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Sample records for density-dependent population growth

  1. Density regulation in Northeast Atlantic fish populations: Density dependence is stronger in recruitment than in somatic growth.

    Science.gov (United States)

    Zimmermann, Fabian; Ricard, Daniel; Heino, Mikko

    2018-05-01

    Population regulation is a central concept in ecology, yet in many cases its presence and the underlying mechanisms are difficult to demonstrate. The current paradigm maintains that marine fish populations are predominantly regulated by density-dependent recruitment. While it is known that density-dependent somatic growth can be present too, its general importance remains unknown and most practical applications neglect it. This study aimed to close this gap by for the first time quantifying and comparing density dependence in growth and recruitment over a large set of fish populations. We fitted density-dependent models to time-series data on population size, recruitment and age-specific weight from commercially exploited fish populations in the Northeast Atlantic Ocean and the Baltic Sea. Data were standardized to enable a direct comparison within and among populations, and estimated parameters were used to quantify the impact of density regulation on population biomass. Statistically significant density dependence in recruitment was detected in a large proportion of populations (70%), whereas for density dependence in somatic growth the prevalence of density dependence depended heavily on the method (26% and 69%). Despite age-dependent variability, the density dependence in recruitment was consistently stronger among age groups and between alternative approaches that use weight-at-age or weight increments to assess growth. Estimates of density-dependent reduction in biomass underlined these results: 97% of populations with statistically significant parameters for growth and recruitment showed a larger impact of density-dependent recruitment on population biomass. The results reaffirm the importance of density-dependent recruitment in marine fishes, yet they also show that density dependence in somatic growth is not uncommon. Furthermore, the results are important from an applied perspective because density dependence in somatic growth affects productivity and

  2. Local environment and density-dependent feedbacks determine population growth in a forest herb

    DEFF Research Database (Denmark)

    Dahlgren, Johan Petter; Östergård, Hannah; Ehrlén, Johan

    2014-01-01

    Linking spatial variation in environmental factors to variation in demographic rates is essential for a mechanistic understanding of the dynamics of populations. However, we still know relatively little about such links, partly because feedbacks via intraspecific density make them difficult...... to observe in natural populations. We conducted a detailed field study and investigated simultaneous effects of environmental factors and the intraspecific density of individuals on the demography of the herb Lathyrus vernus. In regression models of vital rates we identified effects associated with spring...... shade on survival and growth, while density was negatively correlated with these vital rates. Density was also negatively correlated with average individual size in the study plots, which is consistent with self-thinning. In addition, average plant sizes were larger than predicted by density in plots...

  3. Density-dependent growth in invasive Lionfish (Pterois volitans).

    Science.gov (United States)

    Benkwitt, Cassandra E

    2013-01-01

    Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans) is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss) were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration) of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion.

  4. Density-dependent growth in invasive Lionfish (Pterois volitans.

    Directory of Open Access Journals (Sweden)

    Cassandra E Benkwitt

    Full Text Available Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion.

  5. A mechanistic analysis of density dependence in algal population dynamics

    Directory of Open Access Journals (Sweden)

    Adrian eBorlestean

    2015-04-01

    Full Text Available Population density regulation is a fundamental principle in ecology, but the specific process underlying functional expression of density dependence remains to be fully elucidated. One view contends that patterns of density dependence are largely fixed across a species irrespective of environmental conditions, whereas another is that the strength and expression of density dependence are fundamentally variable depending on the nature of exogenous or endogenous constraints acting on the population. We conducted a study investigating the expression of density dependence in Chlamydomonas spp. grown under a gradient from low to high nutrient density. We predicted that the relationship between per capita growth rate (pgr and population density would vary from concave up to concave down as nutrient density became less limiting and populations experienced weaker density regulation. Contrary to prediction, we found that the relationship between pgr and density became increasingly concave-up as nutrient levels increased. We also found that variation in pgr increased, and pgr levels reached higher maxima in nutrient-limited environments. Most likely, these results are attributable to population growth suppression in environments with high intraspecific competition due to limited nutrient resources. Our results suggest that density regulation is strongly variable depending on exogenous and endogenous processes acting on the population, implying that expression of density dependence depends extensively on local conditions. Additional experimental work should reveal the mechanisms influencing how the expression of density dependence varies across populations through space and time.

  6. Linking individual phenotype to density-dependent population growth: the influence of body size on the population dynamics of malaria vectors

    Science.gov (United States)

    Russell, Tanya L.; Lwetoijera, Dickson W.; Knols, Bart G. J.; Takken, Willem; Killeen, Gerry F.; Ferguson, Heather M.

    2011-01-01

    Understanding the endogenous factors that drive the population dynamics of malaria mosquitoes will facilitate more accurate predictions about vector control effectiveness and our ability to destabilize the growth of either low- or high-density insect populations. We assessed whether variation in phenotypic traits predict the dynamics of Anopheles gambiae sensu lato mosquitoes, the most important vectors of human malaria. Anopheles gambiae dynamics were monitored over a six-month period of seasonal growth and decline. The population exhibited density-dependent feedback, with the carrying capacity being modified by rainfall (97% wAICc support). The individual phenotypic expression of the maternal (p = 0.0001) and current (p = 0.040) body size positively influenced population growth. Our field-based evidence uniquely demonstrates that individual fitness can have population-level impacts and, furthermore, can mitigate the impact of exogenous drivers (e.g. rainfall) in species whose reproduction depends upon it. Once frontline interventions have suppressed mosquito densities, attempts to eliminate malaria with supplementary vector control tools may be attenuated by increased population growth and individual fitness. PMID:21389034

  7. Linking individual phenotype to density-dependent population growth: the influence of body size on the population dynamics of malaria vectors

    NARCIS (Netherlands)

    Russell, T.L.; Lwetoijera, D.W.; Knols, B.G.J.; Takken, W.; Killeen, G.F.; Ferguson, H.M.

    2011-01-01

    Understanding the endogenous factors that drive the population dynamics of malaria mosquitoes will facilitate more accurate predictions about vector control effectiveness and our ability to destabilize the growth of either low- or high-density insect populations. We assessed whether variation in

  8. Linking individual phenotype to density-dependent population growth: the influence of body size on the population dynamics of malaria vectors

    NARCIS (Netherlands)

    Russell, T.L.; Lwetoijera, D.W.; Knols, B.G.J.; Takken, W.; Killeen, G.F.; Ferguson, H.M.

    2011-01-01

    Understanding the endogenous factors that drive the population dynamics of malaria mosquitoes will facilitate more accurate predictions about vector control effectiveness and our ability to destabilize the growth of either low-or high-density insect populations. We assessed whether variation in

  9. Density-dependent feedbacks can mask environmental drivers of populations

    DEFF Research Database (Denmark)

    Dahlgren, Johan Petter

    I present some results from studies identifying environmental drivers of vital rates and population dynamics when controlling for intraspecific density statistically or experimentally, show that density dependence can be strong even in populations of slow-growing species in stressful habitats, an...

  10. Global asymptotic stability of density dependent integral population projection models.

    Science.gov (United States)

    Rebarber, Richard; Tenhumberg, Brigitte; Townley, Stuart

    2012-02-01

    Many stage-structured density dependent populations with a continuum of stages can be naturally modeled using nonlinear integral projection models. In this paper, we study a trichotomy of global stability result for a class of density dependent systems which include a Platte thistle model. Specifically, we identify those systems parameters for which zero is globally asymptotically stable, parameters for which there is a positive asymptotically stable equilibrium, and parameters for which there is no asymptotically stable equilibrium. Copyright © 2011 Elsevier Inc. All rights reserved.

  11. Modelling interactions of toxicants and density dependence in wildlife populations

    Science.gov (United States)

    Schipper, Aafke M.; Hendriks, Harrie W.M.; Kauffman, Matthew J.; Hendriks, A. Jan; Huijbregts, Mark A.J.

    2013-01-01

    1. A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. 2. Here, we incorporated both density dependence and anthropogenic stressors in a stage-based matrix population model and parameterized it for a density-dependent population of peregrine falcons Falco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene (DDE) and polybrominated diphenyl ethers (PBDEs)]. Log-logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. 3. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant-induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. 4. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g−1 fresh weight for DDE and PBDEs, respectively. 5. Synthesis and applications. Our modelling results showed that particular life stages of a density-limited population may be relatively insensitive to

  12. Explaining density-dependent regulation in earthworm populations using life-history analysis

    NARCIS (Netherlands)

    Kammenga, J.E.; Spurgeon, D.J.; Svendsen, C.; Weeks, J.M.

    2003-01-01

    At present there is little knowledge about how density regulates population growth rate and to what extent this is determined by life-history patterns. We compared density dependent population consequences in the Nicholsonian sense based oil experimental observations and life-history modeling for

  13. Density Dependence and Growth Rate: Evolutionary Effects on Resistance Development to Bt (Bacillus thuringiensis).

    Science.gov (United States)

    Martinez, Jeannette C; Caprio, Michael A; Friedenberg, Nicholas A

    2018-02-09

    It has long been recognized that pest population dynamics can affect the durability of a pesticide, but dose remains the primary component of insect resistance management (IRM). For transgenic pesticidal traits such as Bt (Bacillus thuringiensis Berliner (Bacillales: Bacillaceae)), dose (measured as the mortality of susceptibles caused by a toxin) is a relatively fixed characteristic and often falls below the standard definition of high dose. Hence, it is important to understand how pest population dynamics modify durability and what targets they present for IRM. We used a deterministic model of a generic arthropod pest to examine how timing and strength of density dependence interacted with population growth rate and Bt mortality to affect time to resistance. As in previous studies, durability typically reached a minimum at intermediate doses. However, high population growth rates could eliminate benefits of high dose. The timing of density dependence had a more subtle effect. If density dependence operated simultaneously with Bt mortality, durability was insensitive to its strengths. However, if density dependence was driven by postselection densities, decreasing its strength could increase durability. The strength of density dependence could affect durability of both single traits and pyramids, but its influence depended on the timing of density dependence and size of the refuge. Our findings suggest the utility of a broader definition of high dose, one that incorporates population-dynamic context. That maximum growth rates and timing and strength of interactions causing density dependent mortality can all affect durability, also highlights the need for ecologically integrated approaches to IRM research. © The Author(s) 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  14. Density dependence in a recovering osprey population: demographic and behavioural processes.

    Science.gov (United States)

    Bretagnolle, V; Mougeot, F; Thibault, J-C

    2008-09-01

    1. Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions.

  15. Dispersal, density dependence, and population dynamics of a fungal microbe on leaf surfaces.

    Science.gov (United States)

    Woody, Scott T; Ives, Anthony R; Nordheim, Erik V; Andrews, John H

    2007-06-01

    Despite the ubiquity and importance of microbes in nature, little is known about their natural population dynamics, especially for those that occupy terrestrial habitats. Here we investigate the dynamics of the yeast-like fungus Aureobasidium pullulans (Ap) on apple leaves in an orchard. We asked three questions. (1) Is variation in fungal population density among leaves caused by variation in leaf carrying capacities and strong density-dependent population growth that maintains densities near carrying capacity? (2) Do resident populations have competitive advantages over immigrant cells? (3) Do Ap dynamics differ at different times during the growing season? To address these questions, we performed two experiments at different times in the growing season. Both experiments used a 2 x 2 factorial design: treatment 1 removed fungal cells from leaves to reveal density-dependent population growth, and treatment 2 inoculated leaves with an Ap strain engineered to express green fluorescent protein (GFP), which made it possible to track the fate of immigrant cells. The experiments showed that natural populations of Ap vary greatly in density due to sustained differences in carrying capacities among leaves. The maintenance of populations close to carrying capacities indicates strong density-dependent processes. Furthermore, resident populations are strongly competitive against immigrants, while immigrants have little impact on residents. Finally, statistical models showed high population growth rates of resident cells in one experiment but not in the other, suggesting that Ap experiences relatively "good" and "bad" periods for population growth. This picture of Ap dynamics conforms to commonly held, but rarely demonstrated, expectations of microbe dynamics in nature. It also highlights the importance of local processes, as opposed to immigration, in determining the abundance and dynamics of microbes on surfaces in terrestrial systems.

  16. Density-dependent growth and metamorphosis in the larval bronze ...

    Indian Academy of Sciences (India)

    Effects of density and kinship on growth and metamorphosis in tadpoles of Rana temporalis were studied in a 2 × 4 factorial experiment. Fifteen egg masses were collected from streams in the Western Ghat region of south India. The tadpoles were raised as siblings or in groups of non-siblings at increasing density levels, viz ...

  17. Effective size of density-dependent two-sex populations: the effect of mating systems.

    Science.gov (United States)

    Myhre, A M; Engen, S; SAEther, B-E

    2017-08-01

    Density dependence in vital rates is a key feature affecting temporal fluctuations of natural populations. This has important implications for the rate of random genetic drift. Mating systems also greatly affect effective population sizes, but knowledge of how mating system and density regulation interact to affect random genetic drift is poor. Using theoretical models and simulations, we compare N e in short-lived, density-dependent animal populations with different mating systems. We study the impact of a fluctuating, density-dependent sex ratio and consider both a stable and a fluctuating environment. We find a negative relationship between annual N e /N and adult population size N due to density dependence, suggesting that loss of genetic variation is reduced at small densities. The magnitude of this decrease was affected by mating system and life history. A male-biased, density-dependent sex ratio reduces the rate of genetic drift compared to an equal, density-independent sex ratio, but a stochastic change towards male bias reduces the N e /N ratio. Environmental stochasticity amplifies temporal fluctuations in population size and is thus vital to consider in estimation of effective population sizes over longer time periods. Our results on the reduced loss of genetic variation at small densities, particularly in polygamous populations, indicate that density regulation may facilitate adaptive evolution at small population sizes. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

  18. Roles of density-dependent growth and life history evolution in accounting for fisheries-induced trait changes.

    Science.gov (United States)

    Eikeset, Anne Maria; Dunlop, Erin S; Heino, Mikko; Storvik, Geir; Stenseth, Nils C; Dieckmann, Ulf

    2016-12-27

    The relative roles of density dependence and life history evolution in contributing to rapid fisheries-induced trait changes remain debated. In the 1930s, northeast Arctic cod (Gadus morhua), currently the world's largest cod stock, experienced a shift from a traditional spawning-ground fishery to an industrial trawl fishery with elevated exploitation in the stock's feeding grounds. Since then, age and length at maturation have declined dramatically, a trend paralleled in other exploited stocks worldwide. These trends can be explained by demographic truncation of the population's age structure, phenotypic plasticity in maturation arising through density-dependent growth, fisheries-induced evolution favoring faster-growing or earlier-maturing fish, or a combination of these processes. Here, we use a multitrait eco-evolutionary model to assess the capacity of these processes to reproduce 74 y of historical data on age and length at maturation in northeast Arctic cod, while mimicking the stock's historical harvesting regime. Our results show that model predictions critically depend on the assumed density dependence of growth: when this is weak, life history evolution might be necessary to prevent stock collapse, whereas when a stronger density dependence estimated from recent data is used, the role of evolution in explaining fisheries-induced trait changes is diminished. Our integrative analysis of density-dependent growth, multitrait evolution, and stock-specific time series data underscores the importance of jointly considering evolutionary and ecological processes, enabling a more comprehensive perspective on empirically observed stock dynamics than previous studies could provide.

  19. Bayesian inference on the effect of density dependence and weather on a guanaco population from Chile

    DEFF Research Database (Denmark)

    Zubillaga, Maria; Skewes, Oscar; Soto, Nicolás

    2014-01-01

    Understanding the mechanisms that drive population dynamics is fundamental for management of wild populations. The guanaco (Lama guanicoe) is one of two wild camelid species in South America. We evaluated the effects of density dependence and weather variables on population regulation based...

  20. An experimental field study of delayed density dependence in natural populations of Aedes albopictus.

    Directory of Open Access Journals (Sweden)

    Rachael K Walsh

    Full Text Available Aedes albopictus, a species known to transmit dengue and chikungunya viruses, is primarily a container-inhabiting mosquito. The potential for pathogen transmission by Ae. albopictus has increased our need to understand its ecology and population dynamics. Two parameters that we know little about are the impact of direct density-dependence and delayed density-dependence in the larval stage. The present study uses a manipulative experimental design, under field conditions, to understand the impact of delayed density dependence in a natural population of Ae. albopictus in Raleigh, North Carolina. Twenty liter buckets, divided in half prior to experimentation, placed in the field accumulated rainwater and detritus, providing oviposition and larval production sites for natural populations of Ae. albopictus. Two treatments, a larvae present and larvae absent treatment, were produced in each bucket. After five weeks all larvae were removed from both treatments and the buckets were covered with fine mesh cloth. Equal numbers of first instars were added to both treatments in every bucket. Pupae were collected daily and adults were frozen as they emerged. We found a significant impact of delayed density-dependence on larval survival, development time and adult body size in containers with high larval densities. Our results indicate that delayed density-dependence will have negative impacts on the mosquito population when larval densities are high enough to deplete accessible nutrients faster than the rate of natural food accumulation.

  1. Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent

    DEFF Research Database (Denmark)

    Leirs, Herwig; Steneth, Nils Chr.; Nichols, James D.

    1997-01-01

    , but clear examples of both processes acting in the same population are rare(7,8). Key-factor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide...... no information on actual demographic rates(9,10). Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammute rat Mastomys natalensis (Smith, 1834), using statistical capture-recapture models, Both effects occur simultaneously, but we also demonstrate...

  2. The ideal free distribution as an evolutionarily stable state in density-dependent population games

    Czech Academy of Sciences Publication Activity Database

    Cressman, R.; Křivan, Vlastimil

    2010-01-01

    Roč. 119, č. 8 (2010), s. 1231-1242 ISSN 0030-1299 R&D Projects: GA AV ČR IAA100070601 Institutional research plan: CEZ:AV0Z50070508 Keywords : density-dependent population games Subject RIV: EH - Ecology, Behaviour Impact factor: 3.393, year: 2010

  3. Disentangling the effects of climate, density dependence, and harvest on an iconic large herbivore's population dynamics

    DEFF Research Database (Denmark)

    Koons, David; Colchero, Fernando; Hersey, Kent

    2015-01-01

    Understanding the relative effects of climate, harvest, and density dependence on population dynamics is critical for guiding sound population management, especially for ungulates in arid and semi-arid environments experiencing climate change. To address these issues for bison in southern Utah, we...... than precipitation and other temperature-related variables (model weight > 3 times more than that for other climate variables). Although we hypothesized that harvest is the primary driving force of bison population dynamics in southern Utah, our elasticity analysis indicated that changes in early...... spring temperature could have a greater ‘relative effect’ on equilibrium abundance than either harvest or the strength of density dependence. Our findings highlight the utility of incorporating elasticity analyses into state-space population models, and the need to include climatic processes in wildlife...

  4. Effects of hepatocyte growth factor on glutathione synthesis, growth, and apoptosis is cell density-dependent

    International Nuclear Information System (INIS)

    Yang Heping; Magilnick, Nathaniel; Xia Meng; Lu, Shelly C.

    2008-01-01

    Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen that exerts opposing effects depending on cell density. Glutathione (GSH) is the main non-protein thiol in mammalian cells that modulates growth and apoptosis. We previously showed that GSH level is inversely related to cell density of hepatocytes and is positively related to growth. Our current work examined whether HGF can modulate GSH synthesis in a cell density-dependent manner and how GSH in turn influence HGF's effects. We found HGF treatment of H4IIE cells increased cell GSH levels only under subconfluent density. The increase in cell GSH under low density was due to increased transcription of GSH synthetic enzymes. This correlated with increased protein levels and nuclear binding activities of c-Jun, c-Fos, p65, p50, Nrf1 and Nrf2 to the promoter region of these genes. HGF acts as a mitogen in H4IIE cells under low cell density and protects against tumor necrosis factor α (TNFα)-induced apoptosis by limiting JNK activation. However, HGF is pro-apoptotic under high cell density and exacerbates TNFα-induced apoptosis by potentiating JNK activation. The increase in cell GSH under low cell density allows HGF to exert its full mitogenic effect but is not necessary for its anti-apoptotic effect

  5. Density dependence governs when population responses to multiple stressors are magnified or mitigated.

    Science.gov (United States)

    Hodgson, Emma E; Essington, Timothy E; Halpern, Benjamin S

    2017-10-01

    Population endangerment typically arises from multiple, potentially interacting anthropogenic stressors. Extensive research has investigated the consequences of multiple stressors on organisms, frequently focusing on individual life stages. Less is known about population-level consequences of exposure to multiple stressors, especially when exposure varies through life. We provide the first theoretical basis for identifying species at risk of magnified effects from multiple stressors across life history. By applying a population modeling framework, we reveal conditions under which population responses from stressors applied to distinct life stages are either magnified (synergistic) or mitigated. We find that magnification or mitigation critically depends on the shape of density dependence, but not the life stage in which it occurs. Stressors are always magnified when density dependence is linear or concave, and magnified or mitigated when it is convex. Using Bayesian numerical methods, we estimated the shape of density dependence for eight species across diverse taxa, finding support for all three shapes. © 2017 by the Ecological Society of America.

  6. On the numerical simulation of population dynamics with density-dependent migrations and the Allee effects

    International Nuclear Information System (INIS)

    Sweilam, H N; Khader, M M; Al-Bar, F R

    2008-01-01

    In this paper, the variational iteration method (VIM) and the Adomian decomposition method (ADM) are presented for the numerical simulation of the population dynamics model with density-dependent migrations and the Allee effects. The convergence of ADM is proved for the model problem. The results obtained by these methods are compared to the exact solution. It is found that these methods are always converges to the right solutions with high accuracy. Furthermore, VIM needs relative less computational work than ADM

  7. A consumer-resource approach to the density-dependent population dynamics of mutualism.

    Science.gov (United States)

    Holland, J Nathaniel; DeAngelis, Donald L

    2010-05-01

    Like predation and competition, mutualism is now recognized as a consumer-resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant-mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

  8. A consumer-resource approach to the density-dependent population dynamics of mutualism

    Science.gov (United States)

    Holland, J. Nathaniel; DeAngelis, Donald L.

    2010-01-01

    Like predation and competition, mutualism is now recognized as a consumer resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant- mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

  9. Integration of Density Dependence and Concentration Response Models Provides an Ecologically Relevant Assessment of Populations Exposed to Toxicants

    Science.gov (United States)

    The assessment of toxic exposure on wildlife populations involves the integration of organism level effects measured in toxicity tests (e.g., chronic life cycle) and population models. These modeling exercises typically ignore density dependence, primarily because information on ...

  10. Density dependence, density independence, and recruitment in the American shad (Alosa sapidissima) population of the Connecticut River

    International Nuclear Information System (INIS)

    Leggett, W.C.

    1977-01-01

    The role of density-dependent and density-independent factors in the regulation of the stock-recruitment relationship of the American shad (Alosa sapidissima) population of the Connecticut River was investigated. Significant reductions in egg-to-adult survival and juvenile growth rates occurred in the Holyoke--Turners Falls region in response to increases in the intensity of spawning in this area. For the Connecticut River population as a whole, egg-to-adult survival was estimated to be 0.00056 percent at replacement levels, and 0.00083 percent at the point of maximum population growth. Density-independent factors result in significant annual deviations from recruitment levels predicted by the density-dependent model. Temperature and flow regimes during spawning and early larval development are involved, but they explain only a small portion (less than 16 percent) of the total variation. In spite of an extensive data base, the accuracy of predictions concerning the potential effects of additional mortality to pre-recruit stages is low. The implications of these findings for environmental impact assessment are discussed

  11. Dynamics of a recovering Arctic bird population: the importance of climate, density dependence, and site quality

    Science.gov (United States)

    Bruggeman, Jason E.; Swem, Ted; Andersen, David E.; Kennedy, Patricia L.; Nigro, Debora A.

    2015-01-01

    Intrinsic and extrinsic factors affect vital rates and population-level processes, and understanding these factors is paramount to devising successful management plans for wildlife species. For example, birds time migration in response, in part, to local and broadscale climate fluctuations to initiate breeding upon arrival to nesting territories, and prolonged inclement weather early in the breeding season can inhibit egg-laying and reduce productivity. Also, density-dependent regulation occurs in raptor populations, as territory size is related to resource availability. Arctic Peregrine Falcons (Falco peregrinus tundrius; hereafter Arctic peregrine) have a limited and northern breeding distribution, including the Colville River Special Area (CRSA) in the National Petroleum Reserve–Alaska, USA. We quantified influences of climate, topography, nest productivity, prey habitat, density dependence, and interspecific competition affecting Arctic peregrines in the CRSA by applying the Dail-Madsen model to estimate abundance and vital rates of adults on nesting cliffs from 1981 through 2002. Arctic peregrine abundance increased throughout the 1980s, which spanned the population's recovery from DDT-induced reproductive failure, until exhibiting a stationary trend in the 1990s. Apparent survival rate (i.e., emigration; death) was negatively correlated with the number of adult Arctic peregrines on the cliff the previous year, suggesting effects of density-dependent population regulation. Apparent survival and arrival rates (i.e., immigration; recruitment) were higher during years with earlier snowmelt and milder winters, and apparent survival was positively correlated with nesting season maximum daily temperature. Arrival rate was positively correlated with average Arctic peregrine productivity along a cliff segment from the previous year and initial abundance was positively correlated with cliff height. Higher cliffs with documented higher productivity (presumably

  12. Population-Level Density Dependence Influences the Origin and Maintenance of Parental Care.

    Directory of Open Access Journals (Sweden)

    Elijah Reyes

    Full Text Available Parental care is a defining feature of animal breeding systems. We now know that both basic life-history characteristics and ecological factors influence the evolution of care. However, relatively little is known about how these factors interact to influence the origin and maintenance of care. Here, we expand upon previous work and explore the relationship between basic life-history characteristics (stage-specific rates of mortality and maturation and the fitness benefits associated with the origin and the maintenance of parental care for two broad ecological scenarios: the scenario in which egg survival is density dependent and the case in which adult survival is density dependent. Our findings suggest that high offspring need is likely critical in driving the origin, but not the maintenance, of parental care regardless of whether density dependence acts on egg or adult survival. In general, parental care is more likely to result in greater fitness benefits when baseline adult mortality is low if 1 egg survival is density dependent or 2 adult mortality is density dependent and mutant density is relatively high. When density dependence acts on egg mortality, low rates of egg maturation and high egg densities are less likely to lead to strong fitness benefits of care. However, when density dependence acts on adult mortality, high levels of egg maturation and increasing adult densities are less likely to maintain care. Juvenile survival has relatively little, if any, effect on the origin and maintenance of egg-only care. More generally, our results suggest that the evolution of parental care will be influenced by an organism's entire life history characteristics, the stage at which density dependence acts, and whether care is originating or being maintained.

  13. Population-Level Density Dependence Influences the Origin and Maintenance of Parental Care.

    Science.gov (United States)

    Reyes, Elijah; Thrasher, Patsy; Bonsall, Michael B; Klug, Hope

    2016-01-01

    Parental care is a defining feature of animal breeding systems. We now know that both basic life-history characteristics and ecological factors influence the evolution of care. However, relatively little is known about how these factors interact to influence the origin and maintenance of care. Here, we expand upon previous work and explore the relationship between basic life-history characteristics (stage-specific rates of mortality and maturation) and the fitness benefits associated with the origin and the maintenance of parental care for two broad ecological scenarios: the scenario in which egg survival is density dependent and the case in which adult survival is density dependent. Our findings suggest that high offspring need is likely critical in driving the origin, but not the maintenance, of parental care regardless of whether density dependence acts on egg or adult survival. In general, parental care is more likely to result in greater fitness benefits when baseline adult mortality is low if 1) egg survival is density dependent or 2) adult mortality is density dependent and mutant density is relatively high. When density dependence acts on egg mortality, low rates of egg maturation and high egg densities are less likely to lead to strong fitness benefits of care. However, when density dependence acts on adult mortality, high levels of egg maturation and increasing adult densities are less likely to maintain care. Juvenile survival has relatively little, if any, effect on the origin and maintenance of egg-only care. More generally, our results suggest that the evolution of parental care will be influenced by an organism's entire life history characteristics, the stage at which density dependence acts, and whether care is originating or being maintained.

  14. Impact of entrainment and impingement on fish populations in the Hudson River Estuary. Volume II. Impingement impact analyses, evaluations of alternative screening devices, and critiques of utility testimony relating to density-dependent growth, the age-composition of the striped bass spawning stock, and the LMS real-time life cycle model

    International Nuclear Information System (INIS)

    Barnthouse, L.W.; Van Winkle, W.; Golumbek, J.; Cada, G.F.; Goodyear, C.P.; Christensen, S.W.; Cannon, J.B.; Lee, D.W.

    1982-04-01

    This volume includes a series of four exhibits relating to impacts of impingement on fish populations, together with a collection of critical evaluations of testimony prepared for the utilities by their consultants. The first exhibit is a quantitative evaluation of four sources of bias (collection efficiency, reimpingement, impingement on inoperative screens, and impingement survival) affecting estimates of the number of fish killed at Hudson River power plants. The two following exhibits contain, respectively, a detailed assessment of the impact of impingement on the Hudson River white perch population and estimates of conditional impingement mortality rates for seven Hudson River fish populations. The fourth exhibit is an evaluation of the engineering feasibility and potential biological effectiveness of several types of modified intake structures proposed as alternatives to cooling towers for reducing impingement impacts. The remainder of Volume II consists of critical evaluations of the utilities' empirical evidence for the existence of density-dependent growth in young-of-the-year striped bass and white perch, of their estimate of the age-composition of the striped bass spawning stock in the Hudson River, and of their use of the Lawler, Matusky, and Skelly (LMS) Real-Time Life Cycle Model to estimate the impact of entrainment and impingement on the Hudson River striped bass population

  15. Partitioning the sources of demographic variation reveals density-dependent nest predation in an island bird population.

    Science.gov (United States)

    Sofaer, Helen R; Sillett, T Scott; Langin, Kathryn M; Morrison, Scott A; Ghalambor, Cameron K

    2014-07-01

    Ecological factors often shape demography through multiple mechanisms, making it difficult to identify the sources of demographic variation. In particular, conspecific density can influence both the strength of competition and the predation rate, but density-dependent competition has received more attention, particularly among terrestrial vertebrates and in island populations. A better understanding of how both competition and predation contribute to density-dependent variation in fecundity can be gained by partitioning the effects of density on offspring number from its effects on reproductive failure, while also evaluating how biotic and abiotic factors jointly shape demography. We examined the effects of population density and precipitation on fecundity, nest survival, and adult survival in an insular population of orange-crowned warblers (Oreothlypis celata) that breeds at high densities and exhibits a suite of traits suggesting strong intraspecific competition. Breeding density had a negative influence on fecundity, but it acted by increasing the probability of reproductive failure through nest predation, rather than through competition, which was predicted to reduce the number of offspring produced by successful individuals. Our results demonstrate that density-dependent nest predation can underlie the relationship between population density and fecundity even in a high-density, insular population where intraspecific competition should be strong.

  16. Are populations of European earwigs, Forficula auricularia, density dependent?

    DEFF Research Database (Denmark)

    Moerkens, R.; Leirs, H; Peusens, G.

    2009-01-01

    Biocontrol using naturally occurring predators is often limited by population parameters of those predators. Earwigs, Forficula auricularia L. (Dermaptera: Forficulidae), are important predators in fruit orchards. They are capable of suppressing outbreaks of pest species, such as pear psyllid and...

  17. A test of density-dependent pollination within three populations of endangered Pentachaeta lyonii

    Directory of Open Access Journals (Sweden)

    Jocelyn R. Holt

    2014-02-01

    Full Text Available A major concern with endangered plants is that they might attract insufficient numbers of pollinators, produce low numbers of seeds, and decline towards extinction. We examined effects of density as it varied within populations on the pollination of Pentachaeta lyonii, an endangered species that requires pollinators for seed set. Generalist bee-flies and bees were abundant pollinators at three sites for two years. Per-capita visitation rates did not decline at sparse points or for plants placed on the order of 10 m away from other flowering individuals. Seed production was not pollinator-limited within patches, but seed set was low beyond 10 m from neighbours. Considering prior findings, factors such as habitat loss, competition with alien plants, and poor establishment of new populations likely contribute to the rarity of P. lyonii more than pollination failure.

  18. Spatio-temporal dynamics of a fish predator: Density-dependent and hydrographic effects on Baltic Sea cod population.

    Directory of Open Access Journals (Sweden)

    Valerio Bartolino

    Full Text Available Understanding the mechanisms of spatial population dynamics is crucial for the successful management of exploited species and ecosystems. However, the underlying mechanisms of spatial distribution are generally complex due to the concurrent forcing of both density-dependent species interactions and density-independent environmental factors. Despite the high economic value and central ecological importance of cod in the Baltic Sea, the drivers of its spatio-temporal population dynamics have not been analytically investigated so far. In this paper, we used an extensive trawl survey dataset in combination with environmental data to investigate the spatial dynamics of the distribution of the Eastern Baltic cod during the past three decades using Generalized Additive Models. The results showed that adult cod distribution was mainly affected by cod population size, and to a minor degree by small-scale hydrological factors and the extent of suitable reproductive areas. As population size decreases, the cod population concentrates to the southern part of the Baltic Sea, where the preferred more marine environment conditions are encountered. Using the fitted models, we predicted the Baltic cod distribution back to the 1970s and a temporal index of cod spatial occupation was developed. Our study will contribute to the management and conservation of this important resource and of the ecosystem where it occurs, by showing the forces shaping its spatial distribution and therefore the potential response of the population to future exploitation and environmental changes.

  19. Epidermal growth factor receptor-induced activato protein 1 activity controls density-dependent growht inhibition in normal rat kidney fibroblasts.

    NARCIS (Netherlands)

    Hornberg, J.J.; Dekker, H.; Peters, P.H.J.; Langerak, P.; Westerhoff, H.V.; Lankelma, J.; Zoelen, E.J.J.

    2006-01-01

    Density-dependent growth inhibition secures tissue homeostasis. Dysfunction of the mechanisms, which regulate this type of growth control is a major cause of neoplasia. In confluent normal rat kidney (NRK) fibroblasts, epidermal growth factor (EGF) receptor levels decline, ultimately rendering these

  20. Density dependence and climate effects in Rocky Mountain elk: an application of regression with instrumental variables for population time series with sampling error.

    Science.gov (United States)

    Creel, Scott; Creel, Michael

    2009-11-01

    1. Sampling error in annual estimates of population size creates two widely recognized problems for the analysis of population growth. First, if sampling error is mistakenly treated as process error, one obtains inflated estimates of the variation in true population trajectories (Staples, Taper & Dennis 2004). Second, treating sampling error as process error is thought to overestimate the importance of density dependence in population growth (Viljugrein et al. 2005; Dennis et al. 2006). 2. In ecology, state-space models are used to account for sampling error when estimating the effects of density and other variables on population growth (Staples et al. 2004; Dennis et al. 2006). In econometrics, regression with instrumental variables is a well-established method that addresses the problem of correlation between regressors and the error term, but requires fewer assumptions than state-space models (Davidson & MacKinnon 1993; Cameron & Trivedi 2005). 3. We used instrumental variables to account for sampling error and fit a generalized linear model to 472 annual observations of population size for 35 Elk Management Units in Montana, from 1928 to 2004. We compared this model with state-space models fit with the likelihood function of Dennis et al. (2006). We discuss the general advantages and disadvantages of each method. Briefly, regression with instrumental variables is valid with fewer distributional assumptions, but state-space models are more efficient when their distributional assumptions are met. 4. Both methods found that population growth was negatively related to population density and winter snow accumulation. Summer rainfall and wolf (Canis lupus) presence had much weaker effects on elk (Cervus elaphus) dynamics [though limitation by wolves is strong in some elk populations with well-established wolf populations (Creel et al. 2007; Creel & Christianson 2008)]. 5. Coupled with predictions for Montana from global and regional climate models, our results

  1. Evidence for density-dependent changes in growth, downstream movement, and size of Chinook salmon subyearlings in a large-river landscape

    Science.gov (United States)

    Connor, William P.; Tiffan, Kenneth F.; Plumb, John M.; Moffit, Christine M.

    2013-01-01

    We studied the growth rate, downstream movement, and size of naturally produced fall Chinook Salmon Oncorhynchus tshawytscha subyearlings (age 0) for 20 years in an 8th-order river landscape with regulated riverine upstream rearing areas and an impounded downstream migration corridor. The population transitioned from low to high abundance in association with U.S. Endangered Species Act and other federally mandated recovery efforts. The mean growth rate of parr in the river did not decline with increasing abundance, but during the period of higher abundance the timing of dispersal from riverine habitat into the reservoir averaged 17 d earlier and the average size at the time of downstream dispersal was smaller by 10 mm and 1.8 g. Changes in apparent abundance, measured by catch per unit effort, largely explained the time of dispersal, measured by median day of capture, in riverine habitat. The growth rate of smolts in the reservoir declined from an average of 0.6 to 0.2 g/d between the abundance periods because the reduction in size at reservoir entry was accompanied by a tendency to migrate rather than linger and by increasing concentrations of smolts in the reservoir. The median date of passage through the reservoir was 14 d earlier on average, and average smolt size was smaller by 38 mm and 22.0 g, in accordance with density-dependent behavioral changes reflected by decreased smolt growth. Unexpectedly, smolts during the high-abundance period had begun to reexpress the migration timing and size phenotypes observed before the river was impounded, when abundance was relatively high. Our findings provide evidence for density-dependent phenotypic change in a large river that was influenced by the expansion of a recovery program. Thus, this study shows that efforts to recover native fishes can have detectable effects in large-river landscapes. The outcome of such phenotypic change, which will be an important area of future research, can only be fully judged by

  2. Implications of late-in-life density-dependent growth for fishery size-at-entry leading to maximum sustainable yield

    DEFF Research Database (Denmark)

    van Gemert, Rob; Andersen, Ken Haste

    2018-01-01

    -in-life density-dependent growth: North Sea plaice (Pleuronectes platessa), Northeast Atlantic (NEA) mackerel (Scomber scombrus), and Baltic sprat (Sprattus sprattus balticus). For all stocks, the model predicts exploitation at MSY with a large size-at-entry into the fishery, indicating that late-in-life density...

