY INTERCEPTION IN DRAGONFLIES Robert Olberg TRUSTEES OF UNION COLLEGE IN THE TOWN OF

Body size, swimming speed, or thermal sensitivity? Predator-imposed selection on amphibian larvae.

Science.gov (United States)

Gvoždík, Lumír; Smolinský, Radovan

2015-11-02

Many animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals. Nonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance. In the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator-prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator-prey interactions and food web dynamics.

David and Goliath: potent venom of an ant-eating spider (Araneae) enables capture of a giant prey

Science.gov (United States)

Pekár, Stano; Šedo, Onřej; Líznarová, Eva; Korenko, Stanislav; Zdráhal, Zdeněk

2014-07-01

It is rare to find a true predator that repeatedly and routinely kills prey larger than itself. A solitary specialised ant-eating spider of the genus Zodarion can capture a relatively giant prey. We studied the trophic niche of this spider species and investigated its adaptations (behavioural and venomic) that are used to capture ants. We found that the spider captures mainly polymorphic Messor arenarius ants. Adult female spiders captured large morphs while tiny juveniles captured smaller morphs, yet in both cases ants were giant in comparison with spider size. All specimens used an effective prey capture strategy that protected them from ant retaliation. Juvenile and adult spiders were able to paralyse their prey using a single bite. The venom glands of adults were more than 50 times larger than those of juvenile spiders, but the paralysis latency of juveniles was 1.5 times longer. This suggests that this spider species possesses very potent venom already at the juvenile stage. Comparison of the venom composition between juvenile and adult spiders did not reveal significant differences. We discovered here that specialised capture combined with very effective venom enables the capture of giant prey.

The influence of personal BMI on body size estimations and sensitivity to body size change in anorexia spectrum disorders.

OpenAIRE

Cornelissen, Katri; Bester, Andre; Cairns, Paul; Tovee, Martin; Cornelissen, Piers

2015-01-01

In this cross-sectional study, we investigated the influence of personal BMI on body size estimation in 42 women who have symptoms of anorexia (referred to henceforth as anorexia spectrum disorders, ANSD), and 100 healthy controls. Low BMI control participants over-estimate their size and high BMI controls under-estimate, a pattern which is predicted by a perceptual phenomenon called contraction bias. In addition, control participants' sensitivity to size change declines as their BMI increase...

Colour polymorphic lures exploit innate preferences for spectral versus luminance cues in dipteran prey.

Science.gov (United States)

White, Thomas E; Kemp, Darrell J

2017-08-14

Theory predicts that colour polymorphism may be favored by variation in the visual context under which signals are perceived. The context encompasses all environmental determinants of light availability and propagation, but also the dynamics of perception in receivers. Color vision involves the neural separation of information into spectral versus luminance channels, which often differentially guide specific tasks. Here we explicitly tested whether this discrete perceptual basis contributes to the maintenance of polymorphism in a prey-luring system. The orb-weaving spider Gasteracantha fornicata is known to attract a broad community of primarily dipteran prey due to their conspicuous banded dorsal signal. They occur in two morphs ("white" and "yellow") which should, respectively, generate greater luminance and color contrast in the dipteran eye. Given that arthropods often rely upon luminance-versus-spectral cues for relatively small-versus-large stimulus detection, we predicted a switch in relative attractiveness among morphs according to apparent spider size. Our experimental tests used colour-naïve individuals of two known prey species (Drosophila hydei and Musca domestica) in replicate Y-maze choice trials designed to manipulate the apparent size of spider models via the distance at which they are viewed. Initial trials confirmed that flies were attracted to each G. fornicata morph in single presentations. When given a simultaneous choice between morphs against a viewing background typical of those encountered in nature, flies exhibited no preference regardless of the visual angle subtended by models. However, when backgrounds were adjusted to nearer the extremes of those of each morph in the wild, flies were more attracted by white morphs when presented at longer range (consistent with a reliance on achromatic cues), yet were unbiased in their close-range choice. While not fully consistent with predictions (given the absence of a differential preference for

Children's estimates of food portion size: the development and evaluation of three portion size assessment tools for use with children.

Science.gov (United States)

Foster, E; Matthews, J N S; Lloyd, J; Marshall, L; Mathers, J C; Nelson, M; Barton, K L; Wrieden, W L; Cornelissen, P; Harris, J; Adamson, A J

2008-01-01

A number of methods have been developed to assist subjects in providing an estimate of portion size but their application in improving portion size estimation by children has not been investigated systematically. The aim was to develop portion size assessment tools for use with children and to assess the accuracy of children's estimates of portion size using the tools. The tools were food photographs, food models and an interactive portion size assessment system (IPSAS). Children (n 201), aged 4-16 years, were supplied with known quantities of food to eat, in school. Food leftovers were weighed. Children estimated the amount of each food using each tool, 24 h after consuming the food. The age-specific portion sizes represented were based on portion sizes consumed by children in a national survey. Significant differences were found between the accuracy of estimates using the three tools. Children of all ages performed well using the IPSAS and food photographs. The accuracy and precision of estimates made using the food models were poor. For all tools, estimates of the amount of food served were more accurate than estimates of the amount consumed. Issues relating to reporting of foods left over which impact on estimates of the amounts of foods actually consumed require further study. The IPSAS has shown potential for assessment of dietary intake with children. Before practical application in assessment of dietary intake of children the tool would need to be expanded to cover a wider range of foods and to be validated in a 'real-life' situation.

Behavior of prey links midwater and demersal piscivorous reef fishes

Directory of Open Access Journals (Sweden)

Peter J. Auster

Full Text Available Pelagic and demersal guilds of piscivorous fishes are linked by a variety of biological and physical processes that mediate interactions with common prey species. Understanding the behaviors of predators and prey can provide insight into the conditions that make such linkages possible. Here we report on the behaviors of mid-water piscivorous fishes and the responses of prey that produce feeding opportunities for demersal piscivorous fishes associated with "live bottom" ledge habitats off the coast of Georgia (northwest Atlantic Ocean. Prey taxa reduced nearest neighbor distances and retreated towards the seafloor during predatory attacks by mid-water fishes. Demersal fishes subsequently attacked and consumed prey in these ephemeral high density patches. No predation by demersal fishes was observed when prey species were at background densities. If the predator-prey interactions of demersal piscivorous fishes are commonly mediated by the predatory behavior of midwater piscivorous fishes and their prey, such indirect facilitative behaviors may be important in terms of the population processes (e.g., prey consumption and growth rates of these demersal fishes.

The influence of particle size of dietary prey on food consumption and ecological conversion efficiency of young-of-the-year sand lance, Ammodytes personatus

Science.gov (United States)

Sun, Yao; Liu, Yong; Liu, Xinfu; Tang, Oisheng

2010-06-01

The Eggers model was used to study the influence of two particle sizes of dietary prey on food consumption and ecological conversion efficiency of young-of-the-year sand lance, Ammodytes personatus, in continuous flow-through seawater in 2.5-m 3 tanks in the laboratory. The sand lances (average body weight 0.85 ± 0.21 g) were fed larval (average body length 0.56 ± 0.08 mm) or adult (average body length 10.12 ± 1.61 mm) Artemia salina. The gastric evacuation rate of the fish feeding on larval Artemia was 0.214, higher than that of those feeding on adult Artemia (0.189). The daily food consumption of the fish feeding on larval Artemia was 60.14 kJ/100 g in terms of energy content, higher than that of the fish feeding on adult Artemia (51.69 kJ/100 g), but the daily growth rate of fish feeding on larval Artemia was 14.86 kJ/100 g, significantly lower than that of the fish feeding on adult Artemia (19.50 kJ/100 g), indicating that less energy was used for growth when the food particles were smaller. Slow growth of sand lances preying on larval Artemia was probably due to the high energy consumption during predation, consistent with the basic suppositions of optimal foraging theory.

A specialized araneophagic predator's short-term nutrient utilization depends on the macronutrient content of prey rather than on prey taxonomic affiliation

DEFF Research Database (Denmark)

Toft, Søren; Li, Daiqin; Mayntz, David

2010-01-01

rate of high-protein flies than of high-lipid flies and spiders but, after 5 days of feeding, there is no significant difference in growth between treatments, and the diets lead to significant changes in the macronutrient composition of P. quei as a result of variable extraction and utilization...... of the prey. The short-term utilization of spider prey is similar to that of high-lipid flies and both differ in several respects from the utilization of high-protein flies. Thus, the short-term nutrient utilization is better explained by prey macronutrient content than by whether the prey is a spider or not....... The results suggest that spider prey may have a more optimal macronutrient composition for P. quei and that P. quei does not depend on spider-specific substances....

Diet choice of a predator in the wild: overabundance of prey and missed opportunities along the prey capture sequence

OpenAIRE

Brechbühl, Rolf; Casas, Jérôme; Bacher, Sven

2012-01-01

Optimal diet theory (ODT) postulates that predators adjust their foraging decisions by calculating a prey value from the potential biomass gain, handling time, prey vulnerability and encounter rate. Tests of ODT have however so far mainly been restricted to laboratory settings. By video surveillance, we gathered a large data set of more than 2000 field observations of crab spider (Misumena vatia) encounters with potential prey. We then tested whether the complex ODT or two simpler models (pre...

The Peculiarities of Territorial Distribution and Abundance of Birds of Prey in Kharkiv Region, Ukraine

Directory of Open Access Journals (Sweden)

Stanislav G. Viter

2014-11-01

Full Text Available This study investigates the features of the spatial distribution and abundance of birds of prey in the Kharkov region, Ukraine. Investigations were carried out in 2003–2013 years. Totaly we found 1569 nest sites of Falconiformes. There are 29 species of raptors in avifauna of Kharkiv region. Nine of them are wintering species and 16 – nesting. The highest number of nest sites we found in agricultural landscapes – 677 pairs. However, population density here is low, and high number of nest sites can be explained by large extension of this type of habitat. Also significant populations of birds of prey inhabit forest-steppe areas of Central Russian Upland (East European Plain – 468 pairs, steppe areas of Central Russian Upland – at least 279 pairs (notable that the size of steppe areas are 4 times smaller then forest-steppe areas, and gully forests on the spurs of Donets Ridge – 205 pairs (the size of this habitat in Kharkiv region is no more than 3 000 km2. The other habitats includes highlands in the forest-steppe zone covered with oak forests – 431 pairs, and floodplain forests in the valley of river Siverskyi Donets – 148 pairs (with rather small area of this habitat. These last two habitats are refuge for local populations of Booted Eagle (Hieraaetus pennata and Honey Buzzard (Pernis apivorus because these areas held the most stable nest sites and the highest density of these two species. The same could be said about gully forests on the spurs of Donets Ridge. The estimate number of breeding pairs of Falconiformes in gully forests is around 290 pairs. In this study, we also assessed the total number of breeding Birds of Prey in Kharkiv region. Here are our estimates: Honey Buzzard – 142–156 pairs, Black Kite (Milvus migrans – 133–148 pairs, White-Tailed Eagle (Haliaeetus albicilla – 26–28 pairs, Montagu’s Harrier (Circus pygargus – 174–191, Marsh Harrier (C. aeruginosus – 344–359, Northern Goshawk

Prey selectivity affects reproductive success of a corallivorous reef fish.

Science.gov (United States)

Brooker, Rohan M; Jones, Geoffrey P; Munday, Philip L

2013-06-01

Most animals consume a narrower range of food resources than is potentially available in the environment, but the underlying basis for these preferences is often poorly understood. Foraging theory predicts that prey selection should represent a trade-off between prey preferences based on nutritional value and prey availability. That is, species should consume preferred prey when available, but select less preferred prey when preferred prey is rare. We employed both field observation and laboratory experiments to examine the relationship between prey selection and preferences in the obligate coral-feeding filefish, Oxymonacanthus longirostris. To determine the drivers of prey selection, we experimentally established prey preferences in choice arenas and tested the consequences of prey preferences for key fitness-related parameters. Field studies showed that individuals fed almost exclusively on live corals from the genus Acropora. While diet was dominated by the most abundant species, Acropora nobilis, fish appeared to preferentially select rarer acroporids, such as A. millepora and A. hyacinthus. Prey choice experiments confirmed strong preferences for these corals, suggesting that field consumption is constrained by availability. In a longer-term feeding experiment, reproductive pairs fed on non-preferred corals exhibited dramatic reductions to body weight, and in hepatic and gonad condition, compared with those fed preferred corals. The majority of pairs fed preferred corals spawned frequently, while no spawning was observed for any pairs fed a non-preferred species of coral. These experiments suggest that fish distinguish between available corals based on their intrinsic value as prey, that reproductive success is dependent on the presence of particular coral species, and that differential loss of preferred corals could have serious consequences for the population success of these dietary specialists.

Are single odorous components of a predator sufficient to elicit defensive behaviors in prey species?

Science.gov (United States)

Apfelbach, Raimund; Parsons, Michael H; Soini, Helena A; Novotny, Milos V

2015-01-01

When exposed to the odor of a sympatric predator, prey animals typically display escape or defensive responses. These phenomena have been well-documented, especially in rodents, when exposed to the odor of a cat, ferret, or fox. As a result of these experiments new discussions center on the following questions: (1) is a single volatile compound such as a major or a minor mixture constituent in urine or feces, emitted by the predator sufficient to cause defensive reactions in a potential prey species or (2) is a whole array of odors required to elicit a response and (3) will the relative size or escapability of the prey as compared to the predator influence responsiveness. Most predator-prey studies on this topic have been performed in the laboratory or under semi-natural conditions. Field studies could help to find answers to these questions. Australian mammals are completely naïve toward the introduced placental carnivores. That offers ideal opportunities to analyze in the field the responses of potential prey species to unknown predator odors. During the last decades researchers have accumulated an enormous amount of data exploring the effects of eutherian predator odors on native marsupial mammals. In this review, we will give a survey about the development of olfactory research, chemical signals and their influence on the behavior and-in some cases-physiology of prey species. In addition, we report on the effects of predator odor experiments performed under natural conditions in Australia. When studying all these literature we learned that data gained under controlled laboratory conditions elucidate the role of individual odors on brain structures and ultimately on a comparatively narrow range behaviors. In contrast to single odors odor arrays mimic much more the situation prey animals are confronted to in nature. Therefore, a broad range of methodology-from chemistry to ecology including anatomy, physiology, and behavior-is needed to understand all the

A predator from East Africa that chooses malaria vectors as preferred prey.

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Ximena J Nelson

Full Text Available BACKGROUND: All vectors of human malaria, a disease responsible for more than one million deaths per year, are female mosquitoes from the genus Anopheles. Evarcha culicivora is an East African jumping spider (Salticidae that feeds indirectly on vertebrate blood by selecting blood-carrying female mosquitoes as preferred prey. METHODOLOGY/PRINCIPAL FINDINGS: By testing with motionless lures made from mounting dead insects in lifelike posture on cork discs, we show that E. culicivora selects Anopheles mosquitoes in preference to other mosquitoes and that this predator can identify Anopheles by static appearance alone. Tests using active (grooming virtual mosquitoes rendered in 3-D animation show that Anopheles' characteristic resting posture is an important prey-choice cue for E. culicivora. Expression of the spider's preference for Anopheles varies with the spider's size, varies with its prior feeding condition and is independent of the spider gaining a blood meal. CONCLUSIONS/SIGNIFICANCE: This is the first experimental study to show that a predator of any type actively chooses Anopheles as preferred prey, suggesting that specialized predators having a role in the biological control of disease vectors is a realistic possibility.

Fine-scale tracking and diet information of a marine predator reveals the origin and contrasting spatial distribution of prey

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Alonso, Hany; Granadeiro, José P.; Dias, Maria P.; Catry, Teresa; Catry, Paulo

2018-03-01

The distribution of many marine organisms is still poorly understood, particularly in oceanic regions. Seabirds, as aerial predators which cover extensive areas across the oceans, can potentially be used to enhance our knowledge on the distribution and abundance of their prey. In this study, we combined tracking data and dietary data from individual Cory's shearwaters Calonectris borealis (n = 68) breeding in Selvagens archipelago, Madeira, Portugal, during the chick-rearing periods of 2011 and 2016, in order to infer prey origin within shearwaters' main foraging areas. The digestion state of each prey item in the diet was assessed and classified; and compared to digestion states from known prey items fed to captive birds. In a novel approach, we combined tracking data with information on the prey digestion duration and data on the transit times from foraging grounds to the colony to estimate the location of prey capture. We found a consistent heterogeneity in prey distribution across four different marine domains: Selvagens, deep-sea, seamounts, and continental shelf. In oceanic areas, the chub mackerel Scomber colias, the main prey of Cory's shearwaters, was strongly associated with seamounts and insular shelves, whereas oceanic species like pilot-fish, flying-squid, flying-fish were clearly associated with deep-sea waters. Sardines Sardina pilchardus, anchovies Engraulis encrasicolus and other coastal species were associated with the African shelf. Prey origin assignment was robust across three different sets of assumptions, and was also supported by information on the digestion state of prey collected over a large independent sampling period (671 samples, collected in 2008-2010). The integration of fine-scale dietary and foraging trip data from marine predators provides a new framework to gain insights into the distribution and abundance of prey species in poorly known oceanic areas.

Rates of consumption of juvenile salmonids and alternative prey fish by northern squawfish, walleyes, smallmouth bass, and channel catfish in John Day Reservoir, Columbia River

International Nuclear Information System (INIS)

Vigg, S.; Poe, T.P.; Prendergast, L.A.; Hansel, H.C.

1991-01-01

Adult northern squawfish Ptychocheilus oregonesis, walleyes Stizostedion vitreum, smallmouth bass Micropterus dolomieu, and channel catfish Ictalurus punctatus were sampled from four regions of John Day Reservoir from April to August 1983-1986 to quantify their consumption of 13 species of prey fish, particularly seaward-migrating juvenile Pacific salmon and steelhead (Oncorhynchus spp.). Consumption rates were estimated from field data on stomach contents and digestion rate relations determined in previous investigations. For each predator, consumption rates varied by reservoir area, month, time of day, and predator size or age. The greatest daily consumption of salmonids by northern squawfish and channel catfish occurred in the upper end of the reservoir below McNary Dam. Greatest daily predation by walleyes and smallmouth bass occurred in the middle and lower reservoir. Consumption rates of all predators were highest in July, concurrent with maximum temperature and abundance of juvenile salmonids. Feeding by the predators tended to peak after dawn and near midnight. Northern squawfish below McNary Dam exhibited this pattern, but fed mainly in the morning hours down-reservoir. The daily ration of total prey fish was highest for northern squawfish over 451 mm fork length, for walleyes 201-250 mm, for smallmouth bass 176-200 mm, and for channel catfish 401-450 mm. Averaged over all predator sizes and sampling months (April-August), the total daily ration (fish plus other prey) of smallmouth bass was about twice that of channel catfish, northern squawfish, and walleyes. However, northern squawfish was clearly the major predator on juvenile salmonids

Release from prey preservation behavior via prey switch allowed diversification of cuticular hydrocarbon profiles in digger wasps.

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Wurdack, Mareike; Polidori, Carlo; Keller, Alexander; Feldhaar, Heike; Schmitt, Thomas

2017-11-01

The cuticle of insects is covered by a layer of hydrocarbons (CHC), whose original function is the protection from desiccation and pathogens. However, in most insects CHC profiles are species specific. While this variability among species was largely linked to communication and recognition functions, additional selective forces may shape insect CHC profiles. Here, we show that in Philanthinae digger wasps (Crabronidae) the CHC profile coevolved with a peculiar brood-care strategy. In particular, we found that the behavior to embalm prey stored in the nest with hydrocarbons is adaptive to protect larval food from fungi in those species hunting for Hymenoptera. The prey embalming secretion is identical in composition to the alkene-dominated CHC profile in these species, suggesting that their profile is adaptively conserved for this purpose. In contrast, prey embalming is not required in those species that switched to Coleoptera as prey. Released from this chemical brood-care strategy, Coleoptera-hunting species considerably diversified their CHC profiles. Differential needs to successfully protect prey types used as larval food have thus driven the diversification of CHCs profiles of female Philanthinae wasps. To the best of our knowledge, this is the first evidence of a direct link between selection pressure for food preservation and CHC diversity. © 2017 The Author(s). Evolution © 2017 The Society for the Study of Evolution.

Size-based estimation of the status of fish stocks: simulation analysis and comparison with age-based estimations

DEFF Research Database (Denmark)

Kokkalis, Alexandros; Thygesen, Uffe Høgsbro; Nielsen, Anders

, were investigated and our estimations were compared to the ICES advice. Only size-specific catch data were used, in order to emulate data limited situations. The simulation analysis reveals that the status of the stock, i.e. F/Fmsy, is estimated more accurately than the fishing mortality F itself....... Specific knowledge of the natural mortality improves the estimation more than having information about all other life history parameters. Our approach gives, at least qualitatively, an estimated stock status which is similar to the results of an age-based assessment. Since our approach only uses size...

Size Estimates in Inverse Problems

KAUST Repository

Di Cristo, Michele

2014-01-06

Detection of inclusions or obstacles inside a body by boundary measurements is an inverse problems very useful in practical applications. When only finite numbers of measurements are available, we try to detect some information on the embedded object such as its size. In this talk we review some recent results on several inverse problems. The idea is to provide constructive upper and lower estimates of the area/volume of the unknown defect in terms of a quantity related to the work that can be expressed with the available boundary data.

Myxobacteria Are Able to Prey Broadly upon Clinically-Relevant Pathogens, Exhibiting a Prey Range Which Cannot Be Explained by Phylogeny

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Paul G. Livingstone

2017-08-01

Full Text Available Myxobacteria are natural predators of microorganisms and the subjects of concerted efforts to identify novel antimicrobial compounds. Myxobacterial predatory activity seems to require more than just the possession of specific antimicrobial metabolites. Thus a holistic approach to studying predation promises novel insights into antimicrobial action. Here, we report the isolation of 113 myxobacteria from samples of soil taken from a range of habitats in mid Wales. Predatory activity of each isolate was quantified against a panel of clinically important prey organisms, including Klebsiella pneumoniae, Proteus mirabilis, Candida albicans, Enterococcus faecalis, and three species of Staphylococcus. Myxobacterial isolates exhibited a wide range of predation activity profiles against the panel of prey. Efficient predation of all prey by isolates within the collection was observed, with K. pneumoniae and C. albicans proving particularly susceptible to myxobacterial predation. Notably efficient predators tended to be proficient at predating multiple prey organisms, suggesting they possess gene(s encoding a broad range killing activity. However, predatory activity was not congruent with phylogeny, suggesting prey range is subject to relatively rapid specialization, potentially involving lateral gene transfer. The broad but patchy prey ranges observed for natural myxobacterial isolates also implies multiple (potentially overlapping genetic determinants are responsible for dictating predatory activity.