  3. Experimental population dynamics of Rhabdias bufonis (Nematoda) in toads (Bufo bufo): density-dependence in the primary infection

    OpenAIRE

    Goater, C. P.

    2017-01-01

    Density-dependence in worm establishment, numbers, biomass and larval production were examined in primary infections of 0, 10, 40, 80 and 160 larvae of the lung nematode, Rhabdias bufonis in the common toad, Bufo bufo. The infection procedure established 4 non-overlapping levels of infection which persisted until 6 weeks post-infection (p.i.), after which there was an overall decline up to 12 weeks p.i. Worm numbers had no direct effect on adult worm survival but temporal changes in worm weig...

  4. Density dependence and phenological mismatch: consequences for growth and survival of sub-arctic nesting Canada Geese

    Directory of Open Access Journals (Sweden)

    Rodney W. Brook

    2015-06-01

    Full Text Available The extent to which species are plastic in the timing of their reproductive events relative to phenology suggests how climate change might affect their demography. An ecological mismatch between the timing of hatch for avian species and the peak availability in quality and quantity of forage for rapidly growing offspring might ultimately affect recruitment to the breeding population unless individuals can adjust the timing of breeding to adapt to changing phenology. We evaluated effects of goose density, hatch timing relative to forage plant phenology, and weather indices on annual growth of pre-fledging Canada geese (Branta canadensis from 1993-2010 at Akimiski Island, Nunavut. We found effects of both density and hatch timing relative to forage plant phenology; the earlier that eggs hatched relative to forage plant phenology, the larger the mean gosling size near fledging. Goslings were smallest in years when hatch was latest relative to forage plant phenology, and when local abundance of breeding adults was highest. We found no evidence for a trend in relative hatch timing, but it was apparent that in early springs, Canada geese tended to hatch later relative to vegetation phenology, suggesting that geese were not always able to adjust the timing of nesting as rapidly as vegetation phenology was advanced. Analyses using forage biomass information revealed a positive relationship between gosling size and per capita biomass availability, suggesting a causal mechanism for the density effect. The effects of weather parameters explained additional variation in mean annual gosling size, although total June and July rainfall had a small additive effect on gosling size. Modelling of annual first-year survival probability using mean annual gosling size as an annual covariate revealed a positive relationship, suggesting that reduced gosling growth negatively impacts recruitment.

  5. Density dependence and phenological mismatch: consequences for growth and survival of sub-arctic nesting Canada Geese

    Science.gov (United States)

    Brook, Rodney W.; Leafloor, James O.; Douglas, David C.; Abraham, Kenneth F.

    2015-01-01

    The extent to which species are plastic in the timing of their reproductive events relative to phenology suggests how change might affect their demography. An ecological mismatch between the timing of hatch for avian species and the peak availability in quality and quantity of forage for rapidly growing offspring might ultimately affect recruitment to the breeding population unless individuals can adjust the timing of breeding to adapt to changing phenology. We evaluated effects of goose density, hatch timing relative to forage plant phenology, and weather indices on annual growth of pre-fledging Canada geese (Branta canadensis) from 1993-2010 at Akimiski Island, Nunavut. We found effects of both density and hatch timing relative to forage plant phenology; the earlier that eggs hatched relative to forage plant phenology, the larger the mean gosling size near fledging. Goslings were smallest in years when hatch was latest relative to forage plant phenology, and when local abundance of breeding adults was highest. We found no evidence for a trend in relative hatch timing, but it was apparent that in early springs, Canada geese tended to hatch later relative to vegetation phenology, suggesting that geese were not always able to adjust the timing of nesting as rapidly as vegetation phenology was advanced. Analyses using forage biomass information revealed a positive relationship between gosling size and per capita biomass availability, suggesting a causal mechanism for the density effect. The effects of weather parameters explained additional variation in mean annual gosling size, although total June and July rainfall had a small additive effect on gosling size. Modelling of annual first year survival probability using mean annual gosling size as an annual covariate revealed a positive relationship, suggesting that reduced gosling growth negatively impacts recruitment.

  6. Density-dependence as a size-independent regulatory mechanism

    NARCIS (Netherlands)

    De Vladar, H.P.

    2006-01-01

    The growth function of populations is central in biomathematics. The main dogma is the existence of density-dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the Population. One important class of regulatory functions is the theta-logistic, which

  7. Variation in growth of young and adult size in barnacle geese Branta leucopsis : Evidence for density dependence

    NARCIS (Netherlands)

    Loonen, MJJE; Oosterbeek, K; Drent, RH

    1997-01-01

    A colony of Svalbard Barnacle Geese Branta leucopsis was studied near Ny Alesund, Spitsbergen. Breeding started in 1980 and the colony size followed a sigmoidal curve with little increase in numbers in the period 1992-1995. Over the period 1991-1995 gosling growth declined, mortality during growth

  8. Diameter- and current-density-dependent growth orientation of hexagonal CdSe nanowire arrays via electrodeposition

    International Nuclear Information System (INIS)

    Sun Hongyu; Li Xiaohong; Chen Yan; Guo Defeng; Xie Yanwu; Li Wei; Zhang Xiangyi; Liu Baoting

    2009-01-01

    Controlling the growth orientation of semiconductor nanowire arrays is of vital importance for their applications in the fields of nanodevices. In the present work, hexagonal CdSe nanowire arrays with various preferential growth orientations have been successfully yielded by employing the electrodeposition technique using porous alumina as templates (PATs). We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying either the nanopore diameter of the PATs or the deposited current density, which has significant effects on the optical properties of the CdSe nanowires. The present study provides an alternative approach to tuning the growth direction of electrodeposited nanowires and thus is of importance for the fabrication of nanodevices with controlled functional properties.

  9. Diameter- and current-density-dependent growth orientation of hexagonal CdSe nanowire arrays via electrodeposition

    Energy Technology Data Exchange (ETDEWEB)

    Sun Hongyu; Li Xiaohong; Chen Yan; Guo Defeng; Xie Yanwu; Li Wei; Zhang Xiangyi [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Liu Baoting, E-mail: xyzh66@ysu.edu.c [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)

    2009-10-21

    Controlling the growth orientation of semiconductor nanowire arrays is of vital importance for their applications in the fields of nanodevices. In the present work, hexagonal CdSe nanowire arrays with various preferential growth orientations have been successfully yielded by employing the electrodeposition technique using porous alumina as templates (PATs). We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying either the nanopore diameter of the PATs or the deposited current density, which has significant effects on the optical properties of the CdSe nanowires. The present study provides an alternative approach to tuning the growth direction of electrodeposited nanowires and thus is of importance for the fabrication of nanodevices with controlled functional properties.

  10. Why Density Dependent Propulsion?

    Science.gov (United States)

    Robertson, Glen A.

    2011-01-01

    In 2004 Khoury and Weltman produced a density dependent cosmology theory they call the Chameleon, as at its nature, it is hidden within known physics. The Chameleon theory has implications to dark matter/energy with universe acceleration properties, which implies a new force mechanism with ties to the far and local density environment. In this paper, the Chameleon Density Model is discussed in terms of propulsion toward new propellant-less engineering methods.

  11. Stone crayfish in the Czech Republic: how does its population density depend on basic chemical and physical properties of water?

    Directory of Open Access Journals (Sweden)

    Vlach P.

    2013-03-01

    Full Text Available The stone crayfish (Austropotamobius torrentium Schrank is one of the two native crayfish species in the Czech Republic. The populations as well as physical and chemical parameters of water (pH, conductivity, dissolved oxygen, undissolved particles, NH3, NH4+, NO2−, NO3−, phosphorus, Ca2+ and SO42 −  of 33 streams were examined to find the ecological plasticity of this crayfish and some relations between these parameters and population densities. The mentioned parameters often significantly varied at the sites. Two approaches were applied to find relations between these parameters and observed abundance. At first, the observed streams were compared using RDA (streams  ×  physical-chemical parameters. No significance was found while testing relationship between the streams grouped along the 1st axis of model and the observed abundances of stone crayfish. However, some correlations between abundance and conductivity, calcium, nitrates and sulphates were found using polynomial regression. These relationships are explicable in terms of mutual correlations, underlying geology and other factors which affect abundances. In conclusion, A. torrentium is able to inhabit waters with a large range of physical and chemical parameters of the water without any fundamental influence on population densities. Water properties play an indisputable role as limiting ecological factors at uncommon concentrations, but population densities are probably influenced much more by the types of habitats, habitat features, predation and other ecological factors.

  12. Environmental vs Demographic Stochasticity in Population Growth

    OpenAIRE

    Braumann, C. A.

    2010-01-01

    Compares the effect on population growth of envinonmental stochasticity (random environmental variations described by stochastic differential equations) with demographic stochasticity (random variations in births and deaths described by branching processes and birth-and-death processes), in the density-independent and the density-dependent cases.

  13. Size asymmetry in intraspecific competition and the density-dependence of inbreeding depression in a natural plant population: a case study in cassava (Manihot esculenta Crantz, Euphorbiaceae).

    Science.gov (United States)

    Pujol, B; McKey, D

    2006-01-01

    The effects of competition on the genetic composition of natural populations are not well understood. We combined demography and molecular genetics to study how intraspecific competition affects microevolution in cohorts of volunteer plants of cassava (Manihot esculenta) originating from seeds in slash-and-burn fields of Palikur Amerindians in French Guiana. In this clonally propagated crop, genotypic diversity is enhanced by the incorporation of volunteer plants into farmers' stocks of clonal propagules. Mortality of volunteer plants was density-dependent. Furthermore, the size asymmetry of intraspecific competition increased with local clustering of plants. Size of plants was correlated with their multilocus heterozygosity, and stronger size-dependence of survival in clusters of plants, compared with solitary plants, increased the magnitude of inbreeding depression when competition was severe. The density-dependence of inbreeding depression of volunteer plants helps explain the high heterozygosity of volunteers that survive to harvest time and thus become candidates for clonal propagation. This effect could help favour the maintenance of sex in this 'vegetatively' propagated crop plant.

  14. Density dependent effective interactions

    International Nuclear Information System (INIS)

    Dortmans, P.J.; Amos, K.

    1994-01-01

    An effective nucleon-nucleon interaction is defined by an optimal fit to select on-and half-off-of-the-energy shell t-and g-matrices determined by solutions of the Lippmann-Schwinger and Brueckner-Bethe-Goldstone equations with the Paris nucleon-nucleon interaction as input. As such, it is seen to better reproduce the interaction on which it is based than other commonly used density dependent effective interactions. The new (medium modified) effective interaction when folded with appropriate density matrices, has been used to define proton- 12 C and proton- 16 O optical potentials. With them elastic scattering data are well fit and the medium effects identifiable. 23 refs., 8 figs

  15. Simulating Population Growth.

    Science.gov (United States)

    Byington, Scott

    1997-01-01

    Presents a strategy to help students grasp the important implications of population growth. Involves an interactive demonstration that allows students to experience exponential and logistic population growth followed by a discussion of the implications of population-growth principles. (JRH)

  16. Density-dependence as a size-independent regulatory mechanism.

    Science.gov (United States)

    de Vladar, Harold P

    2006-01-21

    The growth function of populations is central in biomathematics. The main dogma is the existence of density-dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the population. One important class of regulatory functions is the theta-logistic, which generalizes the logistic equation. Using this model as a motivation, this paper introduces a simple dynamical reformulation that generalizes many growth functions. The reformulation consists of two equations, one for population size, and one for the growth rate. Furthermore, the model shows that although population is density-dependent, the dynamics of the growth rate does not depend either on population size, nor on the carrying capacity. Actually, the growth equation is uncoupled from the population size equation, and the model has only two parameters, a Malthusian parameter rho and a competition coefficient theta. Distinct sign combinations of these parameters reproduce not only the family of theta-logistics, but also the van Bertalanffy, Gompertz and Potential Growth equations, among other possibilities. It is also shown that, except for two critical points, there is a general size-scaling relation that includes those appearing in the most important allometric theories, including the recently proposed Metabolic Theory of Ecology. With this model, several issues of general interest are discussed such as the growth of animal population, extinctions, cell growth and allometry, and the effect of environment over a population.

  17. Age and growth of two populations of West Coast steenbras ...

    African Journals Online (AJOL)

    ... density-dependent competition for food, or biochemical genetic variations between the two populations, are possible reasons for the geographic differences found in the growth rates and length-at-age. Slow growth and longevity are characteristics of West Coast steenbras that make it extremely susceptible to overfishing; ...

  18. Population growth and economic growth.

    Science.gov (United States)

    Narayana, D L

    1984-01-01

    This discussion of the issues relating to the problem posed by population explosion in the developing countries and economic growth in the contemporary world covers the following: predictions of economic and social trends; the Malthusian theory of population; the classical or stationary theory of population; the medical triage model; ecological disaster; the Global 2000 study; the limits to growth; critiques of the Limits to Growth model; nonrenewable resources; food and agriculture; population explosion and stabilization; space and ocean colonization; and the limits perspective. The Limits to Growth model, a general equilibrium anti-growth model, is the gloomiest economic model ever constructed. None of the doomsday models, the Malthusian theory, the classical stationary state, the neo-Malthusian medical triage model, the Global 2000 study, are so far reaching in their consequences. The course of events that followed the publication of the "Limits to Growth" in 1972 in the form of 2 oil shocks, food shock, pollution shock, and price shock seemed to bear out formally the gloomy predictions of the thesis with a remarkable speed. The 12 years of economic experience and the knowledge of resource trends postulate that even if the economic pressures visualized by the model are at work they are neither far reaching nor so drastic. Appropriate action can solve them. There are several limitations to the Limits to Growth model. The central theme of the model, which is overshoot and collapse, is unlikely to be the course of events. The model is too aggregative to be realistic. It exaggerates the ecological disaster arising out of the exponential growth of population and industry. The gross underestimation of renewable resources is a basic flaw of the model. The most critical weakness of the model is its gross underestimation of the historical trend of technological progress and the technological possiblities within industry and agriculture. The model does correctly emphasize

  19. Modeling Exponential Population Growth

    Science.gov (United States)

    McCormick, Bonnie

    2009-01-01

    The concept of population growth patterns is a key component of understanding evolution by natural selection and population dynamics in ecosystems. The National Science Education Standards (NSES) include standards related to population growth in sections on biological evolution, interdependence of organisms, and science in personal and social…

  20. Wildlife disease elimination and density dependence

    KAUST Repository

    Potapov, A.

    2012-05-16

    Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent (DD) transmission, is ineffective for controlling diseases that are subject to frequency-dependent (FD) transmission. We investigate control for horizontally transmitted diseases with FD transmission where the control is via culling or harvest that is non-selective with respect to infection and the population can compensate through DD recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are FD. Eradication can be achieved under FD transmission when DD birth or recruitment induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination, and there is high enough transmission coefficient, application of both controls may be less efficient than vaccination alone. We illustrate the effects of these control approaches on disease prevalence for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment.

  1. density-dependent selection revisited

    Indian Academy of Sciences (India)

    Unknown

    is a more useful way of looking at density-dependent selection, and then go on ... these models was that the condition for maintenance of ... In a way, their formulation may be viewed as ... different than competition among species, and typical.

  2. Density dependent hadron field theory

    International Nuclear Information System (INIS)

    Fuchs, C.; Lenske, H.; Wolter, H.H.

    1995-01-01

    A fully covariant approach to a density dependent hadron field theory is presented. The relation between in-medium NN interactions and field-theoretical meson-nucleon vertices is discussed. The medium dependence of nuclear interactions is described by a functional dependence of the meson-nucleon vertices on the baryon field operators. As a consequence, the Euler-Lagrange equations lead to baryon rearrangement self-energies which are not obtained when only a parametric dependence of the vertices on the density is assumed. It is shown that the approach is energy-momentum conserving and thermodynamically consistent. Solutions of the field equations are studied in the mean-field approximation. Descriptions of the medium dependence in terms of the baryon scalar and vector density are investigated. Applications to infinite nuclear matter and finite nuclei are discussed. Density dependent coupling constants obtained from Dirac-Brueckner calculations with the Bonn NN potentials are used. Results from Hartree calculations for energy spectra, binding energies, and charge density distributions of 16 O, 40,48 Ca, and 208 Pb are presented. Comparisons to data strongly support the importance of rearrangement in a relativistic density dependent field theory. Most striking is the simultaneous improvement of charge radii, charge densities, and binding energies. The results indicate the appearance of a new ''Coester line'' in the nuclear matter equation of state

  3. Evolution of density-dependent movement during experimental range expansions.

    Science.gov (United States)

    Fronhofer, E A; Gut, S; Altermatt, F

    2017-12-01

    Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. Although it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intrastrain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

  4. Rapid population growth.

    Science.gov (United States)

    1972-01-01

    At the current rate of population growth, world population by 2000 is expected to reach 7 billion or more, with developing countries accounting for some 5.4 billion, and economically advanced nations accounting for 1.6 billion. 'Population explosion' is the result of falling mortality rates and continuing high birth rates. Many European countries, and Japan, have already completed what is termed as demographic transition, that is, birth rates have fallen to below 20 births per 1000 population, death rates to 10/1000 population, and annual growth rates are 1% or less; annual growth rates for less developed countries ranged from 2 to 3.5%. Less developed countries can be divided into 3 groups: 1) countries with both high birth and death rates; 2) countries with high birth rates and low death rates; and 3) countries with intermediate and declining birth rates and low death rates. Rapid population growth has serious economic consequences. It encourages inequities in income distribution; it limits rate of growth of gross national product by holding down level of savings and capital investments; it exerts pressure on agricultural production and land; and it creates unemployment problems. In addition, the quality of education for increasing number of chidren is adversely affected, as high proportions of children reduce the amount that can be spent for the education of each child out of the educational budget; the cost and adequacy of health and welfare services are affected in a similar way. Other serious consequences of rapid population growth are maternal death and illness, and physical and mental retardation of children of very poor families. It is very urgent that over a billion births be prevented in the next 30 years to reduce annual population growth rate from the current 2% to 1% per year.

  5. Population growth and consumption.

    Science.gov (United States)

    Chalkley, K

    1997-04-01

    The relationship between population growth, resource consumption, and environmental degradation is complex. The rise in "greenhouse gases" that will cause climatic change is clearly due to human activity, and pollutants are often concentrated in densely populated areas. However, even an area with a negative population growth, such as Russia, can experience severe environmental degradation due to poor management. Consumption patterns have the most effect on ozone depletion, while population growth threatens biodiversity of and within species through the destruction of ecosystems. Migration joins population growth and social factors, such as land inequality, as major causes of deforestation, and global demand for water is expected to increase faster than the rate of population growth. Coastal development and over-fishing threaten to deplete the oceans, while soil quality is threatened by inappropriate land use. Estimates of the earth's carrying capacity range from less than 3 billion to more than 44 billion people, indicating how difficult it is to assess this figure. Development efforts throughout the world may lead to human gains that will ultimately be negated by environmental losses. These factors have led to growing support for environmentally sustainable development.

  6. Perspectives on population growth.

    Science.gov (United States)

    1996-09-01

    Assume that everyone has the same information on population growth. There are many different opinions on what that information means and what should be done about it. Some people worry about current rates of growth, especially in the context of growing per capita consumption, and believe that all reasonable steps should be taken to reduce rates and stabilize population size. Others believe that growing populations can be accommodated by reducing consumption in rich countries, that technological progress will supply the new resources needed, that the development needed to support a larger population can be sustained, that large population size fosters prosperity, or that birth rates are falling and current growth is just temporary. These are all valid positions worthy of at least debate. Interest groups commonly acknowledgement population growth as a significant issue, but offer no response to it. Sometimes the issue goes unrecognized because it conflicts with a more highly valued personal agenda item. Finally, some responses come from confusion and anger rather than reasoning or self-interest. The proponents of these latter arguments bring nothing constructive to the debate.

  7. Spatial and temporal variation in the relative contribution of density dependence, climate variation and migration to fluctuations in the size of great tit populations

    NARCIS (Netherlands)

    Grøtan, V.; Sæther, B-E.; Engen, S.; van Balen, J.H.; Perdeck, A.C.; Visser, M.E.

    2009-01-01

    1. The aim of the present study is to model the stochastic variation in the size of five populations of great tit Parus major in the Netherlands, using a combination of individual-based demographic data and time series of population fluctuations. We will examine relative contribution of

  8. Density-dependent cladogenesis in birds.

    Directory of Open Access Journals (Sweden)

    Albert B Phillimore

    2008-03-01

    Full Text Available A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stronger slowdowns than small clades, even if the probability of speciation and extinction remains constant through time. This is a consequence of exponential growth: clades, which, by chance, diversify at above the average rate early in their history, will tend to be large. They will also tend to regress back to the average diversification rate later on, and therefore show a slowdown. We conducted a meta-analysis of the distribution of speciation events through time, focusing on sequence-based phylogenies for 45 clades of birds. Thirteen of the 23 clades (57% that include more than 20 species show significant slowdowns. The high frequency of slowdowns observed in large clades is even more extreme than expected under a purely stochastic constant-rate model, but is consistent with the adaptive radiation model. Taken together, our data strongly support a model of density-dependent speciation in birds, whereby speciation slows as ecological opportunities and geographical space place limits on clade growth.

  9. Anthropogenically-Mediated Density Dependence in a Declining Farmland Bird.

    Directory of Open Access Journals (Sweden)

    Jenny C Dunn

    Full Text Available Land management intrinsically influences the distribution of animals and can consequently alter the potential for density-dependent processes to act within populations. For declining species, high densities of breeding territories are typically considered to represent productive populations. However, as density-dependent effects of food limitation or predator pressure may occur (especially when species are dependent upon separate nesting and foraging habitats, high territory density may limit per-capita productivity. Here, we use a declining but widespread European farmland bird, the yellowhammer Emberiza citrinella L., as a model system to test whether higher territory densities result in lower fledging success, parental provisioning rates or nestling growth rates compared to lower densities. Organic landscapes held higher territory densities, but nests on organic farms fledged fewer nestlings, translating to a 5 times higher rate of population shrinkage on organic farms compared to conventional. In addition, when parental provisioning behaviour was not restricted by predation risk (i.e., at times of low corvid activity, nestling provisioning rates were higher at lower territory densities, resulting in a much greater increase in nestling mass in low density areas, suggesting that food limitation occurred at high densities. These findings in turn suggest an ecological trap, whereby preferred nesting habitat does not provide sufficient food for rearing nestlings at high population density, creating a population sink. Habitat management for farmland birds should focus not simply on creating a high nesting density, but also on ensuring heterogeneous habitats to provide food resources in close proximity to nesting birds, even if this occurs through potentially restricting overall nest density but increasing population-level breeding success.

  10. Experimental examination of intraspecific density-dependent competition during the breeding period in monarch butterflies (Danaus plexippus.

    Directory of Open Access Journals (Sweden)

    D T Tyler Flockhart

    Full Text Available A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.

  11. [Economic growth with zero population growth and with declining population].

    Science.gov (United States)

    Kurz, R

    1982-05-01

    The effects of both zero population growth and a declining population on economic growth are considered. Although the neoclassical theory of economic growth leads to optimistic results in such cases, the author suggests that this theory cannot be used as a basis for political action. The need for further research into the economic effects of a stationary or declining population is stressed. (summary in ENG)

  12. Prevalence and strength of density-dependent tree recruitment

    Science.gov (United States)

    Kai Zhu; Christopher W. Woodall; Joao V.D. Monteiro; James S. Clark

    2015-01-01

    Density dependence could maintain diversity in forests, but studies continue to disagree on its role. Part of the disagreement results from the fact that different studies have evaluated different responses (survival, recruitment, or growth) of different stages (seeds, seedlings, or adults) to different inputs (density of seedlings, density or distance to adults). Most...

  13. Population growth, poverty and health.

    Science.gov (United States)

    Kibirige, J S

    1997-07-01

    One of the most popular explanations for the many problems that face Africa is population growth. Africa's population has doubled since 1960. Africa has the highest fertility rate in the world and the rate of population growth is higher than in any other region. At the same time, Africa faces a social and economic situation that is viewed by many as alarming. Among the problems that devastate Africa is that of persistent poor health. Africa has lower life expectancy, higher mortality rates and is affected by more disease and illness conditions than any other region. Focusing on sub-Saharan Africa, this paper examines the relationship between population growth, poverty and poor health. While most analyses have focused on population growth as an original cause of poverty and underdevelopment, this paper argues that while both population growth and poor health play a significant role in exacerbating the problem of poverty, they are themselves primary consequences of poverty rather than its cause.

  14. Density dependence of line intensities and application to plasma diagnostics

    International Nuclear Information System (INIS)

    Masai, Kuniaki.

    1993-02-01

    Electron density dependence of spectral lines are discussed in view of application to density diagnostics of plasmas. The dependence arises from competitive level population processes, radiative and collisional transitions from the excited states. Results of the measurement on tokamak plasmas are presented to demonstrate the usefulness of line intensity ratios for density diagnostics. Also general characteristics related to density dependence are discussed with atomic-number scaling for H-like and He-like systems to be helpful for application to higher density plasmas. (author)

  15. Experimental evidence for density dependence of reproduction in great tits

    NARCIS (Netherlands)

    Both, Christiaan

    1998-01-01

    1.  Density dependence of avian reproduction has often been analysed using correlations between annual mean reproductive output and population density. Experiments are necessary to prove that density is the cause of the observed patterns, but so far, three out of four experimental studies do not

  16. Experimental evidence for density dependence of reproduction in great tits

    NARCIS (Netherlands)

    Both, C.

    1998-01-01

    1. Density dependence of avian reproduction has often been analysed using correlations between annual mean reproductive output and population density. Experiments are necessary to prove that density is the cause of the observed patterns, but so far, three out of four experimental studies do not

  17. Population growth and infant mortality

    OpenAIRE

    Fabella, Christina

    2008-01-01

    The relationship between population growth and economic outcomes is an issue of great policy significance. In the era of the Millennium Development Goals, poverty and its correlates have become the compelling issues. Economic growth may not automatically translate into reductions in poverty and its correlates (may not trickle down) if income distribution is at the same time worsening. We therefore investigate the direct effect of population growth on infant mortality for various income catego...

  18. City Population Growth and Economic Growth

    DEFF Research Database (Denmark)

    Freire-Gibb, L. Carlos

    2008-01-01

    This article looks at the relationship between city population growth (intimately related to population proximity), and economic development. The hypothesis is that wherever dynamic and inclusive networks exist, there are more opportunities for economic development in this place. When these types...... of networks choose a tool (project, policy) to implement in the city, success will be more likely. Furthermore, virtuous circles will arise. The author gives an overview of two historical cases in urban growth, in Europe (1200-1800) and the U.S.A. (1800 to today)....

  19. How can we model selectively neutral density dependence in evolutionary games.

    Science.gov (United States)

    Argasinski, Krzysztof; Kozłowski, Jan

    2008-03-01

    The problem of density dependence appears in all approaches to the modelling of population dynamics. It is pertinent to classic models (i.e., Lotka-Volterra's), and also population genetics and game theoretical models related to the replicator dynamics. There is no density dependence in the classic formulation of replicator dynamics, which means that population size may grow to infinity. Therefore the question arises: How is unlimited population growth suppressed in frequency-dependent models? Two categories of solutions can be found in the literature. In the first, replicator dynamics is independent of background fitness. In the second type of solution, a multiplicative suppression coefficient is used, as in a logistic equation. Both approaches have disadvantages. The first one is incompatible with the methods of life history theory and basic probabilistic intuitions. The logistic type of suppression of per capita growth rate stops trajectories of selection when population size reaches the maximal value (carrying capacity); hence this method does not satisfy selective neutrality. To overcome these difficulties, we must explicitly consider turn-over of individuals dependent on mortality rate. This new approach leads to two interesting predictions. First, the equilibrium value of population size is lower than carrying capacity and depends on the mortality rate. Second, although the phase portrait of selection trajectories is the same as in density-independent replicator dynamics, pace of selection slows down when population size approaches equilibrium, and then remains constant and dependent on the rate of turn-over of individuals.

  20. and density-dependent quark mass model

    Indian Academy of Sciences (India)

    Since a fair proportion of such dense proto stars are likely to be ... the temperature- and density-dependent quark mass (TDDQM) model which we had em- ployed in .... instead of Tc ~170 MeV which is a favoured value for the ud matter [26].

  1. Density-dependent effects on physical condition and reproduction in North American elk: an experimental test.

    Science.gov (United States)

    Kelley M. Stewart; R. Terry Bowyer; Brian L. Dick; Bruce K. Johnson; John G. Kie

    2005-01-01

    Density dependence plays a key role in life-history characteristics and population ecology of large, herbivorous mammals. We designed a manipulative experiment to test hypotheses relating effects of density-dependent mechanisms on physical condition and fecundity of North American elk (Cervus elaphus) by creating populations at low and high density...

  2. Canada's population: growth and dualism.

    Science.gov (United States)

    Beaujot, R P

    1978-04-01

    In Canada the current 1.3% population growth rate is causing some concern. Those concerned argue that such a rate of growth in combination with high levels of consumption could jeopardize the country's resource base and its comfortable style of living. Many Canadians are questioning high levels of immigration, for now that the fertility level is below replacement level, net immigration contributes substantially to population growth (over 1/3 in 1976). The growing proportion of non-Europeans among recent immigrants is causing resentment, and, in a tight job market, immigrants are regarded as threats to the World War 2 baby boom cohort who are now at working ages. The baby boom generation also puts stress on housing and health services, and it will increase the need for pension checks as it ages. Although French fertility is no longer high and immigration is no longer dominated by the British, the French group's 200-year struggle to preserve its identity continues on in the current effort of the Quebec government to enforce the use of French language by law within that province. Geography and climate dictate another demographic fact that divides the country and pervades its history. In addition to intense regionalism, uneven population distribution is responsible for 2 other concerns: the rapid growth of several already large cities and depopulation of many small communities. Focus in this discussion is on Canada's population growth in the past and as projected for the future, historical and current fertility, mortality and immigration trends, the search for a new immigration policy, the impact of the baby boom generation on the population's age structure and the problems this creates, and recent shifts in population distribution and in the country's ethnic and linguistic makeup. The population policy proposals evolved thus far involve to a great extent the use of immigration as a lever for achieving given population objectives.

  3. Life-history and spatial determinants of somatic growth dynamics in Komodo dragon populations.

    Science.gov (United States)

    Laver, Rebecca J; Purwandana, Deni; Ariefiandy, Achmad; Imansyah, Jeri; Forsyth, David; Ciofi, Claudio; Jessop, Tim S

    2012-01-01

    Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world's largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs) and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species.

  4. Life-history and spatial determinants of somatic growth dynamics in Komodo dragon populations.

    Directory of Open Access Journals (Sweden)

    Rebecca J Laver

    Full Text Available Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world's largest lizard the Komodo dragon (Varanus komodoensis. The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species.

  5. Life-History and Spatial Determinants of Somatic Growth Dynamics in Komodo Dragon Populations

    Science.gov (United States)

    Laver, Rebecca J.; Purwandana, Deni; Ariefiandy, Achmad; Imansyah, Jeri; Forsyth, David; Ciofi, Claudio; Jessop, Tim S.

    2012-01-01

    Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world’s largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs) and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species. PMID:23028983

  6. Long-term persistence, density dependence and effects of climate change on rosyside dace (Cyprinidae)

    Science.gov (United States)

    Gary D. Grossman; Gary Sundin; Robert E. Ratajczak

    2016-01-01

    SummaryWe used long-term population data for rosyside dace (Clinostomus funduloides), a numerically dominant member of a stochastically organised fish assemblage, to evaluate the relative importance of density-dependent and density-independent processes to population...

  7. The outlook for population growth.

    Science.gov (United States)

    Lee, Ronald

    2011-07-29

    Projections of population size, growth rates, and age distribution, although extending to distant horizons, shape policies today for the economy, environment, and government programs such as public pensions and health care. The projections can lead to costly policy adjustments, which in turn can cause political and economic turmoil. The United Nations projects global population to grow from about 7 billion today to 9.3 billion in 2050 and 10.1 billion in 2100, while the Old Age Dependency Ratio doubles by 2050 and triples by 2100. How are such population projections made, and how certain can we be about the trends they foresee?

  8. Modeling Population Growth and Extinction

    Science.gov (United States)

    Gordon, Sheldon P.

    2009-01-01

    The exponential growth model and the logistic model typically introduced in the mathematics curriculum presume that a population grows exclusively. In reality, species can also die out and more sophisticated models that take the possibility of extinction into account are needed. In this article, two extensions of the logistic model are considered,…

  9. Population growth and its implications

    Directory of Open Access Journals (Sweden)

    Badii, M. H.

    2005-01-01

    Full Text Available Human populations have grown at an unprecedented rate over the past three centuries. By 2001, the world population stood at 6.2 billion people. If the current trend of 1.4 % per year persists, the population will double in 51years. Most of that growth will occur in the less developed countries of Asia, Africa, and Latin America. There is a serious concern that the number of humans in the world and our impact on the environment will overload the life support systems of the earth. The crude birth rate is the number of births in a year divided by the average population. A more accurate measure of growth is the general fertility rate, which takes into account the age structure and fecundity of the population. The crude birth rate minus the crude death rate gives the rate of natural increase. When this rate reaches a level at which people are just replacing themselves, zero population growth is achieved. In the more highly developed countries of the world, growth has slowed are even reversed in recent years so that without immigration from other areas, population would be declining. The change from high birth and death rates that accompanies in industrialization is called a demographic transition. Many developing nations have already begun this transition. Death rates have fallen, but birth rates remain high. Some demographers believe that as infant mortality drops and economic development progresses so that people in these countries can be sure of secure future, they will complete the transition to a stable population or a high standard living. While larger populations bring many problems, they also may be a valuable resource of energy, intelligence, and enterprise that will make it possible to overcome resource limitation problems. A social just view argues that a more equitable distribution of wealth might reduce both excess population growth and environmental degradation. We have many more options now for controlling fertility than were available

  10. Political economy of population growth.

    Science.gov (United States)

    Mehta, S; Mehta, H S

    1987-01-01

    Tracing the origin of political economy as a class-science, this paper focuses on the political economy of population growth. Exposing the limitations of Malthusian ideas and their invalidity even for the capitalist economies, it discusses the subsequent revival of the Malthusian model during the period of de-colonization and the misinterpretation of the relationship between population growth and development in the developing and developed countries. Taking India, China, and Japan as some case studies, the paper examines the relationship between birth rate levels and some correlates. It elaborates on the Indian experience, emphasizing the association of population growth with poverty and unemployment and lays bare some of the hidden causes of these phenomena. The authors examine some interstate variations in India and identify constraints and prospects of the existing population policy. The paper proposes outlines of a democratic population policy as an integral part of India's development strategy which should recognize human beings not simply as consumers but also as producers of material values. It pleads for 1) restructuring of property relations; 2) bringing down the mortality rates and raising of the literacy levels, especially among females; and 3) improving nutritional levels, as prerequisites for bringing down birth rates.

  11. Experimental evidence for density-dependent reproduction in a cooperatively breeding passerine

    NARCIS (Netherlands)

    Brouwer, Lyanne; Tinbergen, Joost M.; Both, Christiaan; Bristol, Rachel; Richardson, David S.; Komdeur, Jan; Sauer, J.R.

    Temporal variation in survival, fecundity, and dispersal rates is associated with density-dependent and density-independent processes. Stable natural populations are expected to be regulated by density-dependent factors. However, detecting this by investigating natural variation in density is

  12. Modes of competition: adding and removing brown trout in the wild to understand the mechanisms of density-dependence.

    Directory of Open Access Journals (Sweden)

    Rasmus Kaspersson

    Full Text Available While the prevalence of density-dependence is well-established in population ecology, few field studies have investigated its underlying mechanisms and their relative population-level importance. Here, we address these issues, and more specifically, how differences in body-size influence population regulation. For this purpose, two experiments were performed in a small coastal stream on the Swedish west coast, using juvenile brown trout (Salmo trutta as a study species. We manipulated densities of large and small individuals, and observed effects on survival, migration, condition and individual growth rate in a target group of intermediate-sized individuals. The generality of the response was investigated by reducing population densities below and increasing above the natural levels (removing and adding large and small individuals. Reducing the density (relaxing the intensity of competition had no influence on the response variables, suggesting that stream productivity was not a limiting factor at natural population density. Addition of large individuals resulted in a negative density-dependent response, while no effect was detected when adding small individuals or when maintaining the natural population structure. We found that the density-dependent response was revealed as reduced growth rate rather than increased mortality and movement, an effect that may arise from exclusion to suboptimal habitats or increased stress levels among inferior individuals. Our findings confirm the notion of interference competition as the primary mode of competition in juvenile salmonids, and also show that the feedback-mechanisms of density-dependence are primarily acting when increasing densities above their natural levels.