Loggerhead turtles (Caretta caretta use vision to forage on gelatinous prey in mid-water.

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Tomoko Narazaki

Full Text Available Identifying characteristics of foraging activity is fundamental to understanding an animals' lifestyle and foraging ecology. Despite its importance, monitoring the foraging activities of marine animals is difficult because direct observation is rarely possible. In this study, we use an animal-borne imaging system and three-dimensional data logger simultaneously to observe the foraging behaviour of large juvenile and adult sized loggerhead turtles (Caretta caretta in their natural environment. Video recordings showed that the turtles foraged on gelatinous prey while swimming in mid-water (i.e., defined as epipelagic water column deeper than 1 m in this study. By linking video and 3D data, we found that mid-water foraging events share the common feature of a marked deceleration phase associated with the capture and handling of the sluggish prey. Analysis of high-resolution 3D movements during mid-water foraging events, including presumptive events extracted from 3D data using deceleration in swim speed as a proxy for foraging (detection rate = 0.67, showed that turtles swam straight toward prey in 171 events (i.e., turning point absent but made a single turn toward the prey an average of 5.7±6.0 m before reaching the prey in 229 events (i.e., turning point present. Foraging events with a turning point tended to occur during the daytime, suggesting that turtles primarily used visual cues to locate prey. In addition, an incident of a turtle encountering a plastic bag while swimming in mid-water was recorded. The fact that the turtle's movements while approaching the plastic bag were analogous to those of a true foraging event, having a turning point and deceleration phase, also support the use of vision in mid-water foraging. Our study shows that integrated video and high-resolution 3D data analysis provides unique opportunities to understand foraging behaviours in the context of the sensory ecology involved in prey location.

Metabolic expenditures of lunge feeding rorquals across scale: implications for the evolution of filter feeding and the limits to maximum body size.

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Jean Potvin

Full Text Available Bulk-filter feeding is an energetically efficient strategy for resource acquisition and assimilation, and facilitates the maintenance of extreme body size as exemplified by baleen whales (Mysticeti and multiple lineages of bony and cartilaginous fishes. Among mysticetes, rorqual whales (Balaenopteridae exhibit an intermittent ram filter feeding mode, lunge feeding, which requires the abandonment of body-streamlining in favor of a high-drag, mouth-open configuration aimed at engulfing a very large amount of prey-laden water. Particularly while lunge feeding on krill (the most widespread prey preference among rorquals, the effort required during engulfment involve short bouts of high-intensity muscle activity that demand high metabolic output. We used computational modeling together with morphological and kinematic data on humpback (Megaptera noveaangliae, fin (Balaenoptera physalus, blue (Balaenoptera musculus and minke (Balaenoptera acutorostrata whales to estimate engulfment power output in comparison with standard metrics of metabolic rate. The simulations reveal that engulfment metabolism increases across the full body size of the larger rorqual species to nearly 50 times the basal metabolic rate of terrestrial mammals of the same body mass. Moreover, they suggest that the metabolism of the largest body sizes runs with significant oxygen deficits during mouth opening, namely, 20% over maximum VO2 at the size of the largest blue whales, thus requiring significant contributions from anaerobic catabolism during a lunge and significant recovery after a lunge. Our analyses show that engulfment metabolism is also significantly lower for smaller adults, typically one-tenth to one-half VO2|max. These results not only point to a physiological limit on maximum body size in this lineage, but also have major implications for the ontogeny of extant rorquals as well as the evolutionary pathways used by ancestral toothed whales to transition from hunting

Effects of prey abundance, distribution, visual contrast and morphology on selection by a pelagic piscivore

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Hansen, Adam G.; Beauchamp, David A.

2014-01-01

Most predators eat only a subset of possible prey. However, studies evaluating diet selection rarely measure prey availability in a manner that accounts for temporal–spatial overlap with predators, the sensory mechanisms employed to detect prey, and constraints on prey capture.We evaluated the diet selection of cutthroat trout (Oncorhynchus clarkii) feeding on a diverse planktivore assemblage in Lake Washington to test the hypothesis that the diet selection of piscivores would reflect random (opportunistic) as opposed to non-random (targeted) feeding, after accounting for predator–prey overlap, visual detection and capture constraints.Diets of cutthroat trout were sampled in autumn 2005, when the abundance of transparent, age-0 longfin smelt (Spirinchus thaleichthys) was low, and 2006, when the abundance of smelt was nearly seven times higher. Diet selection was evaluated separately using depth-integrated and depth-specific (accounted for predator–prey overlap) prey abundance. The abundance of different prey was then adjusted for differences in detectability and vulnerability to predation to see whether these factors could explain diet selection.In 2005, cutthroat trout fed non-randomly by selecting against the smaller, transparent age-0 longfin smelt, but for the larger age-1 longfin smelt. After adjusting prey abundance for visual detection and capture, cutthroat trout fed randomly. In 2006, depth-integrated and depth-specific abundance explained the diets of cutthroat trout well, indicating random feeding. Feeding became non-random after adjusting for visual detection and capture. Cutthroat trout selected strongly for age-0 longfin smelt, but against similar sized threespine stickleback (Gasterosteus aculeatus) and larger age-1 longfin smelt in 2006. Overlap with juvenile sockeye salmon (O. nerka) was minimal in both years, and sockeye salmon were rare in the diets of cutthroat trout.The direction of the shift between random and non-random selection

Assessing the impact on birds of prey of nine established wind farms in Thrace, NE Greece

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Kret, Elzbieta; Carcamo, Beatriz; Zografou, Christina; Vasilakis, Dimitris

2011-07-01

Full text: In this study, we evaluate the impact on birds of prey of nine already established wind farms in Thrace, where a large scale wind farm development project of at least 930 MW is under development. Moreover, the area is acknowledged as of high ornithological interest, used for nesting, wintering and passage by rare territorial birds of prey, including the Near Threatened black vultures that use it for foraging. Finally, ca 50% of the wind farm development project area is covered by Natura 2000 sites. During the monitoring (2008-2010), carcass surveys were carried out in order to estimate mortality. In addition, avian space use surveys were carried out, in order to calculate indexes and to establish comparisons with a previous monitoring study run in 2004-05. In total, 14 birds of prey were found dead (one black vulture, four griffon vultures, one booted eagle, two short-toed eagles, one western marsh harrier, one Eurasian sparrow hawk, three common buzzards, one hawk species). The estimated mortality rate was 0.152 birds of prey (including vultures/turbine/year). Griffon vultures, black vultures and common buzzards comprised more than 50% of observations in the study area. Crossing densities between wind turbines were positively correlated with east exposition and the inclination of the slope, and the length of the wind turbines. gaps, while it was negatively correlated with north exposition. The use of the area was more intensive four years after the initial monitoring, but numbers of common buzzard observations drastically decreased. We suggest that during the planning phase of wind farms it is important to avoid steep slopes, east expositions and to take into account the distance between consecutive wind turbines. Our findings indicate that running a post-construction monitoring during only one year may not be enough to properly assess the impact of wind farms on birds of prey. (Author)

Determining Sample Size for Accurate Estimation of the Squared Multiple Correlation Coefficient.

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Algina, James; Olejnik, Stephen

2000-01-01

Discusses determining sample size for estimation of the squared multiple correlation coefficient and presents regression equations that permit determination of the sample size for estimating this parameter for up to 20 predictor variables. (SLD)

Energetic constraints, size gradients, and size limits in benthic marine invertebrates.

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Sebens, Kenneth P

2002-08-01

Populations of marine benthic organisms occupy habitats with a range of physical and biological characteristics. In the intertidal zone, energetic costs increase with temperature and aerial exposure, and prey intake increases with immersion time, generating size gradients with small individuals often found at upper limits of distribution. Wave action can have similar effects, limiting feeding time or success, although certain species benefit from wave dislodgment of their prey; this also results in gradients of size and morphology. The difference between energy intake and metabolic (and/or behavioral) costs can be used to determine an energetic optimal size for individuals in such populations. Comparisons of the energetic optimal size to the maximum predicted size based on mechanical constraints, and the ensuing mortality schedule, provides a mechanism to study and explain organism size gradients in intertidal and subtidal habitats. For species where the energetic optimal size is well below the maximum size that could persist under a certain set of wave/flow conditions, it is probable that energetic constraints dominate. When the opposite is true, populations of small individuals can dominate habitats with strong dislodgment or damage probability. When the maximum size of individuals is far below either energetic optima or mechanical limits, other sources of mortality (e.g., predation) may favor energy allocation to early reproduction rather than to continued growth. Predictions based on optimal size models have been tested for a variety of intertidal and subtidal invertebrates including sea anemones, corals, and octocorals. This paper provides a review of the optimal size concept, and employs a combination of the optimal energetic size model and life history modeling approach to explore energy allocation to growth or reproduction as the optimal size is approached.

Effects of habitat features on size-biased predation on salmon by bears.

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Andersson, Luke C; Reynolds, John D

2017-05-01

Predators can drive trait divergence among populations of prey by imposing differential selection on prey traits. Habitat characteristics can mediate predator selectivity by providing refuge for prey. We quantified the effects of stream characteristics on biases in the sizes of spawning salmon caught by bears (Ursus arctos and U. americanus) on the central coast of British Columbia, Canada by measuring size-biased predation on spawning chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon in 12 streams with varying habitat characteristics. We tested the hypotheses that bears would catch larger than average salmon (size-biased predation) and that this bias toward larger fish would be higher in streams that provide less protection to spawning salmon from predation (e.g., less pools, wood, undercut banks). We then we tested for how such size biases in turn translate into differences among populations in the sizes of the fish. Bears caught larger-than-average salmon as the spawning season progressed and as predicted, this was most pronounced in streams with fewer refugia for the fish (i.e., wood and undercut banks). Salmon were marginally smaller in streams with more pronounced size-biased predation but this predictor was less reliable than physical characteristics of streams, with larger fish in wider, deeper streams. These results support the hypothesis that selective forces imposed by predators can be mediated by habitat characteristics, with potential consequences for physical traits of prey.

Revealing the role of predator interference in a predator-prey system with disease in prey population

DEFF Research Database (Denmark)

Chakraborty, Subhendu; Kooi, B.W.; Biswas, B.

2015-01-01

Predation on a species subjected to an infectious disease can affect both the infection level and the population dynamics. There is an ongoing debate about the act of managing disease in natural populations through predation. Recent theoretical and empirical evidence shows that predation...... on infected populations can have both positive and negative influences on disease in prey populations. Here, we present a predator-prey system where the prey population is subjected to an infectious disease to explore the impact of predator on disease dynamics. Specifically, we investigate how...... on the strength of interference among predators, predators enhance or control disease outbreaks and population persistence. Moreover, the presence of multistable regimes makes the system very sensitive to perturbations and facilitates a number of regime shifts. Since, the habitat structure and the choice...

Estimating search engine index size variability: a 9-year longitudinal study.

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van den Bosch, Antal; Bogers, Toine; de Kunder, Maurice

One of the determining factors of the quality of Web search engines is the size of their index. In addition to its influence on search result quality, the size of the indexed Web can also tell us something about which parts of the WWW are directly accessible to the everyday user. We propose a novel method of estimating the size of a Web search engine's index by extrapolating from document frequencies of words observed in a large static corpus of Web pages. In addition, we provide a unique longitudinal perspective on the size of Google and Bing's indices over a nine-year period, from March 2006 until January 2015. We find that index size estimates of these two search engines tend to vary dramatically over time, with Google generally possessing a larger index than Bing. This result raises doubts about the reliability of previous one-off estimates of the size of the indexed Web. We find that much, if not all of this variability can be explained by changes in the indexing and ranking infrastructure of Google and Bing. This casts further doubt on whether Web search engines can be used reliably for cross-sectional webometric studies.

Reliability of different mark-recapture methods for population size estimation tested against reference population sizes constructed from field data.

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Annegret Grimm

Full Text Available Reliable estimates of population size are fundamental in many ecological studies and biodiversity conservation. Selecting appropriate methods to estimate abundance is often very difficult, especially if data are scarce. Most studies concerning the reliability of different estimators used simulation data based on assumptions about capture variability that do not necessarily reflect conditions in natural populations. Here, we used data from an intensively studied closed population of the arboreal gecko Gehyra variegata to construct reference population sizes for assessing twelve different population size estimators in terms of bias, precision, accuracy, and their 95%-confidence intervals. Two of the reference populations reflect natural biological entities, whereas the other reference populations reflect artificial subsets of the population. Since individual heterogeneity was assumed, we tested modifications of the Lincoln-Petersen estimator, a set of models in programs MARK and CARE-2, and a truncated geometric distribution. Ranking of methods was similar across criteria. Models accounting for individual heterogeneity performed best in all assessment criteria. For populations from heterogeneous habitats without obvious covariates explaining individual heterogeneity, we recommend using the moment estimator or the interpolated jackknife estimator (both implemented in CAPTURE/MARK. If data for capture frequencies are substantial, we recommend the sample coverage or the estimating equation (both models implemented in CARE-2. Depending on the distribution of catchabilities, our proposed multiple Lincoln-Petersen and a truncated geometric distribution obtained comparably good results. The former usually resulted in a minimum population size and the latter can be recommended when there is a long tail of low capture probabilities. Models with covariates and mixture models performed poorly. Our approach identified suitable methods and extended options to

Fishing destabilizes the biomass flow in the marine size spectrum.

Science.gov (United States)

Rochet, M-J; Benoît, E

2012-01-22

Fishing impacts on marine food webs are predicted by simulations of a size spectrum community model. In this model, predation is determined by predator and prey size and abundance, and drives predator growth and prey mortality. Fishing amplifies temporal oscillations in the biomass flow. Oscillations appear at lower fishing intensity and have wider amplitude when fishing is selective (removes a narrow size range) and/or when large fish are targeted, than when fishing is more balanced (catching a larger size range) or when small fish are targeted. A novel index of size diversity is developed, and is shown to be sensitive to both fishing intensity and selectivity. To avoid unstable food web dynamics with potential harmful consequences for fisheries, limiting both fishing intensity and selectivity might be an appropriate exploitation strategy.

Children's accuracy of portion size estimation using digital food images: effects of interface design and size of image on computer screen.

Science.gov (United States)

Baranowski, Tom; Baranowski, Janice C; Watson, Kathleen B; Martin, Shelby; Beltran, Alicia; Islam, Noemi; Dadabhoy, Hafza; Adame, Su-heyla; Cullen, Karen; Thompson, Debbe; Buday, Richard; Subar, Amy

2011-03-01

To test the effect of image size and presence of size cues on the accuracy of portion size estimation by children. Children were randomly assigned to seeing images with or without food size cues (utensils and checked tablecloth) and were presented with sixteen food models (foods commonly eaten by children) in varying portion sizes, one at a time. They estimated each food model's portion size by selecting a digital food image. The same food images were presented in two ways: (i) as small, graduated portion size images all on one screen or (ii) by scrolling across large, graduated portion size images, one per sequential screen. Laboratory-based with computer and food models. Volunteer multi-ethnic sample of 120 children, equally distributed by gender and ages (8 to 13 years) in 2008-2009. Average percentage of correctly classified foods was 60·3 %. There were no differences in accuracy by any design factor or demographic characteristic. Multiple small pictures on the screen at once took half the time to estimate portion size compared with scrolling through large pictures. Larger pictures had more overestimation of size. Multiple images of successively larger portion sizes of a food on one computer screen facilitated quicker portion size responses with no decrease in accuracy. This is the method of choice for portion size estimation on a computer.

Comparison of known food weights with image-based portion-size automated estimation and adolescents' self-reported portion size.

Science.gov (United States)

Lee, Christina D; Chae, Junghoon; Schap, TusaRebecca E; Kerr, Deborah A; Delp, Edward J; Ebert, David S; Boushey, Carol J

2012-03-01

Diet is a critical element of diabetes self-management. An emerging area of research is the use of images for dietary records using mobile telephones with embedded cameras. These tools are being designed to reduce user burden and to improve accuracy of portion-size estimation through automation. The objectives of this study were to (1) assess the error of automatically determined portion weights compared to known portion weights of foods and (2) to compare the error between automation and human. Adolescents (n = 15) captured images of their eating occasions over a 24 h period. All foods and beverages served were weighed. Adolescents self-reported portion sizes for one meal. Image analysis was used to estimate portion weights. Data analysis compared known weights, automated weights, and self-reported portions. For the 19 foods, the mean ratio of automated weight estimate to known weight ranged from 0.89 to 4.61, and 9 foods were within 0.80 to 1.20. The largest error was for lettuce and the most accurate was strawberry jam. The children were fairly accurate with portion estimates for two foods (sausage links, toast) using one type of estimation aid and two foods (sausage links, scrambled eggs) using another aid. The automated method was fairly accurate for two foods (sausage links, jam); however, the 95% confidence intervals for the automated estimates were consistently narrower than human estimates. The ability of humans to estimate portion sizes of foods remains a problem and a perceived burden. Errors in automated portion-size estimation can be systematically addressed while minimizing the burden on people. Future applications that take over the burden of these processes may translate to better diabetes self-management. © 2012 Diabetes Technology Society.

The hydrodynamics of predator-prey interactions in zebrafish

Science.gov (United States)

McHenry, Matthew; Soto, Alberto; Carrillo, Andres; Byron, Margaret

2017-11-01

Hydrodynamics govern the behavior of fishes when they operate as predators or prey. In addition to the role of fluid forces in propulsion, fishes relay on flow stimuli to sense a predatory threat and to localize palatable prey. We have performed a series of experiments on zebrafish (Danio rerio) that aim to resolve the major factors that determine whether prey survive an encounter with a predator. Zebrafish serve as a model system in this pursuit because the adults prey on larvae of the same species and the larvae are often successful in evading the attacks of the adults. We use a combination of theoretical and experimental approaches to resolve the behavioral algorithms and kinematics that determined the outcome of these interactions. In this context, the hydrodynamics of intermediate Reynolds numbers largely determines the range of flow stimuli and the limits to locomotor performance at dictate prey survival. These principles have the potential to apply to a broad diversity of fishes and other aquatic animals. ONR: N00014-15-1-2249.

Are single odorous components of a predator sufficient to elicit defensive behaviors in prey species?

Directory of Open Access Journals (Sweden)

Raimund eApfelbach

2015-07-01

Full Text Available When exposed to the odor of a sympatric predator, prey animals typically display escape or defensive responses. These phenomena have been well-documented, especially in rodents, when exposed to the odor of a cat, ferret or fox. As a result of these experiments new discussions center on the following questions: 1 is a single volatile compound such as a major or a minor mixture constituent in urine or feces, emitted by the predator sufficient to cause defensive reactions in a potential prey species or 2 is a whole array of odors required to elicit a response and 3 will the relative size or escapability of the prey as compared to the predator influence responsiveness. Most predator-prey studies on this topic have been performed in the laboratory or under semi-natural conditions. Field studies could help to find answers to these questions. Australian mammals are completely naïve towards the introduced placental carnivores. That offers ideal opportunities to analyze in the field the responses of potential prey species to unknown predator odors. During the last decades researchers have accumulated an enormous amount of data exploring the effects of eutherian predator odors on native marsupial mammals. In this review, we will give a survey about the development of olfactory research, chemical signals and their influence on the behavior and - in some cases - physiology of prey species. In addition, we report on the effects of predator odor experiments performed under natural conditions in Australia. When studying all these literature we learned that data gained under controlled laboratory conditions elucidate the role of individual odors on brain structures and ultimately on a comparatively narrow range behaviors. In contrast to single odors odor arrays mimic much more the situation prey animals are confronted to in nature. Therefore, a broad range of methodology — from chemistry to ecology including anatomy, physiology and behavior — is needed to

Optimum sample size to estimate mean parasite abundance in fish parasite surveys

Directory of Open Access Journals (Sweden)

Shvydka S.

2018-03-01

Full Text Available To reach ethically and scientifically valid mean abundance values in parasitological and epidemiological studies this paper considers analytic and simulation approaches for sample size determination. The sample size estimation was carried out by applying mathematical formula with predetermined precision level and parameter of the negative binomial distribution estimated from the empirical data. A simulation approach to optimum sample size determination aimed at the estimation of true value of the mean abundance and its confidence interval (CI was based on the Bag of Little Bootstraps (BLB. The abundance of two species of monogenean parasites Ligophorus cephali and L. mediterraneus from Mugil cephalus across the Azov-Black Seas localities were subjected to the analysis. The dispersion pattern of both helminth species could be characterized as a highly aggregated distribution with the variance being substantially larger than the mean abundance. The holistic approach applied here offers a wide range of appropriate methods in searching for the optimum sample size and the understanding about the expected precision level of the mean. Given the superior performance of the BLB relative to formulae with its few assumptions, the bootstrap procedure is the preferred method. Two important assessments were performed in the present study: i based on CIs width a reasonable precision level for the mean abundance in parasitological surveys of Ligophorus spp. could be chosen between 0.8 and 0.5 with 1.6 and 1x mean of the CIs width, and ii the sample size equal 80 or more host individuals allows accurate and precise estimation of mean abundance. Meanwhile for the host sample size in range between 25 and 40 individuals, the median estimates showed minimal bias but the sampling distribution skewed to the low values; a sample size of 10 host individuals yielded to unreliable estimates.

Mean size estimation yields left-side bias: Role of attention on perceptual averaging.

Science.gov (United States)

Li, Kuei-An; Yeh, Su-Ling

2017-11-01

The human visual system can estimate mean size of a set of items effectively; however, little is known about whether information on each visual field contributes equally to the mean size estimation. In this study, we examined whether a left-side bias (LSB)-perceptual judgment tends to depend more heavily on left visual field's inputs-affects mean size estimation. Participants were instructed to estimate the mean size of 16 spots. In half of the trials, the mean size of the spots on the left side was larger than that on the right side (the left-larger condition) and vice versa (the right-larger condition). Our results illustrated an LSB: A larger estimated mean size was found in the left-larger condition than in the right-larger condition (Experiment 1), and the LSB vanished when participants' attention was effectively cued to the right side (Experiment 2b). Furthermore, the magnitude of LSB increased with stimulus-onset asynchrony (SOA), when spots on the left side were presented earlier than the right side. In contrast, the LSB vanished and then induced a reversed effect with SOA when spots on the right side were presented earlier (Experiment 3). This study offers the first piece of evidence suggesting that LSB does have a significant influence on mean size estimation of a group of items, which is induced by a leftward attentional bias that enhances the prior entry effect on the left side.

Availability and abundance of prey for the red-cockaded woodpecker.

Energy Technology Data Exchange (ETDEWEB)

Hanula, James, L.; Horn, Scott

2004-12-31

Red-cockaded woodpecker; Road to Recovery. Proceedings of the 4th Red-cockaded woodpecker Symposium. Ralph Costa and Susan J. Daniels, eds. Savannah, Georgia. January, 2003. Chapter 11. Prey, Fire, and Community Ecology. Pp 633-645. Abstract: Over a 10-year period we investigated red-cockaded woodpecker (Picoides borealis) prey use, sources of prey, prey distribution within trees and stands, and how forest management decisions affect prey abundance in South Carolina, Alabama, Georgia and Florida. Cameras were operated at 31 nest cavities to record nest visits with prey in 4 locations that ranged in foraging habitat from pine stands established in old fields to an old-growth stand in South Georgia. Examination of nearly 12,000 photographs recorded over 5 years revealed that, although red-cockaded woodpeckers used over 40 arthropods for food, the majority of the nestling diet is comprised of a relatively small number of common arthropods.

Biomechanics of predator-prey arms race in lion, zebra, cheetah and impala

Science.gov (United States)

Wilson, Alan M.; Hubel, Tatjana Y.; Wilshin, Simon D.; Lowe, John C.; Lorenc, Maja; Dewhirst, Oliver P.; Bartlam-Brooks, Hattie L. A.; Diack, Rebecca; Bennitt, Emily; Golabek, Krystyna A.; Woledge, Roger C.; McNutt, J. Weldon; Curtin, Nancy A.; West, Timothy G.

2018-02-01

The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator-prey pairs, lion-zebra and cheetah-impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator-prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate.

Bias in estimating food consumption of fish from stomach-content analysis

DEFF Research Database (Denmark)

Rindorf, Anna; Lewy, Peter

2004-01-01

This study presents an analysis of the bias introduced by using simplified methods to calculate food intake of fish from stomach contents. Three sources of bias were considered: (1) the effect of estimating consumption based on a limited number of stomach samples, (2) the effect of using average......, a serious positive bias was introduced by estimating food intake from the contents of pooled stomach samples. An expression is given that can be used to correct analytically for this bias. A new method, which takes into account the distribution and evacuation of individual prey types as well as the effect...... of other food in the stomach on evacuation, is suggested for estimating the intake of separate prey types. Simplifying the estimation by ignoring these factors biased estimates of consumption of individual prey types by up to 150% in a data example....

Influence of group size on the success of wolves hunting bison.

Science.gov (United States)

MacNulty, Daniel R; Tallian, Aimee; Stahler, Daniel R; Smith, Douglas W

2014-01-01

An intriguing aspect of social foraging behaviour is that large groups are often no better at capturing prey than are small groups, a pattern that has been attributed to diminished cooperation (i.e., free riding) in large groups. Although this suggests the formation of large groups is unrelated to prey capture, little is known about cooperation in large groups that hunt hard-to-catch prey. Here, we used direct observations of Yellowstone wolves (Canis lupus) hunting their most formidable prey, bison (Bison bison), to test the hypothesis that large groups are more cooperative when hunting difficult prey. We quantified the relationship between capture success and wolf group size, and compared it to previously reported results for Yellowstone wolves hunting elk (Cervus elaphus), a prey that was, on average, 3 times easier to capture than bison. Whereas improvement in elk capture success levelled off at 2-6 wolves, bison capture success levelled off at 9-13 wolves with evidence that it continued to increase beyond 13 wolves. These results are consistent with the hypothesis that hunters in large groups are more cooperative when hunting more formidable prey. Improved ability to capture formidable prey could therefore promote the formation and maintenance of large predator groups, particularly among predators that specialize on such prey.

Influence of group size on the success of wolves hunting bison.

Directory of Open Access Journals (Sweden)

Daniel R MacNulty

Full Text Available An intriguing aspect of social foraging behaviour is that large groups are often no better at capturing prey than are small groups, a pattern that has been attributed to diminished cooperation (i.e., free riding in large groups. Although this suggests the formation of large groups is unrelated to prey capture, little is known about cooperation in large groups that hunt hard-to-catch prey. Here, we used direct observations of Yellowstone wolves (Canis lupus hunting their most formidable prey, bison (Bison bison, to test the hypothesis that large groups are more cooperative when hunting difficult prey. We quantified the relationship between capture success and wolf group size, and compared it to previously reported results for Yellowstone wolves hunting elk (Cervus elaphus, a prey that was, on average, 3 times easier to capture than bison. Whereas improvement in elk capture success levelled off at 2-6 wolves, bison capture success levelled off at 9-13 wolves with evidence that it continued to increase beyond 13 wolves. These results are consistent with the hypothesis that hunters in large groups are more cooperative when hunting more formidable prey. Improved ability to capture formidable prey could therefore promote the formation and maintenance of large predator groups, particularly among predators that specialize on such prey.

Killer whale prey - Determining prey selection by southern resident killer whales (SRKW)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Prey selectivity by southern resident killer whales is being determined by analyses of fish scales and tissue from predation events and feces. Information on killer...

Quenching behaviour for a singular predator–prey model

International Nuclear Information System (INIS)

Ducrot, Arnaud; Guo, Jong-Shenq

2012-01-01

In this paper, we study the quenching behaviour for a system of two reaction–diffusion equations arising in the modelling of the spatio-temporal interaction of prey and predator populations in fragile environment. We first provide some sufficient conditions on the initial data to have finite time quenching. Then we classify the initial data to distinguish type I quenching and type II quenching, by introducing a delicate energy functional along with the help of some a priori estimates. Finally, we present some results on the quenching set. It can be a singleton, the whole domain, or a compact subset of the domain

Morphology of seahorse head hydrodynamically aids in capture of evasive prey.

Science.gov (United States)

Gemmell, Brad J; Sheng, Jian; Buskey, Edward J

2013-01-01

Syngnathid fish (seahorses, pipefish and sea dragons) are slow swimmers yet capture evasive prey (copepods) using a technique known as the 'pivot' feeding, which involves rapid movement to overcome prey escape capabilities. However, this feeding mode functions only at short range and requires approaching very closely to hydrodynamically sensitive prey without triggering an escape. Here we investigate the role of head morphology on prey capture using holographic and particle image velocimetry (PIV). We show that head morphology functions to create a reduced fluid deformation zone, minimizing hydrodynamic disturbance where feeding strikes occur (above the end of the snout), and permits syngnathid fish to approach highly sensitive copepod prey (Acartia tonsa) undetected. The results explain how these animals can successfully employ short range 'pivot' feeding effectively on evasive prey. The need to approach prey with stealth may have selected for a head shape that produces lower deformation rates than other fish.

Rapid prey evolution can alter the structure of predator-prey communities

NARCIS (Netherlands)

Friman, V. -P.; Jousset, A.; Buckling, A.

Although microevolution has been shown to play an important role in pairwise antagonistic species interactions, its importance in more complex communities has received little attention. Here, we used two Pseudomonas fluorescens prey bacterial strains (SBW25 and F113) and Tetrahymena thermophila

On multi-team predator-prey models

International Nuclear Information System (INIS)

Elettreby, M.F.; Saker, S.H.; Ahmed, E.

2005-05-01

Many creatures form teams. This has, at least, two main advantages: the first is the improvement in foraging, since looking for food in a team is more efficient than doing it alone. The second is that living in a team reduces predation risk due to early spotting of predators and that existing in a team gives a higher probability that the predator will attack another member of the team. In this paper models are given where two teams of predators interact with two teams of preys. The teams of each group (predators or preys) help each other. In this paper we propose three different versions of the multi-team predator prey model. We study the equilibrium solutions, the conditions of their local asymptotic stability, persistence and the global stability of the solution of one of the models. Some numerical simulations are done. (author)

Estimating minimum polycrystalline aggregate size for macroscopic material homogeneity

International Nuclear Information System (INIS)

Kovac, M.; Simonovski, I.; Cizelj, L.

2002-01-01

During severe accidents the pressure boundary of reactor coolant system can be subjected to extreme loadings, which might cause failure. Reliable estimation of the extreme deformations can be crucial to determine the consequences of severe accidents. Important drawback of classical continuum mechanics is idealization of inhomogenous microstructure of materials. Classical continuum mechanics therefore cannot predict accurately the differences between measured responses of specimens, which are different in size but geometrical similar (size effect). A numerical approach, which models elastic-plastic behavior on mesoscopic level, is proposed to estimate minimum size of polycrystalline aggregate above which it can be considered macroscopically homogeneous. The main idea is to divide continuum into a set of sub-continua. Analysis of macroscopic element is divided into modeling the random grain structure (using Voronoi tessellation and random orientation of crystal lattice) and calculation of strain/stress field. Finite element method is used to obtain numerical solutions of strain and stress fields. The analysis is limited to 2D models.(author)

Webometrics: Some Critical Issues of WWW Size Estimation Methods

Directory of Open Access Journals (Sweden)

Srinivasan Mohana Arunachalam

2018-04-01

Full Text Available The number of webpages in the Internet has increased tremendously over the last two decades however only a part of it is indexed by various search engines. This small portion is the indexable web of the Internet and can be usually reachable from a Search Engine. Search engines play a big role in making the World Wide Web accessible to the end user, and how much of the World Wide Web is accessible on the size of the search engine’s index. Researchers have proposed several ways to estimate this size of the indexable web using search engines with and without privileged access to the search engine’s database. Our report provides a summary of methods used in the last two decades to estimate the size of the World Wide Web, as well as describe how this knowledge can be used in other aspects/tasks concerning the World Wide Web.

Impacts of Mesopredator Control on Conservation of Mesopredators and Their Prey.

Directory of Open Access Journals (Sweden)

L Mike Conner

Full Text Available Declining large carnivore populations, increased habitat fragmentation, declining interests in fur trapping, and other anthropogenic factors can all lead to increased mesopredator populations and these may negatively impact biodiversity. Lethal mesopredator control potentially mitigates some of these effects but can be controversial, largely because impacts on mesopredator populations have not been evaluated. Estimating these impacts may reduce controversies while increasing our understanding of when lethal control may be beneficial. Therefore, we analyzed published mesopredator removal data to determine if mesopredator removal rates changed over time. Removals of medium,(e.g., raccoons (Procyon lotor or red foxes (Vulpes vulpes, and large, i.e., bobcats (Lynx rufus or coyotes (Canis latrans, mesopredators were consistent from year to year and over the duration of study (i.e., number removed during the first and last years of studies were similar. In contrast, removals of small mesopredators, e.g., weasels (Mustela spp. or spotted skunks (Spilogale putorius, declined over the duration of study. Study area size, number of species targeted for removal, and duration of removal effort were poor predictors of removal rates. Our analyses suggest that: (1 control, as typically implemented, is unlikely to cause negative long-term impacts on populations of medium and large mesopredators but may negatively impact small mesopredators, (2 if mesopredator control benefits prey, recurring removals will generally be needed to maintain benefits, and (3 timing of removals will be important to achieve management goals. We suggest that mesopredator control efforts are frequently spatially structured harvests from continuously distributed populations. This may explain (1 why removal of small mesopredators declined over time; whereas, medium and large mesopredator removals remained consistent, and (2 why some prey failed to respond to mesopredator control efforts.

a Predator-Prey Model Based on the Fully Parallel Cellular Automata

Science.gov (United States)

He, Mingfeng; Ruan, Hongbo; Yu, Changliang

We presented a predator-prey lattice model containing moveable wolves and sheep, which are characterized by Penna double bit strings. Sexual reproduction and child-care strategies are considered. To implement this model in an efficient way, we build a fully parallel Cellular Automata based on a new definition of the neighborhood. We show the roles played by the initial densities of the populations, the mutation rate and the linear size of the lattice in the evolution of this model.

Estimation of myocardial infarct size by vectocardiography

International Nuclear Information System (INIS)

Takimiya, Akihiko

1987-01-01

Correlations between the vectorcardiogram (VCG) indice and infarct size (% defect) obtained from myocardial emission computed tomography with thallium-201 were studied in 45 patients with old infero-posterior myocardial infarction. The patients were divided into two groups, one consisting of eight patients who showed abnormal superior deviation of the QRS loop in a counterclockwise rotation beyond 30 msec in the frontal plane of VCG (referred to hereafter as CCW group), and another a non-CCW group consisting of 37 patients. The results obtained were as follows. (1) In the non-CCW group, there were significant negative correlations between the elevation and the Y-axial component of each instantaneous vector of the QRS loop at 30 msec, 35 msec, 40 msec, 45 msec, and between the Y-axial component of 50 msec instantaneous vector and the % defect. The correlation for both the elevation and the Y-axial component was closest at 40 msec, and there was most significantly close correlation between the elevation of 40 msec instantaneous vector and the % defect. (2) In the non-CCW group, there was also a significant correlation between the elevation of QRS area vector and the % defect. (3) In the CCW group, the infarct size could be estimated by the elevation of 30 msec instantaneous vector. An association with left anterior fascicular block was also indicated in the CCW group. (4) In infero-posterior myocardial infarction, the infarct size can be estimated using these VCG indices. (author)

Evidence for the Higher Importance of Signal Size Over Body Size in Aposematic Signaling in Insects

OpenAIRE

Remmel, Triinu; Tammarub, Toomas

2011-01-01

To understand the evolution of warning coloration, it is important to distinguish between different aspects of conspicuous color patterns. As an example, both pattern element size and body size of prey have been shown to enhance the effectiveness of warning signals. However, it is unclear whether the effect of body size is merely a side effect of proportionally increasing pattern elements, or if there is an effect of body size per se. These possibilities were evaluated by offering different s...

A simple method for estimating the size of nuclei on fractal surfaces

Science.gov (United States)

Zeng, Qiang

2017-10-01

Determining the size of nuclei on complex surfaces remains a big challenge in aspects of biological, material and chemical engineering. Here the author reported a simple method to estimate the size of the nuclei in contact with complex (fractal) surfaces. The established approach was based on the assumptions of contact area proportionality for determining nucleation density and the scaling congruence between nuclei and surfaces for identifying contact regimes. It showed three different regimes governing the equations for estimating the nucleation site density. Nuclei in the size large enough could eliminate the effect of fractal structure. Nuclei in the size small enough could lead to the independence of nucleation site density on fractal parameters. Only when nuclei match the fractal scales, the nucleation site density is associated with the fractal parameters and the size of the nuclei in a coupling pattern. The method was validated by the experimental data reported in the literature. The method may provide an effective way to estimate the size of nuclei on fractal surfaces, through which a number of promising applications in relative fields can be envisioned.

Structuring of zooplankton and fish larvae assemblages in a freshwater-influenced Greenlandic fjord- influence from hydrography and prey availability

DEFF Research Database (Denmark)

Swalethorp, Rasmus; Malanski, Evandro; Munk, Peter

2015-01-01

The recent increase in temperature and freshwater runoff in the Arctic will influence the functioning of the plankton ecosystem and hence the life of the fish larvae residing in these areas. Here, we studied the strength of physical– biological linkages and the adaptability of individual larval...... of the individual larval fish species. Larvae were feeding on a variety of prey taxa and sizes; some larval species were generalists, while others were more specialized or fed on alternative prey taxa. Differences in feeding strategies might have the consequence that the species will be differently affected...

Microbiological survey of birds of prey pellets.

Science.gov (United States)

Dipineto, Ludovico; Bossa, Luigi Maria De Luca; Pace, Antonino; Russo, Tamara Pasqualina; Gargiulo, Antonio; Ciccarelli, Francesca; Raia, Pasquale; Caputo, Vincenzo; Fioretti, Alessandro

2015-08-01

A microbiological survey of 73 pellets collected from different birds of prey species housed at the Wildlife Rescue and Rehabilitation Center of Napoli (southern Italy) was performed. Pellets were analyzed by culture and biochemical methods as well as by serotyping and polymerase chain reaction. We isolated a wide range of bacteria some of them also pathogens for humans (i.e. Salmonella enterica serotype Typhimurium, Campylobacter coli, Escherichia coli O serogroups). This study highlights the potential role of birds of prey as asymptomatic carriers of pathogenic bacteria which could be disseminated in the environment not only through the birds of prey feces but also through their pellets. Copyright © 2015 Elsevier Ltd. All rights reserved.

Individual prey choices of octopuses: Are they generalist or specialist?

Directory of Open Access Journals (Sweden)

Jennifer A. MATHER, Tatiana S. LEITE, Allan T. BATISTA

2012-08-01

Full Text Available Prey choice is often evaluated at the species or population level. Here, we analyzed the diet of octopuses of different populations with the aim to assess the importance of individual feeding habits as a factor affecting prey choice. Two methods were used, an assessment of the extent to which an individual octopus made choices of species representative of those population (PSi and IS and 25% cutoff values for number of choices and percentage intake of individual on their prey. In one population of Octopus cf vulgaris in Bermuda individuals were generalist by IS=0.77, but most chose many prey of the same species, and were specialists on it by >75% intake. Another population had a wider prey selection, still generalist with PSi=0.66, but two individuals specialized by choices. In Bonaire, there was a wide range of prey species chosen, and the population was specialists by IS= 0.42. Individual choices revealed seven specialists and four generalists. A population of Octopus cyanea in Hawaii all had similar choices of crustaceans, so the population was generalist by IS with 0.74. But by individual choices, three were considered a specialist. A population of Enteroctopus dofleini from Puget Sound had a wide range of preferences, in which seven were also specialists, IS=0.53. By individual choices, thirteen were also specialists. Given the octopus specialty of learning during foraging, we hypothesize that both localized prey availability and individual personality differences could influence the exploration for prey and this translates into different prey choices across individuals and populations showed in this study [Current Zoology 58 (4: 597-603, 2012].

Prey change behaviour with predation threat, but demographic effects vary with prey density: experiments with grasshoppers and birds.

Science.gov (United States)

Belovsky, Gary E; Laws, Angela Nardoni; Slade, Jennifer B

2011-04-01

Increasingly, ecologists emphasize that prey frequently change behaviour in the presence of predators and these behavioural changes can reduce prey survival and reproduction as much or more than predation itself. However, the effects of behavioural changes on survival and reproduction may vary with prey density due to intraspecific competition. In field experiments, we varied grasshopper density and threat of avian predation and measured grasshopper behaviour, survival and reproduction. Grasshopper behaviour changed with the threat of predation and these behavioural changes were invariant with grasshopper density. Behavioural changes with the threat of predation decreased per capita reproduction over all grasshopper densities; whereas the behavioural changes increased survival at low grasshopper densities and then decreased survival at high densities. At low grasshopper densities, the total reproductive output of the grasshopper population remained unchanged with predation threat, but declined at higher densities. The effects of behavioural changes with predation threat varied with grasshopper density because of a trade-off between survival and reproduction as intraspecific competition increased with density. Therefore, resource availability may need to be considered when assessing how prey behavioural changes with predation threat affect population and food web dynamics. © 2011 Blackwell Publishing Ltd/CNRS.

Zebra mussel beds: an effective feeding ground for Ponto-Caspian gobies or suitable shelter for their prey?

Science.gov (United States)

Kobak, Jarosław; Poznańska, Małgorzata; Jermacz, Łukasz; Kakareko, Tomasz; Prądzynski, Daniel; Łodygowska, Małgorzata; Montowska, Karolina; Bącela-Spychalska, Karolina

2016-01-01

Aggregations of the Ponto-Caspian invasive zebra mussel ( Dreissena polymorpha ) constitute a suitable habitat for macroinvertebrates, considerably increasing their abundance and providing effective antipredator protection. Thus, the overall effect of a mussel bed on particular predator species may vary from positive to negative, depending on both prey density increase and predator ability to prey in a structurally complex habitat. Alien Ponto-Caspian goby fish are likely to be facilitated when introduced into new areas by zebra mussels, provided that they are capable of utilizing mussel beds as habitat and feeding grounds. We ran laboratory experiments to find which prey (chironomid larvae) densities (from ca. 500 to 2,000 individuals m -2 ) in a mussel bed make it a more beneficial feeding ground for the racer goby Babka gymnotrachelus (RG) and western tubenose goby Proterorhinus semilunaris (WTG) compared to sandy and stone substrata (containing the basic prey density of 500 ind. m -2 ). Moreover, we checked how food availability affects habitat selection by fish. Mussel beds became more suitable for fish than alternative mineral substrata when food abundance was at least two times higher (1,000 vs. 500 ind. m -2 ), regardless of fish size and species. WTG was associated with mussel beds regardless of its size and prey density, whereas RG switched to this habitat when it became a better feeding ground than alternative substrata. Larger RG exhibited a stronger affinity for mussels than small individuals. WTG fed more efficiently from a mussel bed at high food abundances than RG. A literature review has shown that increasing chironomid density, which in our study was sufficient to make a mussel habitat an attractive feeding ground for the gobies, is commonly observed in mussel beds in the field. Therefore, we conclude that zebra mussels may positively affect the alien goby species and are likely to facilitate their establishment in novel areas, contributing to an

Zebra mussel beds: an effective feeding ground for Ponto-Caspian gobies or suitable shelter for their prey?