  13. Density dependence drives habitat production and survivorship of Acropora cervicornis used for restoration on a Caribbean coral reef

    Directory of Open Access Journals (Sweden)

    Mark C Ladd

    2016-12-01

    Full Text Available AbstractCoral restoration is gaining traction as a viable strategy to help restore degraded reefs. While the nascent field of coral restoration has rapidly progressed in the past decade, significant knowledge gaps remain regarding the drivers of restoration success that may impede our ability to effectively restore coral reef communities. Here, we conducted a field experiment to investigate the influence of coral density on the growth, habitat production, and survival of corals outplanted for restoration. We used nursery-raised colonies of Acropora cervicornis to experimentally establish populations of corals with either 3, 6, 12, or 24 corals within 4m2 plots, generating a gradient of coral densities ranging from 0.75 corals m-2 to 12 corals m-2. After 13 months we found that density had a significant effect on the growth, habitat production, and survivorship of restored corals. We found that coral survivorship increased as colony density decreased. Importantly, the signal of density dependent effects was context dependent. Our data suggest that positive density dependent effects influenced habitat production at densities of 3 corals m-2, but further increases in density resulted in negative density dependent effects with decreasing growth and survivorship of corals. These findings highlight the importance of density dependence for coral restoration planning and demonstrate the need to evaluate the influence of density for other coral species used for restoration. Further work focused on the mechanisms causing density dependence such as increased herbivory, rapid disease transmission, or altered predation rates are important next steps to advance our ability to effectively restore coral reefs.

  14. Does density-dependent diversification mirror ecological competitive exclusion?

    Directory of Open Access Journals (Sweden)

    Melanie J Monroe

    Full Text Available Density-dependence is a term used in ecology to describe processes such as birth and death rates that are regulated by the number of individuals in a population. Evolutionary biologists have borrowed the term to describe decreasing rates of species accumulation, suggesting that speciation and extinction rates depend on the total number of species in a clade. If this analogy with ecological density-dependence holds, diversification of clades is restricted because species compete for limited resources. We hypothesize that such competition should not only affect numbers of species, but also prevent species from being phenotypically similar. Here, we present a method to detect whether competitive interactions between species have ordered phenotypic traits on a phylogeny, assuming that competition prevents related species from having identical trait values. We use the method to analyze clades of birds and mammals, with body size as the phenotypic trait. We find no sign that competition has prevented species from having the same body size. Thus, since body size is a key ecological trait and competition does not seem to be responsible for differences in body size between species, we conclude that the diversification slowdown that is prevalent in these clades is unlikely due to the ecological interference implied by the term density dependence.

  15. Environmental impact of population growth

    Science.gov (United States)

    Naylor, Rosamond; Matson, Pamela

    Earth's population currently numbers 5.4 billion; even given optimistic assumptions for reduction in growth rates, the number will double by the middle of the next century with most of the increase in the developing countries. Rapid population growth in the developing world raises the fundamental dilemma of how to alleviate chronic hunger and poverty in the short run while preserving the atmosphere and ecosystem services required for long-term human and biospheric sustenance. This dilemma, and the compromises required to solve it, were discussed by twenty-five researchers from five countries at the Aspen Global Change Institute 1992 Summer Science Session III, Food, Conservation, and Global Environmental Change: Is Compromise Possible?, held from August 16 to 28, in Aspen, Colo.

  16. Population growth and economic development.

    Science.gov (United States)

    Corbridge, S

    1989-01-01

    The Malthusian and neo-Malthusian approaches to the role of population growth in economic development and resource depletion are briefly outlined. Three arguments are then presented that emphasize demographic determinism, empirical evidence, and cause and effect. The author concludes that non-coercive family planning programs may have a role to play in countries that are unable to reduce inequalities, particularly for the poor and for women.

  17. Demographic models reveal the shape of density dependence for a specialist insect herbivore on variable host plants.

    Science.gov (United States)

    Miller, Tom E X

    2007-07-01

    1. It is widely accepted that density-dependent processes play an important role in most natural populations. However, persistent challenges in our understanding of density-dependent population dynamics include evaluating the shape of the relationship between density and demographic rates (linear, concave, convex), and identifying extrinsic factors that can mediate this relationship. 2. I studied the population dynamics of the cactus bug Narnia pallidicornis on host plants (Opuntia imbricata) that varied naturally in relative reproductive effort (RRE, the proportion of meristems allocated to reproduction), an important plant quality trait. I manipulated per-plant cactus bug densities, quantified subsequent dynamics, and fit stage-structured models to the experimental data to ask if and how density influences demographic parameters. 3. In the field experiment, I found that populations with variable starting densities quickly converged upon similar growth trajectories. In the model-fitting analyses, the data strongly supported a model that defined the juvenile cactus bug retention parameter (joint probability of surviving and not dispersing) as a nonlinear decreasing function of density. The estimated shape of this relationship shifted from concave to convex with increasing host-plant RRE. 4. The results demonstrate that host-plant traits are critical sources of variation in the strength and shape of density dependence in insects, and highlight the utility of integrated experimental-theoretical approaches for identifying processes underlying patterns of change in natural populations.

  18. Population Growth and National Population Policy of India

    Science.gov (United States)

    Thukral, A. K.; Singh, B. P.

    2008-01-01

    The population growth in India may overtake China by the year 2030. The National Population Policy of India targets population stabilization in India by the year 2045. The present paper carries out objective analysis of the population growth in India in terms of change in specific growth. At the present rate of specific growth rate decline, the population by the end of the century will be 2.49 billion. For the population to achieve zero growth by the year 2045, a decline in specific growth rate will have to be achieved at the rate of 0.000428 per year.

  19. Nuclear spectroscopy with density dependent effective interactions

    International Nuclear Information System (INIS)

    Krewald, S.

    1976-07-01

    The paper investigates excited nuclear states with density-dependent effective interactions. In the first part of the paper, the structure and the width of the multipole giant resonances discovered in 1972 are derived microscopically. Because of their high excitation energy, these giant resonances are unstable to particle emission and thus often have a considerable decay width. Due to their collective structure, the giant resonances can be described by RPA in good approximation. In this paper, the continuum RPA is applied to the spherical nuclei 16 O, 40 Ca, 90 Zr and 208 Pb. The experimental centroid energy are in very good agreement with the calculations performed in the paper. (orig./WL) [de

  20. Intercohort density dependence drives brown trout habitat selection

    Science.gov (United States)

    Ayllón, Daniel; Nicola, Graciela G.; Parra, Irene; Elvira, Benigno; Almodóvar, Ana

    2013-01-01

    Habitat selection can be viewed as an emergent property of the quality and availability of habitat but also of the number of individuals and the way they compete for its use. Consequently, habitat selection can change across years due to fluctuating resources or to changes in population numbers. However, habitat selection predictive models often do not account for ecological dynamics, especially density dependent processes. In stage-structured population, the strength of density dependent interactions between individuals of different age classes can exert a profound influence on population trajectories and evolutionary processes. In this study, we aimed to assess the effects of fluctuating densities of both older and younger competing life stages on the habitat selection patterns (described as univariate and multivariate resource selection functions) of young-of-the-year, juvenile and adult brown trout Salmo trutta. We observed all age classes were selective in habitat choice but changed their selection patterns across years consistently with variations in the densities of older but not of younger age classes. Trout of an age increased selectivity for positions highly selected by older individuals when their density decreased, but this pattern did not hold when the density of younger age classes varied. It suggests that younger individuals are dominated by older ones but can expand their range of selected habitats when density of competitors decreases, while older trout do not seem to consider the density of younger individuals when distributing themselves even though they can negatively affect their final performance. Since these results may entail critical implications for conservation and management practices based on habitat selection models, further research should involve a wider range of river typologies and/or longer time frames to fully understand the patterns of and the mechanisms underlying the operation of density dependence on brown trout habitat

  1. Development and application of a density dependent matrix ...

    Science.gov (United States)

    Ranging along the Atlantic coast from US Florida to the Maritime Provinces of Canada, the Atlantic killifish (Fundulus heteroclitus) is an important and well-studied model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems. Matrix population models are useful tools for ecological risk assessment because they integrate effects across the life cycle, provide a linkage between endpoints observed in the individual and ecological risk to the population as a whole, and project outcomes for many generations in the future. We developed a density dependent matrix population model for Atlantic killifish by modifying a model developed for fathead minnow (Pimephales promelas) that has proved to be extremely useful, e.g. to incorporate data from laboratory studies and project effects of endocrine disrupting chemicals. We developed a size-structured model (as opposed to one that is based upon developmental stages or age class structure) so that we could readily incorporate output from a Dynamic Energy Budget (DEB) model, currently under development. Due to a lack of sufficient data to accurately define killifish responses to density dependence, we tested a number of scenarios realistic for other fish species in order to demonstrate the outcome of including this ecologically important factor. We applied the model using published data for killifish exposed to dioxin-like compounds, and compared our results to those using

  2. A stochastic population model to evaluate Moapa dace (Moapa coriacea) population growth under alternative management scenarios

    Science.gov (United States)

    Perry, Russell W.; Jones, Edward; Scoppettone, G. Gary

    2015-07-14

    The primary goal of this research project was to evaluate the response of Moapa dace (Moapa coriacea) to the potential effects of changes in the amount of available habitat due to human influences such as ground water pumping, barriers to movement, and extirpation of Moapa dace from the mainstem Muddy River. To understand how these factors affect Moapa dace populations and to provide a tool to guide recovery actions, we developed a stochastic model to simulate Moapa dace population dynamics. Specifically, we developed an individual based model (IBM) to incorporate the critical components that drive Moapa dace population dynamics. Our model is composed of several interlinked submodels that describe changes in Moapa dace habitat as translated into carrying capacity, the influence of carrying capacity on demographic rates of dace, and the consequent effect on equilibrium population sizes. The model is spatially explicit and represents the stream network as eight discrete stream segments. The model operates at a monthly time step to incorporate seasonally varying reproduction. Growth rates of individuals vary among stream segments, with growth rates increasing along a headwater to mainstem gradient. Movement and survival of individuals are driven by density-dependent relationships that are influenced by the carrying capacity of each stream segment.

  3. Experimental evidence that density dependence strongly influences plant invasions through fragmented landscapes.

    Science.gov (United States)

    Williams, Jennifer L; Levine, Jonathan M

    2018-04-01

    Populations of range expanding species encounter patches of both favorable and unfavorable habitat as they spread across landscapes. Theory shows that increasing patchiness slows the spread of populations modeled with continuously varying population density when dispersal is not influence by the environment or individual behavior. However, as is found in uniformly favorable landscapes, spread remains driven by fecundity and dispersal from low density individuals at the invasion front. In contrast, when modeled populations are composed of discrete individuals, patchiness causes populations to build up to high density before dispersing past unsuitable habitat, introducing an important influence of density dependence on spread velocity. To test the hypothesized interaction between habitat patchiness and density dependence, we simultaneously manipulated these factors in a greenhouse system of annual plants spreading through replicated experimental landscapes. We found that increasing the size of gaps and amplifying the strength of density dependence both slowed spread velocity, but contrary to predictions, the effect of amplified density dependence was similar across all landscape types. Our results demonstrate that the discrete nature of individuals in spreading populations has a strong influence on how both landscape patchiness and density dependence influence spread through demographic and dispersal stochasticity. Both finiteness and landscape structure should be critical components to theoretical predictions of future spread for range expanding native species or invasive species colonizing new habitat. © 2018 by the Ecological Society of America.

  4. Wildlife disease elimination and density dependence

    KAUST Repository

    Potapov, A.; Merrill, E.; Lewis, M. A.

    2012-01-01

    Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective

  5. Hispanic Population Growth and Rural Income Inequality

    Science.gov (United States)

    Parrado, Emilio A.; Kandel, William A.

    2010-01-01

    We analyze the relationship between Hispanic population growth and changes in U.S. rural income inequality from 1990 through 2000. Applying comparative approaches used for urban areas we disentangle Hispanic population growth's contribution to inequality by comparing and statistically modeling changes in the family income Gini coefficient across…

  6. Environmental degradation, energy consumption, population growth ...

    African Journals Online (AJOL)

    Based on the result, there is no evidence of unidirectional causality running from CO2 emissions and energy consumption to economic growth and strong unidirectional causality running from CO2 emissions, energy consumption and economic growth to population growth was found. The long run and short run estimates ...

  7. Density dependence of dielectronic recombination in selenium

    International Nuclear Information System (INIS)

    Hagelstein, P.L.; Rosen, M.D.; Jacobs, V.L.

    1986-01-01

    Dielectronic recombination has been found to be the dominant recombination process in the determination of the ionization balance of selenium near the Ne-like sequence under conditions relevant to the exploding-foil EUV laser plasmas. The dielectronic recombination process tends to populate excited levels, and these levels in turn are more susceptible to subsequent excitation and ionization than are the ground-state ions. If one defines an effective recombination rate which includes, in addition to the primary recombination, the subsequent excitation and ionization of the additional excited-state population due to the primary recombination, then this effective recombination rate can be density-sensitive at relatively low electron density. We present results for this effective dielectronic recombination rate at an electron density of 3 x 10/sup 20/ electrons/cm 3 for recombination from Ne-like to Na-like selenium and from F-like to Ne-like selenium. In the former case, the effective recombination rate coefficient is found to be 1.8 x 10/sup -11/ cm 3 /sec at 1.0 keV, which is to be compared with the zero-density value of 2.8 x 10/sup -11/ cm 3 /sec. In the latter case (F-like to Ne-like), the effective recombination rate coefficient is found to be 1.3 x 10/sup -11/ cm 3 /sec, which is substantially reduced from the zero-density result of 3.3 x 10/sup -11/ cm 3 /sec. We have examined the effects of dielectronic recombination on the laser gain of the dominant Ne-like 3p-3s transitions and have compared our results with those presented by Whitten et al. [Phys. Rev. A 33, 2171 (1986)

  8. Growth rate, population entropy, and perturbation theory.

    OpenAIRE

    Demetrius, L.

    1989-01-01

    This paper is concerned with the connection between two classes of population variables: measures of population growth rate—the Malthusian parameter, the net reproduction rate, the gross reproduction rate, and the mean life expectancy; and measures of demographic heterogeneity—population entropy. It is shown that the entropy functions predict the response of the growth rate parameters to perturbations in the age-specific fecundity and mortality schedule. These results are invoked to introduce...

  9. On population growth near protected areas.

    Directory of Open Access Journals (Sweden)

    Lucas N Joppa

    Full Text Available Protected areas are the first, and often only, line of defense in efforts to conserve biodiversity. They might be detrimental or beneficial to rural communities depending on how they alter economic opportunities and access to natural resources. As such, protected areas may attract or repel human settlement. Disproportionate increases in population growth near protected area boundaries may threaten their ability to conserve biodiversity.Using decadal population datasets, we analyze population growth across 45 countries and 304 protected areas. We find no evidence for population growth near protected areas to be greater than growth of rural areas in the same country. Furthermore, we argue that what growth does occur near protected areas likely results from a general expansion of nearby population centers.Our results contradict those from a recent study by Wittemyer et al., who claim overwhelming evidence for increased human population growth near protected areas. To understand the disagreement, we re-analyzed the protected areas in Wittemyer et al.'s paper. Their results are simply artifacts of mixing two incompatible datasets. Protected areas may experience unusual population pressures near their edges; indeed, individual case studies provide examples. There is no evidence, however, of a general pattern of disproportionate population growth near protected areas.

  10. Density-dependent habitat selection and performance by a large mobile reef fish.

    Science.gov (United States)

    Lindberg, William J; Frazer, Thomas K; Portier, Kenneth M; Vose, Frederic; Loftin, James; Murie, Debra J; Mason, Doran M; Nagy, Brian; Hart, Mary K

    2006-04-01

    condition. Density-dependent habitat selection for shelter and individual growth dynamics were therefore interdependent ecological processes that help to explain how patchy reef habitat sustains gag production. Moreover, gag selected shelter at the expense of maximizing their growth. Thus, mobile reef fishes could experience density-dependent effects on growth, survival, and/or reproduction (i.e., demographic parameters) despite reduced stock sizes as a consequence of fishing.

  11. Kinetic Model of Growth of Arthropoda Populations

    Science.gov (United States)

    Ershov, Yu. A.; Kuznetsov, M. A.

    2018-05-01

    Kinetic equations were derived for calculating the growth of crustacean populations ( Crustacea) based on the biological growth model suggested earlier using shrimp ( Caridea) populations as an example. The development cycle of successive stages for populations can be represented in the form of quasi-chemical equations. The kinetic equations that describe the development cycle of crustaceans allow quantitative prediction of the development of populations depending on conditions. In contrast to extrapolation-simulation models, in the developed kinetic model of biological growth the kinetic parameters are the experimental characteristics of population growth. Verification and parametric identification of the developed model on the basis of the experimental data showed agreement with experiment within the error of the measurement technique.

  12. Population growth changes targets for immunization.

    Science.gov (United States)

    Tuljapurkar, S; John, A M

    1995-01-01

    The faster the rate of population growth in developing countries, the less likely it is that current protocols for immunization against measles, rubella, and mumps will eradicate these childhood diseases. Standard protocols (timing, percentage of children to be immunized) do not take into account the rapid rates of population growth in developing countries (3.0% per year on average in sub-Saharan Africa and 2.0% in the rest of Africa, in Latin America, and in Asia, excluding China). Most public health planning models in this area were created based on static infant populations. The World Health Organization advises vaccinating at least 85% of children aged 6 to 9 months, a 3-month immunization window during which maternal antibodies are low (so the vaccination takes) and herd immunity is high (the probability that a child will encounter the disease is low because most children have been immunized). In practice, the immunization window in developing countries is 1 year or more. More susceptible children are present than assumed by the models. A larger number of susceptible babies are added each year during rapid population growth. As the age range for immunization widens, a higher percentage of children must be vaccinated to eradicate disease (chart). The proportion of each birth cohort that must be immunized rises as the population growth rate increases. At zero population growth, 94% must be vaccinated; at population growth rates greater than 3%, 98% must be vaccinated.

  13. Density dependence triggers runaway selection of reduced senescence.

    Directory of Open Access Journals (Sweden)

    Robert M Seymour

    2007-12-01

    Full Text Available In the presence of exogenous mortality risks, future reproduction by an individual is worth less than present reproduction to its fitness. Senescent aging thus results inevitably from transferring net fertility into younger ages. Some long-lived organisms appear to defy theory, however, presenting negligible senescence (e.g., hydra and extended lifespans (e.g., Bristlecone Pine. Here, we investigate the possibility that the onset of vitality loss can be delayed indefinitely, even accepting the abundant evidence that reproduction is intrinsically costly to survival. For an environment with constant hazard, we establish that natural selection itself contributes to increasing density-dependent recruitment losses. We then develop a generalized model of accelerating vitality loss for analyzing fitness optima as a tradeoff between compression and spread in the age profile of net fertility. Across a realistic spectrum of senescent age profiles, density regulation of recruitment can trigger runaway selection for ever-reducing senescence. This novel prediction applies without requirement for special life-history characteristics such as indeterminate somatic growth or increasing fecundity with age. The evolution of nonsenescence from senescence is robust to the presence of exogenous adult mortality, which tends instead to increase the age-independent component of vitality loss. We simulate examples of runaway selection leading to negligible senescence and even intrinsic immortality.

  14. The end of world population growth

    NARCIS (Netherlands)

    Lutz, W; Sanderson, W; Scherbov, S

    2001-01-01

    There has been enormous concern about the consequences of human population growth for the environment and for social and economic development. But this growth is likely to come to an end in the foreseeable future. Improving on earlier methods of probabilistic forecasting(1), here we show that there

  15. Population growth and development: the Kenyan experience.

    Science.gov (United States)

    Nyamwange, M

    1995-01-01

    Rapid population growth in Kenya and high fertility impacts negatively on economic development. The growth and high fertility results in declines in gross national product, per capita food consumption, and land quality; a high dependency ratio; urban crowding; and inadequate health systems. East Africa has the highest crude birth rates in Africa, and Kenya has the highest birth rate of 54/1000 population in East Africa. The African crude death rate is 50% higher than the world average, but Kenya's death rate is the lowest in East Africa and comparable to North American and European death rates. Kenya has the highest rate of natural increase of about 4%. Population growth rates rose over the decades. Kenya's average population density is well above the sub-Saharan African average and much lower than very high density countries. Population is unequally distributed. Regional densities are widely divergent, and the highest densities in Western province are well above densities in Rwanda and Burundi. Urban growth has increased, as has migration to urban areas. Nairobi has 57% of urban population. Improved health and nutrition have contributed to increased life expectancy. The desired family size is large. The impact of demographic factors on economic conditions is evident in the decline in gross national product per capita growth to under 1% during 1972-88. A slight upswing occurred during 1988-93, but other crises are emerging. Food production has not kept pace with population growth. Production has been low due to serious land degradation, short fallow periods, and traditional farming practices. Population pressure has forced families to shift agriculture onto marginal lands, and desertification has increased. A growing proportion of the population is unemployed or underemployed. Population programs should address the underlying conditions for fertility decline.

  16. Detection of density dependence requires density manipulations and calculation of lambda.

    Science.gov (United States)

    Fowler, N L; Overath, R Deborah; Pease, Craig M

    2006-03-01

    To investigate density-dependent population regulation in the perennial bunchgrass Bouteloua rigidiseta, we experimentally manipulated density by removing adults or adding seeds to replicate quadrats in a natural population for three annual intervals. We monitored the adjacent control quadrats for 14 annual intervals. We constructed a population projection matrix for each quadrat in each interval, calculated lambda, and did a life table response experiment (LTRE) analysis. We tested the effects of density upon lambda by comparing experimental and control quadrats, and by an analysis of the 15-year observational data set. As measured by effects on lambda and on N(t+1/Nt in the experimental treatments, negative density dependence was strong: the population was being effectively regulated. The relative contributions of different matrix elements to treatment effect on lambda differed among years and treatments; overall the pattern was one of small contributions by many different life cycle stages. In contrast, density dependence could not be detected using only the observational (control quadrats) data, even though this data set covered a much longer time span. Nor did experimental effects on separate matrix elements reach statistical significance. These results suggest that ecologists may fail to detect density dependence when it is present if they have only descriptive, not experimental, data, do not have data for the entire life cycle, or analyze life cycle components separately.

  17. Dynamical Analysis of Density-dependent Selection in a Discrete one-island Migration Model

    Science.gov (United States)

    James H. Roberds; James F. Selgrade

    2000-01-01

    A system of non-linear difference equations is used to model the effects of density-dependent selection and migration in a population characterized by two alleles at a single gene locus. Results for the existence and stability of polymorphic equilibria are established. Properties for a genetically important class of equilibria associated with complete dominance in...

  18. Cell-density-dependent lysis and sporulation of Myxococcus xanthus in agarose microbeads.

    OpenAIRE

    Rosenbluh, A; Nir, R; Sahar, E; Rosenberg, E

    1989-01-01

    Vegetative cells of Myxococcus xanthus were immobilized in 25-microns-diameter agarose microbeads and incubated in either growth medium or sporulation buffer. In growth medium, the cells multiplied, glided to the periphery, and then filled the beads. In sporulation buffer, up to 90% of the cells lysed and ca. 50% of the surviving cells formed resistant spores. A strong correlation between sporulation and cell lysis was observed; both phenomena were cell density dependent. Sporulation proficie...

  19. Population Growth Types in India, 1961-71

    Science.gov (United States)

    Chakravarti, A. K.

    1976-01-01

    An effective means of cartographic representation of India's population growth and its spatial characteristics is the focus of this paper. A population growth index and population growth types are discussed. (Author/ND)

  20. Modelling the effect of autotoxicity on density-dependent phytotoxicity.

    Science.gov (United States)

    Sinkkonen, A

    2007-01-21

    An established method to separate resource competition from chemical interference is cultivation of monospecific, even-aged stands. The stands grow at several densities and they are exposed to homogenously spread toxins. Hence, the dose received by individual plants is inversely related to stand density. This results in distinguishable alterations in dose-response slopes. The method is often recommended in ecological studies of allelopathy. However, many plant species are known to release autotoxic compounds. Often, the probability of autotoxicity increases as sowing density increases. Despite this, the possibility of autotoxicity is ignored when experiments including monospecific stands are designed and when their results are evaluated. In this paper, I model mathematically how autotoxicity changes the outcome of dose-response slopes as different densities of monospecific stands are grown on homogenously phytotoxic substrata. Several ecologically reasonable relations between plant density and autotoxin exposure are considered over a range of parameter values, and similarities between different relations are searched for. The models indicate that autotoxicity affects the outcome of density-dependent dose-response experiments. Autotoxicity seems to abolish the effects of other phytochemicals in certain cases, while it may augment them in other cases. Autotoxicity may alter the outcome of tests using the method of monospecific stands even if the dose of autotoxic compounds per plant is a fraction of the dose of non-autotoxic phytochemicals with similar allelopathic potential. Data from the literature support these conclusions. A faulty null hypothesis may be accepted if the autotoxic potential of a test species is overlooked in density-response experiments. On the contrary, if test species are known to be non-autotoxic, the method of monospecific stands does not need fine-tuning. The results also suggest that the possibility of autotoxicity should be investigated in

  1. Founder takes all: density-dependent processes structure biodiversity.

    Science.gov (United States)

    Waters, Jonathan M; Fraser, Ceridwen I; Hewitt, Godfrey M

    2013-02-01

    Density-dependent processes play a key role in the spatial structuring of biodiversity. Specifically, interrelated demographic processes, such as gene surfing, high-density blocking, and competitive exclusion, can generate striking geographic contrasts in the distributions of genes and species. Here, we propose that well-studied evolutionary and ecological biogeographic patterns of postglacial recolonization, progressive island colonization, microbial sectoring, and even the 'Out of Africa' pattern of human expansion, are fundamentally similar, underpinned by a 'founder takes all' density-dependent principle. Additionally, we hypothesize that older historic constraints of density-dependent processes are seen today in the dramatic biogeographic shifts that occur in response to human-mediated extinction events, whereby surviving lineages rapidly expand their ranges to replace extinct sister taxa. Copyright © 2012 Elsevier Ltd. All rights reserved.

  2. Economic analyses of rapid population growth.

    Science.gov (United States)

    Birdsall, N

    1989-01-01

    "Discussion of the macroeconomic consequences of rapid population growth is organized into three schools: pessimists, optimists, and the recent revisionists. For the revisionists, differing views are presented about the pervasiveness and relevance of market failures, such as the negative externalities of childbearing, and about the ability of families and institutions to adjust rapidly to changes brought on by rapid population growth. A welfare economics approach is used to review the merits of various public policies to reduce fertility, including public financing of family planning services and taxes and incentives associated with childbearing." The focus is on developing countries. excerpt

  3. Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks: a 37-year observation of cotton bollworms.

    Science.gov (United States)

    Ouyang, Fang; Hui, Cang; Ge, Saiying; Men, Xin-Yuan; Zhao, Zi-Hua; Shi, Pei-Jian; Zhang, Yong-Sheng; Li, Bai-Lian

    2014-09-01

    Understanding drivers of population fluctuation, especially for agricultural pests, is central to the provision of agro-ecosystem services. Here, we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and, thus, the stable equilibrium of the pest population, often to a higher level, posing considerable risks to the provision of agro-ecosystem services and regional food security. Efficient and timely measures of pest management in the era of Anthropocene should target the strengthening and revival of weakening density dependence caused by climate change and human activities.

  4. Exile and demographic population growth in Serbia

    Directory of Open Access Journals (Sweden)

    Stevanović Radoslav

    2005-01-01

    Full Text Available The data of the 2002 population census on refugee population are analyzed in this paper with a basic aim to determine the significance (contribution of refugee corpus in demographic development of the Republic of Serbia. By analyzing the data, it has been determined that the refugee corpus does not significantly differ from the domicile population in the basic, above all demographic and other qualitative characteristics. The differences which can be noticed with certain (primarily socio-economic characteristics, due to the proportionally small participation of refugee persons in relation to the total (domicile population, could not significantly influence the total demographic, socio-economic and other characteristics of the population of central Serbia and Vojvodina. The most significant contribution of refugee (classifying the refugee corpus in the country's total population is reflected in the mitigation of the depopulation trend, namely population growth, not only both micro-entities, but also lower administrative-territorial entities (districts depending on the enumerated refugee population in them. However, population projections indicate that by the middle of this century (2050 the positive effects of the basically larger number of inhabitants will be lost caused by the inflow of refugee population.

  5. Population growth in Shanghai and its characteristics.

    Science.gov (United States)

    Zhang, K

    1985-07-01

    There has been an astonishing change in Shanghai's natural population growth over the past 34 years, with a significant difference between urban and suburban areas. In 1954, the birth rate reached as high as 52.6/1000 and the death rate dropped as low as 7.1/1000, the natural growth rate being 45.4/1000. The substantial decline in the rate of natural increase in Shanghai is due to the enormous achievements of family planning programs. In 1983, the 1-child rate of Shanghai areas was 96.56%, with that in urban areas reaching 99.36% and that in rural areas 92.4%. In the last decade, with the development of industrial production, several satellite cities have been built, attracting some of the urban residents from the city proper. The 5 characteristics relating to Shanghai's population growth are: 1) population density is high and population distribution is uneven; 2) fertility declined drastically in the 1970s; 3) the proportion of young is declining and the proportion of aged is increasing; 4) the mortality has been declining steadily, resulting in a longer life expectancy; and 5) the sex ratio has evened out since the liberation when males greatly outnumbered females. These factors point out the arduous task for family planning in the coming years. The enormous population and the increasing number of young people at child bearing ages point out the necessity of carrying on the family planning program.

  6. Density-dependent electron scattering in photoexcited GaAs

    DEFF Research Database (Denmark)

    Mics, Zoltán; D'’Angio, Andrea; Jensen, Søren A.

    2013-01-01

    —In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...

  7. Changes in seasonal climate outpace compensatory density-dependence in eastern brook trout

    Science.gov (United States)

    Bassar, Ronald D.; Letcher, Benjamin H.; Nislow, Keith H.; Whiteley, Andrew R.

    2016-01-01

    Understanding how multiple extrinsic (density-independent) factors and intrinsic (density-dependent) mechanisms influence population dynamics has become increasingly urgent in the face of rapidly changing climates. It is particularly unclear how multiple extrinsic factors with contrasting effects among seasons are related to declines in population numbers and changes in mean body size and whether there is a strong role for density-dependence. The primary goal of this study was to identify the roles of seasonal variation in climate driven environmental direct effects (mean stream flow and temperature) versus density-dependence on population size and mean body size in eastern brook trout (Salvelinus fontinalis). We use data from a 10-year capture-mark-recapture study of eastern brook trout in four streams in Western Massachusetts, USA to parameterize a discrete-time population projection model. The model integrates matrix modeling techniques used to characterize discrete population structures (age, habitat type and season) with integral projection models (IPMs) that characterize demographic rates as continuous functions of organismal traits (in this case body size). Using both stochastic and deterministic analyses we show that decreases in population size are due to changes in stream flow and temperature and that these changes are larger than what can be compensated for through density-dependent responses. We also show that the declines are due mostly to increasing mean stream temperatures decreasing the survival of the youngest age class. In contrast, increases in mean body size over the same period are the result of indirect changes in density with a lesser direct role of climate-driven environmental change.

  8. Density-dependent vulnerability of forest ecosystems to drought

    Science.gov (United States)

    Alessandra Bottero; Anthony W. D' Amato; Brian J. Palik; John B. Bradford; Shawn Fraver; Mike A. Battaglia; Lance A. Asherin; Harald Bugmann

    2017-01-01

    Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a given area, is a primary...

  9. On the theory of global population growth

    International Nuclear Information System (INIS)

    Kapitza, Sergei P

    2010-01-01

    Ours is an epoch of global demographic revolution, a time of a rapid transition from explosive population growth to a low reproduction level. This, possibly the most momentous change ever witnessed by humankind has, first and foremost, important implications for the dynamics of population. But it also affects billions of people in all aspects of their lives, and it is for this reason that demographic processes have grown into a vast problem, both globally and in Russia. Their fundamental understanding will to a large extent impact the present, the short-term future following the current critical epoch, the stable and uniform global development and its priorities, and indeed global security. Quantitative treatment of historical processes is reached using the phenomenological theory of mankind's population growth. This theory relies on the concepts and methods of physics and its conclusions should take into account the ideas of economics and genetics. (interdisciplinary physics)

  10. Density-dependent intraspecific aggression regulates survival in northern Yellowstone wolves (Canis lupus).

    Science.gov (United States)

    Cubaynes, Sarah; MacNulty, Daniel R; Stahler, Daniel R; Quimby, Kira A; Smith, Douglas W; Coulson, Tim

    2014-11-01

    Understanding the population dynamics of top-predators is essential to assess their impact on ecosystems and to guide their management. Key to this understanding is identifying the mechanisms regulating vital rates. Determining the influence of density on survival is necessary to understand the extent to which human-caused mortality is compensatory or additive. In wolves (Canis lupus), empirical evidence for density-dependent survival is lacking. Dispersal is considered the principal way in which wolves adjust their numbers to prey supply or compensate for human exploitation. However, studies to date have primarily focused on exploited wolf populations, in which density-dependent mechanisms are likely weak due to artificially low wolf densities. Using 13 years of data on 280 collared wolves in Yellowstone National Park, we assessed the effect of wolf density, prey abundance and population structure, as well as winter severity, on age-specific survival in two areas (prey-rich vs. prey-poor) of the national park. We further analysed cause-specific mortality and explored the factors driving intraspecific aggression in the prey-rich northern area of the park. Overall, survival rates decreased during the study. In northern Yellowstone, density dependence regulated adult survival through an increase in intraspecific aggression, independent of prey availability. In the interior of the park, adult survival was less variable and density-independent, despite reduced prey availability. There was no effect of prey population structure in northern Yellowstone, or of winter severity in either area. Survival was similar among yearlings and adults, but lower for adults older than 6 years. Our results indicate that density-dependent intraspecific aggression is a major driver of adult wolf survival in northern Yellowstone, suggesting intrinsic density-dependent mechanisms have the potential to regulate wolf populations at high ungulate densities. When low prey availability or high

  11. Impact of demographic policy on population growth.

    Science.gov (United States)

    Podyashchikh, P

    1968-01-01

    Various bourgeois theories, including the reactionary Malthusianism and its variants, challenge the Marxist-Leninist revolutionary theory on the growth of population. Bourgeois science maintains that unchanging biological laws of proliferation form the foundation of social life. Malthus, in his "An Essay on the Principle of Population," contends that population increases in a geometric rate, while means of subsistence tend to increase only in an arithmetic rate: neither the way of production nor social conditions but this law of nature in control of proliferation had been the cause of overpopulation, which again leads to misery, hunger, and unemployment. From this follows the possible conclusion that the working classes should be concerned not about how to change the social order but how to reduce the number of childbirths. Progressive science views the laws of social life in a totally different way. Marxism-Leninism teaches that population size, despite the markedly important role played by it in historical progress, fails to represent that main force of social progress which determines the mode of production and of the distribution of material goods, but just the reverse: the mode of production determines the growth of population, the changes in its density and composition. Marxism-Leninism teaches that each historical stage of production (slavery, feudalism, capitalism) has its own special, historically valid demographic law. Bourgeois science maintains that humankind faces an absolute overpopulation caused by the means of production lagging behind the growth of population. Actually this is only a relative overpopulation due to the fact that capitalistic production is subjected to the interests of increasing capitalistic profit and not to those of meeting the demands of population. In socialist countries, production is incessantly developing and expanding, and employment of the entire productive population is ensured. Consequently, the problem of relative

  12. Comparison of customised growth charts v. standard population

    African Journals Online (AJOL)

    pregnant diabetic population using population-based growth charts and customised growth charts. Methods. ... Of the patients, 44 had type 1, 66 type 2 and 173 gestational diabetes. The growth of .... with diabetic ketoacidosis, of whom one.

  13. Decadal declines in avian herbivore reproduction: density-dependent nutrition and phenological mismatch in the Arctic.

    Science.gov (United States)

    Ross, Megan V; Alisauskas, Ray T; Douglas, David C; Kellett, Dana K

    2017-07-01

    A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992-2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May-30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment, leading

  14. Decadal declines in avian herbivore reproduction: density-dependent nutrition and phenological mismatch in the Arctic

    Science.gov (United States)

    Ross, Megan V.; Alisaukas, Ray T.; Douglas, David C.; Kellett, Dana K.

    2017-01-01

    A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992–2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May–30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment

  15. Endogenous population growth may imply chaos.

    Science.gov (United States)

    Prskawetz, A; Feichtinger, G

    1995-01-01

    The authors consider a discrete-time neoclassical growth model with an endogenous rate of population growth. The resulting one-dimensional map for the capital intensity has a tilted z-shape. Using the theory of nonlinear dynamical systems, they obtain numerical results on the qualitative behavior of time paths for changing parameter values. Besides stable and periodic solutions, erratic time paths may result. In particular, myopic and far-sighted economies--assumed to be characterized by low and high savings rate respectively--are characterized by stable per capita capital stocks, while solutions with chaotic windows exist between these two extremes.

  16. Stochastic dynamics and logistic population growth

    Science.gov (United States)

    Méndez, Vicenç; Assaf, Michael; Campos, Daniel; Horsthemke, Werner

    2015-06-01

    The Verhulst model is probably the best known macroscopic rate equation in population ecology. It depends on two parameters, the intrinsic growth rate and the carrying capacity. These parameters can be estimated for different populations and are related to the reproductive fitness and the competition for limited resources, respectively. We investigate analytically and numerically the simplest possible microscopic scenarios that give rise to the logistic equation in the deterministic mean-field limit. We provide a definition of the two parameters of the Verhulst equation in terms of microscopic parameters. In addition, we derive the conditions for extinction or persistence of the population by employing either the momentum-space spectral theory or the real-space Wentzel-Kramers-Brillouin approximation to determine the probability distribution function and the mean time to extinction of the population. Our analytical results agree well with numerical simulations.

  17. The importance of spatial models for estimating the strength of density dependence

    DEFF Research Database (Denmark)

    Thorson, James T.; Skaug, Hans J.; Kristensen, Kasper

    2014-01-01

    the California Coast. In this case, the nonspatial model estimates implausible oscillatory dynamics on an annual time scale, while the spatial model estimates strong autocorrelation and is supported by model selection tools. We conclude by discussing the importance of improved data archiving techniques, so...... that spatial models can be used to re-examine classic questions regarding the presence and strength of density dependence in wild populations Read More: http://www.esajournals.org/doi/abs/10.1890/14-0739.1...