Directory of Open Access Journals (Sweden)

Jarosław Kobak

2016-11-01

Full Text Available Aggregations of the Ponto-Caspian invasive zebra mussel (Dreissena polymorpha constitute a suitable habitat for macroinvertebrates, considerably increasing their abundance and providing effective antipredator protection. Thus, the overall effect of a mussel bed on particular predator species may vary from positive to negative, depending on both prey density increase and predator ability to prey in a structurally complex habitat. Alien Ponto-Caspian goby fish are likely to be facilitated when introduced into new areas by zebra mussels, provided that they are capable of utilizing mussel beds as habitat and feeding grounds. We ran laboratory experiments to find which prey (chironomid larvae densities (from ca. 500 to 2,000 individuals m−2 in a mussel bed make it a more beneficial feeding ground for the racer goby Babka gymnotrachelus (RG and western tubenose goby Proterorhinus semilunaris (WTG compared to sandy and stone substrata (containing the basic prey density of 500 ind. m−2. Moreover, we checked how food availability affects habitat selection by fish. Mussel beds became more suitable for fish than alternative mineral substrata when food abundance was at least two times higher (1,000 vs. 500 ind. m−2, regardless of fish size and species. WTG was associated with mussel beds regardless of its size and prey density, whereas RG switched to this habitat when it became a better feeding ground than alternative substrata. Larger RG exhibited a stronger affinity for mussels than small individuals. WTG fed more efficiently from a mussel bed at high food abundances than RG. A literature review has shown that increasing chironomid density, which in our study was sufficient to make a mussel habitat an attractive feeding ground for the gobies, is commonly observed in mussel beds in the field. Therefore, we conclude that zebra mussels may positively affect the alien goby species and are likely to facilitate their establishment in novel areas

Relating marten scat contents to prey consumed

Science.gov (United States)

William J. Zielinski

1986-01-01

A European ferret, Mustela putorius furo, was fed typical marten food items to discover the relationship between prey weight and number of scats produced per unit weight of prey. A correction factor was derived that was used in the analysis of pine marten, Martes americana, scats to produce a method capable of comparing foods on a...

Lake Ontario benthic prey fish assessment, 2015

Science.gov (United States)

Weidel, Brian C.; Walsh, Maureen; Holden, Jeremy P.; Connerton, Michael J.

2016-01-01

Benthic prey fishes are a critical component of the Lake Ontario food web, serving as energy vectors from benthic invertebrates to native and introduced piscivores. Since the late 1970’s, Lake Ontario benthic prey fish status was primarily assessed using bottom trawl observations confined to the lake’s south shore, in waters from 8 – 150 m (26 – 492 ft). In 2015, the Benthic Prey Fish Survey was cooperatively adjusted and expanded to address resource management information needs including lake-wide benthic prey fish population dynamics. Effort increased from 55 bottom trawl sites to 135 trawl sites collected in depths from 8 - 225m (26 – 738 ft). The spatial coverage of sampling was also expanded and occurred in all major lake basins. The resulting distribution of tow depths more closely matched the available lake depth distribution. The additional effort illustrated how previous surveys were underestimating lake-wide Deepwater Sculpin, Myoxocephalus thompsonii, abundance by not sampling in areas of highest density. We also found species richness was greater in the new sampling sites relative to the historic sites with 11 new fish species caught in the new sites including juvenile Round Whitefish, Prosopium cylindraceum, and Mottled sculpin, Cottus bairdii. Species-specific assessments found Slimy Sculpin, Cottus cognatus abundance increased slightly in 2015 relative to 2014, while Deepwater Sculpin and Round Goby, Neogobius melanostomus, dramatically increased in 2015, relative to 2014. The cooperative, lake-wide Benthic Prey Fish Survey expanded our understanding of benthic fish population dynamics and habitat use in Lake Ontario. This survey’s data and interpretations influence international resource management decision making, such as informing the Deepwater Sculpin conservation status and assessing the balance between sport fish consumption and prey fish populations. Additionally a significant Lake Ontario event occurred in May 2015 when a single

Sizing up arthropod genomes: an evaluation of the impact of environmental variation on genome size estimates by flow cytometry and the use of qPCR as a method of estimation.

Science.gov (United States)

Gregory, T Ryan; Nathwani, Paula; Bonnett, Tiffany R; Huber, Dezene P W

2013-09-01

A study was undertaken to evaluate both a pre-existing method and a newly proposed approach for the estimation of nuclear genome sizes in arthropods. First, concerns regarding the reliability of the well-established method of flow cytometry relating to impacts of rearing conditions on genome size estimates were examined. Contrary to previous reports, a more carefully controlled test found negligible environmental effects on genome size estimates in the fly Drosophila melanogaster. Second, a more recently touted method based on quantitative real-time PCR (qPCR) was examined in terms of ease of use, efficiency, and (most importantly) accuracy using four test species: the flies Drosophila melanogaster and Musca domestica and the beetles Tribolium castaneum and Dendroctonus ponderosa. The results of this analysis demonstrated that qPCR has the tendency to produce substantially different genome size estimates from other established techniques while also being far less efficient than existing methods.

The functional response to prey density in an acarine system

NARCIS (Netherlands)

Fransz, H.G.

1974-01-01

Predacious mites are considered to be important natural enemies of phytophagous mites. Their efficiency in the natural control of prey populations depends on the relationships of the number of prey killed per predator per time unit and the oviposition rate on the one hand and prey density on the

Whale sharks target dense prey patches of sergestid shrimp off Tanzania

KAUST Repository

Rohner, C. A.; Armstrong, A. J.; Pierce, S. J.; Prebble, C. E. M.; Cagua, E. F.; Cochran, J. E. M.; Berumen, Michael L.; Richardson, A. J.

2015-01-01

Large planktivores require high-density prey patches to make feeding energetically viable. This is a major challenge for species living in tropical and subtropical seas, such as whale sharks Rhincodon typus. Here, we characterize zooplankton biomass, size structure and taxonomic composition from whale shark feeding events and background samples at Mafia Island, Tanzania. The majority of whale sharks were feeding (73%, 380 of 524 observations), with the most common behaviour being active surface feeding (87%). We used 20 samples collected from immediately adjacent to feeding sharks and an additional 202 background samples for comparison to show that plankton biomass was ∼10 times higher in patches where whale sharks were feeding (25 vs. 2.6 mg m-3). Taxonomic analyses of samples showed that the large sergestid Lucifer hanseni (∼10 mm) dominated while sharks were feeding, accounting for ∼50% of identified items, while copepods (<2 mm) dominated background samples. The size structure was skewed towards larger animals representative of L.hanseni in feeding samples. Thus, whale sharks at Mafia Island target patches of dense, large, zooplankton dominated by sergestids. Large planktivores, such as whale sharks, which generally inhabit warm oligotrophic waters, aggregate in areas where they can feed on dense prey to obtain sufficient energy. © 2015 © The Author 2015. Published by Oxford University Press. All rights reserved.

Whale sharks target dense prey patches of sergestid shrimp off Tanzania

KAUST Repository

Rohner, C. A.

2015-03-17

Large planktivores require high-density prey patches to make feeding energetically viable. This is a major challenge for species living in tropical and subtropical seas, such as whale sharks Rhincodon typus. Here, we characterize zooplankton biomass, size structure and taxonomic composition from whale shark feeding events and background samples at Mafia Island, Tanzania. The majority of whale sharks were feeding (73%, 380 of 524 observations), with the most common behaviour being active surface feeding (87%). We used 20 samples collected from immediately adjacent to feeding sharks and an additional 202 background samples for comparison to show that plankton biomass was ∼10 times higher in patches where whale sharks were feeding (25 vs. 2.6 mg m-3). Taxonomic analyses of samples showed that the large sergestid Lucifer hanseni (∼10 mm) dominated while sharks were feeding, accounting for ∼50% of identified items, while copepods (<2 mm) dominated background samples. The size structure was skewed towards larger animals representative of L.hanseni in feeding samples. Thus, whale sharks at Mafia Island target patches of dense, large, zooplankton dominated by sergestids. Large planktivores, such as whale sharks, which generally inhabit warm oligotrophic waters, aggregate in areas where they can feed on dense prey to obtain sufficient energy. © 2015 © The Author 2015. Published by Oxford University Press. All rights reserved.

Prey capture by freely swimming flagellates

Science.gov (United States)

Andersen, Anders; Dolger, Julia; Nielsen, Lasse Tor; Kiorboe, Thomas

2017-11-01

Flagellates are unicellular microswimmers that propel themselves using one or several beating flagella. Here, we explore the dependence of swimming kinematics and prey clearance rate on flagellar arrangement and determine optimal flagellar arrangements and essential trade-offs. To describe near-cell flows around freely swimming flagellates we consider a model in which the cell is represented by a no-slip sphere and each flagellum by a point force. For uniflagellates pulled by a single flagellum the model suggests that a long flagellum favors fast swimming, whereas high clearance rate is favored by a very short flagellum. For biflagellates with both a longitudinal and a transversal flagellum we explore the helical swimming kinematics and the prey capture sites. We compare our predictions with observations of swimming kinematics, prey capture, and flows around common marine flagellates. The Centre for Ocean Life is a VKR Centre of Excellence supported by the Villum Foundation.

Swimming and escape behavior of copepod nauplii: implications for predator-prey interactions among copepods

DEFF Research Database (Denmark)

Titelman, Josefin

2001-01-01

This study focuses on how prey behavior may affect predation risk through encounter rates and the escape success of the prey given an encounter. Temora longicornis nauplii require stronger hydrodynamic signals to elicit escape than Acartia tonsa nauplii (critical fluid deformation rates, Delta......* of 2.8 to 4.0 and 1.2 to 2.5 s(-1), respectively) suggesting that T. longicornis may be more susceptible to predation. Quantification of naupliar motility behavior and subsequent estimation of the hydrodynamic signals which the nauplii generate suggest that an adult female Centropages typicus may......, the behavior of A. tonsa acts predominantly at the post-encounter stage where its sensitivity to hydrodynamic signals (i,e., low Delta*) effectively compensates for the high predator encounter rate generated by its motility....

Tactile Experience Shapes Prey-Capture Behavior in Etruscan Shrews

Directory of Open Access Journals (Sweden)

Michael eBrecht

2012-06-01

Full Text Available A crucial role of tactile experience for the maturation of neural response properties in the somatosensory system is well established, but little is known about the role of tactile experience in the development of tactile behaviors. Here we study how tactile experience affects prey capture behavior in Etruscan shrews, Suncus etruscus. Prey capture in adult shrews is a high-speed behavior that relies on precise attacks guided by tactile Gestalt cues. We studied the role of tactile experience by three different approaches. First, we analyzed the hunting skills of young shrews right after weaning. We found that prey capture in young animals is most but not all aspects similar to that of adults. Second we performed whisker trimming for three to four weeks after birth. Such deprivation resulted in a lasting disruption of prey capture even after whisker re-growth: attacks lacked precise targeting and had a lower success rate. Third, we presented adult shrews with an entirely novel prey species, the giant cockroach. The shape of this roach is very different from the shrew’s normal (cricket prey and the thorax – the preferred point of attack in crickets – is protected a heavy cuticle. Initially shrews attacked giant roaches the same way they attack crickets and targeted the thoracic region. With progressive experience, however, shrews adopted a new attack strategy targeting legs and underside of the roaches while avoiding other body parts. Speed and efficiency of attacks improved. These data suggest that tactile experience shapes prey capture behavior.

The international food unit: a new measurement aid that can improve portion size estimation.

Science.gov (United States)

Bucher, T; Weltert, M; Rollo, M E; Smith, S P; Jia, W; Collins, C E; Sun, M

2017-09-12

Portion size education tools, aids and interventions can be effective in helping prevent weight gain. However consumers have difficulties in estimating food portion sizes and are confused by inconsistencies in measurement units and terminologies currently used. Visual cues are an important mediator of portion size estimation, but standardized measurement units are required. In the current study, we present a new food volume estimation tool and test the ability of young adults to accurately quantify food volumes. The International Food Unit™ (IFU™) is a 4x4x4 cm cube (64cm 3 ), subdivided into eight 2 cm sub-cubes for estimating smaller food volumes. Compared with currently used measures such as cups and spoons, the IFU™ standardizes estimation of food volumes with metric measures. The IFU™ design is based on binary dimensional increments and the cubic shape facilitates portion size education and training, memory and recall, and computer processing which is binary in nature. The performance of the IFU™ was tested in a randomized between-subject experiment (n = 128 adults, 66 men) that estimated volumes of 17 foods using four methods; the IFU™ cube, a deformable modelling clay cube, a household measuring cup or no aid (weight estimation). Estimation errors were compared between groups using Kruskall-Wallis tests and post-hoc comparisons. Estimation errors differed significantly between groups (H(3) = 28.48, p studies should investigate whether the IFU™ can facilitate portion size training and whether portion size education using the IFU™ is effective and sustainable without the aid. A 3-dimensional IFU™ could serve as a reference object for estimating food volume.

Allee effect in a discrete-time predator-prey system

International Nuclear Information System (INIS)

Celik, Canan; Duman, Oktay

2009-01-01

In this paper, we study the stability of a discrete-time predator-prey system with and without Allee effect. By analyzing both systems, we first obtain local stability conditions of the equilibrium points without the Allee effect and then exhibit the impact of the Allee effect on stability when it is imposed on prey population. We also show the stabilizing effect of Allee effect by numerical simulations and verify that when the prey population is subject to an Allee effect, the trajectory of the solutions approximates to the corresponding equilibrium point much faster. Furthermore, for some fixed parameter values satisfying necessary conditions, we show that the corresponding equilibrium point moves from instability to stability under the Allee effect on prey population.

An adaptable but threatened big cat: density, diet and prey selection of the Indochinese leopard (Panthera pardus delacouri) in eastern Cambodia.

Science.gov (United States)

Rostro-García, Susana; Kamler, Jan F; Crouthers, Rachel; Sopheak, Keo; Prum, Sovanna; In, Visattha; Pin, Chanratana; Caragiulo, Anthony; Macdonald, David W

2018-02-01

We studied the Indochinese leopard ( Panthera pardus delacouri ) in eastern Cambodia, in one of the few potentially remaining viable populations in Southeast Asia. The aims were to determine the: (i) current leopard density in Srepok Wildlife Sanctuary (SWS) and (ii) diet, prey selection and predation impact of leopard in SWS. The density, estimated using spatially explicit capture-recapture models, was 1.0 leopard/100 km 2 , 72% lower than an estimate from 2009 at the same site, and one of the lowest densities ever reported in Asia. Dietary analysis of 73 DNA confirmed scats showed leopard consumed 13 prey species, although ungulates comprised 87% of the biomass consumed (BC). The overall main prey (42% BC) was banteng ( Bos javanicus ), making this the only known leopard population whose main prey had adult weight greater than 500 kg. Consumption of wild pig ( Sus scrofa ) was also one of the highest ever reported (22% BC), indicating leopard consistently predated on ungulates with some of the largest adult weights in SWS. There were important differences in diet and prey selection between sexes, as males consumed mostly banteng (62% BC) in proportion to availability, but few muntjac ( Muntiacus vaginalis ; 7% BC), whereas females selectively consumed muntjac (56% BC) and avoided banteng (less than 1% BC). Predation impact was low (0.5-3.2% of populations) for the three ungulate species consumed. We conclude that the Indochinese leopard is an important apex predator in SWS, but this unique population is declining at an alarming rate and will soon be eradicated unless effective protection is provided.

Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability.

Science.gov (United States)

Sherley, Richard B; Botha, Philna; Underhill, Les G; Ryan, Peter G; van Zyl, Danie; Cockcroft, Andrew C; Crawford, Robert J M; Dyer, Bruce M; Cook, Timothée R

2017-12-01

Human activities are important drivers of marine ecosystem functioning. However, separating the synergistic effects of fishing and environmental variability on the prey base of nontarget predators is difficult, often because prey availability estimates on appropriate scales are lacking. Understanding how prey abundance at different spatial scales links to population change can help integrate the needs of nontarget predators into fisheries management by defining ecologically relevant areas for spatial protection. We investigated the local population response (number of breeders) of the Bank Cormorant (Phalacrocorax neglectus), a range-restricted endangered seabird, to the availability of its prey, the heavily fished west coast rock lobster (Jasus lalandii). Using Bayesian state-space modeled cormorant counts at 3 colonies, 22 years of fisheries-independent data on local lobster abundance, and generalized additive modeling, we determined the spatial scale pertinent to these relationships in areas with different lobster availability. Cormorant numbers responded positively to lobster availability in the regions with intermediate and high abundance but not where regime shifts and fishing pressure had depleted lobster stocks. The relationships were strongest when lobsters 20-30 km offshore of the colony were considered, a distance greater than the Bank Cormorant's foraging range when breeding, and may have been influenced by prey availability for nonbreeding birds, prey switching, or prey ecology. Our results highlight the importance of considering the scale of ecological relationships in marine spatial planning and suggest that designing spatial protection around focal species can benefit marine predators across their full life cycle. We propose the precautionary implementation of small-scale marine protected areas, followed by robust assessment and adaptive-management, to confirm population-level benefits for the cormorants, their prey, and the wider ecosystem, without

Stationary Patterns in One-Predator Two-Prey Models

DEFF Research Database (Denmark)

Pedersen, Michael; Zhigui, Lin

1999-01-01

Weakly-coupled elliptic system decribing models of simple three-species food webs such as the one-predator, two-prey modelis discussed. We show thatthere is no non-constant solution if diffusions or inter-specific competitions are strong, or if the intrinsic growths of the prey are slow...

Interactive effects of prey and weather on golden eagle reproduction

Science.gov (United States)

Steenhof, Karen; Kochert, Michael N.; McDonald, T.L.

1997-01-01

1. The reproduction of the golden eagle Aquila chrysaetos was studied in southwestern Idaho for 23 years, and the relationship between eagle reproduction and jackrabbit Lepus californicus abundance, weather factors, and their interactions, was modelled using general linear models. Backward elimination procedures were used to arrive at parsimonious models.2. The number of golden eagle pairs occupying nesting territories each year showed a significant decline through time that was unrelated to either annual rabbit abundance or winter severity. However, eagle hatching dates were significantly related to both winter severity and jackrabbit abundance. Eagles hatched earlier when jackrabbits were abundant, and they hatched later after severe winters.3. Jackrabbit abundance influenced the proportion of pairs that laid eggs, the proportion of pairs that were successful, mean brood size at fledging, and the number of young fledged per pair. Weather interacted with prey to influence eagle reproductive rates.4. Both jackrabbit abundance and winter severity were important in predicting the percentage of eagle pairs that laid eggs. Percentage laying was related positively to jackrabbit abundance and inversely related to winter severity.5. The variables most useful in predicting percentage of laying pairs successful were rabbit abundance and the number of extremely hot days during brood-rearing. The number of hot days and rabbit abundance were also significant in a model predicting eagle brood size at fledging. Both success and brood size were positively related to jackrabbit abundance and inversely related to the frequency of hot days in spring.6. Eagle reproduction was limited by rabbit abundance during approximately twothirds of the years studied. Weather influenced how severely eagle reproduction declined in those years.7. This study demonstrates that prey and weather can interact to limit a large raptor population's productivity. Smaller raptors could be affected more

Estimation of Tooth Size Discrepancies among Different Malocclusion Groups

OpenAIRE

Hasija, Narender; Bala, Madhu; Goyal, Virender

2014-01-01

ABSTRACT Regards and Tribute: Late Dr Narender Hasija was a mentor and visionary in the light of knowledge and experience. We pay our regards with deepest gratitude to the departed soul to rest in peace. Bolton’s ratios help in estimating overbite, overjet relationships, the effects of contemplated extractions on posterior occlusion, incisor relationships and identification of occlusal misfit produced by tooth size discrepancies. Aim: To determine any difference in tooth size discrepancy in a...

Sample size for estimation of the Pearson correlation coefficient in cherry tomato tests

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Bruno Giacomini Sari

2017-09-01

Full Text Available ABSTRACT: The aim of this study was to determine the required sample size for estimation of the Pearson coefficient of correlation between cherry tomato variables. Two uniformity tests were set up in a protected environment in the spring/summer of 2014. The observed variables in each plant were mean fruit length, mean fruit width, mean fruit weight, number of bunches, number of fruits per bunch, number of fruits, and total weight of fruits, with calculation of the Pearson correlation matrix between them. Sixty eight sample sizes were planned for one greenhouse and 48 for another, with the initial sample size of 10 plants, and the others were obtained by adding five plants. For each planned sample size, 3000 estimates of the Pearson correlation coefficient were obtained through bootstrap re-samplings with replacement. The sample size for each correlation coefficient was determined when the 95% confidence interval amplitude value was less than or equal to 0.4. Obtaining estimates of the Pearson correlation coefficient with high precision is difficult for parameters with a weak linear relation. Accordingly, a larger sample size is necessary to estimate them. Linear relations involving variables dealing with size and number of fruits per plant have less precision. To estimate the coefficient of correlation between productivity variables of cherry tomato, with a confidence interval of 95% equal to 0.4, it is necessary to sample 275 plants in a 250m² greenhouse, and 200 plants in a 200m² greenhouse.

Winter wolf predation in a multiple ungulate prey system, Gates of the Arctic National Park, Alaska

Science.gov (United States)

Dale, Bruce W.; Adams, Layne G.; Bowyer, R. Terry; Carbyn, Ludwig N.; Fritts, Steven H.; Seip, Dale R.

1995-01-01

We investigated patterns of winter wolf predation, including prey selection, prey switching, kill rates, carcass utilization, and consumption rates for four wolf packs during three different study periods (March 1989, March 1990, and November 1990) in Gates of the Arctic National Park and Preserve, Alaska. Wolves killed predominantly caribou (165 caribou, seven moose, and five Dall sheep) even when moose and sheep were more abundant. Prey selection varied between study periods. More moose were killed in march 1989, a particularly deep snow year, and more sheep were killed in November 1990 than during other periods. Overall kill rates ranged from 0-8 days/ungulate killed (x̅ = 2.0, SD = 1.6) and did not vary between study periods.  Pack size and species killed explained significant variation in the length of time intervals between kills. Although caribou density varied nearly 40-fold between pack territories, it had little influence on predation characteristics except at low densities, when kill rates may have declined. Caribou distribution had marked effects on wolf predation rate.

Impact of Base Functional Component Types on Software Functional Size based Effort Estimation

OpenAIRE

Gencel, Cigdem; Buglione, Luigi

2008-01-01

Software effort estimation is still a significant challenge for software management. Although Functional Size Measurement (FSM) methods have been standardized and have become widely used by the software organizations, the relationship between functional size and development effort still needs further investigation. Most of the studies focus on the project cost drivers and consider total software functional size as the primary input to estimation models. In this study, we investigate whether u...

Predator-prey encounters in turbulent waters

DEFF Research Database (Denmark)

Mann, J.; Ott, Søren; Pécseli, H.L.

2002-01-01

With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous and isot......With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous...

Stationary Patterns in One-Predator Two-Prey Models

DEFF Research Database (Denmark)

Pedersen, Michael; Zhigui, Lin

1999-01-01

Weakly-coupled elliptic system decribing models of simple three-species food webs such as the one-predator, two-prey model is discussed. We show that there is no non-constant solution if diffusions or inter-specific competitions are strong, or if the intrinsic growths of the prey are slow...