  18. Density-Dependent Phase Polyphenism in Nonmodel Locusts: A Minireview

    Directory of Open Access Journals (Sweden)

    Hojun Song

    2011-01-01

    Full Text Available Although the specific mechanisms of locust phase transformation are wellunderstood for model locust species such as the desert locust Schistocerca gregaria and the migratory locust Locusta migratoria, the expressions of density-dependent phase polyphenism in other nonmodel locust species are not wellknown. The present paper is an attempt to review and synthesize what we know about these nonmodel locusts. Based on all available data, I find that locust phase polyphenism is expressed in many different ways in different locust species and identify a pattern that locust species often belong to large taxonomic groups which contain mostly nonswarming grasshopper species. Although locust phase polyphenism has evolved multiple times within Acrididae, I argue that its evolution should be studied from a phylogenetic perspective because I find similar density-dependent phenotypic plasticity among closely related species. Finally, I emphasize the importance of comparative analyses in understanding the evolution of locust phase and propose a phylogeny-based research framework.

  19. Native birds and alien insects: spatial density dependence in songbird predation of invading oak gallwasps.

    Directory of Open Access Journals (Sweden)

    Karsten Schönrogge

    Full Text Available Revealing the interactions between alien species and native communities is central to understanding the ecological consequences of range expansion. Much has been learned through study of the communities developing around invading herbivorous insects. Much less, however, is known about the significance of such aliens for native vertebrate predators for which invaders may represent a novel food source. We quantified spatial patterns in native bird predation of invading gall-inducing Andricus wasps associated with introduced Turkey oak (Quercus cerris at eight sites across the UK. These gallwasps are available at high density before the emergence of caterpillars that are the principle spring food of native insectivorous birds. Native birds showed positive spatial density dependence in gall attack rates at two sites in southern England, foraging most extensively on trees with highest gall densities. In a subsequent study at one of these sites, positive spatial density dependence persisted through four of five sequential week-long periods of data collection. Both patterns imply that invading galls are a significant resource for at least some native bird populations. Density dependence was strongest in southern UK bird populations that have had longest exposure to the invading gallwasps. We hypothesise that this pattern results from the time taken for native bird populations to learn how to exploit this novel resource.

  20. Determining the functional form of density dependence: deductive approaches for consumer-resource systems having a single resource.

    Science.gov (United States)

    Abrams, Peter A

    2009-09-01

    Consumer-resource models are used to deduce the functional form of density dependence in the consumer population. A general approach to determining the form of consumer density dependence is proposed; this involves determining the equilibrium (or average) population size for a series of different harvest rates. The relationship between a consumer's mortality and its equilibrium population size is explored for several one-consumer/one-resource models. The shape of density dependence in the resource and the shape of the numerical and functional responses all tend to be "inherited" by the consumer's density dependence. Consumer-resource models suggest that density dependence will very often have both concave and convex segments, something that is impossible under the commonly used theta-logistic model. A range of consumer-resource models predicts that consumer population size often declines at a decelerating rate with mortality at low mortality rates, is insensitive to or increases with mortality over a wide range of intermediate mortalities, and declines at a rapidly accelerating rate with increased mortality when mortality is high. This has important implications for management and conservation of natural populations.

  1. Nuclear symmetry energy in density dependent hadronic models

    International Nuclear Information System (INIS)

    Haddad, S.

    2008-12-01

    The density dependence of the symmetry energy and the correlation between parameters of the symmetry energy and the neutron skin thickness in the nucleus 208 Pb are investigated in relativistic Hadronic models. The dependency of the symmetry energy on density is linear around saturation density. Correlation exists between the neutron skin thickness in the nucleus 208 Pb and the value of the nuclear symmetry energy at saturation density, but not with the slope of the symmetry energy at saturation density. (author)

  2. Density dependence, whitebark pine, and vital rates of grizzly bears

    Science.gov (United States)

    van Manen, Frank T.; Haroldson, Mark A.; Bjornlie, Daniel D.; Ebinger, Michael R.; Thompson, Daniel J.; Costello, Cecily M.; White, Gary C.

    2016-01-01

    Understanding factors influencing changes in population trajectory is important for effective wildlife management, particularly for populations of conservation concern. Annual population growth of the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem, USA has slowed from 4.2–7.6% during 1983–2001 to 0.3–2.2% during 2002–2011. Substantial changes in availability of a key food source and bear population density have occurred. Whitebark pine (Pinus albicaulis), the seeds of which are a valuable but variable fall food for grizzly bears, has experienced substantial mortality primarily due to a mountain pine beetle (Dendroctonus ponderosae) outbreak that started in the early 2000s. Positive growth rates of grizzly bears have resulted in populations reaching high densities in some areas and have contributed to continued range expansion. We tested research hypotheses to examine if changes in vital rates detected during the past decade were more associated with whitebark pine decline or, alternatively, increasing grizzly bear density. We focused our assessment on known-fate data to estimate survival of cubs-of-the-year (cubs), yearlings, and independent bears (≥2 yrs), and reproductive transition of females from having no offspring to having cubs. We used spatially and temporally explicit indices for grizzly bear density and whitebark pine mortality as individual covariates. Models indicated moderate support for an increase in survival of independent male bears over 1983–2012, whereas independent female survival did not change. Cub survival, yearling survival, and reproductive transition from no offspring to cubs all changed during the 30-year study period, with lower rates evident during the last 10–15 years. Cub survival and reproductive transition were negatively associated with an index of grizzly bear density, indicating greater declines where bear densities were higher. Our analyses did not support a similar relationship for the

  3. Density dependence of avian clutch size in resident and migrant species: is there a constraint on the predictability of competitor density?

    NARCIS (Netherlands)

    Both, C.

    2000-01-01

    The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One

  4. Population ageing alongside health care spending growth

    Directory of Open Access Journals (Sweden)

    Jakovljević Mihajlo

    2017-01-01

    Full Text Available The Silver Tsunami or population ageing has become a globally widespread phenomenon. The purpose of this review is to observe its dynamics and consequences from a local Balkan perspective. The main drivers of this unique demographic evolution are extended longevity, improved early childhood survival, absorption of women into the labor markets, and consequences of sexual revolution leading to falling female fertility. This process lasting well over a century is taking its toll on contemporary societies. Major side effects are shrinking young labor force and growing pool of elderly and retired citizens in many countries. This equation tends to worsen further in the future threatening long-term financial sustainability of public social and health insurance funds. Notable health expenditure growth, accelerating worldwide since the 1960s, is to a large degree attributable to ageing itself. Growing share of senior citizens increases demand for medical services and costs of health care provision. Home-based care provided by the family caregivers presents another important reality putting a huge burden on modern communities. Serbs are no exception in this landscape. Historical demographic evolution of this nation gives a clear evidence of advanced and accelerated ageing, which is well documented in post-World War II era. This synthesis of rich published evidence shows clear upward parallel trend between the pace of population aging and the growth of health expenditure. National authorities shall be forced to consider reform of the current health care financing pattern inherited from the demographic growth era. This might be the only way to smooth out the impact of population ageing on the financial sustainability of the health system and long-term medical care in Serbia. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 175014

  5. Population growth, demographic change, and cultural landscapes.

    Science.gov (United States)

    Woodgate, G; Sage, C

    1994-01-01

    The inclusion of both ecological and socioeconomic components within landscapes makes possible the perception of the hierarchical character of landscape organization. A research approach is needed to conceptualize cultural landscapes as the product of interaction between society and nature. Richard Norgaard's 1984 paper on coevolutionary agricultural development attempts to meet this challenge. Coevolution is the interactive synthesis of natural and social mechanisms of change that characterize the relationship between social systems and ecosystems. The relationship between population, consumption, and environmental changes is complex. Currently industrialized countries present the biggest threat to global environmental resources. The issue of carrying capacity is the corollary of population and the environment. It is primarily the technological factor rather than population that needs to be controlled. The relationship between rich and poor countries is determined by superior economic power. An analysis of landscape change is made, tracing the coevolution of society and environment from the end of the feudal era and making comparisons with continental Europe. Over the years since 1945 the need to realize potential economies of scale has resulted in a wholesale loss of woodlands, hedgerows, and small ponds in the UK. In a global context the likely impacts of population growth and demographic change on landscapes will be influenced by such socioeconomic factors as technology and affluence; policies that ignore cause and effect; and the traditional tendency to treat the environment as a waste repository and a supply depot.

  6. Density dependence of reactor performance with thermal confinement scalings

    International Nuclear Information System (INIS)

    Stotler, D.P.

    1992-03-01

    Energy confinement scalings for the thermal component of the plasma published thus far have a different dependence on plasma density and input power than do scalings for the total plasma energy. With such thermal scalings, reactor performance (measured by Q, the ratio of the fusion power to the sum of the ohmic and auxiliary input powers) worsens with increasing density. This dependence is the opposite of that found using scalings based on the total plasma energy, indicating that reactor operation concepts may need to be altered if this density dependence is confirmed in future research

  7. [African population growth: status and prospects].

    Science.gov (United States)

    Tabutin, D

    1991-01-01

    Despite great improvements over the past several years, the quality of demographic data in Africa is still a problem, and Africa remains the least well known continent. Population growth is extremely rapid, with all countries growing at annual rates of over 3%. The natural increase rate even shows some signs of increasing slightly in the next decade or so. Africa's population was estimated at 220 million in 1950, 650 million at present, and is projected at 1.5 billion by 2025. Africans represented 9% of the world population in 1960, but will increase to 19% around 2025. The rapid population growth is the result of declining mortality since the 1950s unmatched by changes in fertility. There are significant socioeconomic and rural-urban mortality differentials in Africa, but as yet only highly educated urbanites have measurably reduced their family size. 2 consequences of this rapid growth are the youth of the population, with almost 50% under 20 years, and its high density in some areas. By 2025, 18 countries will have densities of over 100 persons per sq km. Almost everywhere in Africa, family sizes are at least 6 children/woman. 3 factors explaining this high level of fertility are the earliness and universality of marriage, rates of contraceptive usage of only 4-10% in most countries, and declining durations of breast feeding and sexual abstinence, which traditionally served as brakes on fertility. As a rule, women marry young and remain married until the end of their reproductive years. Divorce and widowhood are common, but remarriage is usually rapid if the woman is still of reproductive age. Life expectancy at birth in sub-Saharan Africa has increased from some 36 years around 1950 to 50 years at present. Progress in control of mortality, and especially infant mortality, has been slower than expected, and Africa still has by far the lowest life expectancy of any major region. Regional, rural-urban, and socioeconomic mortality differentials are considerable and

  8. A Holling Type II Pest and Natural Enemy Model with Density Dependent IPM Strategy

    Directory of Open Access Journals (Sweden)

    Xia Wang

    2017-01-01

    Full Text Available Resource limitations and density dependent releasing of natural enemies during the pest control and integrated pest management will undoubtedly result in nonlinear impulsive control. In order to investigate the effects of those nonlinear control strategies on the successful pest control, we have proposed a pest-natural enemy system concerning integrated pest management with density dependent instant killing rate and releasing rate. In particular, the releasing rate depicts how the number of natural enemy populations released was guided by their current density at the fixed moment. The threshold condition which ensures the existence and global stability of pest-free periodic solution has been discussed first, and the effects of key parameters on the threshold condition reveal that reducing the pulse period does not always benefit pest control; that is, frequent releasing of natural enemies may not be beneficial to the eradication of pests when the density dependent releasing method has been implemented. Moreover, the forward and backward bifurcations could occur once the pest-free periodic solution becomes unstable, and the system could exist with very complex dynamics. All those results confirm that the control actions should be carefully designed once the nonlinear impulsive control measures have been taken for pest management.

  9. Density dependence of the nuclear energy-density functional

    Science.gov (United States)

    Papakonstantinou, Panagiota; Park, Tae-Sun; Lim, Yeunhwan; Hyun, Chang Ho

    2018-01-01

    Background: The explicit density dependence in the coupling coefficients entering the nonrelativistic nuclear energy-density functional (EDF) is understood to encode effects of three-nucleon forces and dynamical correlations. The necessity for the density-dependent coupling coefficients to assume the form of a preferably small fractional power of the density ρ is empirical and the power is often chosen arbitrarily. Consequently, precision-oriented parametrizations risk overfitting in the regime of saturation and extrapolations in dilute or dense matter may lose predictive power. Purpose: Beginning with the observation that the Fermi momentum kF, i.e., the cubic root of the density, is a key variable in the description of Fermi systems, we first wish to examine if a power hierarchy in a kF expansion can be inferred from the properties of homogeneous matter in a domain of densities, which is relevant for nuclear structure and neutron stars. For subsequent applications we want to determine a functional that is of good quality but not overtrained. Method: For the EDF, we fit systematically polynomial and other functions of ρ1 /3 to existing microscopic, variational calculations of the energy of symmetric and pure neutron matter (pseudodata) and analyze the behavior of the fits. We select a form and a set of parameters, which we found robust, and examine the parameters' naturalness and the quality of resulting extrapolations. Results: A statistical analysis confirms that low-order terms such as ρ1 /3 and ρ2 /3 are the most relevant ones in the nuclear EDF beyond lowest order. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one density-dependent term in nonrelativistic EDFs. The functional we propose easily accommodates known or adopted properties of nuclear matter near saturation. More importantly, upon extrapolation to dilute or asymmetric matter, it reproduces a range of existing microscopic

  10. Detection of density-dependent effects on caribou numbers from a series of census data

    Directory of Open Access Journals (Sweden)

    Francois Messier

    1991-10-01

    Full Text Available The main objective of this paper is to review and discuss the applicability of statistical procedures for the detection of density dependence based on a series of annual or multi-annual censuses. Regression models for which the statistic value under the null hypothesis of density independence is set a priori (slope = 0 or 1, generate spurious indications of density dependence. These tests are inappropriate because low sample sizes, high variance, and sampling error consistently bias the slope when applied to a finite number of population estimates. Two distribution-free tests are reviewed for which the rejection region for the hypothesis of density independence is derived intrinsically from the data through a computer-assisted permutation process. The "randomization test" gives the best results as the presence of a pronounced trend in the sequence of population estimates does not affect test results. The other non-parametric test, the "permutation test", gives reliable results only if the population fluctuates around a long-term equilibrium density. Both procedures are applied to three sets of data (Pukaskwa herd, Avalon herd, and a hypothetical example that represent quite divergent population trajectories over time.

  11. Landau parameters for finite range density dependent nuclear interactions

    International Nuclear Information System (INIS)

    Farine, M.

    1997-01-01

    The Landau parameters represent the effective particle-hole interaction at Fermi level. Since between the physical observables and the Landau parameters there is a direct relation their derivation from an effective interaction is of great interest. The parameter F 0 determines the incompressibility K of the system. The parameter F 1 determines the effective mass (which controls the level density at the Fermi level). In addition, F 0 ' determines the symmetry energy, G 0 the magnetic susceptibility, and G 0 ' the pion condensation threshold in nuclear matter. This paper is devoted to a general derivation of Landau parameters for an interaction with density dependent finite range terms. Particular carefulness is devoted to the inclusion of rearrangement terms. This report is part of a larger project which aims at defining a new nuclear interaction improving the well-known D1 force of Gogny et al. for describing the average nuclear properties and exotic nuclei and satisfying, in addition, the sum rules

  12. Nuclear ``pasta'' phase within density dependent hadronic models

    Science.gov (United States)

    Avancini, S. S.; Brito, L.; Marinelli, J. R.; Menezes, D. P.; de Moraes, M. M. W.; Providência, C.; Santos, A. M.

    2009-03-01

    In the present paper, we investigate the onset of the “pasta” phase with different parametrizations of the density dependent hadronic model and compare the results with one of the usual parametrizations of the nonlinear Walecka model. The influence of the scalar-isovector virtual δ meson is shown. At zero temperature, two different methods are used, one based on coexistent phases and the other on the Thomas-Fermi approximation. At finite temperature, only the coexistence phases method is used. npe matter with fixed proton fractions and in β equilibrium are studied. We compare our results with restrictions imposed on the values of the density and pressure at the inner edge of the crust, obtained from observations of the Vela pulsar and recent isospin diffusion data from heavy-ion reactions, and with predictions from spinodal calculations.

  13. Nuclear 'pasta' phase within density dependent hadronic models

    International Nuclear Information System (INIS)

    Avancini, S. S.; Marinelli, J. R.; Menezes, D. P.; Moraes, M. M. W. de; Brito, L.; Providencia, C.; Santos, A. M.

    2009-01-01

    In the present paper, we investigate the onset of the 'pasta' phase with different parametrizations of the density dependent hadronic model and compare the results with one of the usual parametrizations of the nonlinear Walecka model. The influence of the scalar-isovector virtual δ meson is shown. At zero temperature, two different methods are used, one based on coexistent phases and the other on the Thomas-Fermi approximation. At finite temperature, only the coexistence phases method is used. npe matter with fixed proton fractions and in β equilibrium are studied. We compare our results with restrictions imposed on the values of the density and pressure at the inner edge of the crust, obtained from observations of the Vela pulsar and recent isospin diffusion data from heavy-ion reactions, and with predictions from spinodal calculations

  14. Temperature- and density-dependent x-ray scattering in a low-Z plasma

    International Nuclear Information System (INIS)

    Brown, R.T.

    1976-06-01

    A computer program is described which calculates temperature- and density-dependent differential and total coherent and incoherent x-ray scattering cross sections for a low-Z scattering medium. Temperature and density are arbitrary within the limitations of the validity of local thermodynamic equilbrium, since ionic populations are calculated under this assumption. Scattering cross sections are calculated in the form factor approximation. The scattering medium may consist of any mixure of elements with Z less than or equal to 8, with this limitation imposed by the availability of atomic data

  15. Ecological change points: The strength of density dependence and the loss of history.

    Science.gov (United States)

    Ponciano, José M; Taper, Mark L; Dennis, Brian

    2018-05-01

    Change points in the dynamics of animal abundances have extensively been recorded in historical time series records. Little attention has been paid to the theoretical dynamic consequences of such change-points. Here we propose a change-point model of stochastic population dynamics. This investigation embodies a shift of attention from the problem of detecting when a change will occur, to another non-trivial puzzle: using ecological theory to understand and predict the post-breakpoint behavior of the population dynamics. The proposed model and the explicit expressions derived here predict and quantify how density dependence modulates the influence of the pre-breakpoint parameters into the post-breakpoint dynamics. Time series transitioning from one stationary distribution to another contain information about where the process was before the change-point, where is it heading and how long it will take to transition, and here this information is explicitly stated. Importantly, our results provide a direct connection of the strength of density dependence with theoretical properties of dynamic systems, such as the concept of resilience. Finally, we illustrate how to harness such information through maximum likelihood estimation for state-space models, and test the model robustness to widely different forms of compensatory dynamics. The model can be used to estimate important quantities in the theory and practice of population recovery. Copyright © 2018 Elsevier Inc. All rights reserved.

  16. Population Growth and Poverty in the Developing World.

    Science.gov (United States)

    Birdsall, Nancy

    1980-01-01

    The link between rapid population growth and the absolute poverty which currently afflicts 780 million people in developing countries (excluding China and other centrally planned economies) is examined. As a result of rapid population growth, many countries suffer slow per capita income growth, a lack of progress in reducing income inequality, and…

  17. Rapid Population Growth-Cause or Result of Global Problems?

    Science.gov (United States)

    Schwartz, Richard H.

    Explosive population growth is a symptom of the world's unjust and inequitable social, political, and economic conditions. The current rate of growth is staggering, particularly in the cities of the underdeveloped countries. While some progress has been made in slowing population growth, several factors still contribute to its momentum. One of…

  18. Implications of population growth for Nigeria's development | Fan ...

    African Journals Online (AJOL)

    Nigeria's population that was 16 million in 1911 is about 140 million today. Attention invariably turns to the implications of this growth to the qualities of life for her inhabitants. The paper notes that high birth rate, low death rate and migration are the sources of the high population growth in Nigeria. The population then ...

  19. 1 2 POPULATION GROWTH AND THE DILEMMA OF RURAL LIFE ...

    African Journals Online (AJOL)

    Dr Ike

    The high as well as the unrestrained population growth rate of the country has, to a ... that it stimulates business and general economic growth cycles and therefore .... The privilege and opportunity of acquiring functional education, for instance ...

  20. Density-dependent expressions for photoionization cross-sections

    Energy Technology Data Exchange (ETDEWEB)

    Sun Weiguo; Ma Xiaoguang; Cheng Yansong

    2004-06-07

    Alternative expressions for photoionization cross-sections and dielectric influence functions are suggested to study the photoionization cross-sections of atoms in solid system. The basic picture is that the photoionization cross-section of atoms in a real system can be described as the coupling between quantum quantity (QQ) and classical quantity (CQ) parts. The QQ part represents the photoionization cross-sections of an isolated particle, while the CQ part may represent most of the important influence of the macroscopic effects (e.g., the interactions of all surrounding polarized particles, and the dielectric property, etc.) on the photoionization cross-sections. The applications to the barium system show that the number-density-dependent new photoionization formula not only obtains the same cross-sections as those from the first order approximation for ideal gas, but also can generate the cross-sections for solid barium by transforming those of ideal gas of the same species using the dielectric influence function.

  1. Density-dependent expressions for photoionization cross-sections

    International Nuclear Information System (INIS)

    Sun Weiguo; Ma Xiaoguang; Cheng Yansong

    2004-01-01

    Alternative expressions for photoionization cross-sections and dielectric influence functions are suggested to study the photoionization cross-sections of atoms in solid system. The basic picture is that the photoionization cross-section of atoms in a real system can be described as the coupling between quantum quantity (QQ) and classical quantity (CQ) parts. The QQ part represents the photoionization cross-sections of an isolated particle, while the CQ part may represent most of the important influence of the macroscopic effects (e.g., the interactions of all surrounding polarized particles, and the dielectric property, etc.) on the photoionization cross-sections. The applications to the barium system show that the number-density-dependent new photoionization formula not only obtains the same cross-sections as those from the first order approximation for ideal gas, but also can generate the cross-sections for solid barium by transforming those of ideal gas of the same species using the dielectric influence function

  2. Adapting to Population Growth: The Evolutionary Alternative to Malthus

    OpenAIRE

    Axel Kristinsson; Árni Daníel Júlíusson

    2016-01-01

    A long-standing debate on the dynamics of population growth in human history has become polarized between a Malthusian stance and a Boserupian one. The former tends to view population growth as limited by carrying capacity, dependent on environment and technology, whereas the latter sees population growth itself as a major inducement to social, economic and technological developments. In this paper the authors experiment with approaching this debate by using recent developments in evolutionar...

  3. The Population Growth and Carrying Capacity in Semarang City

    Science.gov (United States)

    Hariyanto; Hadi, Sudharto P.; Buchori, Imam

    2018-02-01

    Population growth and development of city activities take some lands to carry them. As a result, land use competition happens among persons, society or sector. Land necessity for settlement, industry, or sector has taken over farm land, therefore farm land has been converted intensively and massively. Chronologically, population growth will cause land necessity increase. Unproductive land, especially farm land will be converted. Furthermore, farm land conversion will cause carrying capacity change. Carrying capacity has certain bio capacity. With the population growth, it will increase resource consumption; on the other side, farm land conversion will decrease carrying capacity. The objective of the study is to know about the influence of population growth towards carrying capacity (bio capacity) in Semarang city. Land consumption per capita is indeed influenced by city population, the higher the population is, the lower the land consumption per capita. With the population growth, it will influence carrying capacity. Carrying capacity here is the ratio of area to population. Analytical descriptive method is applied in the study with all sub-districts in Semarang city as the analysis unit. Population here is sub-district area and population per sub-district in Semarang city. Population growth data period is from 2000 until 2015. Main variables of the study are area per sub-district, population, population growth, carrying capacity. Result of the study shows significant influence of carrying capacity decrease, especially some outskirts in Semarang city. This condition happens because the outskirts in Semarang city tend to have dense population growth. Range of carrying capacity in Semarang city is from 0,007 to 0,117 of 0 to 1. Almost all sub-districts in Semarang city show miserable condition, except Mijen and Tugu. The conclusion of the study is that population will decrease carrying capacity. Therefore, the government should control population growth by paying

  4. Migration, urban population growth and regional disparity in China

    OpenAIRE

    Renard, Mary-Françoise; Xu, Zelai; Zhu, Nong

    2011-01-01

    The main objective of this paper is to study the determinants of city population growth in China during the 1990s', as well as the determinants of migrations towards cities, which constitutes the main source of urban population growth in this period. A second objective is to identify regional differences in the urban growth and migrations, that is, whether urban growth and migration patterns are different between coastal and inland provinces. Additionally, we are interested in the differences...

  5. Density dependent interactions between VA mycorrhizal fungi and even-aged seedlings of two perennial Fabaceae species.

    Science.gov (United States)

    Allsopp, N; Stock, W D

    1992-08-01

    The interaction of density and mycorrhizal effects on the growth, mineral nutrition and size distribution of seedlings of two perennial members of the Fabaceae was investigated in pot culture. Seedlings of Otholobium hirtum and Aspalathus linearis were grown at densities of 1, 4, 8 and 16 plants per 13-cm pot with or without vesicular-arbuscular (VA) mycorrhizal inoculum for 120 days. Plant mass, relative growth rates, height and leaf number all decreased with increasing plant density. This was ascribed to the decreasing availability of phosphorus per plant as density increased. O. hirtum was highly dependent on mycorrhizas for P uptake but both mycorrhizal and non-mycorrhizal A. linearis seedlings were able to extract soil P with equal ease. Plant size distribution as measured by the coefficient of variation (CV) of shoot mass was greater at higher densities. CVs of mycorrhizal O. hirtum plants were higher than those of non-mycorrhizal plants. CVs of the facultatively mycorrhizal A. linearis were similar for both mycorrhizal and non-mycorrhizal plants. Higher CVs are attributed to resource preemption by larger individuals. Individuals in populations with high CVs will probably survive stress which would result in the extinction of populations with low CVs. Mass of mycorrhizal plants of both species decreased more rapidly with increasing density than did non-mycorrhizal plant mass. It is concluded that the cost of being mycorrhizal increases as plant density increases, while the benefit decreases. The results suggest that mycorrhizas will influence density-dependent population processes of faculative and obligate mycorrhizal species.

  6. The relative importance of intrinsic and extrinsic drivers to population growth vary among local populations of Greater Sage-Grouse: An integrated population modeling approach

    Science.gov (United States)

    Coates, Peter S.; Prochazka, Brian G.; Ricca, Mark A.; Halstead, Brian J.; Casazza, Michael L.; Blomberg, Erik J.; Brussee, Brianne E.; Wiechman, Lief; Tebbenkamp, Joel; Gardner, Scott C.; Reese, Kerry P.

    2018-01-01

    Consideration of ecological scale is fundamental to understanding and managing avian population growth and decline. Empirically driven models for population dynamics and demographic processes across multiple spatial scales can be powerful tools to help guide conservation actions. Integrated population models (IPMs) provide a framework for better parameter estimation by unifying multiple sources of data (e.g., count and demographic data). Hierarchical structure within such models that include random effects allow for varying degrees of data sharing across different spatiotemporal scales. We developed an IPM to investigate Greater Sage-Grouse (Centrocercus urophasianus) on the border of California and Nevada, known as the Bi-State Distinct Population Segment. Our analysis integrated 13 years of lek count data (n > 2,000) and intensive telemetry (VHF and GPS; n > 350 individuals) data across 6 subpopulations. Specifically, we identified the most parsimonious models among varying random effects and density-dependent terms for each population vital rate (e.g., nest survival). Using a joint likelihood process, we integrated the lek count data with the demographic models to estimate apparent abundance and refine vital rate parameter estimates. To investigate effects of climatic conditions, we extended the model to fit a precipitation covariate for instantaneous rate of change (r). At a metapopulation extent (i.e. Bi-State), annual population rate of change λ (er) did not favor an overall increasing or decreasing trend through the time series. However, annual changes in λ were driven by changes in precipitation (one-year lag effect). At subpopulation extents, we identified substantial variation in λ and demographic rates. One subpopulation clearly decoupled from the trend at the metapopulation extent and exhibited relatively high risk of extinction as a result of low egg fertility. These findings can inform localized, targeted management actions for specific areas

  7. Human Capital, Population Growth and Economic Development: Beyond Correlations

    OpenAIRE

    Rosenzweig, Mark R.

    1987-01-01

    Empirical evidence on three assertions commonly-made by population policy advocates about the relationships among population growth, human capital formation and economic development is discussed and evaluated in the light of economic-biological models of household behavior and of its relevance to population policy. The three assertions are that (a) population growth and human capital investments jointly reflect and respond to changes in the economic environment, (b) larger families directly i...

  8. Causes and consequences of complex population dynamics in an annual plant, Cardamine pensylvanica

    Energy Technology Data Exchange (ETDEWEB)

    Crone, E.E.

    1995-11-08

    The relative importance of density-dependent and density-independent factors in determining the population dynamics of plants has been widely debated with little resolution. In this thesis, the author explores the effects of density-dependent population regulation on population dynamics in Cardamine pensylvanica, an annual plant. In the first chapter, she shows that experimental populations of C. pensylvanica cycled from high to low density in controlled constant-environment conditions. These cycles could not be explained by external environmental changes or simple models of direct density dependence (N{sub t+1} = f[N{sub t}]), but they could be explained by delayed density dependence (N{sub t+1} = f[N{sub t}, N{sub t+1}]). In the second chapter, she shows that the difference in the stability properties of population growth models with and without delayed density dependence is due to the presence of Hopf as well as slip bifurcations from stable to chaotic population dynamics. She also measures delayed density dependence due to effects of parental density on offspring quality in C. pensylvanica and shows that this is large enough to be the cause of the population dynamics observed in C. pensylvanica. In the third chapter, the author extends her analyses of density-dependent population growth models to include interactions between competing species. In the final chapter, she compares the effects of fixed spatial environmental variation and variation in population size on the evolutionary response of C. pensylvanica populations.

  9. Analysis of spatial density dependence in gypsy moth mortality

    Science.gov (United States)

    Andrew Liebhold; Joseph S. Elkinton

    1991-01-01

    The gypsy moth is perhaps the most widely studied forest insect in the world and much of this research has focused on various aspects of population dynamics. But despite this voluminous amount of research we still lack a good understanding of which, if any, natural enemy species regulate gypsy moth populations. The classical approach to analyzing insect population...

  10. Volatility and Growth in Populations of Rural Associations

    Science.gov (United States)

    Wollebaek, Dag

    2010-01-01

    This article uses unique community-level data aggregated from censuses of associations to analyze growth and volatility in rural populations of grassroots associations. A qualitative comparative analysis (QCA) shows that the two main paths to growth were (1) centralization in polycephalous (multicentered) municipalities and (2) population growth…

  11. Beyond the Mean: Sensitivities of the Variance of Population Growth.

    Science.gov (United States)

    Trotter, Meredith V; Krishna-Kumar, Siddharth; Tuljapurkar, Shripad

    2013-03-01

    Populations in variable environments are described by both a mean growth rate and a variance of stochastic population growth. Increasing variance will increase the width of confidence bounds around estimates of population size, growth, probability of and time to quasi-extinction. However, traditional sensitivity analyses of stochastic matrix models only consider the sensitivity of the mean growth rate. We derive an exact method for calculating the sensitivity of the variance in population growth to changes in demographic parameters. Sensitivities of the variance also allow a new sensitivity calculation for the cumulative probability of quasi-extinction. We apply this new analysis tool to an empirical dataset on at-risk polar bears to demonstrate its utility in conservation biology We find that in many cases a change in life history parameters will increase both the mean and variance of population growth of polar bears. This counterintuitive behaviour of the variance complicates predictions about overall population impacts of management interventions. Sensitivity calculations for cumulative extinction risk factor in changes to both mean and variance, providing a highly useful quantitative tool for conservation management. The mean stochastic growth rate and its sensitivities do not fully describe the dynamics of population growth. The use of variance sensitivities gives a more complete understanding of population dynamics and facilitates the calculation of new sensitivities for extinction processes.

  12. Density-dependent selection on mate search and evolution of Allee effects.

    Science.gov (United States)

    Berec, Luděk; Kramer, Andrew M; Bernhauerová, Veronika; Drake, John M

    2018-01-01

    Sexually reproducing organisms require males and females to find each other. Increased difficulty of females finding mates as male density declines is the most frequently reported mechanism of Allee effects in animals. Evolving more effective mate search may alleviate Allee effects, but may depend on density regimes a population experiences. In particular, high-density populations may evolve mechanisms that induce Allee effects which become detrimental when populations are reduced and maintained at a low density. We develop an individual-based, eco-genetic model to study how mating systems and fitness trade-offs interact with changes in population density to drive evolution of the rate at which males or females search for mates. Finite mate search rate triggers Allee effects in our model and we explore how these Allee effects respond to such evolution. We allow a population to adapt to several population density regimes and examine whether high-density populations are likely to reverse adaptations attained at low densities. We find density-dependent selection in most of scenarios, leading to search rates that result in lower Allee thresholds in populations kept at lower densities. This mainly occurs when fecundity costs are imposed on mate search, and provides an explanation for why Allee effects are often observed in anthropogenically rare species. Optimizing selection, where the attained trait value minimizes the Allee threshold independent of population density, depended on the trade-off between search and survival, combined with monogamy when females were searching. Other scenarios led to runaway selection on the mate search rate, including evolutionary suicide. Trade-offs involved in mate search may thus be crucial to determining how density influences the evolution of Allee effects. Previous studies did not examine evolution of a trait related to the strength of Allee effects under density variation. We emphasize the crucial role that mating systems, fitness

  13. Green sea turtle age, growth, population characteristics

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Morphology, sex ratio, body condition, disease status, age structure, and growth patterns were characterized for 448 green sea turtles cold stunned in St. Joseph...

  14. Soil science, population growth and food production: some historical developments

    NARCIS (Netherlands)

    Hartemink, A.E.

    2007-01-01

    The world¿s population has doubled since 1960. Currently, the developing world accounts for about 95% of the population growth with Africa as the world¿s fastest growing continent. The growing population has many implications but most of all it requires an increase in agricultural production to meet

  15. 14 THE RELATIONSHIP BETWEEN POPULATION GROWTH AND ...

    African Journals Online (AJOL)

    have lingered about the plausibility and consequences of population ... food supply, environmental degradation and shortage of infrastructural facilities? .... history punctuated by slave trade, colonialism, imperialiqm and globalization all of ...

  16. [Population: evolution of Rwandan attitudes or the adaptation of the Rwanda population to population growth].

    Science.gov (United States)

    Ngendakumana, M

    1988-04-01

    A consequence of the increasing pressure on Rwanda's ecosystem resulting from population growth has been that demographic factors have played a significant role in modifying attitudes and beliefs of the population. The history of Rwanda demonstrates a constant struggle for survival in the face of increasing population pressure. Migration, colonization of new agricultural lands, adoption of new crops and new forms of animal husbandry have been responses to population pressures. Recent unprecedented population growth has exceeded the capacity of older systems of cultivation and combinations of agricultural and animal husbandry to support the population. Smaller animals have largely replaced the cattle that once roamed freely in extensive pastures, and new techniques of stabling animals, use of organic or chemical fertilizers, and new tools adapted to the shrinking size of farm plots have represented responses to the new demographic realities. The concept of the family is likewise undergoing modification in the face of population growth and modernization. Children, who once were valued as a source of labor and constrained to conform to the wishes of the parents in return for the eventual inheritance of the goods and livelihood, now increasingly look beyond the household for education and employment. Family land holdings have become too small to support all the members with a claim on them. The greater distances between family members inevitably mean that relations between them lose closeness. The choice of a marriage partner is increasingly assumed by the young people themselves and not by their families. Old traditions of food sharing and hospitality have been curtailed because of the increasing scarcity of food. Despite the changes engendered by increasing population pressure, pronatalist sentiments are still widespread. But the desire to assure the future of each child rather than to await his services, a new conception of women less dependent on their reproductive

  17. Making a stand: five centuries of population growth in colonizing populations of Pinus ponderosa.

    Science.gov (United States)

    Lesser, Mark R; Jackson, Stephen T

    2012-05-01

    The processes underlying the development of new populations are important for understanding how species colonize new territory and form viable long-term populations. Life-history-mediated processes such as Allee effects and dispersal capability may interact with climate variability and site-specific factors to govern population success and failure over extended time frames. We studied four disjunct populations of ponderosa pine in the Bighorn Basin of north-central Wyoming to examine population growth spanning more than five centuries. The study populations are separated from continuous ponderosa pine forest by distances ranging from 15 to >100 km. Strong evidence indicates that the initial colonizing individuals are still present, yielding a nearly complete record of population history. All trees in each population were aged using dendroecological techniques. The populations were all founded between 1530 and 1655 cal yr CE. All show logistic growth patterns, with initial exponential growth followed by a slowing during the mid to late 20th century. Initial population growth was slower than expectations from a logistic regression model at all four populations, but increased during the mid-18th century. Initial lags in population growth may have been due to strong Allee effects. A combination of overcoming Allee effects and a transition to favorable climate conditions may have facilitated a mid-18th century pulse in population growth rate.

  18. Non-integrable dynamics of matter-wave solitons in a density-dependent gauge theory

    Science.gov (United States)

    Dingwall, R. J.; Edmonds, M. J.; Helm, J. L.; Malomed, B. A.; Öhberg, P.

    2018-04-01

    We study interactions between bright matter-wave solitons which acquire chiral transport dynamics due to an optically-induced density-dependent gauge potential. Through numerical simulations, we find that the collision dynamics feature several non-integrable phenomena, from inelastic collisions including population transfer and radiation losses to the formation of short-lived bound states and soliton fission. An effective quasi-particle model for the interaction between the solitons is derived by means of a variational approximation, which demonstrates that the inelastic nature of the collision arises from a coupling of the gauge field to velocities of the solitons. In addition, we derive a set of interaction potentials which show that the influence of the gauge field appears as a short-range potential, that can give rise to both attractive and repulsive interactions.

  19. Curbing population growth in Republic of Korea.

    Science.gov (United States)

    Woo-hyun, S

    1983-01-26

    The population of Korea is expected to increase by another 1/4 of the current population by the year 2000 if the government family planning program is successful. Aggravating Korea's demographic situation is the worldwide phenomenon of urban congestion. According to official statistics, Seoul's population increased from only 1 million in 1953 to 8.5 million in 1980, the latest year for which figures are available. While Seoul's population alone accounts for 22.3% of the total population, that of the greater Seoul area comprises 13,542,000 people or 35.5% of Korea's population. Most of the country's best institutions of higher learning are concentrated in Seoul, and in 1979 Seoul accounted for nearly half (47.7%) of the nation's college and graduate students. Seoul is also the center of the country's political, economic and cultural life and provides better employment opportunities than elsewhere in the country. The exodus of young people from rural areas and the growing census figures have triggered fears that the subsequently reduced agricultural productivity would result in a food supply crisis. In an attempt to remedy the demographic disparity between urban and rural areas, the government initiated a 10-year program in 1982 to promote jobs and improve medicare and the educational system in provincial cities. The plan encourages the establishment of factories and other auxiliary facilities outside the Seoul area that are necessary to support the 1988 Seoul Olympics. The program's success remains in question as it requires consistent, determined, and well coordinated efforts on the part of policy makers to curb the historical trend which has been gaining momentum over the past 100 years. 2 approaches have been adopted in the government's efforts to integrate population dynamics into the development process, overseas migration, and planned parenthood. Despite the 1981 liberalization of overseas travel for Koreans, Korean migration overseas is not expected to grow

  20. Health, family planning and population growth.

    Science.gov (United States)

    Kessler, A; Standley, C C

    1973-01-01

    Maternal age over 35, close spacing of births, parity over 4, and unwanted pregnancy are discussed as factors that are associated with increased maternal and infant mortality. The likelihood of death due to childbearing is twice as high in the 30-40 age group as in the 20-30 age group and increases 4-to five-fold in the 40+ group. Brith Birth of less than 24-30 months are associated with a two-fold increase in neonatal and infant deaths. Health objectives of large scale family planning programs are geared toward avoiding such births. This paper proposes that these objectives would result in a decrease in maternal and child deaths and thereby lead to growth. A simultaneous lowering of birth rates, however, should offset this growth.

  1. Social structural consequences of population growth.

    Science.gov (United States)

    Adams, R E

    1981-01-01

    Estimates from archaeological data of the numbers in the elite classes, nonelite occupational specialists, density of population, city size, and size of political units in the ancient Maya civilization suggest that there was a quantum shift in rate of development in the Early Classic period, associated with intensification of agriculture, and that the social structure approximated to a generalized feudal pattern.

  2. Using Lemna to Study Geometric Population Growth.

    Science.gov (United States)

    DeBuhr, Larry E.

    1991-01-01

    An experiment in which students collect and analyze data on the population size of a real organism rather that on a model is presented. The activity allows for the integration of mathematics, graphing techniques, and the use of computers. The lesson is designed to follow the learning cycle format. (KR)

  3. Urban population and economic growth: South Asia perspective

    Directory of Open Access Journals (Sweden)

    Sandip Sarker

    2016-07-01

    Full Text Available Previously economic growth was generally discussed in terms of foreign direct investment (FDI, educational growth, savings, investments, inflation as well as trade openness of a nation. Very recently it has been identified that population is one of the major determinants of economic growth of a nation. In the recent years, the study of urbanization has gained a matter of concern in developing countries as it has been recognized as part of a larger process of economic development which is affecting developing countries. South Asian countries are one of the emerging economics and growing at a faster rate over the past few years. At the same time, population of South Asia is growing at a significant rate. Therefore the study has attempted to identify the causal relationship between urban population and economic growth in South Asia using a panel data analysis. The study makes use of the Augmented Dickey-Fuller (ADF and Phillips-Perron (PP, Pesaran as well as Fisher methods for panel unit root test. The panel Pedroni cointegration test suggests that there is long run relationship between the variables. The further panel Vector Error Correction Model (VECM suggests that there is long run causality running from urban population growth to economic growth in South Asia. The study concludes that the growth of urban population can have significant impact on economic growth in South Asia in the long run.

  4. Innovation and the growth of human population.

    Science.gov (United States)

    Weinberger, V P; Quiñinao, C; Marquet, P A

    2017-12-05

    Biodiversity is sustained by and is essential to the services that ecosystems provide. Different species would use these services in different ways, or adaptive strategies, which are sustained in time by continuous innovations. Using this framework, we postulate a model for a biological species ( Homo sapiens ) in a finite world where innovations, aimed at increasing the flux of ecosystem services (a measure of habitat quality), increase with population size, and have positive effects on the generation of new innovations (positive feedback) as well as costs in terms of negatively affecting the provision of ecosystem services. We applied this model to human populations, where technological innovations are driven by cumulative cultural evolution. Our model shows that depending on the net impact of a technology on the provision of ecosystem services ( θ ), and the strength of technological feedback ( ξ ), different regimes can result. Among them, the human population can fill the entire planet while maximizing their well-being, but not exhaust ecosystem services. However, this outcome requires positive or green technologies that increase the provision of ecosystem services with few negative externalities or environmental costs, and that have a strong positive feedback in generating new technologies of the same kind. If the feedback is small, then the technological stock can collapse together with the human population. Scenarios where technological innovations generate net negative impacts may be associated with a limited technological stock as well as a limited human population at equilibrium and the potential for collapse. The only way to fill the planet with humans under this scenario of negative technologies is by reducing the technological stock to a minimum. Otherwise, the only feasible equilibrium is associated with population collapse. Our model points out that technological innovations per se may not help humans to grow and dominate the planet. Instead

  5. Seasonal mortality and sequential density dependence in a migratory bird

    NARCIS (Netherlands)

    Rakhimberdiev, Eldar; van den Hout, Piet J.; Brugge, Maarten; Spaans, Bernard; Piersma, Theunis

    2015-01-01

    Migratory bird populations may be limited during one or more seasons, and thus at one or more places, but there is a dearth of empirical examples of this possibility. We analyse seasonal survival in a migratory shellfish-eating shorebird (red knot Calidris canutus islandica) during a series of years

  6. Poverty-led higher population growth in Bangladesh.

    Science.gov (United States)

    Nakibullah, A; Rahman, A

    1996-01-01

    This article discusses the issue whether population growth is exogenous or endogenous in the economic development of Bangladesh. Overpopulation adversely affects food supplies, foreign exchange, and human resources. Moreover, it depresses savings per capita and retards growth of physical capital per labor. Underdeveloped countries, like Bangladesh, are faced with the problem of allocating resources between infrastructure, education, and health service that are essential for human capital development and population control measures. With this, determination whether fertility is exogenous or endogenous is important for policy purposes in the context of Bangladesh. Results showed that there is a correlation between population growth and real gross domestic products per capita. Based on Granger causality test, population growth is endogenous in the development process of Bangladesh and its overpopulation is due to poverty. Thus, there is a need for appropriate policy to take measures to improve human capital and decrease fertility rates.

  7. The Growth of Older Inmate Populations: How Population Aging Explains Rising Age at Admission.

    Science.gov (United States)

    Luallen, Jeremy; Cutler, Christopher

    2017-09-01

    Older inmates are the fastest growing segment of the prison population; however, the reasons for this are not well understood. One explanation is that the general population is aging, driving prison age distributions to change. For this article, we study the role of population aging in prison growth by investigating how the baby boom phenomenon of post-World War II has contributed to the growth of older inmate populations. We identify the impact of population aging using simulation methods that explain prison growth as the combination of criminal justice processes. Overall, we find evidence that population aging has played a significant role in explaining the growth of older inmate populations, in particular among inmates aged between 50 and 64 years, contributing to as much as half of the observed increase in these groups since 2000. This finding stands in contrast to the notion that population aging has little explanatory power in describing the growth of prison populations and implies that older inmate groups are more sensitive to compositional changes in the general population. We argue that prediction-based modeling of prison growth should more seriously consider the impacts and consequences of demographic shifts among older prisoner populations. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  8. Quorum sensing and density-dependent dispersal in an aquatic model system.

    Directory of Open Access Journals (Sweden)

    Simon Fellous

    Full Text Available Many organisms use cues to decide whether to disperse or not, especially those related to the composition of their environment. Dispersal hence sometimes depends on population density, which can be important for the dynamics and evolution of sub-divided populations. But very little is known about the factors that organisms use to inform their dispersal decision. We investigated the cues underlying density-dependent dispersal in inter-connected microcosms of the freshwater protozoan Paramecium caudatum. In two experiments, we manipulated (i the number of cells per microcosm and (ii the origin of their culture medium (supernatant from high- or low-density populations. We found a negative relationship between population density and rates of dispersal, suggesting the use of physical cues. There was no significant effect of culture medium origin on dispersal and thus no support for chemical cues usage. These results suggest that the perception of density - and as a result, the decision to disperse - in this organism can be based on physical factors. This type of quorum sensing may be an adaptation optimizing small scale monitoring of the environment and swarm formation in open water.

  9. Diet quality limits summer growth of field vole populations.

    Directory of Open Access Journals (Sweden)

    Kristian M Forbes

    Full Text Available Marked variation occurs in both seasonal and multiannual population density peaks of northern European small mammal species, including voles. The availability of dietary proteins is a key factor limiting the population growth of herbivore species. The objective of this study is to investigate the degree to which protein availability influences the growth of increasing vole populations. We hypothesise that the summer growth of folivorous vole populations is positively associated with dietary protein availability. A field experiment was conducted over a summer reproductive period in 18 vegetated enclosures. Populations of field voles (Microtus agrestis were randomised amongst three treatment groups: 1 food supplementation with ad libitum high protein (30% dry weight pellets, 2 food supplementation with ad libitum low protein (1% dry weight; both supplemented foods had equivalent energy content pellets, and 3 control (no food supplementation, n = 6 per treatment. Vole density, survival, demographic attributes and condition indicators were monitored with live-trapping and blood sampling. Highest final vole densities were attained in populations that received high protein supplementation and lowest in low protein populations. Control populations displayed intermediate densities. The survival rate of voles was similar in all treatment groups. The proportion of females, and of those that were pregnant or lactating, was highest in the high protein supplemented populations. This suggests that variation in reproductive, rather than survival rates of voles, accounted for density differences between the treatment groups. We found no clear association between population demography and individual physiological condition. Our results demonstrate that dietary protein availability limits vole population growth during the summer growing season. This suggests that the nutritional quality of forage may be an underestimated source of interannual variation in the

  10. Parameter Estimates in Differential Equation Models for Population Growth

    Science.gov (United States)

    Winkel, Brian J.

    2011-01-01

    We estimate the parameters present in several differential equation models of population growth, specifically logistic growth models and two-species competition models. We discuss student-evolved strategies and offer "Mathematica" code for a gradient search approach. We use historical (1930s) data from microbial studies of the Russian biologist,…

  11. Population growth, economic security, and cultural change in wilderness counties

    Science.gov (United States)

    Paul A. Lorah

    2000-01-01

    A familiar version of the “jobs versus the environment” argument asserts that wilderness areas limit economic growth by locking up potentially productive natural resources. Analysis of the development paths of rural Western counties shows that this is unlikely: the presence of Wilderness is correlated with income, employment and population growth. Similarly, Wilderness...

  12. Impact of Population Aging on Asia's Future Growth

    OpenAIRE

    Park, Donghyun; Shin, Kwanho

    2011-01-01

    First, the expert contributors argue, Asia must find ways to sustain rapid economic growth in the face of less favorable demographics, which implies slower growth of the workforce. Second, they contend, Asia must find ways to deliver affordable, adequate, and sustainable old-age economic security for its growing elderly population. Underpinned by rigorous analysis, a wide range of concrete policy options for sustaining economic growth while delivering economic security for the elderly are the...

  13. Density-dependent microbial turnover improves soil carbon model predictions of long-term litter manipulations

    Science.gov (United States)

    Georgiou, Katerina; Abramoff, Rose; Harte, John; Riley, William; Torn, Margaret

    2017-04-01

    Climatic, atmospheric, and land-use changes all have the potential to alter soil microbial activity via abiotic effects on soil or mediated by changes in plant inputs. Recently, many promising microbial models of soil organic carbon (SOC) decomposition have been proposed to advance understanding and prediction of climate and carbon (C) feedbacks. Most of these models, however, exhibit unrealistic oscillatory behavior and SOC insensitivity to long-term changes in C inputs. Here we diagnose the sources of instability in four models that span the range of complexity of these recent microbial models, by sequentially adding complexity to a simple model to include microbial physiology, a mineral sorption isotherm, and enzyme dynamics. We propose a formulation that introduces density-dependence of microbial turnover, which acts to limit population sizes and reduce oscillations. We compare these models to results from 24 long-term C-input field manipulations, including the Detritus Input and Removal Treatment (DIRT) experiments, to show that there are clear metrics that can be used to distinguish and validate the inherent dynamics of each model structure. We find that widely used first-order models and microbial models without density-dependence cannot readily capture the range of long-term responses observed across the DIRT experiments as a direct consequence of their model structures. The proposed formulation improves predictions of long-term C-input changes, and implies greater SOC storage associated with CO2-fertilization-driven increases in C inputs over the coming century compared to common microbial models. Finally, we discuss our findings in the context of improving microbial model behavior for inclusion in Earth System Models.

  14. The old age security hypothesis and optimal population growth.

    Science.gov (United States)

    Bental, B

    1989-03-01

    The application of the Samuelson-Diamond overlapping generations framework to the old age security hypothesis indicates that government intervention schemes can influence the relationship between population growth and capital accumulation. The most direct means of optimizing population growth is through taxes or subsidies that relate to the intergenerational transfer of wealth. A pay-as-you-go social security scheme, in which payment is predicated on the number of children the receiver has and is financed by taxes levied on the working population, emerges as the most likely intervention to produce the optimal steady state equilibrium. This system is able to correct any distortions the private sector may build into it. In contrast, a child support system, in which the government subsidizes or taxes workers according to their family size, can guarantee the optimal capital:labor ratio but not the optimal population growth rate. Thus, if the government seeks to decrease the population growth rate, the appropriate intervention is to levy a lump-sum social-security tax on workers and transfer the revenues to the old; the direction should be reversed if the goal is to increase population growth. Another alternative, a lump sum social security system, can guarantee optimal population growth but not a desirable capital:labor ratio. Finally, the introduction of money as a valued commodity into an economy with a high capital:labor ratio will also serve to decrease the population growth rate and solve the intergenerational transfer problem through the private sector without any need for government intervention.

  15. Effects of Density-Dependent Bag Constant and Strange Star Rotation

    Institute of Scientific and Technical Information of China (English)

    ZHOU Qiao-Er; GUO Hua

    2003-01-01

    With the emphasis on the effects of the density-dependent bag constant and the rotation of strange star the limiting mass of strange star is calculated. The obtained results show that the limiting mass and the corresponding radius of strange star increase as the rotation frequency increases, and tend to be lowered when the density-dependent bag constant is considered.

  16. A Role for M-Matrices in Modelling Population Growth

    Science.gov (United States)

    James, Glyn; Rumchev, Ventsi

    2006-01-01

    Adopting a discrete-time cohort-type model to represent the dynamics of a population, the problem of achieving a desired total size of the population under a balanced growth (contraction) and the problem of maintaining the desired size, once achieved, are studied. Properties of positive-time systems and M-matrices are used to develop the results,…

  17. Communication and The Challenges of Rapid Population Growth in ...

    African Journals Online (AJOL)

    2005) which projected the African Population at 1,349 million by 2025 and 1,969 million by 2050. These figures are so frightening that the use of communication to contribute to checking the high population growth is challenged. We discuss ...

  18. A new population growth map with variable coefficients

    International Nuclear Information System (INIS)

    Jannussis, A.

    1986-01-01

    In the present paper it is investigated a simple population growth map with variable coefficients. Moreover, it is studied the new population map of the form xsub(j+1) = axsub(j) (1/(1 + bxsub(j)) -1/(1 + cxsub(j))), c not= b, j = 0, 1,..., which is transformed in an equivalent logistic map

  19. Psychologists and the problem of population growth : Reply to Bridgeman

    NARCIS (Netherlands)

    Clayton, Susan; Carrico, Amanda; Steg, Linda; Swim, Janet K.; Bonnes, Mirilia; Devine-Wright, Patrick

    2017-01-01

    Bridgeman (2017) describes the important role of population growth in contributing to environmental problems. The present essay argues that population is an important component of human impact on the environment, but it must be considered in combination with consumption rates. A place-based

  20. Metropolitan migration and population growth in selected developing countries.

    Science.gov (United States)

    1983-01-01

    The purpose of this article is to estimate the components of metropolitan population growth in selected developing countries during 1960-1970 period. The study examines population growth in 26 cities: 5 are in Africa, 8 in Asia, and 13 in Latin America, using data from national census publications. These cities in general are the political capitals of their countries, but some additional large cities were selected in Brazil, Mexico, and South Africa. All cities, at the beginning of the 1960-1970 decade had over 500,000 population; Accra, the only exception, reached this population level during the 1960s. Some cities had over 4 million residents in 1970. Net migration contributed about 37% to total metropolitan population growth; the remainder of the growth is attributable to natural increase. Migration has a much stronger impact on metropolitan growth than suggested by the above figure: 1) Several metropolitan areas, for various reasons, are unlikely to receive many migrants; without those cities, the share of metropolitan growth from net migration is 44%. 2) Estimates of the natural increase of migrants after their arrival in the metropolitan areas, when added to migration itself, changes the total contribution of migration to 49% in some metropolitan areas. 3) Even where net migration contributes a smaller proportion to metropolitan growth than natural increase, the rates of net migration are generally high and should be viewed in the context of rapid metropolitan population growth from natural increase alone. Finally, the paper also compares the components of metropolitan growth with the components of growth in the remaining urban areas. The results show that the metropolitan areas, in general, grow faster than the remaining urban areas, and that this more rapid growth is mostly due to a higher rate of net migration. Given the significance of migration for metropolitan growth, further investigations of the effects of these migration streams, particularly with

  1. Lebensraum: paradoxically, population growth may eventually end wars.

    Science.gov (United States)

    Simon, J L

    1989-03-01

    Population growth may progressively reduce 1 of the motives for making war. Namely, population growth threatens shortages of resources, and especially land. Impending shortages cause a search for ways to mitigate the shortages. The discoveries eventually produce greater availability of resources than if population growth and pressure on resources had never occurred. The argument runs as follows: 1) Rhetoric about resources scarcity induced by population density has often contributed to international conflict, even if economics has not been the main motive in making war. 2) In the pre-modern era, war to obtain land and other resources may sometimes have been an economically sound policy. 3) Politicians and others in industrially developed nations believe resources may still be a casus belli. 4) Land and other productive resources are no longer worth acquiring at the cost of war.

  2. Phase separation driven by density-dependent movement: A novel mechanism for ecological patterns.

    Science.gov (United States)

    Liu, Quan-Xing; Rietkerk, Max; Herman, Peter M J; Piersma, Theunis; Fryxell, John M; van de Koppel, Johan

    2016-12-01

    Many ecosystems develop strikingly regular spatial patterns because of small-scale interactions between organisms, a process generally referred to as spatial self-organization. Self-organized spatial patterns are important determinants of the functioning of ecosystems, promoting the growth and survival of the involved organisms, and affecting the capacity of the organisms to cope with changing environmental conditions. The predominant explanation for self-organized pattern formation is spatial heterogeneity in establishment, growth and mortality, resulting from the self-organization processes. A number of recent studies, however, have revealed that movement of organisms can be an important driving process creating extensive spatial patterning in many ecosystems. Here, we review studies that detail movement-based pattern formation in contrasting ecological settings. Our review highlights that a common principle, where movement of organisms is density-dependent, explains observed spatial regular patterns in all of these studies. This principle, well known to physics as the Cahn-Hilliard principle of phase separation, has so-far remained unrecognized as a general mechanism for self-organized complexity in ecology. Using the examples presented in this paper, we explain how this movement principle can be discerned in ecological settings, and clarify how to test this mechanism experimentally. Our study highlights that animal movement, both in isolation and in unison with other processes, is an important mechanism for regular pattern formation in ecosystems. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. TOPICAL PROBLEMS: The phenomenological theory of world population growth

    Science.gov (United States)

    Kapitza, Sergei P.

    1996-01-01

    Of all global problems world population growth is the most significant. Demographic data describe this process in a concise and quantitative way in its past and present. Analysing this development it is possible by applying the concepts of systems analysis and synergetics, to work out a mathematical model for a phenomenological description of the global demographic process and to project its trends into the future. Assuming self-similarity as the dynamic principle of development, growth can be described practically over the whole of human history, assuming the growth rate to be proportional to the square of the number of people. The large parameter of the theory and the effective size of a coherent population group is of the order of 105 and the microscopic parameter of the phenomenology is the human lifespan. The demographic transition — a transition to a stabilised world population of some 14 billion in a foreseeable future — is a systemic singularity and is determined by the inherent pattern of growth of an open system, rather than by the lack of resources. The development of a quantitative nonlinear theory of the world population is of interest for interdisciplinary research in anthropology and demography, history and sociology, for population genetics and epidemiology, for studies in evolution of humankind and the origin of man. The model also provides insight into the stability of growth and the present predicament of humankind, and provides a setting for discussing the main global problems.

  4. Nigerian population growth and its implications for economic development.

    Science.gov (United States)

    Okpala, A O

    1990-12-01

    The population of Nigeria is growing at a rate of 3.75%/year indicating a doubling of the population every 22 years. Demographers estimated the population to be 91,178,000 in 1985. Even though population density is high (288 people/square mile), it is not equally distributed. It is highest in the south and southwest urban areas such as Lagos (1045 people/square mile) and lowest in the northeast (75 people/square mile). Moreover rural-urban migration is growing. A major reason for rural-urban migration is the dual nature of the economy in Nigeria. In urban areas, economic development brings about higher standards of living, but, in rural areas, a subsistence economy predominates. This coupled with rapid population growth results in small or no growth in per capita income. Only if the government were to integrate redistribution policies into complete economic development plans should it consider redistributing the population. It should stress rural development (e.g., incentives for firms to set up in rural areas). Further it should move some government offices to rural areas. The government also needs to adopt population policies encouraging the lowering of fertility levels. If it were to provide education through the secondary and prevocational education level free of charge, educated women will lower their fertility. Sex education should be included in the curriculum. Further the government must play an active role in family planning programs, especially educating rural women about family planning. It should also use the mass media to promote small family size, but it should not dictate family size. It also needs to recognize that population growth puts much pressure on the environment. For example, population growth causes soil erosion, nutrient exhaustion, rapid deforestation, and other problems which render the land unusable for agriculture.

  5. Population growth, human development, and deforestation in biodiversity hotspots.

    Science.gov (United States)

    Jha, S; Bawa, K S

    2006-06-01

    Human population and development activities affect the rate of deforestation in biodiversity hotspots. We quantified the effect of human population growth and development on rates of deforestation and analyzed the relationship between these causal factors in the 1980s and 1990s. We compared the averages of population growth, human development index (HDI, which measures income, health, and education), and deforestation rate and computed correlations among these variables for countries that contain biodiversity hotspots. When population growth was high and HDI was low there was a high rate of deforestation, but when HDI was high, rate of deforestation was low, despite high population growth. The correlation among variables was significant for the 1990s but not for the 1980s. The relationship between population growth and HDI had a regional pattern that reflected the historical process of development. Based on the changes in HDI and deforestation rate over time, we identified two drivers of deforestation: policy choice and human-development constraints. Policy choices that disregard conservation may cause the loss of forests even in countries that are relatively developed. Lack of development in other countries, on the other hand, may increase the pressure on forests to meet the basic needs of the human population. Deforestation resulting from policy choices may be easier to fix than deforestation arising from human development constraints. To prevent deforestation in the countries that have such constraints, transfer of material and intellectual resources from developed countries may be needed. Popular interest in sustainable development in developed countries can facilitate the transfer of these resources.

  6. Inflation, GDP growth and population change in the USA

    OpenAIRE

    Ivan Kitov

    2005-01-01

    Inflation in the USA between 1960 and 2004 is studied in the framework of the revealed rigidity of the personal income distribution normalized to the total nominal GDP. Inflation is found to be a mechanism, which prevents changes in the relative incomes induced by economic growth and population changes - both in number and age structure. A model is developed linking CPI to GDP growth rate and relative change of the number of people of some specific age. The GDP growth rate is characterized by...

  7. Populational Growth Models Proportional to Beta Densities with Allee Effect

    Science.gov (United States)

    Aleixo, Sandra M.; Rocha, J. Leonel; Pestana, Dinis D.

    2009-05-01

    We consider populations growth models with Allee effect, proportional to beta densities with shape parameters p and 2, where the dynamical complexity is related with the Malthusian parameter r. For p>2, these models exhibit a population dynamics with natural Allee effect. However, in the case of 1

  8. Urban Ecology: Patterns of Population Growth and Ecological Effects

    Science.gov (United States)

    Wayne C. Zipperer; Steward T.A. Pickett

    2012-01-01

    Currently, over 50% of the world’s population lives in urban areas. By 2050, this estimate is expected to be 70%. This urban growth, however, is not uniformly distributed around the world. The majority of it will occur in developing nations and create megacities whose populations exceed at least 10 million people. Not all urban areas, however, are growing. Some are...

  9. Optimization of human corneal endothelial cell culture: density dependency of successful cultures in vitro.

    Science.gov (United States)

    Peh, Gary S L; Toh, Kah-Peng; Ang, Heng-Pei; Seah, Xin-Yi; George, Benjamin L; Mehta, Jodhbir S

    2013-05-03

    Global shortage of donor corneas greatly restricts the numbers of corneal transplantations performed yearly. Limited ex vivo expansion of primary human corneal endothelial cells is possible, and a considerable clinical interest exists for development of tissue-engineered constructs using cultivated corneal endothelial cells. The objective of this study was to investigate the density-dependent growth of human corneal endothelial cells isolated from paired donor corneas and to elucidate an optimal seeding density for their extended expansion in vitro whilst maintaining their unique cellular morphology. Established primary human corneal endothelial cells were propagated to the second passage (P2) before they were utilized for this study. Confluent P2 cells were dissociated and seeded at four seeding densities: 2,500 cells per cm2 ('LOW'); 5,000 cells per cm2 ('MID'); 10,000 cells per cm2 ('HIGH'); and 20,000 cells per cm2 ('HIGH(×2)'), and subsequently analyzed for their propensity to proliferate. They were also subjected to morphometric analyses comparing cell sizes, coefficient of variance, as well as cell circularity when each culture became confluent. At the two lower densities, proliferation rates were higher than cells seeded at higher densities, though not statistically significant. However, corneal endothelial cells seeded at lower densities were significantly larger in size, heterogeneous in shape and less circular (fibroblastic-like), and remained hypertrophic after one month in culture. Comparatively, cells seeded at higher densities were significantly homogeneous, compact and circular at confluence. Potentially, at an optimal seeding density of 10,000 cells per cm2, it is possible to obtain between 10 million to 25 million cells at the third passage. More importantly, these expanded human corneal endothelial cells retained their unique cellular morphology. Our results demonstrated a density dependency in the culture of primary human corneal endothelial

  10. Intraspecific density dependence and a guild of consumers coexisting on one resource.

    Science.gov (United States)

    McPeek, Mark A

    2012-12-01

    The importance of negative intraspecific density dependence to promoting species coexistence in a community is well accepted. However, such mechanisms are typically omitted from more explicit models of community dynamics. Here I analyze a variation of the Rosenzweig-MacArthur consumer-resource model that includes negative intraspecific density dependence for consumers to explore its effect on the coexistence of multiple consumers feeding on a single resource. This analysis demonstrates that a guild of multiple consumers can easily coexist on a single resource if each limits its own abundance to some degree, and stronger intraspecific density dependence permits a wider variety of consumers to coexist. The mechanism permitting multiple consumers to coexist works in a fashion similar to apparent competition or to each consumer having its own specialized predator. These results argue for a more explicit emphasis on how negative intraspecific density dependence is generated and how these mechanisms combine with species interactions to shape overall community structure.

  11. The effects of density dependent resource limitation on size of wild reindeer.

    Science.gov (United States)

    Skogland, Terje

    1983-11-01

    A density-dependent decrement in size for wild reindeer from 12 different Norwegian herds at 16 different densities was shown using lower jawbone-length as the criterion of size. This criterion was tested and found to adequately predict body size of both bucks and does. Lactation in does did not affect jaw length but significantly affected dressed weights.A decrement in the size of does as a result of gross density was found. This size decrement was further analysed in relation to the habitat densities in winter (R 2 =0.85) and in summer (R 2 =0.75) separately, in order to estimate the relative effects of each factor. For herds with adequate food in winter (no signs of overgrazing of lichens) density in relation to summer habitat and mires yielded the highest predictive power in a multiple regression. For herds with adequate summer pastures, densities per winter habitat and lichen volumes showed likewise a highly significant correlation. The inclusion of the lichen volume data in the regression increased its predictive power. The major effect of resource limitation was to delay the time of calving because a maternal carry-over effect allowed the calf a shorter period of growth to be completed during its first summer. Neonate size at birth was highly correlated with maternal size regardless of the mean calving date although the latter was significantly delayed for small-sized does in food resource-limited herds. Likewise the postnatal growth rate of all calves were not significantly different during 50 days postpartum regardless of maternal conditions in winter feeding. The summer growth rates of bucks ≧1 year did not vary significantly between herds. The age of maturity of food resource-limited does was delayed by one year and growth ceased after the initiation of reproduction. This shows that under conditions of limited resources the does with delayed births of calves allocated less energy to body growth simply because they had less time to replenish body

  12. Economic consequences of population size, structure and growth.

    Science.gov (United States)

    Lee, R

    1983-01-01

    There seems to be 4 major approaches to conceptualizing and modeling demographic influences on economic and social welfare. These approaches are combined in various ways to construct richer and more comprehensive models. The basic approaches are: demographic influences on household or family behavior; population growth and reproducible capital; population size and fixed factors; and population and advantages of scale. These 4 models emphasize the supply side effects of population. A few of the ways in which these theories have been combined are sketched. Neoclassical growth models often have been combined with age distributed populations of individuals (or households), assumed to pursue optimal life cycle consumption and saving. In some well known development models, neoclassical growth models for the modern sector are linked by labor markets and migration to fixed factor (land) models of the traditional (agricultural) sector. A whole series of macro simulation models for developed and developing countries was based on single sector neoclassical growth models with age distributed populations. Yet, typically the household level foundations of assumed age distribution effects were not worked out. Simon's (1977) simulation models are in a class by themselves, for they are the only models that attempt to incorporate all the kinds of effects discussed. The economic demography of the individual and family cycle, as it is affected by regimes of fertility, mortality, and nuptiality, taken as given, are considered. The examination touches on many of the purported consequences of aggregate population growth and age composition, since so many of these are based implicitly or explicitly on assertions about micro level behavior. Demographic influences on saving and consumption, on general labor supply and female labor supply, and on problems of youth and old age dependency frequently fall in this category. Finally, attention is focused specifically on macro economic issues in

  13. Density-dependent reduction and induction of milkweed cardenolides by a sucking insect herbivore.

    Science.gov (United States)

    Martel, John W; Malcolm, Stephen B

    2004-03-01

    The effect of aphid population size on host-plant chemical defense expression and the effect of plant defense on aphid population dynamics were investigated in a milkweed-specialist herbivore system. Density effects of the aposematic oleander aphid, Aphis nerii, on cardenolide expression were measured in two milkweed species, Asclepias curassavica and A. incarnata. These plants vary in constitutive chemical investment with high mean cardenolide concentration in A. curassavica and low to zero in A. incarnata. The second objective was to determine whether cardenolide expression in these two host plants impacts mean A. nerii colony biomass (mg) and density. Cardenolide concentration (microgram/g) of A. curassavica in both aphid-treated leaves and opposite, herbivore-free leaves decreased initially in comparison with aphid-free controls, and then increased significantly with A. nerii density. Thus, A. curassavica responds to aphid herbivory initially with density-dependent phytochemical reduction, followed by induction of cardenolides to concentrations above aphid-free controls. In addition, mean cardenolide concentration of aphid-treated leaves was significantly higher than that of opposite, herbivore-free leaves. Therefore, A. curassavica induction is strongest in herbivore-damage tissue. Conversely, A. incarnata exhibited no such chemical response to aphid herbivory. Furthermore, neither host plant responded chemically to herbivore feeding duration time (days) or to the interaction between herbivore initial density and feeding duration time. There were also no significant differences in mean colony biomass or population density of A. nerii reared on high cardenolide (A. curassavica) and low cardenolide (A. incarnata) hosts.

  14. Poverty, population growth, and youth violence in DRC's cities ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    2016-04-28

    Apr 28, 2016 ... Poverty, population growth, and youth violence in DRC's cities ... Learn more about what drives DRC's urban violence and how it is linked to poverty ... ​Youth violence and the shift of land disputes from rural communities into ...

  15. The relationship between population growth and poverty in Africa: a ...

    African Journals Online (AJOL)

    The mainstream view from these debates and discussions is that rapid population growth in Africa has put pressure on the environment, leading to environmental degradation which translates into shortfall in food production and atrophied development. This view is as a result of ritualistic adherence to narrow ideological ...

  16. Is There Hidden Potential for Rural Population Growth in Sweden?

    Science.gov (United States)

    Niedomysl, Thomas; Amcoff, Jan

    2011-01-01

    Rural depopulation is a concern in many countries, and various policy initiatives have been taken to combat such trends. This article examines whether hidden potential for rural population growth can be found in Sweden. If such potential exists, it implies that the development prospects for many rural areas are not as unpromising as they may seem…

  17. The Vatican & Population Growth Control: Why an American Confrontation?

    Science.gov (United States)

    Mumford, Stephen D.

    1983-01-01

    The Vatican, because of its position on population growth, threatens the security of all nations. Catholic countries with right-wing dictatorships cannot confront the Vatican on family planning and survive. U.S. Catholics must confront the Vatican on this issue. American lay Catholics must break the American church away from the Vatican control.…

  18. 525 Population Growth, Hysteresis and Development Outcomes in ...

    African Journals Online (AJOL)

    technique of analysis is the Auto-Regressive Distributed Lag (ARDL) Bound test for long-run ..... Where; y is the actual income; λ is the adjustment factor and gy is output per ... income per capita if population growth leaves the ratio of workers to total ..... 0.00 and 0.01 probability values are not normally distributed around the.

  19. Optimal growth entails risky localization in population dynamics

    Science.gov (United States)

    Gueudré, Thomas; Martin, David G.

    2018-03-01

    Essential to each other, growth and exploration are jointly observed in alive and inanimate entities, such as animals, cells or goods. But how the environment's structural and temporal properties weights in this balance remains elusive. We analyze a model of stochastic growth with time correlations and diffusive dynamics that sheds light on the way populations grow and spread over general networks. This model suggests natural explanations of empirical facts in econo-physics or ecology, such as the risk-return trade-off and the Zipf law. We conclude that optimal growth leads to a localized population distribution, but such risky position can be mitigated through the space geometry. These results have broad applicability and are subsequently illustrated over an empirical study of financial data.

  20. The interaction between the spatial distribution of resource patches and population density: consequences for intraspecific growth and morphology.

    Science.gov (United States)

    Jacobson, Bailey; Grant, James W A; Peres-Neto, Pedro R

    2015-07-01

    and less angled pectoral fins. The different degrees of within-population growth variance at the same density level found here, as a function of spatial resource distribution, provide an explanation for the inconsistencies in within-site growth variance and population regulation often noted with regard to density dependence in natural landscapes. © 2015 The Authors. Journal of Animal Ecology © 2015 British Ecological Society.

  1. Population and prehistory I: Food-dependent population growth in constant environments.

    Science.gov (United States)

    Lee, Charlotte T; Tuljapurkar, Shripad

    2008-06-01

    We present a demographic model that describes the feedbacks between food supply, human mortality and fertility rates, and labor availability in expanding populations, where arable land area is not limiting. This model provides a quantitative framework to describe how environment, technology, and culture interact to influence the fates of preindustrial agricultural populations. We present equilibrium conditions and derive approximations for the equilibrium population growth rate, food availability, and other food-dependent measures of population well-being. We examine how the approximations respond to environmental changes and to human choices, and find that the impact of environmental quality depends upon whether it manifests through agricultural yield or maximum (food-independent) survival rates. Human choices can complement or offset environmental effects: greater labor investments increase both population growth and well-being, and therefore can counteract lower agricultural yield, while fertility control decreases the growth rate but can increase or decrease well-being. Finally we establish equilibrium stability criteria, and argue that the potential for loss of local stability at low population growth rates could have important consequences for populations that suffer significant environmental or demographic shocks.