Estimating the size of non-observed economy in Croatia using the MIMIC approach

Directory of Open Access Journals (Sweden)

Vjekoslav Klarić

2011-03-01

Full Text Available This paper gives a quick overview of the approaches that have been used in the research of shadow economy, starting with the definitions of the terms “shadow economy” and “non-observed economy”, with the accent on the ISTAT/Eurostat framework. Several methods for estimating the size of the shadow economy and the non-observed economy are then presented. The emphasis is placed on the MIMIC approach, one of the methods used to estimate the size of the nonobserved economy. After a glance at the theory behind it, the MIMIC model is then applied to the Croatian economy. Considering the described characteristics of different methods, a previous estimate of the size of the non-observed economy in Croatia is chosen to provide benchmark values for the MIMIC model. Using those, the estimates of the size of non-observed economy in Croatia during the period 1998-2009 are obtained.

Estimating population size of Saddle-billed Storks Ephippiorhynchus ...

African Journals Online (AJOL)

The aim of this study was to estimate the population size within associated confidence limits using a modified mark–recapture field method. The vehicle survey, conducted shortly after rainfall in the area, did not produce results with known precision under these conditions. A repeat of this census in spring, after the peak ...

Shear-wave elastography contributes to accurate tumour size estimation when assessing small breast cancers

International Nuclear Information System (INIS)

Mullen, R.; Thompson, J.M.; Moussa, O.; Vinnicombe, S.; Evans, A.

2014-01-01

Aim: To assess whether the size of peritumoural stiffness (PTS) on shear-wave elastography (SWE) for small primary breast cancers (≤15 mm) was associated with size discrepancies between grey-scale ultrasound (GSUS) and final histological size and whether the addition of PTS size to GSUS size might result in more accurate tumour size estimation when compared to final histological size. Materials and methods: A retrospective analysis of 86 consecutive patients between August 2011 and February 2013 who underwent breast-conserving surgery for tumours of size ≤15 mm at ultrasound was carried out. The size of PTS stiffness was compared to mean GSUS size, mean histological size, and the extent of size discrepancy between GSUS and histology. PTS size and GSUS were combined and compared to the final histological size. Results: PTS of >3 mm was associated with a larger mean final histological size (16 versus 11.3 mm, p < 0.001). PTS size of >3 mm was associated with a higher frequency of underestimation of final histological size by GSUS of >5 mm (63% versus 18%, p < 0.001). The combination of PTS and GSUS size led to accurate estimation of the final histological size (p = 0.03). The size of PTS was not associated with margin involvement (p = 0.27). Conclusion: PTS extending beyond 3 mm from the grey-scale abnormality is significantly associated with underestimation of tumour size of >5 mm for small invasive breast cancers. Taking into account the size of PTS also led to accurate estimation of the final histological size. Further studies are required to assess the relationship of the extent of SWE stiffness and margin status. - Highlights: • Peritumoural stiffness of greater than 3 mm was associated with larger tumour size. • Underestimation of tumour size by ultrasound was associated with peri-tumoural stiffness size. • Combining peri-tumoural stiffness size to ultrasound produced accurate tumour size estimation

Predation risk affects growth and reproduction of an invasive snail and its lethal effect depends on prey size

Science.gov (United States)

Guo, Jing; Martín, Pablo R.; Zhang, Chunxia

2017-01-01

The behavior of invasive species under predation risk has been studied extensively, but their growth and reproductive responses have rarely been investigated. We conducted experiments with juveniles and adults of the invasive freshwater snail Pomacea canaliculata, and we observed changes in growth and reproduction in response to predation risk from a caged predator (Trachemys scripta elegans). P. canaliculata produced eggs earlier in the presence of predators and injured conspecifics compared with the control group (no risk), although the total number of egg masses laid by per female was exceeded by that of the controls after 15 days. Egg hatching success noticeably decreased under predation risk, and the incubation period was significantly prolonged; however, the oviposition height of the snails was not affected. A lethal effect of predation risk was detected in juvenile snails but not in adults. The growth of juvenile P. canaliculata was inhibited under predation risk, probably due to a reduction in food intake. Adult females exhibited a greater reduction in growth under predation risk than males, which likely resulted in part from the high reproductive investment of females in egg laying. These results indicate that P. canaliculata snails under predation risk face a trade-off between predator avoidance and growth and reproduction, where the lethal effect of predation risk is linked to the size of the prey. PMID:29136660

Predation risk affects growth and reproduction of an invasive snail and its lethal effect depends on prey size.

Directory of Open Access Journals (Sweden)

Jing Guo

Full Text Available The behavior of invasive species under predation risk has been studied extensively, but their growth and reproductive responses have rarely been investigated. We conducted experiments with juveniles and adults of the invasive freshwater snail Pomacea canaliculata, and we observed changes in growth and reproduction in response to predation risk from a caged predator (Trachemys scripta elegans. P. canaliculata produced eggs earlier in the presence of predators and injured conspecifics compared with the control group (no risk, although the total number of egg masses laid by per female was exceeded by that of the controls after 15 days. Egg hatching success noticeably decreased under predation risk, and the incubation period was significantly prolonged; however, the oviposition height of the snails was not affected. A lethal effect of predation risk was detected in juvenile snails but not in adults. The growth of juvenile P. canaliculata was inhibited under predation risk, probably due to a reduction in food intake. Adult females exhibited a greater reduction in growth under predation risk than males, which likely resulted in part from the high reproductive investment of females in egg laying. These results indicate that P. canaliculata snails under predation risk face a trade-off between predator avoidance and growth and reproduction, where the lethal effect of predation risk is linked to the size of the prey.

Automated nodule location and size estimation using a multi-scale Laplacian of Gaussian filtering approach.

Science.gov (United States)

Jirapatnakul, Artit C; Fotin, Sergei V; Reeves, Anthony P; Biancardi, Alberto M; Yankelevitz, David F; Henschke, Claudia I

2009-01-01

Estimation of nodule location and size is an important pre-processing step in some nodule segmentation algorithms to determine the size and location of the region of interest. Ideally, such estimation methods will consistently find the same nodule location regardless of where the the seed point (provided either manually or by a nodule detection algorithm) is placed relative to the "true" center of the nodule, and the size should be a reasonable estimate of the true nodule size. We developed a method that estimates nodule location and size using multi-scale Laplacian of Gaussian (LoG) filtering. Nodule candidates near a given seed point are found by searching for blob-like regions with high filter response. The candidates are then pruned according to filter response and location, and the remaining candidates are sorted by size and the largest candidate selected. This method was compared to a previously published template-based method. The methods were evaluated on the basis of stability of the estimated nodule location to changes in the initial seed point and how well the size estimates agreed with volumes determined by a semi-automated nodule segmentation method. The LoG method exhibited better stability to changes in the seed point, with 93% of nodules having the same estimated location even when the seed point was altered, compared to only 52% of nodules for the template-based method. Both methods also showed good agreement with sizes determined by a nodule segmentation method, with an average relative size difference of 5% and -5% for the LoG and template-based methods respectively.

Seasonal foraging ecology of non-migratory cougars in a system with migrating prey.

Directory of Open Access Journals (Sweden)

L Mark Elbroch

Full Text Available We tested for seasonal differences in cougar (Puma concolor foraging behaviors in the Southern Yellowstone Ecosystem, a multi-prey system in which ungulate prey migrate, and cougars do not. We recorded 411 winter prey and 239 summer prey killed by 28 female and 10 male cougars, and an additional 37 prey items by unmarked cougars. Deer composed 42.4% of summer cougar diets but only 7.2% of winter diets. Males and females, however, selected different proportions of different prey; male cougars selected more elk (Cervus elaphus and moose (Alces alces than females, while females killed greater proportions of bighorn sheep (Ovis canadensis, pronghorn (Antilocapra americana, mule deer (Odocoileus hemionus and small prey than males. Kill rates did not vary by season or between males and females. In winter, cougars were more likely to kill prey on the landscape as: 1 elevation decreased, 2 distance to edge habitat decreased, 3 distance to large bodies of water decreased, and 4 steepness increased, whereas in summer, cougars were more likely to kill in areas as: 1 elevation decreased, 2 distance to edge habitat decreased, and 3 distance from large bodies of water increased. Our work highlighted that seasonal prey selection exhibited by stationary carnivores in systems with migratory prey is not only driven by changing prey vulnerability, but also by changing prey abundances. Elk and deer migrations may also be sustaining stationary cougar populations and creating apparent competition scenarios that result in higher predation rates on migratory bighorn sheep in winter and pronghorn in summer. Nevertheless, cougar predation on rare ungulates also appeared to be influenced by individual prey selection.

The curse of the prey: Sarcoptes mite molecular analysis reveals potential prey-to-predator parasitic infestation in wild animals from Masai Mara, Kenya

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Soriguer Ramón C

2011-10-01

Full Text Available Abstract Background Recently, there have been attempts to understand the molecular epidemiology of Sarcoptes scabiei, to evaluate the gene flow between isolates of S. scabiei from different hosts and geographic regions. However, to our knowledge, a molecular study has not been carried out to assess the molecular diversity and gene flow of Sarcoptes mite in a predator/prey ecosystem. Results Our study revealed an absence of gene flow between the two herbivore (Thomson's gazelle and wildebeest- and between the two carnivore (lion and cheetah-derived Sarcoptes populations from Masai Mara (Kenya, which is in discrepancy with the host-taxon law described for wild animals in Europe. Lion- and wildebeest-derived Sarcoptes mite populations were similar yet different from the Thomson's gazelle-derived Sarcoptes population. This could be attributed to Sarcoptes cross-infestation from wildebeest ("favourite prey" of the lion, but not from Thomson's gazelle. The cheetah-derived Sarcoptes population had different subpopulations: one is cheetah-private, one similar to the wildebeest- and lion-derived Sarcoptes populations, and another similar to the Thomson's gazelle-derived Sarcoptes mite population, where both wildebeest and Thomson's gazelle are "favourite preys" for the cheetah. Conclusions In a predator/prey ecosystem, like Masai Mara in Kenya, it seems that Sarcoptes infestation in wild animals is prey-to-predator-wise, depending on the predator's "favourite prey". More studies on the lion and cheetah diet and behaviour could be of great help to clarify the addressed hypotheses. This study could have further ramification in the epidemiological studies and the monitoring protocols of the neglected Sarcoptes mite in predator/prey ecosystems.

A Heuristic Probabilistic Approach to Estimating Size-Dependent Mobility of Nonuniform Sediment

Science.gov (United States)

Woldegiorgis, B. T.; Wu, F. C.; van Griensven, A.; Bauwens, W.

2017-12-01

Simulating the mechanism of bed sediment mobility is essential for modelling sediment dynamics. Despite the fact that many studies are carried out on this subject, they use complex mathematical formulations that are computationally expensive, and are often not easy for implementation. In order to present a simple and computationally efficient complement to detailed sediment mobility models, we developed a heuristic probabilistic approach to estimating the size-dependent mobilities of nonuniform sediment based on the pre- and post-entrainment particle size distributions (PSDs), assuming that the PSDs are lognormally distributed. The approach fits a lognormal probability density function (PDF) to the pre-entrainment PSD of bed sediment and uses the threshold particle size of incipient motion and the concept of sediment mixture to estimate the PSDs of the entrained sediment and post-entrainment bed sediment. The new approach is simple in physical sense and significantly reduces the complexity and computation time and resource required by detailed sediment mobility models. It is calibrated and validated with laboratory and field data by comparing to the size-dependent mobilities predicted with the existing empirical lognormal cumulative distribution function (CDF) approach. The novel features of the current approach are: (1) separating the entrained and non-entrained sediments by a threshold particle size, which is a modified critical particle size of incipient motion by accounting for the mixed-size effects, and (2) using the mixture-based pre- and post-entrainment PSDs to provide a continuous estimate of the size-dependent sediment mobility.

Effect of Brood Age on Nestling Diet and Prey Composition in a Hedgerow Specialist Bird, the Barred Warbler Sylvia nisoria.

Directory of Open Access Journals (Sweden)

Grzegorz Orłowski

Full Text Available The composition and quality of food provided to nestling birds influence their growth and development and offers key insight into the ecological requirements of birds. One bird species whose feeding ecology is poorly understood is the Barred Warbler (Sylvia nisoria, which utilizes semi-natural shrubby vegetation in agroecosystems. Because Barred Warbler nestlings vary greatly in body mass we hypothesised that diet and prey properties (size, diversity, taxonomic composition, and chitin content and resulting body hardness and digestibility would differ as the nestlings aged. We quantified the diet based on faecal analysis, sampling faecal sacs from the nestlings pooled into three age classes: 2-3 days old, 4-6 d old, and 7-9 d old. Nestlings were provided a wide diversity of food and a strong relationship existed between food characteristics and nestling age. The youngest nestlings (2-3 d old had the lowest values of each dietary characteristic (diversity, number and total biomass of prey, and individual prey weight, that were significantly lower than the oldest nestlings (7-9 d old. Nestlings aged 4-6 d exhibited intermediate dietary characteristics. Differences in dietary composition of the six major food types showed marked differences between the individual broods and age categories. Percentages of the number and biomass of soft-bodied prey were highest in the diet of 2-3 d and 4-6 d old nestlings, and decreased with increasing age, whereas the opposite trend was observed in the percentage of intermediately and heavily chitinised prey. Parent Barred Warblers probably preferentially select soft-bodied prey for the youngest nestlings, and satisfy the greater energy demands of the older ones by providing them with a greater variety of prey containing more chitin, as well as plant food. The provisioning of less-readily digestible prey to older nestlings suggests that as the quality of food decreases the quantity increases, implying that the

Post-attack aposematic display in prey facilitates predator avoidance learning

Directory of Open Access Journals (Sweden)

Changku eKang

2016-04-01

Full Text Available Warning signals protect unpalatable prey from predation because predators who learn the association between the warning signal and prey unprofitability decrease attacks on the prey. Most of the research have focused on visual aposematic signals that are constantly presented and visible to the predators. But a variety of chemically defended insects are rather cryptic when resting, and only in response to predator attacks (post-attack they perform displays of conspicuous abdomens or hindwings normally hidden under forewings. The function of those displays in unpalatable insects is not well understood. We examined two adaptive hypotheses on this facultative aposematic display using wild-caught oriental tits (Parus minor as predators. First, we tested whether the display increases the rejection of the prey by predators upon seeing the display (i.e. at the moment of attack through learning trials (aposematic signaling hypothesis. Second, we tested whether the display facilitates the memory formation between cryptic visible form of the prey and prey defense so that it prevents the predators initiate an attack upon seeing the cryptic form (facilitation hypothesis. We found that predators learned to avoid attacking the prey which supports the facilitation hypothesis. However, the support for the aposematic signaling hypothesis was equivocal. Our results open new directions of research by highlighting the possibility that similar facilitation effects may contribute to the evolution of various forms of post-attack visual displays in chemically, or otherwise, defended animals.

Do phytoseiid mites select the best prey species in terms of reproductive success?

NARCIS (Netherlands)

Dicke, M.; Sabelis, M.W.; Jong, de M.; Alers, M.P.T.

1990-01-01

Optimal foraging theory predicts that predators prefer those prey species that are most rewarding in terms of reproductive success, which is dependent on prey quality and prey availability. To investigate which selection pressures may have moulded prey preference in an acarine system consisting of

Diet and prey availability of terrestrial insectivorous birds prone to extinction in amazonian forest fragments

Directory of Open Access Journals (Sweden)

Luiz Augusto Macedo Mestre

2010-12-01

Full Text Available This study compared niche breath, prey size, and diet variability in two pairs of sympatric species of terrestrial insectivorous birds, each pair containing one species that can persist in small forest fragments and one that does not. The pairs were Myrmeciza ferruginea and Sclerurus rufigularis; and Formicarius colma and F. analis, respectively. The prey availability in forest fragments was also sampled and compared to the availability in continuous forests. Niche breath indices did not differ between pair members, but diet variability differed in the opposite direction from that hypothesized. Although the two bird species most vulnerable to fragmentation fed on larger prey than less vulnerable species, prey availability, including that based on prey size did not differ among fragmented versus continuous forest sites. Thus, diet per se appeared not to be an important cause of extinction-proneness in these species. The simplest explanation proposed, that vulnerability to fragmentation was directly related to territory size, requires testing. However, it was consistent with observations that the bird species feeding on larger prey also need larger territories.Dieta e disponibilidade de presas de aves insetívoras terrestres em fragmentos florestais amazônicos. As aves insetívoras terrestres são um dos grupos mais vulneráveis à fragmentação de florestas tropicais; no entanto algumas espécies desta guilda ainda sobrevivem em fragmentos florestais e em florestas secundárias. Se a sensibilidade destas aves à fragmentação de florestas estivesse associada à dieta, então espécies com a dieta relativamente flexível teriam maior propensão em persistir nos fragmentos florestais. Este estudo comparou sobreposição trófica, amplitude de nicho, tamanho de presas e variabilidade de dieta de dois pares de espécies de aves insetívoras terrestres, onde cada par foi composto por uma espécie que persiste nos fragmentos e outra que n

The discrepancy between emotional vs. rational estimates of body size, actual size, and ideal body ratings: theoretical and clinical implications.

Science.gov (United States)

Thompson, J K; Dolce, J J

1989-05-01

Thirty-two asymptomatic college females were assessed on multiple aspects of body image. Subjects' estimation of the size of three body sites (waist, hips, thighs) was affected by instructional protocol. Emotional ratings, based on how they "felt" about their body, elicited ratings that were larger than actual and ideal size measures. Size ratings based on rational instructions were no different from actual sizes, but were larger than ideal ratings. There were no differences between actual and ideal sizes. The results are discussed with regard to methodological issues involved in body image research. In addition, a working hypothesis that differentiates affective/emotional from cognitive/rational aspects of body size estimation is offered to complement current theories of body image. Implications of the findings for the understanding of body image and its relationship to eating disorders are discussed.

Prey handling using whole-body fluid dynamics in batoids.

Science.gov (United States)

Wilga, Cheryl D; Maia, Anabela; Nauwelaerts, Sandra; Lauder, George V

2012-02-01

Fluid flow generated by body movements is a foraging tactic that has been exploited by many benthic species. In this study, the kinematics and hydrodynamics of prey handling behavior in little skates, Leucoraja erinacea, and round stingrays, Urobatis halleri, are compared using kinematics and particle image velocimetry. Both species use the body to form a tent to constrain the prey with the pectoral fin edges pressed against the substrate. Stingrays then elevate the head, which increases the volume between the body and the substrate to generate suction, while maintaining pectoral fin contact with the substrate. Meanwhile, the tip of the rostrum is curled upwards to create an opening where fluid is drawn under the body, functionally analogous to suction-feeding fishes. Skates also rotate the rostrum upwards although with the open rostral sides and the smaller fin area weaker fluid flow is generated. However, skates also use a rostral strike behavior in which the rostrum is rapidly rotated downwards pushing fluid towards the substrate to potentially stun or uncover prey. Thus, both species use the anterior portion of the body to direct fluid flow to handle prey albeit in different ways, which may be explained by differences in morphology. Rostral stiffness and pectoral fin insertion onto the rostrum differ between skates and rays and this corresponds to behavioral differences in prey handling resulting in distinct fluid flow patterns. The flexible muscular rostrum and greater fin area of stingrays allow more extensive use of suction to handle prey while the stiff cartilaginous rostrum of skates lacking extensive fin insertion is used as a paddle to strike prey as well as to clear away sand cover. Copyright © 2011 Elsevier GmbH. All rights reserved.

Using the ''Epiquant'' automatic analyzer for quantitative estimation of grain size

Energy Technology Data Exchange (ETDEWEB)

Tsivirko, E I; Ulitenko, A N; Stetsenko, I A; Burova, N M [Zaporozhskij Mashinostroitel' nyj Inst. (Ukrainian SSR)

1979-01-01

Application possibility of the ''Epiquant'' automatic analyzer to estimate qualitatively austenite grain in the 18Kh2N4VA steel has been investigated. Austenite grain has been clarified using the methods of cementation, oxidation and etching of the grain boundaries. Average linear size of grain at the length of 15 mm has been determined according to the total length of grain intersection line and the number of intersections at the boundaries. It is shown that the ''Epiquant'' analyzer ensures quantitative estimation of austenite grain size with relative error of 2-4 %.

Estimating Most Productive Scale Size in Data Envelopment Analysis with Integer Value Data

Science.gov (United States)

Dwi Sari, Yunita; Angria S, Layla; Efendi, Syahril; Zarlis, Muhammad

2018-01-01

The most productive scale size (MPSS) is a measurement that states how resources should be organized and utilized to achieve optimal results. The most productive scale size (MPSS) can be used as a benchmark for the success of an industry or company in producing goods or services. To estimate the most productive scale size (MPSS), each decision making unit (DMU) should pay attention the level of input-output efficiency, by data envelopment analysis (DEA) method decision making unit (DMU) can identify units used as references that can help to find the cause and solution from inefficiencies can optimize productivity that main advantage in managerial applications. Therefore, data envelopment analysis (DEA) is chosen to estimating most productive scale size (MPSS) that will focus on the input of integer value data with the CCR model and the BCC model. The purpose of this research is to find the best solution for estimating most productive scale size (MPSS) with input of integer value data in data envelopment analysis (DEA) method.

Estimation of the size of the female sex worker population in Rwanda using three different methods.

Science.gov (United States)

Mutagoma, Mwumvaneza; Kayitesi, Catherine; Gwiza, Aimé; Ruton, Hinda; Koleros, Andrew; Gupta, Neil; Balisanga, Helene; Riedel, David J; Nsanzimana, Sabin

2015-10-01

HIV prevalence is disproportionately high among female sex workers compared to the general population. Many African countries lack useful data on the size of female sex worker populations to inform national HIV programmes. A female sex worker size estimation exercise using three different venue-based methodologies was conducted among female sex workers in all provinces of Rwanda in August 2010. The female sex worker national population size was estimated using capture-recapture and enumeration methods, and the multiplier method was used to estimate the size of the female sex worker population in Kigali. A structured questionnaire was also used to supplement the data. The estimated number of female sex workers by the capture-recapture method was 3205 (95% confidence interval: 2998-3412). The female sex worker size was estimated at 3348 using the enumeration method. In Kigali, the female sex worker size was estimated at 2253 (95% confidence interval: 1916-2524) using the multiplier method. Nearly 80% of all female sex workers in Rwanda were found to be based in the capital, Kigali. This study provided a first-time estimate of the female sex worker population size in Rwanda using capture-recapture, enumeration, and multiplier methods. The capture-recapture and enumeration methods provided similar estimates of female sex worker in Rwanda. Combination of such size estimation methods is feasible and productive in low-resource settings and should be considered vital to inform national HIV programmes. © The Author(s) 2015.