  2. Impact of population growth and population ethics on climate change mitigation policy.

    Science.gov (United States)

    Scovronick, Noah; Budolfson, Mark B; Dennig, Francis; Fleurbaey, Marc; Siebert, Asher; Socolow, Robert H; Spears, Dean; Wagner, Fabian

    2017-11-14

    Future population growth is uncertain and matters for climate policy: higher growth entails more emissions and means more people will be vulnerable to climate-related impacts. We show that how future population is valued importantly determines mitigation decisions. Using the Dynamic Integrated Climate-Economy model, we explore two approaches to valuing population: a discounted version of total utilitarianism (TU), which considers total wellbeing and is standard in social cost of carbon dioxide (SCC) models, and of average utilitarianism (AU), which ignores population size and sums only each time period's discounted average wellbeing. Under both approaches, as population increases the SCC increases, but optimal peak temperature decreases. The effect is larger under TU, because it responds to the fact that a larger population means climate change hurts more people: for example, in 2025, assuming the United Nations (UN)-high rather than UN-low population scenario entails an increase in the SCC of 85% under TU vs. 5% under AU. The difference in the SCC between the two population scenarios under TU is comparable to commonly debated decisions regarding time discounting. Additionally, we estimate the avoided mitigation costs implied by plausible reductions in population growth, finding that large near-term savings ($billions annually) occur under TU; savings under AU emerge in the more distant future. These savings are larger than spending shortfalls for human development policies that may lower fertility. Finally, we show that whether lowering population growth entails overall improvements in wellbeing-rather than merely cost savings-again depends on the ethical approach to valuing population. Copyright © 2017 the Author(s). Published by PNAS.

  3. Habitat-specific population growth of a farmland bird.

    Directory of Open Access Journals (Sweden)

    Debora Arlt

    Full Text Available BACKGROUND: To assess population persistence of species living in heterogeneous landscapes, the effects of habitat on reproduction and survival have to be investigated. METHODOLOGY/PRINCIPAL FINDINGS: We used a matrix population model to estimate habitat-specific population growth rates for a population of northern wheatears Oenanthe oenanthe breeding in farmland consisting of a mosaic of distinct habitat (land use types. Based on extensive long-term data on reproduction and survival, habitats characterised by tall field layers (spring- and autumn-sown crop fields, ungrazed grasslands displayed negative stochastic population growth rates (log lambda(s: -0.332, -0.429, -0.168, respectively, that were markedly lower than growth rates of habitats characterised by permanently short field layers (pastures grazed by cattle or horses, and farmyards, log lambda(s: -0.056, +0.081, -0.059. Although habitats differed with respect to reproductive performance, differences in habitat-specific population growth were largely due to differences in adult and first-year survival rates, as shown by a life table response experiment (LTRE. CONCLUSIONS/SIGNIFICANCE: Our results show that estimation of survival rates is important for realistic assessments of habitat quality. Results also indicate that grazed grasslands and farmyards may act as source habitats, whereas crop fields and ungrazed grasslands with tall field layers may act as sink habitats. We suggest that the strong decline of northern wheatears in Swedish farmland may be linked to the corresponding observed loss of high quality breeding habitat, i.e. grazed semi-natural grasslands.

  4. Population growth is a variable open to change

    Science.gov (United States)

    Potts, M.

    2016-12-01

    The absolute number of people and the rate of population growth have an impact on climate mitigation, adaptation and possible conflict. Half the pregnancies in the US are unintended. Robust quantitative evidence from California demonstrates that improving access to family planning is the single most cost-effective way of mitigating our carbon footprint. Globally, there are 80 million unintended pregnancies annually. Many non-evidence barriers deprive women of the information and means required to separate sex from childbearing. Between 1960 and 1990, meeting the need for family planning led to a rapid fall in family size in much of Asia. Since 1990, funding for family planning has collapsed and fertility decline has stalled. The UN projects that by 2100 global population will increase by 3.8 billion (equal to world population in 1975). 80% of this growth will be in Africa. Studies project that climate change will undermine crop yields in parts of Africa, especially the Sahel. A high ratio of young males to the rest of the population is a risk factor in conflict. Today, only 1% of overseas assistance is allocated to family planning. Based on analysis of the past, doubling that investment would accelerate fertility decline, facilitating climate mitigation and adaptation, and possibly reducing conflict. Population and family planning were pushed off the international agenda by unacceptably and tragic episodes of coercion in China and India. However, there is compelling data that when voluntary family planning is widely available then family size can fall rapidly, as occurred in the Islamic Republic of Iran, where fertility fell more rapidly than in any other country in history. Family planning is listening to what women want not telling people want to do. Population growth is a variable open to change in a human rights framework. Population and family planning are variables relevant to the scientific agenda of the AGU.

  5. Population growth and food supply in sub-Saharan Africa.

    Science.gov (United States)

    Meerman, J; Cochrane, S H

    1982-09-01

    It is argued in this article that sub-Saharan Africa, given its present institutions and endowments of capital and technology, is already dangerously close to overpopulation. The rapid growth of its population projected for the next decades will greatly increase human misery and depress economic development. Specifically, rapid population growth will have disastrous effects on the region's ability to increase exports and provide people with food. There must be a search for new ways in which these effects could be mitigated. In sub-Saharan Africa fertility either continues to be very high or is increasing, in part due to some decline in traditional practices that reduce fertility, such as prolonged breastfeeding. This situation and the expectation of declining mortality imply that African population growth may increase further. Currently, population in sub-Saharan Africa is about half that of India and a third of China. There are 2 main reasons why reduced fertility in the next few decades is unlikely in sub-Saharan Africa as a whole: Africa has low literacy, high infant and child mortality, and low urbanization; and average African fertility rates may even increase for the next 20 years or so. The question that arises is what are the implications of continuing and rapid population growth for the African food supply. The region's cereal production is largely restricted to 4 grains, i.e., millet, sorghum, maize, and rice. The volume of grain production is less, by weight, than 60% of the production of roots and tubers. There are 2 main differences between the output of these crops in sub-Saharan Africa and the rest of the world: yields/hectare are lower in Africa than in elsewhere; and yields have generally been decreasing or largely constant in Africa. The low productivity has several causes. Today, population pressure has brought diminishing returns to traditional agriculture in much of the Sahel and the savanna, in parts of East Africa, Southern Africa, and parts

  6. Population growth to put pressure on some food supplies.

    Science.gov (United States)

    1997-01-01

    Continued high population growth in developing countries is likely to lead to intense pressure to produce more rice, according to estimates from the Manila-based International Rice Research Institute (IRRI). Ms. Mercedita Sombilla, a research scientist with IRRI, said that the projected increase in Asia's population will be the major force in accelerating demand for rice. According to various issues of the ESCAP Population Data Sheet, the population of the region will have increased from 3.3 billion in 1995 to almost 4.6 billion in 2020. The greatest growth in demand is expected to come from the lower-income countries of Asia, such as Bangladesh, India, Myanmar, Philippines, and Viet Nam, she said. However, in terms of overall food supplies, the Organization for Economic Cooperation and Development (OECD) estimates that food supplies will be sufficient. "Expecting reasonably strong productivity growth to be sustainable, no global food crisis seems likely to occur" between now and 2020, the organization stated in its report entitled "The World in 2020: Towards a New Global Age". full text

  7. Adapting to Population Growth: The Evolutionary Alternative to Malthus

    Directory of Open Access Journals (Sweden)

    Axel Kristinsson

    2016-06-01

    Full Text Available A long-standing debate on the dynamics of population growth in human history has become polarized between a Malthusian stance and a Boserupian one. The former tends to view population growth as limited by carrying capacity, dependent on environment and technology, whereas the latter sees population growth itself as a major inducement to social, economic and technological developments. In this paper the authors experiment with approaching this debate by using recent developments in evolutionary theory. According to these, evolutionary principles, as expounded by Charles Darwin and subsequent evolutionary scientists, apply not only to biological evolution but also to social or cultural evolution. Here, the role of genes is taken over by culture and, since culture is much more pliable than our DNA, evolution speeds up. As the only organisms on Earth whose evolution relies as heavily on culture as on genes, humans have become extremely adaptable. Their hyper-adaptability suggest that humans, through their cultural evolution, have managed increasingly to adapt to their own growing population, thus succeeding in accommodating ever-growing numbers. This hypothesis fits the Boserupian approach to population very well but less so the Malthusian one, perhaps indicating a gradual shift from a Malthusian regime to a Boserupian one in human history. The hypothesis is discussed and examined through four case studies: The beginning of farming around Göbekli Tepe in southeast Turkey, the productive farming systems of Tiwanaku in South America, the population crisis of late medieval and early modern Iceland, and the ‘collapse’ of Rapa Nui (Easter Island.

  8. Nuclear matter studies with density-dependent meson-nucleon coupling constants

    International Nuclear Information System (INIS)

    Banerjee, M.K.; Tjon, J.A.; Banerjee, M.K.; Tjon, J.A.

    1997-01-01

    Due to the internal structure of the nucleon, we should expect, in general, that the effective meson nucleon parameters may change in nuclear medium. We study such changes by using a chiral confining model of the nucleon. We use density-dependent masses for all mesons except the pion. Within a Dirac-Brueckner analysis, based on the relativistic covariant structure of the NN amplitude, we show that the effect of such a density dependence in the NN interaction on the saturation properties of nuclear matter, while not large, is quite significant. Due to the density dependence of the g σNN , as predicted by the chiral confining model, we find, in particular, a looping behavior of the binding energy at saturation as a function of the saturation density. A simple model is described, which exhibits looping and which is shown to be mainly caused by the presence of a peak in the density dependence of the medium modified σN coupling constant at low density. The effect of density dependence of the coupling constants and the meson masses tends to improve the results for E/A and density of nuclear matter at saturation. From the present study we see that the relationship between binding energy and saturation density may not be as universal as found in nonrelativistic studies and that more model dependence is exhibited once medium modifications of the basic nuclear interactions are considered. copyright 1997 The American Physical Society

  9. Genomic growth curves of an outbred pig population

    Directory of Open Access Journals (Sweden)

    Fabyano Fonseca e Silva

    2013-01-01

    Full Text Available In the current post-genomic era, the genetic basis of pig growth can be understood by assessing SNP marker effects and genomic breeding values (GEBV based on estimates of these growth curve parameters as phenotypes. Although various statistical methods, such as random regression (RR-BLUP and Bayesian LASSO (BL, have been applied to genomic selection (GS, none of these has yet been used in a growth curve approach. In this work, we compared the accuracies of RR-BLUP and BL using empirical weight-age data from an outbred F2 (Brazilian Piau X commercial population. The phenotypes were determined by parameter estimates using a nonlinear logistic regression model and the halothane gene was considered as a marker for evaluating the assumptions of the GS methods in relation to the genetic variation explained by each locus. BL yielded more accurate values for all of the phenotypes evaluated and was used to estimate SNP effects and GEBV vectors. The latter allowed the construction of genomic growth curves, which showed substantial genetic discrimination among animals in the final growth phase. The SNP effect estimates allowed identification of the most relevant markers for each phenotype, the positions of which were coincident with reported QTL regions for growth traits.

  10. Population growth, accessibility spillovers and persistent borders: Historical growth in West-European municipalities.

    Science.gov (United States)

    Jacobs-Crisioni, Chris; Koomen, Eric

    2017-06-01

    Lack of cross-border transport supply has repeatedly been blamed for the fact that national borders limit spatial interaction and, consequently, the growth of border regions. This study applies an accessibility approach to investigate for most municipalities in ten countries in mainland West Europe if foreign transport supply is lagging behind, and if population growth in these municipalities has been affected by the limits that national borders have imposed on market access. To do so, data describing historical population changes and road networks between 1961 and 2011 have been used. The results show that in the study area, cross-border transport accessibility was not at a disadvantage in 1961 and has since then grown even more than domestic accessibility. However, municipal population growth has depended almost exclusively on domestic market access. Processes of economic international integration in the study area are found to coincide with the growth of cross-border accessibility, but do not have a clear coincidence with the effects of cross-border accessibility on population growth.

  11. [The decline in population growth, income distribution, and economic recession].

    Science.gov (United States)

    Banguero, H

    1983-05-01

    This work uses Keynesian principles and an analysis of the Colombian population in the 1970s to argue that the Colombian policy of slowing population growth, which was adopted with the aim of improving the general welfare of the population, has had shortterm negative effects on effective demand and thus on the level of employment and welfare. These negative effects were caused by the inflexibility of income distribution, which prevented expansion of the internal market, complicated by the stagnant condition of the external sector and the budget deficit. The results of the Colombian case study demonstrate how the deceleration of population growth beginning in the 1960s had a significant impact on the levels of consumption and savings and on the patterns of consumption, leading to low levels of investment and little dynamism. Although the current Colombian economic recession is aggravated by contextual factors such as the world economic recession, the high cost of capital, the industrial recession, and declining food production among others, at the core of the crisis are longer term structural determinants such as the decline in the rate of population growth and the highly unequal distribution of income and wealth, which have contributed to a shrinking of the internal market for some types of goods. Given the unlikelihood of renewed rapid population growth, the Keynesian model suggests that the only alternative for increasing aggregate demand is state intervention through public spending and investment and reorientation of the financial system to achieve a dynamic redistribution of income. Based on these findings and on proposals of other analysts, a stragegy for revitalization is proposed which would imply a gradual income redistribution to allow increased consumption of mass produced goods by the low income groups. Direct consumption subsidies would be avoided because of their inflationary and import-expanding tendencies; rather, incentives and support would be

  12. Rapid population growth and environmental degradation: ultimate versus proximate factors.

    Science.gov (United States)

    Shaw, R P

    1989-01-01

    This philosophical review of 2 arguments about responsibility for and solutions to environmental degradation concludes that both sides are correct: the ultimate and the proximal causes. Ultimate causes of pollution are defined as the technology responsible for a given type of pollution, such as burning fossil fuel; proximate causes are defined as situation-specific factors confounding the problem, such as population density or rate of growth. Commoner and others argue that developed countries with low or negative population growth rates are responsible for 80% of world pollution, primarily in polluting technologies such as automobiles, power generation, plastics, pesticides, toxic wastes, garbage, warfaring, and nuclear weapons wastes. Distortionary policies also contribute; examples are agricultural trade protection, land mismanagement, urban bias in expenditures, and institutional rigidity., Poor nations are responsible for very little pollution because poverty allows little waste or expenditures for polluting, synthetic technologies. The proximal causes of pollution include numbers and rate of growth of populations responsible for the pollution. Since change in the ultimate cause of pollution remains out of reach, altering the numbers of polluters can make a difference. Predictions are made for proportions of the world's total waste production, assuming current 1.6 tons/capita for developed countries and 0.17 tons/capita for developing countries. If developing countries grow at current rates and become more wealthy, they will be emitting half the world's waste by 2025. ON the other hand, unsustainable population growth goes along with inadequate investment in human capital: education, health, employment, infrastructure. The solution is to improve farming technologies in the 117 non-self-sufficient countries, fund development in the most unsustainable enclaves of growing countries, break institutionalized socio-political rigidity in these enclaves, and focus on

  13. Is faster economic growth compatible with reductions in carbon emissions? The role of diminished population growth

    Science.gov (United States)

    Casey, Gregory; Galor, Oded

    2017-01-01

    We provide evidence that lower fertility can simultaneously increase income per capita and lower carbon emissions, eliminating a trade-off central to most policies aimed at slowing global climate change. We estimate the effect of lower fertility on carbon emissions, accounting for the fact that changes in fertility patterns affect carbon emissions through three channels: total population, the age structure of the population, and economic output. Our analysis proceeds in two steps. First, we estimate the elasticity of carbon emissions with respect to population and income per capita in an unbalanced yearly panel of cross-country data from 1950-2010. We demonstrate that the elasticity with respect to population is nearly seven times larger than the elasticity with respect to income per capita and that this difference is statistically significant. Thus, the regression results imply that 1% slower population growth could be accompanied by an increase in income per capita of nearly 7% while still lowering carbon emissions. In the second part of our analysis, we use a recently constructed economic-demographic model of Nigeria to estimate the effect of lower fertility on carbon emissions, accounting for the impacts of fertility on population growth, population age structure, and income per capita. We find that by 2100 C.E. moving from the medium to the low variant of the UN fertility projection leads to 35% lower yearly emissions and 15% higher income per capita. These results suggest that population policies could be part of the approach to combating global climate change.

  14. Population, internal migration, and economic growth: an empirical analysis.

    Science.gov (United States)

    Moreland, R S

    1982-01-01

    The role of population growth in the development process has received increasing attention during the last 15 years, as manifested in the literature in 3 broad categories. In the 1st category, the effects of rapid population growth on the growth of income have been studied with the use of simulation models, which sometimes include endogenous population growth. The 2nd category of the literature is concerned with theoretical and empirical studies of the economic determinants of various demographic rates--most usually fertility. Internal migration and dualism is the 3rd population development category to recieve attention. An attempt is made to synthesize developments in these 3 categories by estimating from a consistent set of data a 2 sector economic demographic model in which the major demographic rates are endogenous. Due to the fact that the interactions between economic and demographic variables are nonlinear and complex, the indirect effects of changes in a particular variable may depend upon the balance of numerical coefficients. For this reason it was felt that the model should be empirically grounded. A brief overview of the model is provided, and the model is compared to some similar existing models. Estimation of the model's 9 behavior equations is discussed, followed by a "base run" simulation of a developing country "stereotype" and a report of a number of policy experiments. The relatively new field of economic determinants of demographic variables was drawn upon in estimating equations to endogenize demographic phenomena that are frequently left exogenous in simulation models. The fertility and labor force participation rate functions are fairly standard, but a step beyong existing literature was taken in the life expectancy and intersectorial migration equations. On the economic side, sectoral savings functions were estimated, and it was found that the marginal propensity to save is lower in agriculture than in nonagriculture. Testing to see the

  15. Color-flavor locked strange quark matter in a mass density-dependent model

    International Nuclear Information System (INIS)

    Chen Yuede; Wen Xinjian

    2007-01-01

    Properties of color-flavor locked (CFL) strange quark matter have been studied in a mass-density-dependent model, and compared with the results in the conventional bag model. In both models, the CFL phase is more stable than the normal nuclear matter for reasonable parameters. However, the lower density behavior of the sound velocity in this model is completely opposite to that in the bag model, which makes the maximum mass of CFL quark stars in the mass-density-dependent model larger than that in the bag model. (authors)

  16. Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

    DEFF Research Database (Denmark)

    Mics, Zoltán; D’Angio, Andrea; Jensen, Søren A.

    2013-01-01

    In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude...... model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find...

  17. Stochastic resonance in a generalized Von Foerster population growth model

    Energy Technology Data Exchange (ETDEWEB)

    Lumi, N.; Mankin, R. [Institute of Mathematics and Natural Sciences, Tallinn University, 25 Narva Road, 10120 Tallinn (Estonia)

    2014-11-12

    The stochastic dynamics of a population growth model, similar to the Von Foerster model for human population, is studied. The influence of fluctuating environment on the carrying capacity is modeled as a multiplicative dichotomous noise. It is established that an interplay between nonlinearity and environmental fluctuations can cause single unidirectional discontinuous transitions of the mean population size versus the noise amplitude, i.e., an increase of noise amplitude can induce a jump from a state with a moderate number of individuals to that with a very large number, while by decreasing the noise amplitude an opposite transition cannot be effected. An analytical expression of the mean escape time for such transitions is found. Particularly, it is shown that the mean transition time exhibits a strong minimum at intermediate values of noise correlation time, i.e., the phenomenon of stochastic resonance occurs. Applications of the results in ecology are also discussed.

  18. Population-Level Density Dependence Influences the Origin and Maintenance of Parental Care

    OpenAIRE

    Reyes, Elijah; Thrasher, Patsy; Bonsall, Michael B.; Klug, Hope

    2016-01-01

    Parental care is a defining feature of animal breeding systems. We now know that both basic life-history characteristics and ecological factors influence the evolution of care. However, relatively little is known about how these factors interact to influence the origin and maintenance of care. Here, we expand upon previous work and explore the relationship between basic life-history characteristics (stage-specific rates of mortality and maturation) and the fitness benefits associated with the...

  19. Density dependence and microevolution interactively determine effects of phenology mismatch on population dynamics

    NARCIS (Netherlands)

    Reed, T.; Gienapp, P.; Visser, M.E.

    2015-01-01

    Life cycle events in plants and animals are typically adaptively tuned to anticipate predictable seasonal changes in environmental conditions or resources. Climate change is expected to affect the temporal component of species’ interactions, e.g. by creating a mismatch between a predator's breeding

  20. Growth anomalies on the coral genera Acropora and Porites are strongly associated with host density and human population size across the Indo-Pacific.

    Directory of Open Access Journals (Sweden)

    Greta S Aeby

    2011-02-01

    Full Text Available Growth anomalies (GAs are common, tumor-like diseases that can cause significant morbidity and decreased fecundity in the major Indo-Pacific reef-building coral genera, Acropora and Porites. GAs are unusually tractable for testing hypotheses about drivers of coral disease because of their pan-Pacific distributions, relatively high occurrence, and unambiguous ease of identification. We modeled multiple disease-environment associations that may underlie the prevalence of Acropora growth anomalies (AGA (n = 304 surveys and Porites growth anomalies (PGA (n = 602 surveys from across the Indo-Pacific. Nine predictor variables were modeled, including coral host abundance, human population size, and sea surface temperature and ultra-violet radiation anomalies. Prevalence of both AGAs and PGAs were strongly host density-dependent. PGAs additionally showed strong positive associations with human population size. Although this association has been widely posited, this is one of the first broad-scale studies unambiguously linking a coral disease with human population size. These results emphasize that individual coral diseases can show relatively distinct patterns of association with environmental predictors, even in similar diseases (growth anomalies found on different host genera (Acropora vs. Porites. As human densities and environmental degradation increase globally, the prevalence of coral diseases like PGAs could increase accordingly, halted only perhaps by declines in host density below thresholds required for disease establishment.

  1. Growth anomalies on the coral genera Acropora and Porites are strongly associated with host density and human population size across the Indo-Pacific

    Science.gov (United States)

    Aeby, Greta S.; Williams, Gareth J.; Franklin, Erik C.; Haapkyla, Jessica; Harvell, C. Drew; Neale, Stephen; Page, Cathie A.; Raymundo, Laurie; Vargas-Angel, Bernardo; Willis, Bette L.; Work, Thierry M.; Davy, Simon K.

    2011-01-01

    Growth anomalies (GAs) are common, tumor-like diseases that can cause significant morbidity and decreased fecundity in the major Indo-Pacific reef-building coral genera, Acropora and Porites. GAs are unusually tractable for testing hypotheses about drivers of coral disease because of their pan-Pacific distributions, relatively high occurrence, and unambiguous ease of identification. We modeled multiple disease-environment associations that may underlie the prevalence of Acropora growth anomalies (AGA) (n = 304 surveys) and Porites growth anomalies (PGA) (n = 602 surveys) from across the Indo-Pacific. Nine predictor variables were modeled, including coral host abundance, human population size, and sea surface temperature and ultra-violet radiation anomalies. Prevalence of both AGAs and PGAs were strongly host density-dependent. PGAs additionally showed strong positive associations with human population size. Although this association has been widely posited, this is one of the first broad-scale studies unambiguously linking a coral disease with human population size. These results emphasize that individual coral diseases can show relatively distinct patterns of association with environmental predictors, even in similar diseases (growth anomalies) found on different host genera (Acropora vs. Porites). As human densities and environmental degradation increase globally, the prevalence of coral diseases like PGAs could increase accordingly, halted only perhaps by declines in host density below thresholds required for disease establishment.

  2. Adult trees cause density-dependent mortality in conspecific seedlings by regulating the frequency of pathogenic soil fungi.

    Science.gov (United States)

    Liang, Minxia; Liu, Xubing; Gilbert, Gregory S; Zheng, Yi; Luo, Shan; Huang, Fengmin; Yu, Shixiao

    2016-12-01

    Negative density-dependent seedling mortality has been widely detected in tropical, subtropical and temperate forests, with soil pathogens as a major driver. Here we investigated how host density affects the composition of soil pathogen communities and consequently influences the strength of plant-soil feedbacks. In field censuses of six 1-ha permanent plots, we found that survival was much lower for newly germinated seedlings that were surrounded by more conspecific adults. The relative abundance of pathogenic fungi in soil increased with increasing conspecific tree density for five of nine tree species; more soil pathogens accumulated around roots where adult tree density was higher, and this greater pathogen frequency was associated with lower seedling survival. Our findings show how tree density influences populations of soil pathogens, which creates plant-soil feedbacks that contribute to community-level and population-level compensatory trends in seedling survival. © 2016 John Wiley & Sons Ltd/CNRS.

  3. Growth of rural population in Punjab, 1971-81.

    Science.gov (United States)

    Gill, M S

    1987-01-01

    Except for the decade 1941-1951, in which Punjab's population declined because of a huge exchange of population between India and Pakistan and a large loss of life, the decade 1971-1981 was the 1st decade since 1911 to experience a deceleration in the growth rate of the rural population of Punjab, India. The deceleration was due to out-migration to urban areas. The scheduled caste population increased 28.37% between 1971 and 1981, while the nonscheduled caste population increased by only 13.32%, which was considerably below the rate of natural increase. Nonscheduled castes had experienced substantial out-migration because of 1) improved transport and communication facilities which enabled them to move to urban centers; 2) mechanization of main farming operations and easy availability of migrant laborers which lessened the need for family labor; 3) the rise of a relatively mobile younger generation with a high literacy rate; 4) rapidly decreasing land holdings which strengthened the push factor in the countryside; and 5) rising aspirations, especially among the younger generation. In 1981, Sikhs constituted 71.3% of the rural population in Punjab, followed by Hindus (26.51%), Christians (1.25%), and Muslims (.89%). From 1971-1981, Muslims experienced the greatest increase (49.29%). Sikhs grew by 20.74% and Hindus by 9.02%. The Sikhs high growth rate was due to 1) a new technique for counting religious affiliation in which all members of a household are considered the same religion as the head of household and 2) conversion of Hindus to Sikhism. Hindus had a low growth rate because 1) the new method of counting religious affiliation and 2) rural-urban migration. The area with the lowest population increase resulted from industrialists and other nonagriculturists buying farmland, causing the agriculturists to move away to less desirable land. Conclusions are 1) the sharp rural-urban division along religious lines should be lessened, 2) Sikhs' lag in urbanization and

  4. A phenomenological theory of world population growth and global problems

    CERN Document Server

    Kapitza, Sergei P

    1996-01-01

    Of all global problems world population growth is the most significant one. To describe this process in its past and project it into the future a mathematical model is worked out. It treats the world population as an entity, seen as an open and evolv The approach is phenomenological and growth over very many generations is assumed to be selfsimilar and described by scaling. In terms of kinetics, the growth rate is proportional to the square of the total number of people and the nonlinear hyperbol of all mechanisms that contribute to our development in a collective interactive process. The model gives an estimate of the beginning of human evolution c.a. 4.4 million years ago and of the total number of people who ever lived c.a. 100 billion. In the scope of the model large scale cycles defined by history and anthropology are shown to be uniformly spaced in time on a logarithmic scale, expressing and inherent periodicity. As we approach the present, this progression of cycles is now termo transition. This is a s...

  5. Population growth and United States politics in the 1970s.

    Science.gov (United States)

    Nash, A E

    1973-01-01

    The 2 themes of this century, increasing environmental fragility and increasing human demands on government, are underlined by the failure of government to effectively govern, and the complex technology and modern communication systems which further divide the developing nations from the developed ones. Population stabilization may help relieve the tension between increasing expectation from government and the fiscal bind in 3 ways: 1)a higher per capita income would increase per capita government revenue which would have a better chance of meeting citizen expectations, 2)a moderately redistributive effect on personal income might occur by decreasing unwanted fertility through the dynamics of economics and increasing the role of government in elevating living standards, and 3)with reduction of government expenditure per capita, the cost of providing any given level of service would decrease. The nuclear age has altered the concept of what constitutes national security. Rapid population growth in the developing countries is also significant, and the United States economy depends on overseas investment. A constructive foreign policy, as opposed to neoimperialism or isolationism, is recommended to help influence world population growth.

  6. Permanence for a Delayed Nonautonomous SIR Epidemic Model with Density-Dependent Birth Rate

    Directory of Open Access Journals (Sweden)

    Li Yingke

    2011-01-01

    Full Text Available Based on some well-known SIR models, a revised nonautonomous SIR epidemic model with distributed delay and density-dependent birth rate was considered. Applying some classical analysis techniques for ordinary differential equations and the method proposed by Wang (2002, the threshold value for the permanence and extinction of the model was obtained.

  7. Tables of density dependent effective interactions between 122 and 800 MeV

    International Nuclear Information System (INIS)

    Dortmans, P.J.; Amos, K.

    1996-01-01

    Coordinate space density dependent effective nucleon-nucleon interaction based upon half-off-shell t and g-matrices are presented. These interactions are based upon the Paris interactions and are presented over a range of energies. 5 refs., 8 tabs

  8. Exponential Extinction of Nicholson's Blowflies System with Nonlinear Density-Dependent Mortality Terms

    Directory of Open Access Journals (Sweden)

    Wentao Wang

    2012-01-01

    Full Text Available This paper presents a new generalized Nicholson’s blowflies system with patch structure and nonlinear density-dependent mortality terms. Under appropriate conditions, we establish some criteria to guarantee the exponential extinction of this system. Moreover, we give two examples and numerical simulations to demonstrate our main results.

  9. Probing the density dependence of the symmetry potential in intermediate-energy heavy ion collisions

    International Nuclear Information System (INIS)

    Li Qingfeng; Li Zhuxia; Soff, Sven; Gupta, Raj K; Bleicher, Marcus; Stoecker, Horst

    2005-01-01

    Based on the ultrarelativistic quantum molecular dynamics model, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies. The calculated results of the Δ - /Δ ++ and π - /π + production ratios show a clear beam-energy dependence on the density-dependent symmetry potential, which is stronger for the π - /π + ratio close to the pion production threshold. The Coulomb potential of the mesons changes the transverse momentum distribution of the π - /π + ratio significantly, though it alters only slightly the π - and π + total yields. The π - yields, especially at midrapidity or at low transverse momenta and the π - /π + ratios at low transverse momenta are shown to be sensitive probes of the density-dependent symmetry potential in dense nuclear matter. The effect of the density-dependent symmetry potential on the production of both K 0 and K + mesons is also investigated

  10. Detecting crop population growth using chlorophyll fluorescence imaging.

    Science.gov (United States)

    Wang, Heng; Qian, Xiangjie; Zhang, Lan; Xu, Sailong; Li, Haifeng; Xia, Xiaojian; Dai, Liankui; Xu, Liang; Yu, Jingquan; Liu, Xu

    2017-12-10

    For both field and greenhouse crops, it is challenging to evaluate their growth information on a large area over a long time. In this work, we developed a chlorophyll fluorescence imaging-based system for crop population growth information detection. Modular design was used to make the system provide high-intensity uniform illumination. This system can perform modulated chlorophyll fluorescence induction kinetics measurement and chlorophyll fluorescence parameter imaging over a large area of up to 45  cm×34  cm. The system can provide different lighting intensity by modulating the duty cycle of its control signal. Results of continuous monitoring of cucumbers in nitrogen deficiency show the system can reduce the judge error of crop physiological status and improve monitoring efficiency. Meanwhile, the system is promising in high throughput application scenarios.

  11. Anthropometric growth study of the ear in a Chinese population.

    Science.gov (United States)

    Zhao, Shichun; Li, Dianguo; Liu, Zhenzhong; Wang, Yibiao; Liu, Lei; Jiang, Duyin; Pan, Bo

    2018-04-01

    A large number of anthropometric studies of the auricle have been reported in different nations, but little data were available in the Chinese population. The aim of this study was to analyze growth changes in the ear by measuring the width and length of ears in a Chinese population. A total of 480 participants were enrolled and classified into 1-, 3-, 5-, 7-, 9-, 12-, 14-, and 18-year groups (half were boys and half were girls in each group). Ear length, ear width, body weight, and body length were measured and recorded; ear index was calculated according to ear length and ear width. The growth of auricle and differences between genders were analyzed. Growth of ear in relation to body height and weight and the degree of emphasis on the length and width of the auricle were also analyzed. Ear length and width increased with age. Ear length achieved its mature size in both 14-year-old males and females. Ear width reached its mature size in males at 7 years and in females at 5 years. Different trends of ear index were shown between males and females. People in this population paid more attention to the length than the width of the auricle. The data indicated that ear development followed increase in age. There were gender and ethnic difference in the development of ear. These results may have potential implications for the diagnosis of congenital malformations, syndromes, and planning of ear reconstruction surgery. Copyright © 2017 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.

  12. Growth in an English population from the Industrial Revolution.

    Science.gov (United States)

    Mays, S; Brickley, M; Ives, R

    2008-05-01

    The rapid urbanization of the Industrial Revolution in 18th-19th century England presented new health challenges. Our aim is to investigate using English skeletal remains whether the living conditions for an urban working class group in the Industrial Revolution negatively impacted upon their skeletal growth compared with a population from a rural agrarian parish. The Industrial Revolution skeletal material is from St Martin's Churchyard, Birmingham (SMB), West Midlands. It dates primarily from the first half of the nineteenth century when Birmingham was a major manufacturing center. The rural group is from Wharram Percy (WP), North Yorkshire, and dates from 10th-19th century AD. The methodology involves plotting diaphyseal bone lengths versus dental age for subadults. No overall difference was found between the two populations in bone length-for-age among the 2- to 18-year cohort. However the younger parts of the SMB cohort were smaller than at WP; the opposite was true of the older parts of the cohort. Growth rate, as inferred from crosssectional data, appeared greater at SMB than at WP. The only result consistent with expectations is the larger bone dimensions in young children from WP, but this likely reflects prolonged breastfeeding at WP not differences in urban and rural environments. That the deleterious health effects that we know accompanied the major transition in human society from a rural agrarian to an urban industrialized living environment should be little manifest in skeletal endochondral growth data is discouraging for those who would use such methodology to monitor health in earlier populations. (c) 2008 Wiley-Liss, Inc.

  13. Project Mahathir: ‘Extraordinary’ Population Growth in Sabah

    OpenAIRE

    Frank, Sina

    2006-01-01

    The Malaysian state of Sabah faced an “extraordinary” population growth during the last decades. Illegal immigrants are said to have been issued Malaysian Identity Cards based on false statutory declarations. The so-called “Project Mahathir” changed Sabah’s ethnic make-up as well as the participation in elections. Politicians are said to have made use of “Phantom voters” in order to decide Sabah elections. Finally, with the help of a petition Sabah-based NGO’s demand an investi...

  14. Social policy and population growth in South-East Asia.

    Science.gov (United States)

    You Poh Seng Rao, B; Shantakumar, G

    1974-01-01

    Social and population policies are considered for the 10 countries comprising Southeast Asia--Burma, Indonesia, the Khmer Republic, Laos, Malaysia, the Philippines, Singapore, Thailand, North Vietnam, and South Vietnam. All but Singapore have high fertility rates and Burma, Indonesia, the Khmer Republic, Laos and the two Vietnams have high mortality rates also. Government expenditures for education and social security systems is expanding throughout the region and it is hoped that their continued growth will contribute substantially to the effective implementation of population policies. Population policies in the 5 countries which have them are discussed. These are Indonesia, Malaysia, the Philippines, Singapore, and Thailand. It is noted, however, that declaration of policy is but the first step. Strategies and programs differ from one country to the next and depend very much on the stage of development, level of literacy, degree of urbanization, and other factors. Family planning activities generally are endogenous to urban social systems but exogenous to rural social systems. Thus, the rural elite has a large role to play in making population policies an integral part of rural life. The possibility is considered of developing workable incentive packages integrating health, education, and social security benefits with suitable emphasis on fertility reduction.

  15. Population growth of Yellowstone grizzly bears: Uncertainty and future monitoring

    Science.gov (United States)

    Harris, R.B.; White, Gary C.; Schwartz, C.C.; Haroldson, M.A.

    2007-01-01

    Grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem of the US Rocky Mountains have recently increased in numbers, but remain vulnerable due to isolation from other populations and predicted reductions in favored food resources. Harris et al. (2006) projected how this population might fare in the future under alternative survival rates, and in doing so estimated the rate of population growth, 1983–2002. We address issues that remain from that earlier work: (1) the degree of uncertainty surrounding our estimates of the rate of population change (λ); (2) the effect of correlation among demographic parameters on these estimates; and (3) how a future monitoring system using counts of females accompanied by cubs might usefully differentiate between short-term, expected, and inconsequential fluctuations versus a true change in system state. We used Monte Carlo re-sampling of beta distributions derived from the demographic parameters used by Harris et al. (2006) to derive distributions of λ during 1983–2002 given our sampling uncertainty. Approximate 95% confidence intervals were 0.972–1.096 (assuming females with unresolved fates died) and 1.008–1.115 (with unresolved females censored at last contact). We used well-supported models of Haroldson et al. (2006) and Schwartz et al. (2006a,b,c) to assess the strength of correlations among demographic processes and the effect of omitting them in projection models. Incorporating correlations among demographic parameters yielded point estimates of λ that were nearly identical to those from the earlier model that omitted correlations, but yielded wider confidence intervals surrounding λ. Finally, we suggest that fitting linear and quadratic curves to the trend suggested by the estimated number of females with cubs in the ecosystem, and using AICc model weights to infer population sizes and λ provides an objective means to monitoring approximate population trajectories in addition to demographic

  16. Density-dependent effects of ants on selection for bumble bee pollination in Polemonium viscosum.

    Science.gov (United States)

    Galen, Candace; Geib, Jennifer C

    2007-05-01

    Mutualisms are commonly exploited by cheater species that usurp rewards without providing reciprocal benefits. Yet most studies of selection between mutualist partners ignore interactions with third species and consequently overlook the impact of cheaters on evolution in the mutualism. Here, we explicitly investigate how the abundance of nectar-thieving ants (cheaters) influences selection in a pollination mutualism between bumble bees and the alpine skypilot, Polemonium viscosum. As suggested in past work with this species, bumble bees accounted for most of the seed production (78% +/- 6% [mean +/- SE]) in our high tundra study population and, in the absence of ants, exerted strong selection for large flowers. We tested for indirect effects of ant abundance on seed set through bumble bee pollination services (pollen delivery and pollen export) and a direct effect through flower damage. Ants reduced seed set per flower by 20% via flower damage. As ant density increased within experimental patches, the rate of flower damage rose, but pollen delivery and export did not vary significantly, showing that indirect effects of increased cheater abundance on pollinator service are negligible in this system. To address how ants affect selection for plant participation in the pollination mutualism we tested the impact of ant abundance on selection for bumble bee-mediated pollination. Results show that the impact of ants on fitness (seed set) accruing under bumble bee pollination is density dependent in P. viscosum. Selection for bumble bee pollination declined with increasing ant abundance in experimental patches, as predicted if cheaters constrain fitness returns of mutualist partner services. We also examined how ant abundance influences selection on flower size, a key component of plant investment in bumble bee pollination. We predicted that direct effects of ants would constrain bumble bee selection for large flowers. However, selection on flower size was significantly

  17. Cell density dependence of Microcystis aeruginosa responses to copper algaecide concentrations: Implications for microcystin-LR release.

    Science.gov (United States)

    Kinley, Ciera M; Iwinski, Kyla J; Hendrikse, Maas; Geer, Tyler D; Rodgers, John H

    2017-11-01

    Along with mechanistic models, predictions of exposure-response relationships for copper are often derived from laboratory toxicity experiments with standardized experimental exposures and conditions. For predictions of copper toxicity to algae, cell density is a critical factor often overlooked. For pulse exposures of copper-based algaecides in aquatic systems, cell density can significantly influence copper sorbed by the algal population, and consequent responses. A cyanobacterium, Microcystis aeruginosa, was exposed to a copper-based algaecide over a range of cell densities to model the density-dependence of exposures, and effects on microcystin-LR (MC-LR) release. Copper exposure concentrations were arrayed to result in a gradient of MC-LR release, and masses of copper sorbed to algal populations were measured following exposures. While copper exposure concentrations eliciting comparable MC-LR release ranged an order of magnitude (24-h EC50s 0.03-0.3mg Cu/L) among cell densities of 10 6 through 10 7 cells/mL, copper doses (mg Cu/mg algae) were similar (24-h EC50s 0.005-0.006mg Cu/mg algae). Comparisons of MC-LR release as a function of copper exposure concentrations and doses provided a metric of the density dependence of algal responses in the context of copper-based algaecide applications. Combined with estimates of other site-specific factors (e.g. water characteristics) and fate processes (e.g. dilution and dispersion, sorption to organic matter and sediments), measuring exposure-response relationships for specific cell densities can refine predictions for in situ exposures and algal responses. These measurements can in turn decrease the likelihood of amending unnecessary copper concentrations to aquatic systems, and minimize risks for non-target aquatic organisms. Copyright © 2017 Elsevier Inc. All rights reserved.

  18. Estimated impact of global population growth on future wilderness extent

    Science.gov (United States)

    Dumont, E.

    2012-06-01

    Wilderness areas in the world are threatened by the environmental impacts of the growing global human population. This study estimates the impact of birth rate on the future surface area of biodiverse wilderness and on the proportion of this area without major extinctions. The following four drivers are considered: human population growth (1), agricultural efficiency (2), groundwater drawdown by irrigation (3), and non-agricultural space used by humans (buildings, gardens, roads, etc.) (4). This study indicates that the surface area of biodiverse unmanaged land will reduce with about 5.4% between 2012 and 2050. Further, it indicates that the biodiverse land without major extinctions will reduce with about 10.5%. These percentages are based on a commonly used population trajectory which assumes that birth rates across the globe will reduce in a similar way as has occurred in the past in many developed countries. Future birth rate is however very uncertain. Plausible future birth rates lower than the expected rates lead to much smaller reductions in surface area of biodiverse unmanaged land (0.7% as opposed to 5.4%), and a reduction in the biodiverse land without major extinctions of about 5.6% (as opposed to 10.5%). This indicates that birth rate is an important factor influencing the quality and quantity of wilderness remaining in the future.

  19. World population growth, family planning, and American foreign policy.

    Science.gov (United States)

    Sharpless, J

    1995-01-01

    The US decision since the 1960s to link foreign policy with family planning and population control is noteworthy for its intention to change the demographic structure of foreign countries and the magnitude of the initiative. The current population ideologies are part of the legacy of 19th century views on science, morality, and political economy. Strong constraints were placed on US foreign policy since World War II, particularly due to presumptions about the role of developing countries in Cold War ideology. Domestic debates revolved around issues of feminism, birth control, abortion, and family political issues. Since the 1960s, environmental degradation and resource depletion were an added global dimension of US population issues. Between 1935 and 1958 birth control movements evolved from the ideologies of utopian socialists, Malthusians, women's rights activists, civil libertarians, and advocates of sexual freedom. There was a shift from acceptance of birth control to questions about the role of national government in supporting distribution of birth control. Immediately postwar the debates over birth control were outside political circles. The concept of family planning as a middle class family issue shifted the focus from freeing women from the burdens of housework to making women more efficient housewives. Family planning could not be taken as a national policy concern without justification as a major issue, a link to national security, belief in the success of intervention, and a justifiable means of inclusion in public policy. US government involvement began with agricultural education, technological assistance, and economic development that would satisfy the world's growing population. Cold War politics forced population growth as an issue to be considered within the realm of foreign policy and diplomacy. US government sponsored family planning was enthusiastic during 1967-74 but restrained during the 1980s. The 1990s has been an era of redefinition of

  20. Relativistic Random-Phase Approximation with Density-dependent Meson-nucleon Couplings at Finite Temperature

    International Nuclear Information System (INIS)

    Niu, Y.; Paar, N.; Vretenar, D.; Meng, J.

    2009-01-01

    The fully self-consistent relativistic random-phase approximation (RRPA) framework based on effective interactions with a phenomenological density dependence is extended to finite temperatures. The RRPA configuration space is built from the spectrum of single-nucleon states at finite temperature obtained by the temperature dependent relativistic mean field (RMF-T) theory based on effective Lagrangian with density dependent meson-nucleon vertex functions. As an illustration, the dependence of binding energy, radius, entropy and single particle levels on temperature for spherical nucleus 2 08P b is investigated in RMF-T theory. The finite temperature RRPA has been employed in studies of giant monopole and dipole resonances, and the evolution of resonance properties has been studied as a function of temperature. In addition, exotic modes of excitation have been systematically explored at finite temperatures, with an emphasis on the case of pygmy dipole resonances.(author)

  1. Isoscalar giant resonances and Landau parameters with density-dependent effective interactions

    International Nuclear Information System (INIS)

    Kohno, Michio; Ando, Kazuhiko

    1979-01-01

    Discussion is given on the relations between the Landau parameters and the isoscalar giant (quadrupole- and monopole-) resonance energies by using general density-dependent interactions. In the limit of infinite nuclear matter, the isoscalar giant quadrupole energy is shown to depend not only on the effective mass but also on the Landau parameter F 2 . Collective energies of the isoscalar giant resonances are calculated for 16 O and 40 Ca with four different effective interactions, G-0, B1, SII and SV, by using the scaling- and constrained Hartree-Fock-methods. It is shown that the dependence of the collective energies on the effective interactions is essentially determined by the Landau parameters. The G-0 force is found to be most successful in reproducing the giant resonance energies. Validity of the RPA-moment theorems is examined for the case of local density-dependent interactions. (author)

  2. Contribution of population growth to per capita income and sectoral output growth in Japan, 1880-1970.

    Science.gov (United States)

    Yamaguchi, M; Kennedy, G

    1984-09-01

    The authors measured the positive and negative contributions of population and labor force growth to the growth of per capita income and sectoral output in Japan in the 1880-1970 period. A 2-sector growth accounting model that treats population and labor growth as separate variables was used. 3 alternative methods were used: the Residual method, the Verdoorn method, and the factor augmenting rate method. The total contribution of population cum labor growth to per capita income growth tended to be negative in the 1880-1930 period and positive in the 1930-40 and 1950-70. Over the 1880-1970 period as a whole, population cum labor growth made a positive contribution to per capita income growth under the Residual method (0.35%/year), the factor augmenting rate method (0.29%/year), and the Verdoorn method (0.01%/year). In addition, population cum labor growth contributed positively to sectoral output growth. The average contribution to agricultural output growth ranged from 1.03% (Verdoorn) - 1.46%/year (factor augmenting rate), while the average contribution to nonagricultural output growth ranged from 1.22% (Verdoorn) - 1.60%/year (Residual). Although these results are dependent on the model used, the fact that all 3 methods yielded consistent results suggests that population cum labor growth did make a positive contribution to per capita income and sectoral output growth in Japan. These findings imply that in economies where the rate of technical change in agricultural and nonagricultural sectors exceeds population growth, policies that reduce agricultural elasticities may be preferable; on the other hand, policies that reduce agricultural elasticities are to be avoided in economies with low rates of technical change. Moreover, in the early stages of economic development, policies that increase agricultural income and price elasticities should be considered.

  3. Population and labour force growth and patterns in ASEAN countries.

    Science.gov (United States)

    Saw, S

    1988-01-01

    "The paper shows that the diverse labor dimensions prevailing in the ASEAN region can be attributed to changes in the structure of the society and economy in the course of recent economic development. It observes the considerable variety in the growth of the population and its effect on the labor force in the ASEAN region.... The paper details the similarity and diversity in the level and type of labor force participation rates. A common feature shared by ASEAN countries is a general pattern in the age-specific participation rate of men. In contrast, the women, aside from participating in the labor force at a much lower level than men at almost all ages, display diverse patterns of participation over the working age range. Lastly, the distribution of the labor force according to major industrial sectors in the six ASEAN countries is presented...." excerpt

  4. Influence of life history strategies on sensitivity, population growth and response to climate for sympatric alpine birds

    Directory of Open Access Journals (Sweden)

    Wilson Scott

    2012-06-01

    Full Text Available Abstract Background The life history strategy of a species can influence how populations of that species respond to environmental variation. In this study, we used a matrix modeling approach to examine how life history differences among sympatric rock and white-tailed ptarmigan affect the influence of demographic rates on population growth (λ and the potential response to a changing climate. Rock ptarmigan have a slower life history strategy than white-tailed ptarmigan in the study region with lower annual reproductive effort but higher adult survival. Results Based on data from a 5-year field study, deterministic estimates of λ indicated that populations were stable for rock ptarmigan (λ = 1.01, but declining for white-tailed ptarmigan (λ = 0.96. The demographic rates with the highest elasticity for rock ptarmigan were the survival of after-second year females, followed by juvenile survival and success of the first nest. For white-tailed ptarmigan, juvenile survival had the highest elasticity followed by success of the first nest and survival of second-year females. Incorporating stochasticity into the demographic rates led to a 2 and 4% drop in λ for rock and white-tailed ptarmigan respectively. Using data from the first three years we also found that population growth rates of both species were depressed following an increased frequency of severe years, but less so for rock ptarmigan which showed greater resilience under these conditions. Conclusions Our results provide evidence that populations of closely related species can vary in their response to environmental change as a consequence of life history differences. Rock ptarmigan, with a slower life history, are more responsive to demographic rates that influence survival and older life stages but this response is tempered by the extent of variability in each of the rates. Thus, predictions need to consider both aspects in modeling population response to a varying climate

  5. Contributions of long-distance dispersal to population growth in colonising Pinus ponderosa populations.

    Science.gov (United States)

    Lesser, Mark R; Jackson, Stephen T

    2013-03-01

    Long-distance dispersal is an integral part of plant species migration and population development. We aged and genotyped 1125 individuals in four disjunct populations of Pinus ponderosa that were initially established by long-distance dispersal in the 16th and 17th centuries. Parentage analysis was used to determine if individuals were the product of local reproductive events (two parents present), long-distance pollen dispersal (one parent present) or long-distance seed dispersal (no parents present). All individuals established in the first century at each site were the result of long-distance dispersal. Individuals reproduced at younger ages with increasing age of the overall population. These results suggest Allee effects, where populations were initially unable to expand on their own, and were dependent on long-distance dispersal to overcome a minimum-size threshold. Our results demonstrate that long-distance dispersal was not only necessary for initial colonisation but also to sustain subsequent population growth during early phases of expansion. © 2012 Blackwell Publishing Ltd/CNRS.

  6. Grassland ecology and population growth: striking a balance.

    Science.gov (United States)

    Hou, D; Duan, C; Zhang, D

    2000-06-01

    Degradation of forest and grasslands in western China attributes to the soil erosion and desertification in the country. Researchers have established that the primary reason for the degradation of grasslands is overgrazing, which in turn is caused by a number of factors, including over-population and over-reliance on animal husbandry. In addition, the existing administrative system has also proved ineffective in ensuring sustainable development. On contrary, many local governments even encourage exploitative development of grassland; thus, localities opened up grassland for growing crops in an effort to increase income. According to estimates, degraded grassland accounts for more than one-third of utilizable acreage and another one-third suffers from a profusion of rats and pests. To redress the situation, central government should implement strategies in achieving sustainable development, such as providing banking and tax incentives for the development of the secondary and tertiary industries, and supporting education and training of youths from herding areas. Moreover, government should increase spending on infrastructural construction and ecological preservation. Finally, the family planning program needs to be enforced to control population growth and improve the quality of peoples¿ lives.

  7. The impact of accelerating faster than exponential population growth on genetic variation.

    Science.gov (United States)

    Reppell, Mark; Boehnke, Michael; Zöllner, Sebastian

    2014-03-01

    Current human sequencing projects observe an abundance of extremely rare genetic variation, suggesting recent acceleration of population growth. To better understand the impact of such accelerating growth on the quantity and nature of genetic variation, we present a new class of models capable of incorporating faster than exponential growth in a coalescent framework. Our work shows that such accelerated growth affects only the population size in the recent past and thus large samples are required to detect the models' effects on patterns of variation. When we compare models with fixed initial growth rate, models with accelerating growth achieve very large current population sizes and large samples from these populations contain more variation than samples from populations with constant growth. This increase is driven almost entirely by an increase in singleton variation. Moreover, linkage disequilibrium decays faster in populations with accelerating growth. When we instead condition on current population size, models with accelerating growth result in less overall variation and slower linkage disequilibrium decay compared to models with exponential growth. We also find that pairwise linkage disequilibrium of very rare variants contains information about growth rates in the recent past. Finally, we demonstrate that models of accelerating growth may substantially change estimates of present-day effective population sizes and growth times.

  8. Density-dependent seedling mortality varies with light availability and species abundance in wet and dry Hawaiian forests

    Science.gov (United States)

    Faith Inman-Narahari; Rebecca Ostertag; Stephen P. Hubbell; Christian P. Giardina; Susan Cordell; Lawren Sack; Andrew MacDougall

    2016-01-01

    Conspecific density may contribute to patterns of species assembly through negative density dependence (NDD) as predicted by the Janzen-Connell hypothesis, or through facilitation (positive density dependence; PDD). Conspecific density effects are expected to be more negative in darker and wetter environments due to higher pathogen abundance and...

  9. Strong persistent growth differences govern individual performance and population dynamics in a tropical forest understorey palm

    NARCIS (Netherlands)

    Jansen, M.; Zuidema, P.A.; Anten, N.P.R.; Martínez-Ramos, M.

    2012-01-01

    1. Persistent variation in growth rate between individual plants can have strong effects on population dynamics as fast growers reach the reproductive size at an earlier age and thus potentially contribute more to population growth than slow growers. In tropical forests, such persistent growth

  10. Population Growth in the 1990s: Patterns within the United States.

    Science.gov (United States)

    Perry, Marc

    2002-01-01

    Examines population growth during the 1990s for a variety of geographic levels including regions, divisions, states, metropolitan areas, counties, and large cities. Compares growth rates for the 1990s with earlier decades to provide an historical context for present-day trends in population growth and decline. Discusses how differential population…

  11. What makes a species common? No evidence of density-dependent recruitment or mortality of the sea urchin Diadema antillarum after the 1983-1984 mass mortality.

    Science.gov (United States)

    Levitan, Don R; Edmunds, Peter J; Levitan, Keeha E

    2014-05-01

    A potential consequence of individuals compensating for density-dependent processes is that rare or infrequent events can produce profound and long-term shifts in species abundance. In 1983-1984 a mass mortality event reduced the numbers of the abundant sea urchin Diadema antillarum by 95-99% throughout the Caribbean and western Atlantic. Following this event, the abundance of macroalgae increased and the few surviving D. antillarum responded by increasing in body size and fecundity. These initial observations suggested that populations of D. antillarum could recover rapidly following release from food limitation. In contrast, published studies of field manipulations indicate that this species had traits making it resistant to density-dependent effects on offspring production and adult mortality; this evidence raises the possibility that density-independent processes might keep populations at a diminished level. Decadal-scale (1983-2011) monitoring of recruitment, mortality, population density and size structure of D. antillarum from St John, US Virgin Islands, indicates that population density has remained relatively stable and more than an order of magnitude lower than that before the mortality event of 1983-1984. We detected no evidence of density-dependent mortality or recruitment since this mortality event. In this location, model estimates of equilibrium population density, assuming density-independent processes and based on parameters generated over the first decade following the mortality event, accurately predict the low population density 20 years later (2011). We find no evidence to support the notion that this historically dominant species will rebound from this temporally brief, but spatially widespread, perturbation.

  12. Experimental design and estimation of growth rate distributions in size-structured shrimp populations

    International Nuclear Information System (INIS)

    Banks, H T; Davis, Jimena L; Ernstberger, Stacey L; Hu, Shuhua; Artimovich, Elena; Dhar, Arun K

    2009-01-01

    We discuss inverse problem results for problems involving the estimation of probability distributions using aggregate data for growth in populations. We begin with a mathematical model describing variability in the early growth process of size-structured shrimp populations and discuss a computational methodology for the design of experiments to validate the model and estimate the growth-rate distributions in shrimp populations. Parameter-estimation findings using experimental data from experiments so designed for shrimp populations cultivated at Advanced BioNutrition Corporation are presented, illustrating the usefulness of mathematical and statistical modeling in understanding the uncertainty in the growth dynamics of such populations

  13. Refitting density dependent relativistic model parameters including Center-of-Mass corrections

    International Nuclear Information System (INIS)

    Avancini, Sidney S.; Marinelli, Jose R.; Carlson, Brett Vern

    2011-01-01

    Full text: Relativistic mean field models have become a standard approach for precise nuclear structure calculations. After the seminal work of Serot and Walecka, which introduced a model Lagrangian density where the nucleons interact through the exchange of scalar and vector mesons, several models were obtained through its generalization, including other meson degrees of freedom, non-linear meson interactions, meson-meson interactions, etc. More recently density dependent coupling constants were incorporated into the Walecka-like models, which are then extensively used. In particular, for these models a connection with the density functional theory can be established. Due to the inherent difficulties presented by field theoretical models, only the mean field approximation is used for the solution of these models. In order to calculate finite nuclei properties in the mean field approximation, a reference set has to be fixed and therefore the translational symmetry is violated. It is well known that in such case spurious effects due to the center-of-mass (COM) motion are present, which are more pronounced for light nuclei. In a previous work we have proposed a technique based on the Pierls-Yoccoz projection operator applied to the mean-field relativistic solution, in order to project out spurious COM contributions. In this work we obtain a new fitting for the density dependent parameters of a density dependent hadronic model, taking into account the COM corrections. Our fitting is obtained taking into account the charge radii and binding energies for He 4 , O 16 , Ca 40 , Ca 48 , Ni 56 , Ni 68 , Sn 100 , Sn 132 and Pb 208 . We show that the nuclear observables calculated using our fit are of a quality comparable to others that can be found in the literature, with the advantage that now a translational invariant many-body wave function is at our disposal. (author)

  14. Density-Dependent Conformable Space-time Fractional Diffusion-Reaction Equation and Its Exact Solutions

    Science.gov (United States)

    Hosseini, Kamyar; Mayeli, Peyman; Bekir, Ahmet; Guner, Ozkan

    2018-01-01

    In this article, a special type of fractional differential equations (FDEs) named the density-dependent conformable fractional diffusion-reaction (DDCFDR) equation is studied. Aforementioned equation has a significant role in the modelling of some phenomena arising in the applied science. The well-organized methods, including the \\exp (-φ (\\varepsilon )) -expansion and modified Kudryashov methods are exerted to generate the exact solutions of this equation such that some of the solutions are new and have been reported for the first time. Results illustrate that both methods have a great performance in handling the DDCFDR equation.

  15. Temperature and carrier density dependence of anisotropy in supercurrent density in layered cuprate superconductors

    International Nuclear Information System (INIS)

    Singh, M.P.; Tewari, B.S.; Ajay

    2006-01-01

    In the present work, we have studied the effect of temperature and carrier density on anisotropy in supercurrent density in bilayer cuprate superconductors. Here, we have considered a tight binding bilayered Hubbard Hamiltonian containing intra and interlayer attractive interactions. The situation considered here is similar to a SIS junction. We have got the expressions for the superconducting order parameters, carrier density and anisotropy in superconducting density (I ab /I c ) for such SIS junction. The numerical analysis show that the anisotropy in the supercurrent density depends on temperature and carrier density in layered high T c cuprates. (author)

  16. Knock-on type exchange and the density dependence of an effective interaction

    International Nuclear Information System (INIS)

    Jeukenne, J.P.; Mahaux, C.

    1981-01-01

    We investigate the origin of the density-dependence of the strength of an effective interaction previously derived from a Brueckner-Hartree-Fock calculation of the optical-model potential in nuclear matter. From the analysis of a model based on the Hartree-Fock approximation and on a Yukawa interaction with a Majorana exchange component, we study to what extent this dependence derives from the momentum-dependence of the exchange contribution of the knock-on type. The model is also used to discuss zero-range pseudopotential methods for including this knock-on contribution. (orig.)

  17. A demographic model to predict future growth of the Addo elephant population

    OpenAIRE

    A.M. Woodd

    1999-01-01

    An age-structured demographic model of the growth of the Addo elephant population was developed using parameters calculated from long-term data on the population. The model was used to provide estimates of future population growth. Expansion of the Addo Elephant National Park is currently underway, and the proposed target population size for elephant within the enlarged park is 2700. The model predicts that this population size will be reached during the year 2043, so that the Addo elephant p...

  18. POPULATION GROWTH AND PREFERENCE CHANGE IN A GENERALIZED SOLOW GROWTH MODEL WITH GENDER TIME DISTRIBUTIONS

    Directory of Open Access Journals (Sweden)

    Wei-Bin Zhang

    2016-09-01

    Full Text Available The study builds a model of dynamic interactions between the birth rate, the mortality rate, the population, wealth accumulation, time distribution between work, leisure and children caring, habit formation and preference change. The production technology and markets are built on the Solow growth model. We base our modeling the population dynamics on the Haavelmo population model and the Barro-Becker fertility choice model. This study takes account of habit formation and preference change. Although it is influenced by the Ramsey growth theory with time preference and habit formation, it uses Zhang’s approach to the household with habit formation and preference change. We synthesize different dynamic forces in a compact framework, using the utility function proposed by Zhang. Analytically, we focus on transitional processes as well as economic equilibrium. As the economic system is given by autonomous nonlinear differential equations, it is not easy to analyze its behavior. We simulate the model to demonstrate the existence of an equilibrium point and plot the motion of the dynamic system. We examine the effects of changes in weights given to the habit stock of children, the wife’s wage rate having negative impact on the propensity to have children, the wife weighing less the habit stock of leisure time, the wife’s habit stock of leisure time having negative impact on the husband’s propensity to use leisure time, the wife’s wage rate having negative impact on the husband’s propensity to use leisure time, woman’s human capital being improved, a rise in the total factor productivity, and the mother spending more time on each child fostering.

  19. Colony Development and Density-Dependent Processes in Breeding Grey Herons

    Directory of Open Access Journals (Sweden)

    Takeshi Shirai

    2013-01-01

    Full Text Available The density-dependent processes that limit the colony size of colonially breeding birds such as herons and egrets remain unclear, because it is difficult to monitor colonies from the first year of their establishment, and the most previous studies have considered mixed-species colonies. In the present study, single-species colonies of the Grey Heron (Ardea cinerea were observed from the first year of their establishment for 16 years in suburban Tokyo. Colony size increased after establishment, illustrating a saturation curve. The breeding duration (days from nest building to fledging by a pair increased, but the number of fledglings per nest decreased, with colony size. The reproductive season in each year began earlier, and there was greater variation in the timing of individual breeding when the colony size was larger. The prolonged duration until nestling feeding by early breeders of the colony suggests that herons at the beginning of the new breeding season exist in an unsteady state with one another, likely owing to interactions with immigrant individuals. Such density-dependent interference may affect reproductive success and limit the colony size of Grey Herons.

  20. Density dependence of SOL power width in ASDEX upgrade L-Mode

    Directory of Open Access Journals (Sweden)

    B. Sieglin

    2017-08-01

    A recent study [4] with an open divertor configuration found an asymmetry of the power fall-off length between inner and outer target with a smaller power fall-off length λq,i on the inner divertor target. Measurements with a closed divertor configuration find a similar asymmetry for low recycling divertor conditions. It is found, in the experiment, that the in/out asymmetry λq,i/λq,o is strongly increasing with increasing density. Most notably the heat flux density at the inner divertor target is reducing with increasing λq,i whilst the total power onto each divertor target stays constant. It is found that λq,o exhibits no significant density dependence for hydrogen and deuterium but increases with about the square root of the electron density for helium. The difference between H,D and He could be due to the different recycling behaviour in the divertor. These findings may help current modelling attempts to parametrize the density dependence of the widening of the power channel and thus allow for detailed comparison to both divertor effects like recycling or increased upstream SOL cross field transport.

  1. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Bajaj, Sanyam, E-mail: bajaj.10@osu.edu; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Reza, Shahed; Chumbes, Eduardo M. [Raytheon Integrated Defense Systems, Andover, Massachusetts 01810 (United States); Khurgin, Jacob [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Material Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2015-10-12

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  2. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Bajaj, Sanyam; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-01-01

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10 7  cm/s at a low sheet charge density of 7.8 × 10 11  cm −2 . An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs

  3. Spatial variability and macro‐scale drivers of growth for native and introduced Flathead Catfish populations

    Science.gov (United States)

    Massie, Danielle L.; Smith, Geoffrey; Bonvechio, Timothy F.; Bunch, Aaron J.; Lucchesi, David O.; Wagner, Tyler

    2018-01-01

    Quantifying spatial variability in fish growth and identifying large‐scale drivers of growth are fundamental to many conservation and management decisions. Although fish growth studies often focus on a single population, it is becoming increasingly clear that large‐scale studies are likely needed for addressing transboundary management needs. This is particularly true for species with high recreational value and for those with negative ecological consequences when introduced outside of their native range, such as the Flathead Catfish Pylodictis olivaris. This study quantified growth variability of the Flathead Catfish across a large portion of its contemporary range to determine whether growth differences existed between habitat types (i.e., reservoirs and rivers) and between native and introduced populations. Additionally, we investigated whether growth parameters varied as a function of latitude and time since introduction (for introduced populations). Length‐at‐age data from 26 populations across 11 states in the USA were modeled using a Bayesian hierarchical von Bertalanffy growth model. Population‐specific growth trajectories revealed large variation in Flathead Catfish growth and relatively high uncertainty in growth parameters for some populations. Relatively high uncertainty was also evident when comparing populations and when quantifying large‐scale patterns. Growth parameters (Brody growth coefficient [K] and theoretical maximum average length [L∞]) were not different (based on overlapping 90% credible intervals) between habitat types or between native and introduced populations. For populations within the introduced range of Flathead Catfish, latitude was negatively correlated with K. For native populations, we estimated an 85% probability that L∞ estimates were negatively correlated with latitude. Contrary to predictions, time since introduction was not correlated with growth parameters in introduced populations of Flathead Catfish

  4. The role of population on economic growth and development: evidence from developing countries

    OpenAIRE

    Atanda, Akinwande A.; Aminu, Salaudeen B.; Alimi, Olorunfemi Y.

    2012-01-01

    The precise relationship between population growth and per capita income has been inconclusive in the literature and the nexus has been found not clearly explain the determinants of rapid population growth in developing countries that lacks fertility control and management framework. This forms the rationale for this study to access the trend of factors that influence rapid population growth in developing countries between 1980 and 2010. This paper examined the comparative trend review of pop...

  5. Geographically distinct Ceratophyllum demersum populations differ in growth, photosynthetic responses and phenotypic plasticity to nitrogen availability

    DEFF Research Database (Denmark)

    Hyldgaard, Benita; Sorrell, Brian Keith; Olesen, Birgit

    2012-01-01

    from New Zealand (NZ) and a noninvasive population from Denmark (DK). The populations were compared with a focus on both morphological and physiological traits. The NZ population had higher relative growth rates (RGRs) and photosynthesis rates (Pmax) (range: RGR, 0.06–0.08 per day; Pmax, 200–395 µmol O......2 g–1 dry mass (DM) h–1) compared with the Danish population (range: RGR, 0.02–0.05 per day; Pmax, 88–169 µmol O2 g–1 DM h–1). The larger, faster-growing NZ population also showed higher plasticity than the DK population in response to nitrogen in traits important for growth. Hence, the observed...... differences in growth behaviour between the two populations are a result of genetic differences and differences in their level of plasticity. Here, we show that two populations of the same species from similar climates but different geographical areas can differ in several ecophysiological traits after growth...

  6. Density-dependence and within-host competition in a semelparous parasite of leaf-cutting ants

    Directory of Open Access Journals (Sweden)

    Thomsen Lene

    2004-11-01

    Full Text Available Abstract Background Parasite heterogeneity and within-host competition are thought to be important factors influencing the dynamics of host-parasite relationships. Yet, while there have been many theoretical investigations of how these factors may act, empirical data is more limited. We investigated the effects of parasite density and heterogeneity on parasite virulence and fitness using four strains of the entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and its leaf-cutting ant host Acromyrmex echinatior as the model system. Results The relationship between parasite density and infection was sigmoidal, with there being an invasion threshold for an infection to occur (an Allee effect. Although spore production was positively density-dependent, parasite fitness decreased with increasing parasite density, indicating within-host scramble competition. The dynamics differed little between the four strains tested. In mixed infections of three strains the infection-growth dynamics were unaffected by parasite heterogeneity. Conclusions The strength of within-host competition makes dispersal the best strategy for the parasite. Parasite heterogeneity may not have effected virulence or the infection dynamics either because the most virulent strain outcompeted the others, or because the interaction involved scramble competition that was impervious to parasite heterogeneity. The dynamics observed may be common for virulent parasites, such as Metarhizium, that produce aggregated transmission stages. Such parasites make useful models for investigating infection dynamics and the impact of parasite competition.

  7. Laboratory calibration of density-dependent lines in the extreme ultraviolet spectral region

    Science.gov (United States)

    Lepson, J. K.; Beiersdorfer, P.; Gu, M. F.; Desai, P.; Bitter, M.; Roquemore, L.; Reinke, M. L.

    2012-05-01

    We have been making spectral measurements in the extreme ultraviolet (EUV) from different laboratory sources in order to investigate the electron density dependence of various astrophysically important emission lines and to test the atomic models underlying the diagnostic line ratios. The measurement are being performed at the Livermore EBIT-I electron beam ion trap, the National Spherical Torus Experiment (NSTX) at Princeton, and the Alcator C-Mod tokamak at the Massachusetts Institute of Technology, which together span an electron density of four orders of magnitude and which allow us to test the various models at high and low density limits. Here we present measurements of Fe XXII and Ar XIV, which include new data from an ultra high resolution (λ/Δλ >4000) spectrometer at the EBIT-I facility. We found good agreement between the measurements and modeling calculations for Fe XXII, but poorer agreement for Ar XIV.

  8. Relativistic Hartree-Fock theory. Part I: density-dependent effective Lagrangians

    Energy Technology Data Exchange (ETDEWEB)

    LongWen Hui [School of Physics, Peking University, 100871 Beijing (China)]|[CNRS-IN2P3, UMR 8608, F-91406 Orsay Cedex (France)]|[Univ Paris-Sud, F-91405 Orsay (France); Giai, Nguyen Van [CNRS-IN2P3, UMR 8608, F-91406 Orsay Cedex (France)]|[Univ Paris-Sud, F-91405 Orsay (France); Meng, Jie [School of Physics, Peking University, 100871 Beijing (China)]|[Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing (China)]|[Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, 730000 Lanzhou (China)

    2006-10-15

    Effective Lagrangians suitable for a relativistic Hartree-Fock description of nuclear systems are presented. They include the 4 effective mesons {sigma}, {omega}, {rho} and {pi} with density-dependent meson-nucleon couplings. The criteria for determining the model parameters are the reproduction of the binding energies in a number of selected nuclei, and the bulk properties of nuclear matter (saturation point, compression modulus, symmetry energy). An excellent description of nuclear binding energies and radii is achieved for a range of nuclei encompassing light and heavy systems. The predictions of the present approach compare favorably with those of existing relativistic mean field models, with the advantage of incorporating the effects of pion-nucleon coupling. (authors)

  9. Density-dependent changes in effective area occupied for sea-bottom-associated marine fishes

    DEFF Research Database (Denmark)

    Thorson, James T.; Rindorf, Anna; Gao, Jin

    2016-01-01

    among taxa and regions. The average relationship is weak but significant (0.6% increase in area for a 10% increase in abundance), whereas only a small proportion of species–region combinations show a negative relationship (i.e. shrinking area when abundance increases). Approximately one...... for every 10% abundance increase) followed by Pleuronectiformes and Scorpaeniformes, and the Eastern Bering Sea shows a strong relationship between abundance and area occupied relative to other regions. We conclude that the BM explains a small but important portion of spatial dynamics for sea......The spatial distribution of marine fishes can change for many reasons, including density-dependent distributional shifts. Previous studies show mixed support for either the proportional-density model (PDM; no relationship between abundance and area occupied, supported by ideal-free distribution...

  10. Plant diversity increases with the strength of negative density dependence at the global scale

    Science.gov (United States)

    LaManna, Joseph A.; Mangan, Scott A.; Alonso, Alfonso; Bourg, Norman; Brockelman, Warren Y.; Bunyavejchewin, Sarayudh; Chang, Li-Wan; Chiang, Jyh-Min; Chuyong, George B.; Clay, Keith; Condit, Richard; Cordell, Susan; Davies, Stuart J.; Furniss, Tucker J.; Giardina, Christian P.; Gunatilleke, I.A.U. Nimal; Gunatilleke, C.V. Savitri; He, Fangliang; Howe, Robert W.; Hubbell, Stephen P.; Hsieh, Chang-Fu; Inman-Narahari, Faith M.; Janik, David; Johnson, Daniel J.; Kenfack, David; Korte, Lisa; Kral, Kamil; Larson, Andrew J.; Lutz, James A.; McMahon, Sean M.; McShea, William J.; Memiaghe, Herve R.; Nathalang, Anuttara; Novotny, Vojtech; Ong, Perry S.; Orwig, David A.; Ostertag, Rebecca; Parker, Geoffrey G.; Phillips, Richard P.; Sack, Lawren; Sun, I-Fang; Tello, J. Sebastian; Thomas, Duncan W.; Turner, Benjamin L.; Vela Diaz, Dilys M.; Vrska, Tomas; Weiblen, George D.; Wolf, Amy; Yap, Sandra; Myers, Jonathan A.

    2017-01-01

    Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities.

  11. Relativistic mean-field approximation with density-dependent screening meson masses in nuclear matter

    International Nuclear Information System (INIS)

    Sun, Baoxi; Lu, Xiaofu; Shen, Pengnian; Zhao, Enguang

    2003-01-01

    The Debye screening masses of the σ, ω and neutral ρ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. A different result with Brown–Rho scaling is shown, which implies a reduction in the mass of all the mesons in the nuclear matter, except the pion. Replacing the masses of the mesons with their corresponding screening masses in the Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the nonlinear self-coupling terms of mesons. (author)

  12. Physical Origin of Density Dependent Force of the Skyrme Type within the Quark Meson Coupling Model

    International Nuclear Information System (INIS)

    Pierre Guichon; Hrayr Matevosyan; N. Sandulescu; Anthony Thomas

    2006-01-01

    A density dependent, effective nucleon-nucleon force of the Skyrme type is derived from the quark-meson coupling model--a self-consistent, relativistic quark level description of nuclear matter. This new formulation requires no assumption that the mean scalar field is small and hence constitutes a significant advance over earlier work. The similarity of the effective interaction to the widely used SkM* force encourages us to apply it to a wide range of nuclear problems, beginning with the binding energies and charge distributions of doubly magic nuclei. Finding impressive results in this conventional arena, we apply the same effective interaction, within the Hartree-Fock-Bogoliubov approach, to the properties of nuclei far from stability. The resulting two neutron drip lines and shell quenching are quite satisfactory. Finally, we apply the relativistic formulation to the properties of dense nuclear matter in anticipation of future application to the properties of neutron stars

  13. The role of density-dependent and -independent processes in spawning habitat selection by salmon in an Arctic riverscape.

    Directory of Open Access Journals (Sweden)

    Brock M Huntsman

    Full Text Available Density-dependent (DD and density-independent (DI habitat selection is strongly linked to a species' evolutionary history. Determining the relative importance of each is necessary because declining populations are not always the result of altered DI mechanisms but can often be the result of DD via a reduced carrying capacity. We developed spatially and temporally explicit models throughout the Chena River, Alaska to predict important DI mechanisms that influence Chinook salmon spawning success. We used resource-selection functions to predict suitable spawning habitat based on geomorphic characteristics, a semi-distributed water-and-energy balance hydrologic model to generate stream flow metrics, and modeled stream temperature as a function of climatic variables. Spawner counts were predicted throughout the core and periphery spawning sections of the Chena River from escapement estimates (DD and DI variables. Additionally, we used isodar analysis to identify whether spawners actively defend spawning habitat or follow an ideal free distribution along the riverscape. Aerial counts were best explained by escapement and reference to the core or periphery, while no models with DI variables were supported in the candidate set. Furthermore, isodar plots indicated habitat selection was best explained by ideal free distributions, although there was strong evidence for active defense of core spawning habitat. Our results are surprising, given salmon commonly defend spawning resources, and are likely due to competition occurring at finer spatial scales than addressed in this study.