Low leopard populations in protected areas of Maputaland: a consequence of poaching, habitat condition, abundance of prey, and a top predator.

Science.gov (United States)

Ramesh, Tharmalingam; Kalle, Riddhika; Rosenlund, Havard; Downs, Colleen T

2017-03-01

Identifying the primary causes affecting population densities and distribution of flagship species are necessary in developing sustainable management strategies for large carnivore conservation. We modeled drivers of spatial density of the common leopard ( Panthera pardus ) using a spatially explicit capture-recapture-Bayesian approach to understand their population dynamics in the Maputaland Conservation Unit, South Africa. We camera-trapped leopards in four protected areas (PAs) of varying sizes and disturbance levels covering 198 camera stations. Ours is the first study to explore the effects of poaching level, abundance of prey species (small, medium, and large), competitors (lion Panthera leo and spotted hyenas Crocuta crocuta ), and habitat on the spatial distribution of common leopard density. Twenty-six male and 41 female leopards were individually identified and estimated leopard density ranged from 1.6 ± 0.62/100 km 2 (smallest PA-Ndumo) to 8.4 ± 1.03/100 km 2 (largest PA-western shores). Although dry forest thickets and plantation habitats largely represented the western shores, the plantation areas had extremely low leopard density compared to native forest. We found that leopard density increased in areas when low poaching levels/no poaching was recorded in dry forest thickets and with high abundance of medium-sized prey, but decreased with increasing abundance of lion. Because local leopard populations are vulnerable to extinction, particularly in smaller PAs, the long-term sustainability of leopard populations depend on developing appropriate management strategies that consider a combination of multiple factors to maintain their optimal habitats.

The relative influence of prey abundance and co-breeders on the ...

African Journals Online (AJOL)

This study investigates if the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax canorus, is governed by the abundance of dominant rodent-prey species or a co-breeding male participating fully in prey being delivered to the female and young. Polyandrous trios in prey-rich habitat, the only habitat ...

Estimation of Tooth Size Discrepancies among Different Malocclusion Groups.

Science.gov (United States)

Hasija, Narender; Bala, Madhu; Goyal, Virender

2014-05-01

Regards and Tribute: Late Dr Narender Hasija was a mentor and visionary in the light of knowledge and experience. We pay our regards with deepest gratitude to the departed soul to rest in peace. Bolton's ratios help in estimating overbite, overjet relationships, the effects of contemplated extractions on posterior occlusion, incisor relationships and identification of occlusal misfit produced by tooth size discrepancies. To determine any difference in tooth size discrepancy in anterior as well as overall ratio in different malocclusions and comparison with Bolton's study. After measuring the teeth on all 100 patients, Bolton's analysis was performed. Results were compared with Bolton's means and standard deviations. The results were also subjected to statistical analysis. Results show that the mean and standard deviations of ideal occlusion cases are comparable with those Bolton but, when the mean and standard deviation of malocclusion groups are compared with those of Bolton, the values of standard deviation are higher, though the mean is comparable. How to cite this article: Hasija N, Bala M, Goyal V. Estimation of Tooth Size Discrepancies among Different Malocclusion Groups. Int J Clin Pediatr Dent 2014;7(2):82-85.

Stochastic population oscillations in spatial predator-prey models

International Nuclear Information System (INIS)

Taeuber, Uwe C

2011-01-01

It is well-established that including spatial structure and stochastic noise in models for predator-prey interactions invalidates the classical deterministic Lotka-Volterra picture of neutral population cycles. In contrast, stochastic models yield long-lived, but ultimately decaying erratic population oscillations, which can be understood through a resonant amplification mechanism for density fluctuations. In Monte Carlo simulations of spatial stochastic predator-prey systems, one observes striking complex spatio-temporal structures. These spreading activity fronts induce persistent correlations between predators and prey. In the presence of local particle density restrictions (finite prey carrying capacity), there exists an extinction threshold for the predator population. The accompanying continuous non-equilibrium phase transition is governed by the directed-percolation universality class. We employ field-theoretic methods based on the Doi-Peliti representation of the master equation for stochastic particle interaction models to (i) map the ensuing action in the vicinity of the absorbing state phase transition to Reggeon field theory, and (ii) to quantitatively address fluctuation-induced renormalizations of the population oscillation frequency, damping, and diffusion coefficients in the species coexistence phase.

Process-based models of feeding and prey selection in larval fish

DEFF Research Database (Denmark)

Fiksen, O.; MacKenzie, Brian

2002-01-01

believed to be important to prey selectivity and environmental regulation of feeding in fish. We include the sensitivity of prey to the hydrodynamic signal generated by approaching larval fish and a simple model of the potential loss of prey due to turbulence whereby prey is lost if it leaves...... jig dry wt l(-1). The spatio-temporal fluctuation of turbulence (tidal cycle) and light (sun height) over the bank generates complex structure in the patterns of food intake of larval fish, with different patterns emerging for small and large larvae....

Mechanisms and feasibility of prey capture in ambush-feeding zooplankton

DEFF Research Database (Denmark)

Kiørboe, Thomas; Andersen, Anders Peter; Langlois, Vincent

2009-01-01

Many marine zooplankters, particularly among copepods, are "ambush feeders" that passively wait for their prey and capture them by fast surprise attacks. This strategy must be very demanding in terms of muscle power and sensing capabilities, but the detailed mechanisms of the attacks are unknown...... of the examined species is close to this size limit and, in contrast to the larger species, uses its largest possible jump velocity for such attacks. The special requirements to ambush feeders with such attacks may explain why this strategy has evolved to perfection only a few times among planktonic suspension...... feeders ( few copepod families and chaetognaths)....

Great Lakes prey fish populations: A cross-basin overview of status and trends in 2008

Science.gov (United States)

Gorman, Owen T.; Bunnell, David B.

2009-01-01

Assessments of prey fishes in the Great Lakes have been conducted annually since the 1970s by the Great Lakes Science Center, sometimes assisted by partner agencies. Prey fish assessments differ among lakes in the proportion of a lake covered, seasonal timing, bottom trawl gear used, sampling design, and the manner in which the trawl is towed (across or along bottom contours). Because each assessment is unique in one or more important aspects, a direct comparison of prey fish catches among lakes is problematic. All of the assessments, however, produce indices of abundance or biomass that can be standardized to facilitate comparisons of trends among lakes and to illustrate present status of the populations. We present indices of abundance for important prey fishes in the Great Lakes standardized to the highest value for a time series within each lake: cisco (Coregonus artedi), bloater (C. hoyi), rainbow smelt (Osmerus mordax), and alewife (Alosa pseudoharengus). We also provide indices for round goby (Neogobius melanostomus), an invasive fish presently spreading throughout the basin. Our intent is to provide a short, informal report emphasizing data presentation rather than synthesis; for this reason we intentionally avoid use of tables and cited references.For each lake, standardized relative indices for annual biomass and density estimates of important prey fishes were calculated as the fraction relative to the largest value observed in the times series. To determine whether basin-wide trends were apparent for each species, we first ranked standardized index values within each lake. When comparing ranked index values from three or more lakes, we calculated the Kendall coefficient of concordance (W), which can range from 0 (complete discordance or disagreement among trends) to 1 (complete concordance or agreement among trends). The P-value for W provides the probability of agreement across the lakes. When comparing ranked index values from two lakes, we calculated

Arctic skate Amblyraja hyperborea preys on remarkably large glacial eelpouts Lycodes frigidus.

Science.gov (United States)

Byrkjedal, I; Christiansen, J S; Karamushko, O V; Langhelle, G; Lynghammar, A

2015-01-01

During scientific surveys on the continental slopes north-west of Spitsbergen and off north-east Greenland (c. 600 and 1000 m depths), two female Arctic skates Amblyraja hyperborea were caught while swallowing extraordinary large individuals of glacial eelpout Lycodes frigidus. The total length (LT) of the prey constituted 50 and 80% of the LT of the skates, which reveal that A. hyperborea are capable predators of fishes of surprisingly large relative size. © 2014 The Fisheries Society of the British Isles.

Estimating population sizes for elusive animals: the forest elephants of Kakum National Park, Ghana.

Science.gov (United States)

Eggert, L S; Eggert, J A; Woodruff, D S

2003-06-01

African forest elephants are difficult to observe in the dense vegetation, and previous studies have relied upon indirect methods to estimate population sizes. Using multilocus genotyping of noninvasively collected samples, we performed a genetic survey of the forest elephant population at Kakum National Park, Ghana. We estimated population size, sex ratio and genetic variability from our data, then combined this information with field observations to divide the population into age groups. Our population size estimate was very close to that obtained using dung counts, the most commonly used indirect method of estimating the population sizes of forest elephant populations. As their habitat is fragmented by expanding human populations, management will be increasingly important to the persistence of forest elephant populations. The data that can be obtained from noninvasively collected samples will help managers plan for the conservation of this keystone species.

Always chew your food: freshwater stingrays use mastication to process tough insect prey.

Science.gov (United States)

Kolmann, Matthew A; Welch, Kenneth C; Summers, Adam P; Lovejoy, Nathan R

2016-09-14

Chewing, characterized by shearing jaw motions and high-crowned molar teeth, is considered an evolutionary innovation that spurred dietary diversification and evolutionary radiation of mammals. Complex prey-processing behaviours have been thought to be lacking in fishes and other vertebrates, despite the fact that many of these animals feed on tough prey, like insects or even grasses. We investigated prey capture and processing in the insect-feeding freshwater stingray Potamotrygon motoro using high-speed videography. We find that Potamotrygon motoro uses asymmetrical motion of the jaws, effectively chewing, to dismantle insect prey. However, CT scanning suggests that this species has simple teeth. These findings suggest that in contrast to mammalian chewing, asymmetrical jaw action is sufficient for mastication in other vertebrates. We also determined that prey capture in these rays occurs through rapid uplift of the pectoral fins, sucking prey beneath the ray's body, thereby dissociating the jaws from a prey capture role. We suggest that the decoupling of prey capture and processing facilitated the evolution of a highly kinetic feeding apparatus in batoid fishes, giving these animals an ability to consume a wide variety of prey, including molluscs, fishes, aquatic insect larvae and crustaceans. We propose Potamotrygon as a model system for understanding evolutionary convergence of prey processing and chewing in vertebrates. © 2016 The Author(s).

Modelling the dynamics of traits involved in fighting-predators-prey system.

Science.gov (United States)

Kooi, B W

2015-12-01

We study the dynamics of a predator-prey system where predators fight for captured prey besides searching for and handling (and digestion) of the prey. Fighting for prey is modelled by a continuous time hawk-dove game dynamics where the gain depends on the amount of disputed prey while the costs for fighting is constant per fighting event. The strategy of the predator-population is quantified by a trait being the proportion of the number of predator-individuals playing hawk tactics. The dynamics of the trait is described by two models of adaptation: the replicator dynamics (RD) and the adaptive dynamics (AD). In the RD-approach a variant individual with an adapted trait value changes the population's strategy, and consequently its trait value, only when its payoff is larger than the population average. In the AD-approach successful replacement of the resident population after invasion of a rare variant population with an adapted trait value is a step in a sequence changing the population's strategy, and hence its trait value. The main aim is to compare the consequences of the two adaptation models. In an equilibrium predator-prey system this will lead to convergence to a neutral singular strategy, while in the oscillatory system to a continuous singular strategy where in this endpoint the resident population is not invasible by any variant population. In equilibrium (low prey carrying capacity) RD and AD-approach give the same results, however not always in a periodically oscillating system (high prey carrying-capacity) where the trait is density-dependent. For low costs the predator population is monomorphic (only hawks) while for high costs dimorphic (hawks and doves). These results illustrate that intra-specific trait dynamics matters in predator-prey dynamics.

Estimation of sample size and testing power (Part 3).

Science.gov (United States)

Hu, Liang-ping; Bao, Xiao-lei; Guan, Xue; Zhou, Shi-guo

2011-12-01

This article introduces the definition and sample size estimation of three special tests (namely, non-inferiority test, equivalence test and superiority test) for qualitative data with the design of one factor with two levels having a binary response variable. Non-inferiority test refers to the research design of which the objective is to verify that the efficacy of the experimental drug is not clinically inferior to that of the positive control drug. Equivalence test refers to the research design of which the objective is to verify that the experimental drug and the control drug have clinically equivalent efficacy. Superiority test refers to the research design of which the objective is to verify that the efficacy of the experimental drug is clinically superior to that of the control drug. By specific examples, this article introduces formulas of sample size estimation for the three special tests, and their SAS realization in detail.

Perceiving the algae: How feeding-current feeding copepods detect their nonmotile prey

DEFF Research Database (Denmark)

Goncalves, Rodrigo J.; Kiørboe, Thomas

2015-01-01

demonstrate that (1) long-range chemical detection is incompatible with known algal leakage rates and reasonable assumptions of sensitivity, (2) that near-field chemical detection is constrained by diffusion across the boundary layer of the sensor and takes longer than observed near-contact times, and (3......Feeding-current feeding copepods detect and capture prey individually, but the mechanism by which nonmotile prey is detected has been unclear. Early reports that copepods detect phytoplankton prey at distances of one body length or more led to the hypothesis that solutes leaking from the prey would......) that most reported detection distances are well predicted by models of fluid mechanical signal generation and detection. We conclude that near-field mechanoreception is the common prey detection mode in pelagic copepods. Prey detection distances are thus governed mainly by the reach of the feeding...

The bottlenose dolphin Tursiops truncatus foraging around a fish farm: Effects of prey abundance on dolphins’ behavior

Directory of Open Access Journals (Sweden)

Bruno Díaz LÓPEZ

2009-08-01

Full Text Available The extent to which prey abundance influences both bottlenose dolphin foraging behavior and group size in the presence of human activities has not previously been studied. The primary aim of this study was to identify and quantify how wild bottlenose dolphins respond, individually and as groups, to the relative abundance of prey around a fish farm. Detailed views of dolphins’ behavior were obtained by focal following individual animals whilst simultaneously collecting surface and underwater behavioral data. A total of 2150 dive intervals were analyzed, corresponding to 342 focal samples, lasting over 34 hours. Bottlenose dolphins remained submerged for a mean duration of 46.4 seconds and a maximum of 249 seconds. This study provides the first quantified data on bottlenose dolphin diving behavior in a marine fin-fish farm area. This study’s results indicate that within a fish farm area used intensively by bottlenose dolphins for feeding, dolphins did not modify dive duration. Additionally, underwater observations confirmed that dolphins find it easier to exploit a concentrated food source and it appears that hunting tactic and not group size plays an important role during feeding activities. Thus, bottlenose dolphins appear capable of modifying their hunting tactics according to the abundance of prey. When top predators display behavioral responses to activities not directed at them, the task of studying all possible effects of human activities can become even more challenging [Current Zoology 55(4: 243–248, 2009].

Short Communication Estimation of size at first maturity in two South ...

African Journals Online (AJOL)

Short Communication Estimation of size at first maturity in two South African coral species. ... African Journal of Marine Science ... PH Montoya-Maya, AHH Macdonald, MH Schleyer ... to differentiate juveniles from adult sizes of corals, an important factor for assessing the condition of scleractinian communities in reefs. Here ...

Estimated spatial requirements of the medium- to large-sized ...

African Journals Online (AJOL)

Conservation planning in the Cape Floristic Region (CFR) of South Africa, a recognised world plant diversity hotspot, required information on the estimated spatial requirements of selected medium- to large-sized mammals within each of 102 Broad Habitat Units (BHUs) delineated according to key biophysical parameters.

Estimation of particle size distribution of nanoparticles from electrical ...

Indian Academy of Sciences (India)

... blockade (CB) phenomena of electrical conduction through atiny nanoparticle. Considering the ZnO nanocomposites to be spherical, Coulomb-blockade model of quantum dot isapplied here. The size distribution of particle is estimated from that model and compared with the results obtainedfrom AFM and XRD analyses.

Complex dynamics of a stochastic discrete modified Leslie-Gower predator-prey model with Michaelis-Menten type prey harvesting

Directory of Open Access Journals (Sweden)

A. Elhassanein

2014-06-01

Full Text Available This paper introduced a stochastic discretized version of the modified Leslie-Gower predator-prey model with Michaelis-Menten type prey harvesting. The dynamical behavior of the proposed model was investigated. The existence and stability of the equilibria of the skeleton were studied. Numerical simulations were employed to show the model's complex dynamics by means of the largest Lyapunov exponents, bifurcations, time series diagrams and phase portraits. The effects of noise intensity on its dynamics and the intermittency phenomenon were also discussed via simulation.

Adaptive evolution of defense ability leads to diversification of prey species.

Science.gov (United States)

Zu, Jian; Wang, Jinliang; Du, Jianqiang

2014-06-01

In this paper, by using the adaptive dynamics approach, we investigate how the adaptive evolution of defense ability promotes the diversity of prey species in an initial one-prey-two-predator community. We assume that the prey species can evolve to a safer strategy such that it can reduce the predation risk, but a prey with a high defense ability for one predator may have a low defense ability for the other and vice versa. First, by using the method of critical function analysis, we find that if the trade-off is convex in the vicinity of the evolutionarily singular strategy, then this singular strategy is a continuously stable strategy. However, if the trade-off is weakly concave near the singular strategy and the competition between the two predators is relatively weak, then the singular strategy may be an evolutionary branching point. Second, we find that after the branching has occurred in the prey strategy, if the trade-off curve is globally concave, then the prey species might eventually evolve into two specialists, each caught by only one predator species. However, if the trade-off curve is convex-concave-convex, the prey species might eventually branch into two partial specialists, each being caught by both of the two predators and they can stably coexist on the much longer evolutionary timescale.

Effect of sublethal levels of ionizing radiation on a predator-prey interaction

International Nuclear Information System (INIS)

Chee, P.C.

1976-01-01

The predator-prey interaction studied was that between the largemouth bass (Micropterus salmoides) and the fathead minnow (Pimephales promelas) in an artificial test environment. Experiments were first conducted to determine the 50% lethal dose at 30 days of the minnow. Three different dose rates were used to test the effect of dose rate on the 50% lethal dose value. After the 50% lethal dose was determined the predator-prey interaction experiment was conducted using 30% of the 50% lethal dose as the highest radiation dose, this dose being considered the upper limit to sublethal radiation levels. A 4 x 4 Latin square design was chosen for the experiment, with four treatment levels (control plus three radiation levels) and four replicates. In each test 10 prey minnow were offered to one predator bass and the number of prey left after 14 days was the parameter of interest. A predator-prey interaction experiment using a single high level of radiation and two types of controls as conducted to ascertain the ability of the test environment to detect changes in the predator-prey interaction. The two types of controls were irradiated prey not exposed to predation and non-irradiated prey exposed to predation. An experiment was also conducted to test the correlation between the physical activity patterns of minnow and different doses of radiation. At a dose rate of 37.8 rad/min the 50% lethal dose at 30 days for minnow was found to be 2650 rad. It was found that dose rate had a strong influence on the 50% lethal dose. In the predator-prey interaction test it was found that the 14-day survival rate of prey was unaffected by sublethal levels of ionizing radiation. No significant correlation was detected between the physical activity patterns of minnow and radiation dose

Interspecific variation in prey capture behavior by co-occurring Nepenthes pitcher plants

Science.gov (United States)

Chin, Lijin; Chung, Arthur YC; Clarke, Charles

2014-01-01

Pitcher plants of the genus Nepenthes capture a wide range of arthropod prey for nutritional benefit, using complex combinations of visual and olfactory signals and gravity-driven pitfall trapping mechanisms. In many localities throughout Southeast Asia, several Nepenthes different species occur in mixed populations. Often, the species present at any given location have strongly divergent trap structures and preliminary surveys indicate that different species trap different combinations of arthropod prey, even when growing at the same locality. On this basis, it has been proposed that co-existing Nepenthes species may be engaged in niche segregation with regards to arthropod prey, avoiding direct competition with congeners by deploying traps that have modifications that enable them to target specific prey types. We examined prey capture among 3 multi-species Nepenthes populations in Borneo, finding that co-existing Nepenthes species do capture different combinations of prey, but that significant interspecific variations in arthropod prey combinations can often be detected only at sub-ordinal taxonomic ranks. In all lowland Nepenthes species examined, the dominant prey taxon is Formicidae, but montane Nepenthes trap few (or no) ants and 2 of the 3 species studied have evolved to target alternative sources of nutrition, such as tree shrew feces. Using similarity and null model analyses, we detected evidence for niche segregation with regards to formicid prey among 5 lowland, sympatric Nepenthes species in Sarawak. However, we were unable to determine whether these results provide support for the niche segregation hypothesis, or whether they simply reflect unquantified variation in heterogeneous habitats and/or ant communities in the study sites. These findings are used to propose improvements to the design of field experiments that seek to test hypotheses about targeted prey capture patterns in Nepenthes. PMID:24481246

Sediment-induced turbidity impairs foraging performance and prey choice of planktivorous coral reef fishes.

Science.gov (United States)

Johansen, J L; Jones, G P

2013-09-01

Sedimentation is a substantial threat to aquatic ecosystems and a primary cause of habitat degradation on near-shore coral reefs. Although numerous studies have demonstrated major impacts of sedimentation and turbidity on corals, virtually nothing is known of the sensitivity of reef fishes. Planktivorous fishes are an important trophic group that funnels pelagic energy sources into reef ecosystems. These fishes are visual predators whose foraging is likely to be impaired by turbidity, but the threshold for such effects and their magnitude are unknown. This study examined the effect of sediment-induced turbidity on foraging in four species of planktivorous damselfishes (Pomacentridae) of the Great Barrier Reef, including inshore and offshore species that potentially differ in tolerance for turbidity. An experimental flow tunnel was used to quantify their ability to catch mobile and immobile planktonic prey under different levels of turbidity and velocity in the range encountered on natural and disturbed reefs. Turbidity of just 4 NTU (nephelometric turbidity units) reduced average attack success by up to 56%, with higher effect sizes for species with offshore distributions. Only the inshore species (Neopomacentrus bankieri), which frequently encounters this turbidity on coastal reefs, could maintain high prey capture success. At elevated turbidity similar to that found on disturbed reefs (8 NTU), attack success was reduced in all species examined by up to 69%. These reductions in attack success led to a 21-24% decrease in foraging rates for all mid to outer-shelf species, in spite of increasing attack rates at high turbidity. Although effects of turbidity varied among species, it always depended heavily on prey mobility and ambient velocity. Attack success was up to 14 times lower on mobile prey, leaving species relatively incapable of foraging on anything but immobile prey at high turbidity. Effects of turbidity were particularly prominent at higher velocities, as

A comparison study of size-specific dose estimate calculation methods

Energy Technology Data Exchange (ETDEWEB)

Parikh, Roshni A. [Rainbow Babies and Children' s Hospital, University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Department of Radiology, Cleveland, OH (United States); University of Michigan Health System, Department of Radiology, Ann Arbor, MI (United States); Wien, Michael A.; Jordan, David W.; Ciancibello, Leslie; Berlin, Sheila C. [Rainbow Babies and Children' s Hospital, University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Department of Radiology, Cleveland, OH (United States); Novak, Ronald D. [Rainbow Babies and Children' s Hospital, University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Department of Radiology, Cleveland, OH (United States); Rebecca D. Considine Research Institute, Children' s Hospital Medical Center of Akron, Center for Mitochondrial Medicine Research, Akron, OH (United States); Klahr, Paul [CT Clinical Science, Philips Healthcare, Highland Heights, OH (United States); Soriano, Stephanie [Rainbow Babies and Children' s Hospital, University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Department of Radiology, Cleveland, OH (United States); University of Washington, Department of Radiology, Seattle, WA (United States)

2018-01-15

The size-specific dose estimate (SSDE) has emerged as an improved metric for use by medical physicists and radiologists for estimating individual patient dose. Several methods of calculating SSDE have been described, ranging from patient thickness or attenuation-based (automated and manual) measurements to weight-based techniques. To compare the accuracy of thickness vs. weight measurement of body size to allow for the calculation of the size-specific dose estimate (SSDE) in pediatric body CT. We retrospectively identified 109 pediatric body CT examinations for SSDE calculation. We examined two automated methods measuring a series of level-specific diameters of the patient's body: method A used the effective diameter and method B used the water-equivalent diameter. Two manual methods measured patient diameter at two predetermined levels: the superior endplate of L2, where body width is typically most thin, and the superior femoral head or iliac crest (for scans that did not include the pelvis), where body width is typically most thick; method C averaged lateral measurements at these two levels from the CT projection scan, and method D averaged lateral and anteroposterior measurements at the same two levels from the axial CT images. Finally, we used body weight to characterize patient size, method E, and compared this with the various other measurement methods. Methods were compared across the entire population as well as by subgroup based on body width. Concordance correlation (ρ{sub c}) between each of the SSDE calculation methods (methods A-E) was greater than 0.92 across the entire population, although the range was wider when analyzed by subgroup (0.42-0.99). When we compared each SSDE measurement method with CTDI{sub vol,} there was poor correlation, ρ{sub c}<0.77, with percentage differences between 20.8% and 51.0%. Automated computer algorithms are accurate and efficient in the calculation of SSDE. Manual methods based on patient thickness provide

Arthropod prey of Wilson's Warblers in the understory of Douglas-fir forests

Science.gov (United States)

Hagar, J.C.; Dugger, K.M.; Starkey, E.E.

2007-01-01

Availability of food resources is an important factor in avian habitat selection. Food resources for terrestrial birds often are closely related to vegetation structure and composition. Identification of plant species important in supporting food resources may facilitate vegetation management to achieve objectives for providing bird habitat. We used fecal analysis to describe the diet of adult Wilson's Warblers (Wilsonia pusilla) that foraged in the understory of Douglas-fir (Pseudotsuga menziesii) forests in western Oregon during the breeding season. We sampled arthropods at the same sites where diet data were collected, and compared abundance and biomass of prey among seven common shrub species. Wilson's Warblers ate more caterpillars (Lepidoptera larvae), flies (Diptera), beetles (Coleoptera), and Homoptera than expected based on availability. Deciduous shrubs supported higher abundances of arthropod taxa and size classes used as prey by Wilson's Warblers than did evergreen shrubs. The development and maintenance of deciduous understory vegetation in conifer forests of the Pacific Northwest may be fundamental for conservation of food webs that support breeding Wilson's Warblers and other shrub-associated, insectivorous songbirds.

The global stability of a delayed predator-prey system with two stage-structure

International Nuclear Information System (INIS)

Wang Fengyan; Pang Guoping

2009-01-01

Based on the classical delayed stage-structured model and Lotka-Volterra predator-prey model, we introduce and study a delayed predator-prey system, where prey and predator have two stages, an immature stage and a mature stage. The time delays are the time lengths between the immature's birth and maturity of prey and predator species. Results on global asymptotic stability of nonnegative equilibria of the delay system are given, which generalize and suggest that good continuity exists between the predator-prey system and its corresponding stage-structured system.

Zooplankton size selection relative to gill raker spacing in rainbow trout

Science.gov (United States)

Budy, P.; Haddix, T.; Schneidervin, R.

2005-01-01

Rainbow trout Oncorhynchus mykiss are one of the most widely stocked salmonids worldwide, often based on the assumption that they will effectively utilize abundant invertebrate food resources. We evaluated the potential for feeding morphology to affect prey selection by rainbow trout using a combination of laboratory feeding experiments and field observations in Flaming Gorge Reservoir, Utah-Wyoming. For rainbow trout collected from the reservoir, inter-gill raker spacing averaged 1.09 mm and there was low variation among fish overall (SD = 0.28). Ninety-seven percent of all zooplankton observed in the diets of rainbow trout collected in the reservoir were larger than the interraker spacing, while only 29% of the zooplankton found in the environment were larger than the interraker spacing. Over the size range of rainbow trout evaluated here (200-475 mm), interraker spacing increased moderately with increasing fish length; however, the size of zooplankton found in the diet did not increase with increasing fish length. In laboratory experiments, rainbow trout consumed the largest zooplankton available; the mean size of zooplankton observed in the diets was significantly larger than the mean size of zooplankton available. Electivity indices for both laboratory and field observations indicated strong selection for larger-sized zooplankton. The size threshold at which electivity switched from selection against smaller-sized zooplankton to selection for larger-sized zooplankton closely corresponded to the mean interraker spacing for both groups (???1-1.2 mm). The combination of results observed here indicates that rainbow trout morphology limits the retention of different-sized zooplankton prey and reinforces the importance of understanding how effectively rainbow trout can utilize the type and sizes of different prey available in a given system. These considerations may improve our ability to predict the potential for growth and survival of rainbow trout within and

Sample size estimation and sampling techniques for selecting a representative sample

Directory of Open Access Journals (Sweden)

Aamir Omair

2014-01-01

Full Text Available Introduction: The purpose of this article is to provide a general understanding of the concepts of sampling as applied to health-related research. Sample Size Estimation: It is important to select a representative sample in quantitative research in order to be able to generalize the results to the target population. The sample should be of the required sample size and must be selected using an appropriate probability sampling technique. There are many hidden biases which can adversely affect the outcome of the study. Important factors to consider for estimating the sample size include the size of the study population, confidence level, expected proportion of the outcome variable (for categorical variables/standard deviation of the outcome variable (for numerical variables, and the required precision (margin of accuracy from the study. The more the precision required, the greater is the required sample size. Sampling Techniques: The probability sampling techniques applied for health related research include simple random sampling, systematic random sampling, stratified random sampling, cluster sampling, and multistage sampling. These are more recommended than the nonprobability sampling techniques, because the results of the study can be generalized to the target population.

The king of snakes: performance and morphology of intraguild predators (Lampropeltis) and their prey (Pantherophis).

Science.gov (United States)

Penning, David A; Moon, Brad R

2017-03-15

Across ecosystems and trophic levels, predators are usually larger than their prey, and when trophic morphology converges, predators typically avoid predation on intraguild competitors unless the prey is notably smaller in size. However, a currently unexplained exception occurs in kingsnakes in the genus Lampropeltis Kingsnakes are able to capture, constrict and consume other snakes that are not only larger than themselves but that are also powerful constrictors (such as ratsnakes in the genus Pantherophis ). Their mechanisms of success as intraguild predators on other constrictors remain unknown. To begin addressing these mechanisms, we studied the scaling of muscle cross-sectional area, pulling force and constriction pressure across the ontogeny of six species of snakes ( Lampropeltis californiae , L. getula , L. holbrooki , Pantherophis alleghaniensis , P. guttatus and P. obsoletus ). Muscle cross-sectional area is an indicator of potential force production, pulling force is an indicator of escape performance, and constriction pressure is a measure of prey-handling performance. Muscle cross-sectional area scaled similarly for all snakes, and there was no significant difference in maximum pulling force among species. However, kingsnakes exerted significantly higher pressures on their prey than ratsnakes. The similar escape performance among species indicates that kingsnakes win in predatory encounters because of their superior constriction performance, not because ratsnakes have inferior escape performance. The superior constriction performance by kingsnakes results from their consistent and distinctive coil posture and perhaps from additional aspects of muscle structure and function that need to be tested in future research. © 2017. Published by The Company of Biologists Ltd.

The Coevolution of "Tyrannosaurus" & Its Prey: Could "Tyrannosaurus" Chase down & Kill a "Triceratops" for Lunch?

Science.gov (United States)

May, S. Randolph

2014-01-01

Students will analyze the coevolution of the predator-prey relationships between "Tyrannosaurus rex" and its prey species using analyses of animal speeds from fossilized trackways, prey-animal armaments, adaptive behaviors, bite marks on prey-animal fossils, predator-prey ratios, and scavenger competition. The students will be asked to…

Effects of sample size on estimates of population growth rates calculated with matrix models.

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Ian J Fiske

Full Text Available BACKGROUND: Matrix models are widely used to study the dynamics and demography of populations. An important but overlooked issue is how the number of individuals sampled influences estimates of the population growth rate (lambda calculated with matrix models. Even unbiased estimates of vital rates do not ensure unbiased estimates of lambda-Jensen's Inequality implies that even when the estimates of the vital rates are accurate, small sample sizes lead to biased estimates of lambda due to increased sampling variance. We investigated if sampling variability and the distribution of sampling effort among size classes lead to biases in estimates of lambda. METHODOLOGY/PRINCIPAL FINDINGS: Using data from a long-term field study of plant demography, we simulated the effects of sampling variance by drawing vital rates and calculating lambda for increasingly larger populations drawn from a total population of 3842 plants. We then compared these estimates of lambda with those based on the entire population and calculated the resulting bias. Finally, we conducted a review of the literature to determine the sample sizes typically used when parameterizing matrix models used to study plant demography. CONCLUSIONS/SIGNIFICANCE: We found significant bias at small sample sizes when survival was low (survival = 0.5, and that sampling with a more-realistic inverse J-shaped population structure exacerbated this bias. However our simulations also demonstrate that these biases rapidly become negligible with increasing sample sizes or as survival increases. For many of the sample sizes used in demographic studies, matrix models are probably robust to the biases resulting from sampling variance of vital rates. However, this conclusion may depend on the structure of populations or the distribution of sampling effort in ways that are unexplored. We suggest more intensive sampling of populations when individual survival is low and greater sampling of stages with high

Effects of sample size on estimates of population growth rates calculated with matrix models.

Science.gov (United States)

Fiske, Ian J; Bruna, Emilio M; Bolker, Benjamin M

2008-08-28

Matrix models are widely used to study the dynamics and demography of populations. An important but overlooked issue is how the number of individuals sampled influences estimates of the population growth rate (lambda) calculated with matrix models. Even unbiased estimates of vital rates do not ensure unbiased estimates of lambda-Jensen's Inequality implies that even when the estimates of the vital rates are accurate, small sample sizes lead to biased estimates of lambda due to increased sampling variance. We investigated if sampling variability and the distribution of sampling effort among size classes lead to biases in estimates of lambda. Using data from a long-term field study of plant demography, we simulated the effects of sampling variance by drawing vital rates and calculating lambda for increasingly larger populations drawn from a total population of 3842 plants. We then compared these estimates of lambda with those based on the entire population and calculated the resulting bias. Finally, we conducted a review of the literature to determine the sample sizes typically used when parameterizing matrix models used to study plant demography. We found significant bias at small sample sizes when survival was low (survival = 0.5), and that sampling with a more-realistic inverse J-shaped population structure exacerbated this bias. However our simulations also demonstrate that these biases rapidly become negligible with increasing sample sizes or as survival increases. For many of the sample sizes used in demographic studies, matrix models are probably robust to the biases resulting from sampling variance of vital rates. However, this conclusion may depend on the structure of populations or the distribution of sampling effort in ways that are unexplored. We suggest more intensive sampling of populations when individual survival is low and greater sampling of stages with high elasticities.

Effective prey attraction in the rare Drosophyllum lusitanicum, a flypaper-trap carnivorous plant.

Science.gov (United States)

Bertol, Nils; Paniw, Maria; Ojeda, Fernando

2015-05-01

Carnivorous plants have unusually modified leaves to trap insects as an adaptation to low-nutrient environments. Disparate mechanisms have been suggested as luring traits to attract prey insects into their deadly leaves, ranging from very elaborate to none at all. Drosophyllum lusitanicum is a rare carnivorous plant with a common flypaper-trap mechanism. Here we tested whether Drosophyllum plants lure prey insects into their leaves or they act just as passive traps. We compared prey capture between live, potted plants and Drosophyllum-shaped artificial mimics coated with odorless glue. Since this species is insect-pollinated, we also explored the possible existence of a pollinator-prey conflict by quantifying the similarity between the pollination and prey guilds in a natural population. All experiments were done in southern Spain. The sticky leaves of Drosophyllum captured significantly more prey than mimics, particularly small dipterans. Prey attraction, likely exerted by scent or visual cues, seems to be unrelated to pollinator attraction by flowers, as inferred from the low similarity between pollinator and prey insect faunas found in this species. Our results illustrate the effectiveness of this carnivorous species at attracting insects to their flypaper-trap leaves. © 2015 Botanical Society of America, Inc.

Foraging efficiency of a predator flock for randomly moving prey: A simulation study

Science.gov (United States)

Lee, Sang-Hee; Kwon, Ohsung

2016-03-01

Flocking behavior of animals is highly advantageous for taking food resources. The degree of the advantage is related to the ability of flock members to detect their prey and the mobility of prey individuals. In this study, to explore the relation, we constructed a model to simulate a predator flock and its randomly moving prey. The predator members have the prey detection ability, which was characterized as sensing distance, R, and a sensing angle, θ. The mobility of the prey individuals was characterized as the maximum traveling distance of an iteration time step, L. The relative flock foraging efficiency, ɛ, was defined as ɛ = 1 - (Td/Tup). Tup and Td represent the spent time for the flock to eat all prey individuals and to uptake the last remaining 10% prey, respectively. Simulation results showed that ɛ increased, maximized, and decreased with the increase of R, regardless of L. As the number of prey, N, increased, the tendency of the increasing and decreasing was diluted. The result was briefly discussed in relation to the flock foraging behavior and the development of the model toward applications for real ecosystems.

Sampling strategies for estimating brook trout effective population size

Science.gov (United States)

Andrew R. Whiteley; Jason A. Coombs; Mark Hudy; Zachary Robinson; Keith H. Nislow; Benjamin H. Letcher

2012-01-01

The influence of sampling strategy on estimates of effective population size (Ne) from single-sample genetic methods has not been rigorously examined, though these methods are increasingly used. For headwater salmonids, spatially close kin association among age-0 individuals suggests that sampling strategy (number of individuals and location from...

Food consumption estimates of Barents Sea harp seals

Directory of Open Access Journals (Sweden)

Kjell T Nilssen

2004-05-01

total consumption, other gadoids (dominated by cod, but also including haddock (Melanogrammus aeglefinus and saithe (Pollachius virens, herring, and "other fish". Using the same set of assumptions as in the previous estimate, the total consumption would have been 3.47 million tonnes, divided between various prey species as follows (in tonnes: polar cod 876,000, codfish (cod, saithe and haddock 359,700, "other fish" 618,800, herring 392,500, and crustaceans 1,204,200. Overall, the largest quantities of food were estimated to be consumed in the period June-September. In 1999, the total Barents Sea harp seal stock size was estimated to be 2.18 (95% CI, 1.79 to 2.58 million animals, which would give an annual food consumption in the range of 2,69 - 3.96 million tonnes (based on upper and lower 95% confidence limits and adjusted for a pup mortality rate of 0.3 if capelin is assumed to be abundant.

Chlorophacinone residues in mammalian prey at a black-tailed prairie dog colony

Science.gov (United States)

Vyas, Nimish B.; Hulse, Craig S.; Rice, Clifford P.

2012-01-01

Black-tailed prairie dogs (BTPDs), Cynomys ludovicianus, are an important prey for raptors; therefore, the use of the rodenticide Rozol (0.005% chlorophacinone active ingredient) to control BTPDs raises concern for secondary poisonings resulting from the consumption of contaminated prey by raptors. In the present study, the authors observed Rozol exposure and adverse effects to mammalian prey on 11 of 12 search days of the study. Mammalian hepatic chlorophacinone residues ranged from 0.44 to 7.56 µg/g. Poisoned prey availability was greater than previously reported.

A self-organized system of smart preys and predators

Energy Technology Data Exchange (ETDEWEB)

Rozenfeld, Alejandro F. [Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, UNLP, CONICET, Suc. 4, C.C. 16 (1900) La Plata (Argentina); Albano, Ezequiel V. [Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, UNLP, CONICET, Suc. 4, C.C. 16 (1900) La Plata (Argentina)]. E-mail: ealbano@inifta.unlp.edu.ar

2004-11-22

Based on the fact that, a standard prey-predator model (SPPM), exhibits irreversible phase transitions, belonging to the universality class of directed percolation (DP), between prey-predator coexistence and predator extinction [Phys. Lett. A 280 (2001) 45], a self-organized prey-predator model (SOPPM) is formulated and studied by means of extensive Monte Carlo simulations. The SOPPM is achieved defining the parameters of the SPPM as functions of the density of species. It is shown that the SOPPM self-organizes into an active state close the absorbing phase of the SPPM, and consequently their avalanche exponents also belong to the universality class of DP.

Boundedness and permanence in a class of periodic time-dependent predator-prey system with prey dispersal and predator density-independence

International Nuclear Information System (INIS)

Zhang Long; Teng Zhidong

2008-01-01

In this paper, we study two species predator-prey Lotka-Volterra type dispersal system with periodic coefficients, in which the prey species can disperse among n patches, while the density-independent predator species is confined to one of the patches and cannot disperse. Sufficient conditions on the boundedness, permanence and existence of positive periodic solution for this system are established. The theoretical results are confirmed by a special example and numerical simulations

Bound on the estimation grid size for sparse reconstruction in direction of arrival estimation

NARCIS (Netherlands)

Coutiño Minguez, M.A.; Pribic, R; Leus, G.J.T.

2016-01-01

A bound for sparse reconstruction involving both the signal-to-noise ratio (SNR) and the estimation grid size is presented. The bound is illustrated for the case of a uniform linear array (ULA). By reducing the number of possible sparse vectors present in the feasible set of a constrained ℓ1-norm

Reliability of fish size estimates obtained from multibeam imaging sonar

Science.gov (United States)

Hightower, Joseph E.; Magowan, Kevin J.; Brown, Lori M.; Fox, Dewayne A.

2013-01-01

Multibeam imaging sonars have considerable potential for use in fisheries surveys because the video-like images are easy to interpret, and they contain information about fish size, shape, and swimming behavior, as well as characteristics of occupied habitats. We examined images obtained using a dual-frequency identification sonar (DIDSON) multibeam sonar for Atlantic sturgeon Acipenser oxyrinchus oxyrinchus, striped bass Morone saxatilis, white perch M. americana, and channel catfish Ictalurus punctatus of known size (20–141 cm) to determine the reliability of length estimates. For ranges up to 11 m, percent measurement error (sonar estimate – total length)/total length × 100 varied by species but was not related to the fish's range or aspect angle (orientation relative to the sonar beam). Least-square mean percent error was significantly different from 0.0 for Atlantic sturgeon (x̄  =  −8.34, SE  =  2.39) and white perch (x̄  = 14.48, SE  =  3.99) but not striped bass (x̄  =  3.71, SE  =  2.58) or channel catfish (x̄  = 3.97, SE  =  5.16). Underestimating lengths of Atlantic sturgeon may be due to difficulty in detecting the snout or the longer dorsal lobe of the heterocercal tail. White perch was the smallest species tested, and it had the largest percent measurement errors (both positive and negative) and the lowest percentage of images classified as good or acceptable. Automated length estimates for the four species using Echoview software varied with position in the view-field. Estimates tended to be low at more extreme azimuthal angles (fish's angle off-axis within the view-field), but mean and maximum estimates were highly correlated with total length. Software estimates also were biased by fish images partially outside the view-field and when acoustic crosstalk occurred (when a fish perpendicular to the sonar and at relatively close range is detected in the side lobes of adjacent beams). These sources of

Generalist predator, cyclic voles and cavity nests: testing the alternative prey hypothesis.

Science.gov (United States)

Pöysä, Hannu; Jalava, Kaisa; Paasivaara, Antti

2016-12-01

The alternative prey hypothesis (APH) states that when the density of the main prey declines, generalist predators switch to alternative prey and vice versa, meaning that predation pressure on the alternative prey should be negatively correlated with the density of the main prey. We tested the APH in a system comprising one generalist predator (pine marten, Martes martes), cyclic main prey (microtine voles, Microtus agrestis and Myodes glareolus) and alternative prey (cavity nests of common goldeneye, Bucephala clangula); pine marten is an important predator of both voles and common goldeneye nests. Specifically, we studied whether annual predation rate of real common goldeneye nests and experimental nests is negatively associated with fluctuation in the density of voles in four study areas in southern Finland in 2000-2011. Both vole density and nest predation rate varied considerably between years in all study areas. However, we did not find support for the hypothesis that vole dynamics indirectly affects predation rate of cavity nests in the way predicted by the APH. On the contrary, the probability of predation increased with vole spring abundance for both real and experimental nests. Furthermore, a crash in vole abundance from previous autumn to spring did not increase the probability of predation of real nests, although it increased that of experimental nests. We suggest that learned predation by pine marten individuals, coupled with efficient search image for cavities, overrides possible indirect positive effects of high vole density on the alternative prey in our study system.

Bifurcations and feedback control of a stage-structure exploited prey ...

African Journals Online (AJOL)

user

Here, we have considered a stage structure prey-predator model with stage structure for ... N over the prey ,N β is the transition rate from mature predator population 2 ...... Mathematical Bioeconomics: The Optimal Management of Renewable ...

Prey selection of lions Panthera leo in a small, enclosed reserve

Directory of Open Access Journals (Sweden)

R.J. Power

2002-12-01

Full Text Available Annual trends in numbers of ungulate species on a 15 km² reserve from 1993 to 1998, were evaluated in the context of lion Panthera leo reintroduction during 1996, and subsequent predation by them. The ungulate prey base was enumerated annually by aerial counts and a road count that took place during 1998. The lion prey record was obtained from direct observations of a radio-located pride of eight lions and daily reserve management records. All ungulate species that underwent precipituous declines were also the most important prey to lions, comprising over 80 % of their prey, and they were preyed upon according to their availability. Lion predation was causal for the declines in wildebeest Connochaetes taurinus, Blesbok Damaliscus pygargus phillipsi and Warthog Phacochoerus africana, while the decline in Kudu Tragelaphus strepsiceros was only partly ascribed to lions, as other non-lion related mortality sources were identified. The only ungulate species to increase subsequent to lion reintroduction was the Impala Aepyceros melampus, which was furthermore under-selected by lions. The uncontrolled population growth of Impala could have elicited ecological degradation, and it was advised to either not stock Impala, or otherwise control their numbers if lions are unable to do so. Lion hunting success and kill rate, were 21 % (n = 63 and 1 kill/4.4 days, respectively. Three bushpigs Potamochoerus larvatus were killed but not utilised,and this finding is corroborated by an intensive study in Kwazulu-Natal, and this aversion is discussed. Predators can cause unprecedented declines of their prey where the prey are confined to small reserves that have no refuge from predation. On an annual basis, prey may need to be augmented to sustain predators on small reserves

Energetic conditions promoting top-down control of prey by predators.

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Kristin N Marshall

Full Text Available Humans remove large amounts of biomass from natural ecosystems, and large bodied high trophic level animals are especially sensitive and vulnerable to exploitation. The effects of removing top-predators on food webs are often difficult to predict because of limited information on species interaction strengths. Here we used a three species predator-prey model to explore relationships between energetic properties of trophodynamic linkages and interaction strengths to provide heuristic rules that indicate observable energetic conditions that are most likely to lead to stable and strong top-down control of prey by predator species. We found that strong top-down interaction strengths resulted from low levels of energy flow from prey to predators. Strong interactions are more stable when they are a consequence of low per capita predation and when predators are subsidized by recruitment. Diet composition also affects stability, but the relationship depends on the form of the functional response. Our results imply that for generalist satiating predators, strong top-down control on prey is most likely for prey items that occupy a small portion of the diet and when density dependent recruitment is moderately high.

Prey resources before spawning influence gonadal investment of female, but not male, white crappie

Science.gov (United States)

Bunnell, D.B.; Thomas, S.E.; Stein, R.A.

2007-01-01

In this study, an outdoor pool experiment was used to evaluate the effect of prey resources during 4 months before spawning on the gonadal investments of male and female white crappie Pomoxis annularis, a popular freshwater sportfish that exhibits erratic recruitment. Fish were assigned one of three feeding treatments: starved, fed once every 5 days (intermediate) or fed daily (high). All measurements of male testes (i.e. wet mass, energy density and spermatocrit) were similar across treatments. Conversely, high-fed females produced larger ovaries than those of intermediate-fed and starved fish, and invested more energy in their ovaries than starved fish. Compared to pre-experiment fish, starved and intermediate-fed females appeared to increase their ovary size by relying on liver energy stores (‘capital’ spawning). Conversely, high-fed females increased liver and gonad mass, implying an ‘income’-spawning strategy (where gonads are built from recently acquired energy). Fecundity did not differ among treatments, but high-fed fish built larger eggs than those starved. Females rarely ‘skipped’ spawning opportunities when prey resources were low, as only 8% of starved females and 8% of intermediate-fed females lacked vitellogenic eggs. These results suggest that limited prey resources during the months before spawning can limit ovary production, which, in turn, can limit reproductive success of white crappies.

Visually driven chaining of elementary swim patterns into a goal-directed motor sequence: a virtual reality study of zebrafish prey capture

Directory of Open Access Journals (Sweden)

Chintan A Trivedi

2013-05-01

Full Text Available Prey capture behavior critically depends on rapid processing of sensory input in order to track, approach and catch the target. When using vision, the nervous system faces the problem of extracting relevant information from a continuous stream of input in order to detect and categorize visible objects as potential prey and to select appropriate motor patterns for approach. For prey capture, many vertebrates exhibit intermittent locomotion, in which discrete motor patterns are chained into a sequence, interrupted by short periods of rest. Here, using high-speed recordings of full-length prey capture sequences performed by freely swimming zebrafish larvae in the presence of a single paramecium, we provide a detailed kinematic analysis of first and subsequent swim bouts during prey capture. Using Fourier analysis, we show that individual swim bouts represent an elementary motor pattern. Changes in orientation are directed towards the target on a graded scale and are implemented by an asymmetric tail bend component superimposed on this basic motor pattern. To further investigate the role of visual feedback on the efficiency and speed of this complex behavior, we developed a closed-loop virtual reality setup in which minimally restrained larvae recapitulated interconnected swim patterns closely resembling those observed during prey capture in freely moving fish. Systematic variation of stimulus properties showed that prey capture is initiated within a narrow range of stimulus size and velocity. Furthermore, variations in the delay and location of swim-triggered visual feedback showed that the reaction time of secondary and later swims is shorter for stimuli that appear within a narrow spatio-temporal window following a swim. This suggests that the larva may generate an expectation of stimulus position, which enables accelerated motor sequencing if the expectation is met by appropriate visual feedback.

Visually driven chaining of elementary swim patterns into a goal-directed motor sequence: a virtual reality study of zebrafish prey capture

Science.gov (United States)

Trivedi, Chintan A.; Bollmann, Johann H.

2013-01-01

Prey capture behavior critically depends on rapid processing of sensory input in order to track, approach, and catch the target. When using vision, the nervous system faces the problem of extracting relevant information from a continuous stream of input in order to detect and categorize visible objects as potential prey and to select appropriate motor patterns for approach. For prey capture, many vertebrates exhibit intermittent locomotion, in which discrete motor patterns are chained into a sequence, interrupted by short periods of rest. Here, using high-speed recordings of full-length prey capture sequences performed by freely swimming zebrafish larvae in the presence of a single paramecium, we provide a detailed kinematic analysis of first and subsequent swim bouts during prey capture. Using Fourier analysis, we show that individual swim bouts represent an elementary motor pattern. Changes in orientation are directed toward the target on a graded scale and are implemented by an asymmetric tail bend component superimposed on this basic motor pattern. To further investigate the role of visual feedback on the efficiency and speed of this complex behavior, we developed a closed-loop virtual reality setup in which minimally restrained larvae recapitulated interconnected swim patterns closely resembling those observed during prey capture in freely moving fish. Systematic variation of stimulus properties showed that prey capture is initiated within a narrow range of stimulus size and velocity. Furthermore, variations in the delay and location of swim triggered visual feedback showed that the reaction time of secondary and later swims is shorter for stimuli that appear within a narrow spatio-temporal window following a swim. This suggests that the larva may generate an expectation of stimulus position, which enables accelerated motor sequencing if the expectation is met by appropriate visual feedback. PMID:23675322

Feeding State Modulates Behavioral Choice and Processing of Prey Stimuli in the Zebrafish Tectum.

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Filosa, Alessandro; Barker, Alison J; Dal Maschio, Marco; Baier, Herwig

2016-05-04

Animals use the sense of vision to scan their environment, respond to threats, and locate food sources. The neural computations underlying the selection of a particular behavior, such as escape or approach, require flexibility to balance potential costs and benefits for survival. For example, avoiding novel visual objects reduces predation risk but negatively affects foraging success. Zebrafish larvae approach small, moving objects ("prey") and avoid large, looming objects ("predators"). We found that this binary classification of objects by size is strongly influenced by feeding state. Hunger shifts behavioral decisions from avoidance to approach and recruits additional prey-responsive neurons in the tectum, the main visual processing center. Both behavior and tectal function are modulated by signals from the hypothalamic-pituitary-interrenal axis and the serotonergic system. Our study has revealed a neuroendocrine mechanism that modulates the perception of food and the willingness to take risks in foraging decisions. Copyright © 2016 Elsevier Inc. All rights reserved.

Temperature and prey capture: opposite relationships in two predator taxa

DEFF Research Database (Denmark)

Kruse, Peter Dalgas; Toft, Søren; Sunderland, Keith

2008-01-01

to catch swiftly moving prey. 2. The first experiment examined the spontaneous locomotor activity of the predators and of fruit flies at different temperatures (5, 10, 15, 20, 25, and 30 °C) and light conditions (light, dark). A second experiment examined the effect of temperature and light...... different prey groups within the set of potential prey at different times of the day or at different seasons. The ability of many carabid beetles to forage at low temperatures may have nutritional benefits and increases the diversity of interactions in terrestrial food webs....

Jaguar interactions with pumas and prey at the northern edge of jaguars’ range

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Carmina E. Gutiérrez-González

2017-01-01

Full Text Available We present the first study that evaluates jaguar-puma interactions in the arid lands of northern Mexico, where jaguars have their northernmost breeding population and both predators are persecuted for livestock depredation. We tested whether jaguars are the dominant species in this unique ecosystem, where: (1 pumas outnumber jaguars, (2 pumas are better adapted to arid environments, and (3 jaguars and pumas are of similar size. We analyzed four years of data with two approaches; a two species conditional occupancy model and an activity patterns analysis. We used camera location and prey presence as covariates for jaguar and puma detection and presence probabilities. We also explored overlap in activities of predators and prey. Where both species were detected, peccary presence was positively correlated with both jaguar and puma presence, whereas in areas where jaguars were detected but pumas were not, deer presence explained the probability of jaguar presence. We found that both predators were more likely to co-occur together than to be found independently, and so we rejected the hypothesis that jaguars were the dominant species in our study area. Predators were mainly nocturnal and their activity patterns overlapped by 60%. Jaguar, as compared with puma, overlapped more with deer and calves; puma overlapped with calves more than with other prey, suggesting a preference. We believe exploring predator relationships at different scales may help elucidate mechanisms that regulate their coexistence.

Predator-prey interactions as macro-scale drivers of species diversity in mammals

DEFF Research Database (Denmark)

Sandom, Christopher James; Sandel, Brody Steven; Dalby, Lars

Background/Question/Methods Understanding the importance of predator-prey interactions for species diversity is a central theme in ecology, with fundamental consequences for predicting the responses of ecosystems to land use and climate change. We assessed the relative support for different...... mechanistic drivers of mammal species richness at macro-scales for two trophic levels: predators and prey. To disentangle biotic (i.e. functional predator-prey interactions) from abiotic (i.e. environmental) and bottom-up from top-down determinants we considered three hypotheses: 1) environmental factors...... that determine ecosystem productivity drive prey and predator richness (the productivity hypothesis, abiotic, bottom-up), 2) consumer richness is driven by resource diversity (the resource diversity hypothesis, biotic, bottom-up) and 3) consumers drive richness of their prey (the top-down hypothesis, biotic, top...

Benthic prey fish assessment, Lake Ontario 2013

Science.gov (United States)

Weidel, Brian C.; Walsh, Maureen; Connerton, Michael J.

2014-01-01

abundance and weight indices increased slightly as compared to 2012. The number index value of 16.6 was 30% of the maximum number observed in 2008 when the number index was 95.2. Round Goby density estimates from the 2013 fall benthic prey fish survey were 33 times greater than fall Slimy Sculpin density, indicating Round Goby are now the dominant Lake Ontario benthic prey fish.

Spatial match-mismatch between juvenile fish and prey provides a mechanism for recruitment variability across contrasting climate conditions in the eastern Bering Sea.

Science.gov (United States)

Siddon, Elizabeth Calvert; Kristiansen, Trond; Mueter, Franz J; Holsman, Kirstin K; Heintz, Ron A; Farley, Edward V

2013-01-01

Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climate-driven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth 'hot spots', for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth 'hot spots' in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.

Effects of an infectious fungus, Batrachochytrium dendrobatidis, on amphibian predator-prey interactions.

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Barbara A Han

2011-02-01

Full Text Available The effects of parasites and pathogens on host behaviors may be particularly important in predator-prey contexts, since few animal behaviors are more crucial for ensuring immediate survival than the avoidance of lethal predators in nature. We examined the effects of an emerging fungal pathogen of amphibians, Batrachochytrium dendrobatidis, on anti-predator behaviors of tadpoles of four frog species. We also investigated whether amphibian predators consumed infected prey, and whether B. dendrobatidis caused differences in predation rates among prey in laboratory feeding trials. We found differences in anti-predator behaviors among larvae of four amphibian species, and show that infected tadpoles of one species (Anaxyrus boreas were more active and sought refuge more frequently when exposed to predator chemical cues. Salamander predators consumed infected and uninfected tadpoles of three other prey species at similar rates in feeding trials, and predation risk among prey was unaffected by B. dendrobatidis. Collectively, our results show that even sub-lethal exposure to B. dendrobatidis can alter fundamental anti-predator behaviors in some amphibian prey species, and suggest the unexplored possibility that indiscriminate predation between infected and uninfected prey (i.e., non-selective predation could increase the prevalence of this widely distributed pathogen in amphibian populations. Because one of the most prominent types of predators in many amphibian systems is salamanders, and because salamanders are susceptible to B. dendrobatidis, our work suggests the importance of considering host susceptibility and behavioral changes that could arise from infection in both predators and prey.

Extinction in a generalized Lotka-Volterra predator-prey model

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Azmy S. Ackleh

2000-01-01

Full Text Available In this paper we discuss the asymptotic behavior of a predator-prey model with distributed growth and mortality rates. We exhibit simple criteria on the parameters which guarantee that all subpopulations but one predator-prey pair are driven to extinction as t→∞. Finally, we present numerical simulations to illustrate the theoretical results.

Formative evaluation of a mobile liquid portion size estimation interface for people with varying literacy skills.

Science.gov (United States)

Chaudry, Beenish Moalla; Connelly, Kay; Siek, Katie A; Welch, Janet L

2013-12-01

Chronically ill people, especially those with low literacy skills, often have difficulty estimating portion sizes of liquids to help them stay within their recommended fluid limits. There is a plethora of mobile applications that can help people monitor their nutritional intake but unfortunately these applications require the user to have high literacy and numeracy skills for portion size recording. In this paper, we present two studies in which the low- and the high-fidelity versions of a portion size estimation interface, designed using the cognitive strategies adults employ for portion size estimation during diet recall studies, was evaluated by a chronically ill population with varying literacy skills. The low fidelity interface was evaluated by ten patients who were all able to accurately estimate portion sizes of various liquids with the interface. Eighteen participants did an in situ evaluation of the high-fidelity version incorporated in a diet and fluid monitoring mobile application for 6 weeks. Although the accuracy of the estimation cannot be confirmed in the second study but the participants who actively interacted with the interface showed better health outcomes by the end of the study. Based on these findings, we provide recommendations for designing the next iteration of an accurate and low literacy-accessible liquid portion size estimation mobile interface.

The importance of predator–prey overlap: predicting North Sea cod recovery with a multispecies assessment model

DEFF Research Database (Denmark)

Kempf, Alexander; Dingsør, Gjert Endre; Huse, Geir

2010-01-01

The overlap between predator and prey is known as a sensitive parameter in multispecies assessment models for fish, and its parameterization is notoriously difficult. Overlap indices were derived from trawl surveys and used to parametrize the North Sea stochastic multispecies model. The effect...... of time-invariant and year- and quarter-specific overlap estimates on the historical (1991–2007) and predicted trophic interactions, as well as the development of predator and prey stocks, was investigated. The focus was set on a general comparison between single-species and multispecies forecasts...... and the sensitivity of the predicted development of North Sea cod for the two types of overlap implementation. The spatial–temporal overlap between cod and its predators increased with increasing temperature, indicating that foodweb processes might reduce the recovery potential of cod during warm periods...

Food photography II: use of food photographs for estimating portion size and the nutrient content of meals.

Science.gov (United States)

Nelson, M; Atkinson, M; Darbyshire, S

1996-07-01

The aim of the present study was to determine the errors in the conceptualization of portion size using photographs. Male and female volunteers aged 18-90 years (n 136) from a wide variety of social and occupational backgrounds completed 602 assessments of portion size in relation to food photographs. Subjects served themselves between four and six foods at one meal (breakfast, lunch or dinner). Portion sizes were weighed by the investigators at the time of serving, and any waste was weighed at the end of the meal. Within 5 min of the end of the meal, subjects were shown photographs depicting each of the foods just consumed. For each food there were eight photographs showing portion sizes in equal increments from the 5th to the 95th centile of the distribution of portion weights observed in The Dietary and Nutritional Survey of British Adults (Gregory et al. 1990). Subjects were asked to indicate on a visual analogue scale the size of the portion consumed in relation to the eight photographs. The nutrient contents of meals were estimated from food composition tables. There were large variations in the estimation of portion sizes from photographs. Butter and margarine portion sizes tended to be substantially overestimated. In general, small portion sizes tended to be overestimated, and large portion sizes underestimated. Older subjects overestimated portion size more often than younger subjects. Excluding butter and margarine, the nutrient content of meals based on estimated portion sizes was on average within +/- 7% of the nutrient content based on the amounts consumed, except for vitamin C (21% overestimate), and for subjects over 65 years (15-20% overestimate for energy and fat). In subjects whose BMI was less than 25 kg/m2, the energy and fat contents of meals calculated from food composition tables and based on estimated portion size (excluding butter and margarine) were 5-10% greater than the nutrient content calculated using actual portion size, but for those

Why liquid displacement methods are sometimes wrong in estimating the pore-size distribution

NARCIS (Netherlands)

Gijsbertsen-Abrahamse, A.J.; Boom, R.M.; Padt, van der A.

2004-01-01

The liquid displacement method is a commonly used method to determine the pore size distribution of micro- and ultrafiltration membranes. One of the assumptions for the calculation of the pore sizes is that the pores are parallel and thus are not interconnected. To show that the estimated pore size

What you need is what you eat? Prey selection by the bat Myotis daubentonii.

Science.gov (United States)

Vesterinen, Eero J; Ruokolainen, Lasse; Wahlberg, Niklas; Peña, Carlos; Roslin, Tomas; Laine, Veronika N; Vasko, Ville; Sääksjärvi, Ilari E; Norrdahl, Kai; Lilley, Thomas M

2016-04-01

Optimal foraging theory predicts that predators are selective when faced with abundant prey, but become less picky when prey gets sparse. Insectivorous bats in temperate regions are faced with the challenge of building up fat reserves vital for hibernation during a period of decreasing arthropod abundances. According to optimal foraging theory, prehibernating bats should adopt a less selective feeding behavior--yet empirical studies have revealed many apparently generalized species to be composed of specialist individuals. Targeting the diet of the bat Myotis daubentonii, we used a combination of molecular techniques to test for seasonal changes in prey selectivity and individual-level variation in prey preferences. DNA metabarcoding was used to characterize both the prey contents of bat droppings and the insect community available as prey. To test for dietary differences among M. daubentonii individuals, we used ten microsatellite loci to assign droppings to individual bats. The comparison between consumed and available prey revealed a preference for certain prey items regardless of availability. Nonbiting midges (Chironomidae) remained the most highly consumed prey at all times, despite a significant increase in the availability of black flies (Simuliidae) towards the end of the season. The bats sampled showed no evidence of individual specialization in dietary preferences. Overall, our approach offers little support for optimal foraging theory. Thus, it shows how novel combinations of genetic markers can be used to test general theory, targeting patterns at both the level of prey communities and individual predators. © 2016 John Wiley & Sons Ltd.

Plastic responses of a sessile prey to multiple predators: a field and experimental study.

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Philipp Emanuel Hirsch

Full Text Available Theory predicts that prey facing a combination of predators with different feeding modes have two options: to express a response against the feeding mode of the most dangerous predator, or to express an intermediate response. Intermediate phenotypes protect equally well against several feeding modes, rather than providing specific protection against a single predator. Anti-predator traits that protect against a common feeding mode displayed by all predators should be expressed regardless of predator combination, as there is no need for trade-offs.We studied phenotypic anti-predator responses of zebra mussels to predation threat from a handling-time-limited (crayfish and a gape-size-limited (roach predator. Both predators dislodge mussels from the substrate but diverge in their further feeding modes. Mussels increased expression of a non-specific defense trait (attachment strength against all combinations of predators relative to a control. In response to roach alone, mussels showed a tendency to develop a weaker and more elongated shell. In response to crayfish, mussels developed a harder and rounder shell. When exposed to either a combination of predators or no predator, mussels developed an intermediate phenotype. Mussel growth rate was positively correlated with an elongated weaker shell and negatively correlated with a round strong shell, indicating a trade-off between anti-predator responses. Field observations of prey phenotypes revealed the presence of both anti-predator phenotypes and the trade-off with growth, but intra-specific population density and bottom substrate had a greater influence than predator density.Our results show that two different predators can exert both functionally equivalent and inverse selection pressures on a single prey. Our field study suggests that abiotic factors and prey population density should be considered when attempting to explain phenotypic diversity in the wild.

ON ESTIMATION AND HYPOTHESIS TESTING OF THE GRAIN SIZE DISTRIBUTION BY THE SALTYKOV METHOD

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Yuri Gulbin

2011-05-01

Full Text Available The paper considers the problem of validity of unfolding the grain size distribution with the back-substitution method. Due to the ill-conditioned nature of unfolding matrices, it is necessary to evaluate the accuracy and precision of parameter estimation and to verify the possibility of expected grain size distribution testing on the basis of intersection size histogram data. In order to review these questions, the computer modeling was used to compare size distributions obtained stereologically with those possessed by three-dimensional model aggregates of grains with a specified shape and random size. Results of simulations are reported and ways of improving the conventional stereological techniques are suggested. It is shown that new improvements in estimating and testing procedures enable grain size distributions to be unfolded more efficiently.