  14. Effects of Snail Density on Growth, Reproduction and Survival of Biomphalaria alexandrina Exposed to Schistosoma mansoni

    Directory of Open Access Journals (Sweden)

    T. D. Mangal

    2010-01-01

    Full Text Available The effects of snail density on Biomphalaria alexandrina parasitized with Schistosoma mansoni were investigated. Laboratory experiments were used to quantify the impact of high density on snail growth, fecundity, and survival. Density-dependent birth rates of snails were determined to inform mathematical models, which, until now, have assumed a linear relationship between density and fecundity. The experiments show that the rate of egg-laying followed a negative exponential distribution with increasing density and this was significantly affected by exposure to parasitic infection. High density also affected the weight of snails and survival to a greater degree than exposure to parasitic infection. Although snail growth rates were initially constrained by high density, they retained the potential for growth suggesting a reversible density-dependent mechanism. These experimental data can be used to parameterise models and confirm that snail populations are regulated by nonlinear density-dependent mechanisms.

  15. A demographic model to predict future growth of the Addo elephant population

    Directory of Open Access Journals (Sweden)

    A.M. Woodd

    1999-07-01

    Full Text Available An age-structured demographic model of the growth of the Addo elephant population was developed using parameters calculated from long-term data on the population. The model was used to provide estimates of future population growth. Expansion of the Addo Elephant National Park is currently underway, and the proposed target population size for elephant within the enlarged park is 2700. The model predicts that this population size will be reached during the year 2043, so that the Addo elephant population can continue to increase for a further 44 years before its target size within the enlarged park is attained.

  16. Selection for life-history traits to maximize population growth in an invasive marine species

    DEFF Research Database (Denmark)

    Jaspers, Cornelia; Marty, Lise; Kiørboe, Thomas

    2018-01-01

    Species establishing outside their natural range, negatively impacting local ecosystems, are of increasing global concern. They often display life-history features characteristic for r-selected populations with fast growth and high reproduction rates to achieve positive population growth rates (r...

  17. Population Growth Rate: Teaching Guide. Measures of Progress Poster Kit Number 2.

    Science.gov (United States)

    World Bank, Washington, DC.

    This teaching guide accompanies the Population Growth Rate poster kit which is designed to teach students about population growth differences between rich and poor nations and about what people in developing countries are doing to help improve their quality of life. The guide is designed for use with: (1) a poster map of the world providing social…

  18. Constant savings rates and quasi-arithmetic population growth under exhaustible resource constraints

    NARCIS (Netherlands)

    Asheim, G.B.; Buchholz, W.; Hartwick, J.M.; Mitra, T.; Withagen, C.A.A.M.

    2007-01-01

    In the Dasgupta–Heal–Solow–Stiglitz (DHSS) model of capital accumulation and resource depletion we show the following equivalence: if an efficient path has constant (gross and net of population growth) savings rates, then population growth must be quasi-arithmetic and the path is a maximin or a

  19. Urban and rural population growth in a spatial panel of municipalities

    NARCIS (Netherlands)

    Costa da Silva, Diego Firmino; Elhorst, J. Paul; Silveira Neto, Raul da Mota

    2017-01-01

    Urban and rural population growth in a spatial panel of municipalities. Regional Studies. Using Bayesian posterior model probabilities and data pertaining to 3659 Brazilian minimum comparable areas (MCAs) over the period 1970-2010, two theoretical settings of population growth dynamics resulting in

  20. Taking Exception. Reduced mortality leads to population growth: an inconvenient truth.

    Science.gov (United States)

    Shelton, James D

    2014-05-01

    Reduced mortality has been the predominant cause of the marked global population growth over the last 3/4 of a century. While improved child survival increases motivation to reduce fertility, it comes too little and too late to forestall substantial population growth. And, beyond motivation, couples need effective means to control their fertility. It is an inconvenient truth that reducing child mortality contributes considerably to the population growth destined to compromise the quality of life of many, particularly in sub-Saharan Africa. Vigorous child survival programming is of course imperative. Wide access to voluntary family planning can help mitigate that growth and provide many other benefits.

  1. Differences in Townsend's chipmunk populations between second- and old-growth forests in western Oregon

    Science.gov (United States)

    D.K. Rosenberg; R.G. Anthony

    1993-01-01

    Because Townsend's chipmunks (Tomias townsendii) may be important in maintaining natural ecosystem processes in forests in the central Oregon Cascade Range, we compared their population characteristics in young second-growth and old-growth forests. We live-trapped Townsend's chipmunks in 5 young (30-60 yr old) second-growth and 5 old-...

  2. Life history and spatial determinants of somatic growth dynamics in Komodo dragon populations

    OpenAIRE

    Laver, Rj; Purwandana, D; Ariefiandy, A; Imansyah, J; Forsyth, D; Ciofi, C; Jessop, Ts

    2012-01-01

    Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world's largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture st...

  3. JOB DISCRIMINATION AGAINST WOMEN AND ENDOGENOUS POPULATION CHANGE IN A GENERALIZED SOLOW GROWTH MODEL

    OpenAIRE

    Wei-Bin ZHANG

    2017-01-01

    This study examines economic growth and population change with discrimination against women in the labor market within the analytical framework of Solow’s neoclassical growth model. The study models dynamic interactions between wealth accumulation, time distribution between work, children caring, and leisure, population change with endogenous birth and mortality rates with gender discrimination. The production technology and markets are built on Solow’s neoclassical growth model. The basic me...

  4. Population Growth, Available Resources, and Quality of Life: China's Post-Reform Economic Development

    Institute of Scientific and Technical Information of China (English)

    Tim Futing Liao; Hua Qin

    2012-01-01

    Two opposing intellectual traditions and their contem- porary developments regarding the relations among population, available resources, and quality of life as reflected in economic growth are reviewed. What is at issue is whether population growth is detrimental to or beneficial for economic development. Neither of the extreme views gives a complete picture of the interplay among population, resources, and quality of life. Following previ- ous literature on the topic, this paper establishes a more balanced approach that considers the function linking population and quality of life not constant but variable and regards the limitedness of resources as not absolute but relative to regions and societies. The proposed approach is more flexible in better explaining the relation between population and economic growth. China is examined as a case in point to shed light on the interaction of population growth, economic development, and available resources, and its recent post-economic reform experiences showcase the appropriateness of the synthetic approach.

  5. The demographic consequences of mutualism: ants increase host-plant fruit production but not population growth

    Science.gov (United States)

    Kevin Ford; Joshua H. Ness; Judith L. Bronstein; William F. Morris

    2015-01-01

    The impact of mutualists on a partner’s demography depends on how they affect the partner’s multiple vital rates and how those vital rates, in turn, affect population growth. However, mutualism studies rarely measure effects on multiple vital rates or integrate them to assess the ultimate impact on population growth. We used vital rate data, population models and...

  6. The demographic consequences of mutualism: ants increase host-plant fruit production but not population growth.

    Science.gov (United States)

    Ford, Kevin R; Ness, Joshua H; Bronstein, Judith L; Morris, William F

    2015-10-01

    The impact of mutualists on a partner's demography depends on how they affect the partner's multiple vital rates and how those vital rates, in turn, affect population growth. However, mutualism studies rarely measure effects on multiple vital rates or integrate them to assess the ultimate impact on population growth. We used vital rate data, population models and simulations of long-term population dynamics to quantify the demographic impact of a guild of ant species on the plant Ferocactus wislizeni. The ants feed at the plant's extrafloral nectaries and attack herbivores attempting to consume reproductive organs. Ant-guarded plants produced significantly more fruit, but ants had no significant effect on individual growth or survival. After integrating ant effects across these vital rates, we found that projected population growth was not significantly different between unguarded and ant-guarded plants because population growth was only weakly influenced by differences in fruit production (though strongly influenced by differences in individual growth and survival). However, simulations showed that ants could positively affect long-term plant population dynamics through services provided during rare but important events (herbivore outbreaks that reduce survival or years of high seedling recruitment associated with abundant precipitation). Thus, in this seemingly clear example of mutualism, the interaction may actually yield no clear benefit to plant population growth, or if it does, may only do so through the actions of the ants during rare events. These insights demonstrate the value of taking a demographic approach to studying the consequences of mutualism.

  7. Life history traits influence the strength of distance- and density-dependence at different life stages of two Amazonian palms.

    Science.gov (United States)

    Choo, Juanita; Carasco, Cecilia; Alvarez-Loayza, Patricia; Simpson, Beryl B; Economo, Evan P

    2017-07-01

    Natural enemies are known to be important in regulating plant populations and contributing to species coexistence (Janzen-Connell effects). The strength of Janzen-Connell effects (both distance- and density-effects) varies across species, but the life history traits that may mediate such a variation are not well understood. This study examined Janzen-Connell effects across the life stages (seed through adult stages) of two sympatric palm species with distinct phenologies and shade tolerances, two traits that may mediate the strength and timing of Janzen-Connell effects. Populations of two common palm species, Attalea phalerata and Astrocaryum murumuru , were studied in Manu National Park, Peru. Seed predation experiments were conducted to assess Janzen-Connell effects at the seed stage. In the post-seed stages, spatial point pattern analyses of the distributions of individuals and biomass were used to infer the strength of distance- and density-effects. Seed predation was both negative distance- and density-dependent consistent with the Janzen-Connell effects. However, only seedling recruitment for asynchronously fruiting Attalea phalerata was depressed near adults while recruitment remained high for synchronously fruiting Astrocaryum murumuru , consistent with weak distance-effects. Negative density-effects were strong in the early stages for shade-intolerant Attalea phalerata but weak or absent in shade-tolerant Astrocaryum murumuru. Distance- and density-effects varied among the life stages of the two palm species in a manner that corresponded to their contrasting phenology and shade tolerance. Generalizing such connections across many species would provide a route to understanding how trait-mediated Janzen-Connell effects scale up to whole communities of species. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

  8. Coupled hydromechanical paleoclimate analyses of density-dependant groundwater flow in discretely fractured crystalline rock settings

    Science.gov (United States)

    Normani, S. D.; Sykes, J. F.; Jensen, M. R.

    2009-04-01

    A high resolution sub-regional scale (84 km2) density-dependent, fracture zone network groundwater flow model with hydromechanical coupling and pseudo-permafrost, was developed from a larger 5734 km2 regional scale groundwater flow model of a Canadian Shield setting in fractured crystalline rock. The objective of the work is to illustrate aspects of regional and sub-regional groundwater flow that are relevant to the long-term performance of a hypothetical nuclear fuel repository. The discrete fracture dual continuum numerical model FRAC3DVS-OPG was used for all simulations. A discrete fracture zone network model delineated from surface features was superimposed onto an 789887 element flow domain mesh. Orthogonal fracture faces (between adjacent finite element grid blocks) were used to best represent the irregular discrete fracture zone network. The crystalline rock between these structural discontinuities was assigned properties characteristic of those reported for the Canadian Shield at the Underground Research Laboratory at Pinawa, Manitoba. Interconnectivity of permeable fracture features is an important pathway for the possibly relatively rapid migration of average water particles and subsequent reduction in residence times. The multiple 121000 year North American continental scale paleoclimate simulations are provided by W.R. Peltier using the University of Toronto Glacial Systems Model (UofT GSM). Values of ice sheet normal stress, and proglacial lake depth from the UofT GSM are applied to the sub-regional model as surface boundary conditions, using a freshwater head equivalent to the normal stress imposed by the ice sheet at its base. Permafrost depth is applied as a permeability reduction to both three-dimensional grid blocks and fractures that lie within the time varying permafrost zone. Two different paleoclimate simulations are applied to the sub-regional model to investigate the effect on the depth of glacial meltwater migration into the subsurface. In

  9. Regulatory design governing progression of population growth phases in bacteria.

    Directory of Open Access Journals (Sweden)

    Agustino Martínez-Antonio

    Full Text Available It has long been noted that batch cultures inoculated with resting bacteria exhibit a progression of growth phases traditionally labeled lag, exponential, pre-stationary and stationary. However, a detailed molecular description of the mechanisms controlling the transitions between these phases is lacking. A core circuit, formed by a subset of regulatory interactions involving five global transcription factors (FIS, HNS, IHF, RpoS and GadX, has been identified by correlating information from the well- established transcriptional regulatory network of Escherichia coli and genome-wide expression data from cultures in these different growth phases. We propose a functional role for this circuit in controlling progression through these phases. Two alternative hypotheses for controlling the transition between the growth phases are first, a continuous graded adjustment to changing environmental conditions, and second, a discontinuous hysteretic switch at critical thresholds between growth phases. We formulate a simple mathematical model of the core circuit, consisting of differential equations based on the power-law formalism, and show by mathematical and computer-assisted analysis that there are critical conditions among the parameters of the model that can lead to hysteretic switch behavior, which--if validated experimentally--would suggest that the transitions between different growth phases might be analogous to cellular differentiation. Based on these provocative results, we propose experiments to test the alternative hypotheses.

  10. Regulatory design governing progression of population growth phases in bacteria.

    Science.gov (United States)

    Martínez-Antonio, Agustino; Lomnitz, Jason G; Sandoval, Santiago; Aldana, Maximino; Savageau, Michael A

    2012-01-01

    It has long been noted that batch cultures inoculated with resting bacteria exhibit a progression of growth phases traditionally labeled lag, exponential, pre-stationary and stationary. However, a detailed molecular description of the mechanisms controlling the transitions between these phases is lacking. A core circuit, formed by a subset of regulatory interactions involving five global transcription factors (FIS, HNS, IHF, RpoS and GadX), has been identified by correlating information from the well- established transcriptional regulatory network of Escherichia coli and genome-wide expression data from cultures in these different growth phases. We propose a functional role for this circuit in controlling progression through these phases. Two alternative hypotheses for controlling the transition between the growth phases are first, a continuous graded adjustment to changing environmental conditions, and second, a discontinuous hysteretic switch at critical thresholds between growth phases. We formulate a simple mathematical model of the core circuit, consisting of differential equations based on the power-law formalism, and show by mathematical and computer-assisted analysis that there are critical conditions among the parameters of the model that can lead to hysteretic switch behavior, which--if validated experimentally--would suggest that the transitions between different growth phases might be analogous to cellular differentiation. Based on these provocative results, we propose experiments to test the alternative hypotheses.

  11. Population size, survival, growth, and movements of Rana sierrae

    Science.gov (United States)

    Fellers, Gary M.; Kleeman, Patrick M.; Miller, David A. W.; Halstead, Brian J.; Link, William

    2013-01-01

    Based on 2431 captures of 757 individual frogs over a 9-yr period, we found that the population of R. sierrae in one meadow–stream complex in Yosemite National Park ranged from an estimated 45 to 115 adult frogs. Rana sierrae at our relatively low elevation site (2200 m) grew at a fast rate (K = 0.73–0.78), had high overwintering survival rates (44.6–95%), lived a long time (up to 16 yr), and tended to be fairly sedentary during the summer (100% minimum convex polygon annual home ranges of 139 m2) but had low year-to-year site fidelity. Even though the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) has been present in the population for at least 13 yr, there was no clear downward trend as might be expected from reports of R. sierrae population declines associated with Bd or from reports of widespread population decline of R. sierrae throughout its range.

  12. Modeling the growth of individuals in plant populations: local density variation in a strand population of Xanthium strumarium (Asteraceae).

    Science.gov (United States)

    Weiner, J; Kinsman, S; Williams, S

    1998-11-01

    We studied the growth of individual Xanthium strumarium plants growing at four naturally occurring local densities on a beach in Maine: (1) isolated plants, (2) pairs of plants ≤1 cm apart, (3) four plants within 4 cm of each other, and (4) discrete dense clumps of 10-39 plants. A combination of nondestructive measurements every 2 wk and parallel calibration harvests provided very good estimates of the growth in aboveground biomass of over 400 individual plants over 8 wk and afforded the opportunity to fit explicit growth models to 293 of them. There was large individual variation in growth and resultant size within the population and within all densities. Local crowding played a role in determining plant size within the population: there were significant differences in final size between all densities except pairs and quadruples, which were almost identical. Overall, plants growing at higher densities were more variable in growth and final size than plants growing at lower densities, but this was due to increased variation among groups (greater variation in local density and/or greater environmental heterogeneity), not to increased variation within groups. Thus, there was no evidence of size asymmetric competition in this population. The growth of most plants was close to exponential over the study period, but half the plants were slightly better fit by a sigmoidal (logistic) model. The proportion of plants better fit by the logistic model increased with density and with initial plant size. The use of explicit growth models over several growth intervals to describe stand development can provide more biological content and more statistical power than "growth-size" methods that analyze growth intervals separately.

  13. Inflammation triggers emergency granulopoiesis through a density-dependent feedback mechanism.

    Directory of Open Access Journals (Sweden)

    Derek W Cain

    Full Text Available Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBPα. Inflammation, however, induces neutrophilia through a distinct pathway of "emergency" granulopoiesis that is dependent on C/EBPβ. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBPβ, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis.

  14. Effect of deformation and orientation on spin orbit density dependent nuclear potential

    Science.gov (United States)

    Mittal, Rajni; Kumar, Raj; Sharma, Manoj K.

    2017-11-01

    Role of deformation and orientation is investigated on spin-orbit density dependent part VJ of nuclear potential (VN=VP+VJ) obtained within semi-classical Thomas Fermi approach of Skyrme energy density formalism. Calculations are performed for 24-54Si+30Si reactions, with spherical target 30Si and projectiles 24-54Si having prolate and oblate shapes. The quadrupole deformation β2 is varying within range of 0.023 ≤ β2 ≤0.531 for prolate and -0.242 ≤ β2 ≤ -0.592 for oblate projectiles. The spin-orbit dependent potential gets influenced significantly with inclusion of deformation and orientation effect. The spin-orbit barrier and position gets significantly influenced by both the sign and magnitude of β2-deformation. Si-nuclei with β220. The possible role of spin-orbit potential on barrier characteristics such as barrier height, barrier curvature and on the fusion pocket is also probed. In reference to prolate and oblate systems, the angular dependence of spin-orbit potential is further studied on fusion cross-sections.

  15. A unified dislocation density-dependent physical-based constitutive model for cold metal forming

    Science.gov (United States)

    Schacht, K.; Motaman, A. H.; Prahl, U.; Bleck, W.

    2017-10-01

    Dislocation-density-dependent physical-based constitutive models of metal plasticity while are computationally efficient and history-dependent, can accurately account for varying process parameters such as strain, strain rate and temperature; different loading modes such as continuous deformation, creep and relaxation; microscopic metallurgical processes; and varying chemical composition within an alloy family. Since these models are founded on essential phenomena dominating the deformation, they have a larger range of usability and validity. Also, they are suitable for manufacturing chain simulations since they can efficiently compute the cumulative effect of the various manufacturing processes by following the material state through the entire manufacturing chain and also interpass periods and give a realistic prediction of the material behavior and final product properties. In the physical-based constitutive model of cold metal plasticity introduced in this study, physical processes influencing cold and warm plastic deformation in polycrystalline metals are described using physical/metallurgical internal variables such as dislocation density and effective grain size. The evolution of these internal variables are calculated using adequate equations that describe the physical processes dominating the material behavior during cold plastic deformation. For validation, the model is numerically implemented in general implicit isotropic elasto-viscoplasticity algorithm as a user-defined material subroutine (UMAT) in ABAQUS/Standard and used for finite element simulation of upsetting tests and a complete cold forging cycle of case hardenable MnCr steel family.

  16. Deriving the coronal hole electron temperature: electron density dependent ionization / recombination considerations

    International Nuclear Information System (INIS)

    Doyle, John Gerard; Perez-Suarez, David; Singh, Avninda; Chapman, Steven; Bryans, Paul; Summers, Hugh; Savin, Daniel Wolf

    2010-01-01

    Comparison of appropriate theoretically derived line ratios with observational data can yield estimates of a plasma's physical parameters, such as electron density or temperature. The usual practice in the calculation of the line ratio is the assumption of excitation by electrons/protons followed by radiative decay. Furthermore, it is normal to use the so-called coronal approximation, i.e. one only considers ionization and recombination to and from the ground-state. A more accurate treatment is to include ionization/recombination to and from metastable levels. Here, we apply this to two lines from adjacent ionization stages, Mg IX 368 A and Mg X 625 A, which has been shown to be a very useful temperature diagnostic. At densities typical of coronal hole conditions, the difference between the electron temperature derived assuming the zero density limit compared with the electron density dependent ionization/recombination is small. This, however, is not the case for flares where the electron density is orders of magnitude larger. The derived temperature for the coronal hole at solar maximum is around 1.04 MK compared to just below 0.82 MK at solar minimum.

  17. Density-dependent effective baryon–baryon interaction from chiral three-baryon forces

    Energy Technology Data Exchange (ETDEWEB)

    Petschauer, Stefan, E-mail: stefan.petschauer@ph.tum.de [Physik Department, Technische Universität München, D-85747 Garching (Germany); Haidenbauer, Johann [Institute for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich (Germany); Kaiser, Norbert [Physik Department, Technische Universität München, D-85747 Garching (Germany); Meißner, Ulf-G. [Institute for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich (Germany); Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, D-53115 Bonn (Germany); Bethe Center for Theoretical Physics, Universität Bonn, D-53115 Bonn (Germany); Weise, Wolfram [Physik Department, Technische Universität München, D-85747 Garching (Germany)

    2017-01-15

    A density-dependent effective potential for the baryon–baryon interaction in the presence of the (hyper)nuclear medium is constructed, based on the leading (irreducible) three-baryon forces derived within SU(3) chiral effective field theory. We evaluate the contributions from three classes: contact terms, one-pion exchange and two-pion exchange. In the strangeness-zero sector we recover the known result for the in-medium nucleon–nucleon interaction. Explicit expressions for the ΛN in-medium potential in (asymmetric) nuclear matter are presented. Our results are suitable for implementation into calculations of (hyper)nuclear matter. In order to estimate the low-energy constants of the leading three-baryon forces we introduce the decuplet baryons as explicit degrees of freedom and construct the relevant terms in the minimal non-relativistic Lagrangian. With these, the constants are estimated through decuplet saturation. Utilizing this approximation we provide numerical results for the effect of the three-body force in symmetric nuclear matter and pure neutron matter on the ΛN interaction. A moderate repulsion that increases with density is found in comparison to the free ΛN interaction.

  18. Thermodynamics of strange quark matter with the density-dependent bag constant

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The thermodynamics of strange quark matter with density dependent bag constant are studied self-consistently in the framework of the general ensemble theory and the MIT bag model.In our treatment,an additional term is found in the expression of pressure.With the additional term,the zero pressure locates exactly at the lowest energy state,indicating that our treatment is a self-consistently thermodynamic treatment.The self-consistent equations of state of strange quark matter in both the normal and color-flavor-locked phase are derived.They are both softer than the inconsistent ones.Strange stars in both the normal and color-flavor locked phase have smaller masses and radii in our treatment.It is also interesting to find that the energy density at a star surface in our treatment is much higher than that in the inconsistent treatment for both phases.Consequently,the surface properties and the corresponding observational properties of strange stars in our treatment are different from those in the inconsistent treatment.

  19. Thermodynamics of strange quark matter with the density-dependent bag constant

    Institute of Scientific and Technical Information of China (English)

    ZHU MingFeng; LIU GuangZhou; YU Zi; XU Yan; SONG WenTao

    2009-01-01

    The thermodynamics of strange quark matter with density dependent bag constant are studied selfconsistently in the framework of the general ensemble theory and the MIT bag model.In our treatment,an additional term Is found in the expression of pressure.With the additional term,the zero pressure locates exactly at the lowest energy state,Indicating that our treatment is a self-consistently thermodynamic treatment.The self-consistent equations of state of strange quark matter in both the normal and color-flavor-locked phase are derived.They are both softer than the inconsistent ones.Strange stars in both the normal and color-flavor locked phase have smaller masses and radii in our treatment.It is also interesting to find that the energy density at a star surface in our treatment is much higher than that In the inconsistent treatment for both phases.Consequently,the surface properties and the corresponding observational properties of strange stars in our treatment are different from those in the inconsistent treatment.

  20. Choice of the density-dependent effective interaction and alpha decay of heavy spherical nuclei

    International Nuclear Information System (INIS)

    Kadmenskij, S.G.; Ratis, Yu.L.; Rybak, K.S.; Furman, V.I.

    1978-01-01

    The parameters of density-dependent effective interaction are studied for some nuclei in the vicinity of a 208 Pb double-magic nucleus. Both nuclei having two nucleons (holes) over magic core and some superfluid nuclei are considered. It is found that the magnitudes of the matrix elements for the zero-range forces (delta forces) are more than three times larger in comparison with the case of the finite-range forces (f forces). Sets of parameters for the effective interaction, which does not lead to the superfluidity of nuclear matter are obtained. Besides, these parameters depend weakly on mass number. It is shown that the attractive part of interaction is substantially larger for the case of f forces than for the delta forces. The theoretical enhancement coefficients for the favoured α decay of 210 Po, 210 Pb and 224 Th nuclei are calculated. For the case of f forces a tendency to saturation of the enhancement coefficients with the increase of the shell-model basis is found

  1. Parental care masks a density-dependent shift from cooperation to competition among burying beetle larvae.

    Science.gov (United States)

    Schrader, Matthew; Jarrett, Benjamin J M; Kilner, Rebecca M

    2015-04-01

    Studies of siblings have focused mainly on their competitive interactions and to a lesser extent on their cooperation. However, competition and cooperation are at opposite ends on a continuum of possible interactions and the nature of these interactions may be flexible with ecological factors tipping the balance toward competition in some environments and cooperation in others. Here we show that the presence of parental care and the density of larvae on the breeding carcass change the outcome of sibling interactions in burying beetle broods. With full parental care there was a strong negative relationship between larval density and larval mass, consistent with sibling competition for resources. In the absence of care, initial increases in larval density had beneficial effects on larval mass but further increases in larval density reduced larval mass. This likely reflects a density-dependent shift between cooperation and competition. In a second experiment, we manipulated larval density and removed parental care. We found that the ability of larvae to penetrate the breeding carcass increased with larval density and that feeding within the carcass resulted in heavier larvae than feeding outside the carcass. However, larval density did not influence carcass decay. © 2015 The Author(s). Evolution published by Wiley Periodicals, Inc. on behalf of The Society for the Study of Evolution.

  2. Modelling breast cancer tumour growth for a stable disease population.

    Science.gov (United States)

    Isheden, Gabriel; Humphreys, Keith

    2017-01-01

    Statistical models of breast cancer tumour progression have been used to further our knowledge of the natural history of breast cancer, to evaluate mammography screening in terms of mortality, to estimate overdiagnosis, and to estimate the impact of lead-time bias when comparing survival times between screen detected cancers and cancers found outside of screening programs. Multi-state Markov models have been widely used, but several research groups have proposed other modelling frameworks based on specifying an underlying biological continuous tumour growth process. These continuous models offer some advantages over multi-state models and have been used, for example, to quantify screening sensitivity in terms of mammographic density, and to quantify the effect of body size covariates on tumour growth and time to symptomatic detection. As of yet, however, the continuous tumour growth models are not sufficiently developed and require extensive computing to obtain parameter estimates. In this article, we provide a detailed description of the underlying assumptions of the continuous tumour growth model, derive new theoretical results for the model, and show how these results may help the development of this modelling framework. In illustrating the approach, we develop a model for mammography screening sensitivity, using a sample of 1901 post-menopausal women diagnosed with invasive breast cancer.

  3. Do Class III patients have a different growth spurt than the general population?

    Science.gov (United States)

    Lee, Yun-Sik; Lee, Shin-Jae; An, Hongseok; Donatelli, Richard E; Kim, Soo-Hwan

    2012-11-01

    Understanding the timing and length of the growth spurt of Class III prognathic patients is fundamental to the strategy of interceptive orthopedic orthodontics as well as to the timing of orthognathic surgery. Consequently, this study was undertaken to determine whether there are any significant differences in the stature growth pattern of Class III subjects compared with non-Class III subjects and the general population. Twelve-year longitudinal stature growth data were collected for 402 randomly selected adolescents in the general population, 55 Class III mandibular prognathic patients, and 37 non-Class III patients. The growth data were analyzed by using the traditional linear interpolation method and nonlinear growth functions. The 6 stature growth parameters were measured: age at takeoff, stature at takeoff, velocity at takeoff, age at peak height velocity, stature at peak height velocity, and velocity at peak height velocity. Comparisons in the stature growth parameters and 15 cephalometric variables among the general population, Class III subjects, and non-Class III subjects were made with multivariate analysis. Patients with Class III prognathism did not have different growth parameters compared with Class II subjects or the general population. This study does not allow meaningful conclusions with regard to the relationship of mandibular size and stature growth pattern. The application of nonlinear growth curves vs the traditional linear interpolation method was also discussed. Copyright © 2012 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

  4. Variation in foraging behavior and body mass in broods of Emperor Geese (Chen canagica): Evidence for interspecific density dependence

    Science.gov (United States)

    Schmutz, J.A.; Laing, K.K.

    2002-01-01

    Broods of geese spend time feeding according to availability and quality of food plants, subject to inherent foraging and digestive constraints. We studied behavioral patterns of broods of Emperor Geese (Chen canagica) on the Yukon–Kuskokwim Delta, Alaska, and examined how feeding and alert behavior varied in relation to habitat and goose density. During 1994–1996, time spent feeding by Emperor Goose goslings and adult females was positively related to multispecies goose densities near observation blinds, and not to just Emperor Goose density. Similarly, body mass of Emperor Goose goslings was more strongly related (negatively) to multispecies goose densities than intraspecific densities. A grazing experiment in 1995 indicated that most above ground primary production by Carex subspathacea, a preferred food plant, was consumed by grazing geese. Those results demonstrate that interspecific competition for food occurred, with greatest support for goslings whose behavioral repertoire is limited primarily to feeding, digesting, and resting. Although the more abundant Cackling Canada Geese (Branta canadensis minima) differed from Emperor Geese in their preferred use of habitats during brooding rearing (Schmutz 2001), the two species occurred in equal abundance in habitats preferred by Emperor Goose broods. Thus, Cackling Canada Geese were a numerically significant competitor with Emperor Geese. Comparing these results to an earlier study, time spent feeding by goslings, adult females, and adult males were greater during 1993–1996 than during 1985–1986. During the interval between those studies, densities of Cackling Canada Geese increased two to three times whereas Emperor Goose numbers remained approximately stable, which implies that interspecific competition affected foraging behavior over a long time period. These density-dependent changes in foraging behavior and body mass indicate that interspecific competition affects nutrient acquisition and gosling

  5. Mortality risks and limits to population growth of fishers

    Science.gov (United States)

    Rick A. Sweitzer; Viorel D. Popescu; Craig M. Thompson; Kathryn L. Purcell; Reginald H. Barrett; Greta M. Wengert; Mourad W. Gabriel; Leslie W. Woods

    2015-01-01

    Fishers (Pekania pennanti) in the west coast states of Washington, Oregon, and California, USA have not recovered from population declines and the United States Fish and Wildlife Service has proposed options for listing them as threatened. Our objectives were to evaluate differences in survival and mortality risk from natural (e.g., predation, disease, injuries,...

  6. Population structure and growth of polydorid polychaetes that infest ...

    African Journals Online (AJOL)

    Polydorid polychaetes can infest cultured abalone thereby reducing productivity. In order to effectively control these pests, their reproductive biology must be understood. The population dynamics and reproduction of polydorids infesting abalone Haliotis midae from two farms in South Africa is described using a ...

  7. Population growth, urban expansion, and private forestry in western Oregon.

    Science.gov (United States)

    Jeffrey D. Kline; David L. Azuma; Ralph J. Alig

    2004-01-01

    Private forestlands in the United States face increasing pressures from growing populations, resulting in greater numbers of people living in closer proximity to forests. What often is called the "wildland/urban interface" is characterized by expansion of residential and other developed land uses onto forested landscapes in a manner that threatens forestlands...

  8. Current and Future Dynamics of the Red-Cockaded Woodpecker Population Inhabiting the Savannah River National Environmental Research Park: Managing For Population Growth

    International Nuclear Information System (INIS)

    Walters, J.R.; Taylor, T.B.; Daniels, S.J.; Crowder, L.B.; Pridd, J.A.

    2001-01-01

    Research aimed to study the dynamics of the SRS population of Red-Cockaded woodpecker and compare to those of other populations to identify factors limiting population growth; recruitment clusters were evaluated to determine what properties of individual cavity trees, surrounding habitat and the surrounding landscape might limit occupancy through natural dispersal. A spatial simulation model was used to project expected dispersal rates and population growth under current conditions and compare those estimates to observed dispersal and population growth. Red cockaded woodpecker populations at SRS are stable considering size. Research reveals that closer placement of recruitment clusters to active territories would produce higher growth rates while decreasing management intensity

  9. Current and Future Dynamics of the Red-Cockaded Woodpecker Population Inhabiting the Savannah River National Environmental Research Park: Managing For Population Growth

    Energy Technology Data Exchange (ETDEWEB)

    Walters, J.R.; Taylor, T.B.; Daniels, S.J.; Crowder, L.B.; Pridd, J.A.

    2001-01-01

    Research aimed to study the dynamics of the SRS population of Red-Cockaded woodpecker and compare to those of other populations to identify factors limiting population growth; recruitment clusters were evaluated to determine what properties of individual cavity trees, surrounding habitat and the surrounding landscape might limit occupancy through natural dispersal. A spatial simulation model was used to project expected dispersal rates and population growth under current conditions and compare those estimates to observed dispersal and population growth. Red cockaded woodpecker populations at SRS are stable considering size. Research reveals that closer placement of recruitment clusters to active territories would produce higher growth rates while decreasing management intensity.

  10. Extension of biomass estimates to pre-assessment periods using density dependent surplus production approach.

    Directory of Open Access Journals (Sweden)

    Jan Horbowy

    Full Text Available Biomass reconstructions to pre-assessment periods for commercially important and exploitable fish species are important tools for understanding long-term processes and fluctuation on stock and ecosystem level. For some stocks only fisheries statistics and fishery dependent data are available, for periods before surveys were conducted. The methods for the backward extension of the analytical assessment of biomass for years for which only total catch volumes are available were developed and tested in this paper. Two of the approaches developed apply the concept of the surplus production rate (SPR, which is shown to be stock density dependent if stock dynamics is governed by classical stock-production models. The other approach used a modified form of the Schaefer production model that allows for backward biomass estimation. The performance of the methods was tested on the Arctic cod and North Sea herring stocks, for which analytical biomass estimates extend back to the late 1940s. Next, the methods were applied to extend biomass estimates of the North-east Atlantic mackerel from the 1970s (analytical biomass estimates available to the 1950s, for which only total catch volumes were available. For comparison with other methods which employs a constant SPR estimated as an average of the observed values, was also applied. The analyses showed that the performance of the methods is stock and data specific; the methods that work well for one stock may fail for the others. The constant SPR method is not recommended in those cases when the SPR is relatively high and the catch volumes in the reconstructed period are low.

  11. Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus).

    Science.gov (United States)

    Vas, Judit; Andersen, Inger Lise

    2015-01-01

    Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus) in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e., distance travelled, nearest and furthest neighbour distance) and activity budgets (e.g., resting, feeding, social activities) were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period). The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation.

  12. Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus.

    Directory of Open Access Journals (Sweden)

    Judit Vas

    Full Text Available Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e., distance travelled, nearest and furthest neighbour distance and activity budgets (e.g., resting, feeding, social activities were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period. The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation.

  13. Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus)

    Science.gov (United States)

    Vas, Judit; Andersen, Inger Lise

    2015-01-01

    Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus) in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e. distance travelled, nearest and furthest neighbour distance) and activity budgets (e.g. resting, feeding, social activities) were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period). The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation. PMID:26657240

  14. [Population development and economic growth. A simulation analysis for Switzerland].

    Science.gov (United States)

    Schmidt, C; Straubhaar, T

    1996-01-01

    "A simulation exercise of a general equilibrium model for Switzerland makes clear that the macroeconomic impacts of aging populations are not very strong. There is no need for urgent policy actions to avoid severe negative economic consequences....However, the aging of population affects negatively the net income of the active labor force. An increasing share of their gross salaries goes to the retirement system to finance the pension payments of a growing number of pensioners. Attempts to moderate the elderly dependency ratio would lower this burden for the active labor force. Options are an increase of the female participation rate, an increase of the labor participation rate of the elderly--[which] also means a higher retirement age--and an increasing flow of immigrants. But socioeconomic problems might probably generate practical limits on the extent to which immigration can be increased." (SUMMARY IN ENG AND FRE) excerpt

  15. A tale of three regions : influence of highway investments on population and traffic growth in Virginia.

    Science.gov (United States)

    2005-01-01

    To what extent may highway investments shape population growth and land development? To answer this question, three decades of data were examined in the Virginia locations of Fairfax County, Spotsylvania County, and Newport News. In each location, a ...

  16. Population structure, growth and production of a recent brachiopod from the Chilean fjord region

    KAUST Repository

    Baumgarten, Sebastian; Laudien, Jü rgen; Jantzen, Carin; Hä ussermann, Verena; Fö rsterra, Gü nter

    2013-01-01

    -57% of that of A. atra in the respective fjords). The high shell growth rate of M. venosa, together with its high overall growth performance may explain the locally high population density of this brachiopod in Comau Fjord. However, the production per biomass

  17. Social Security Reform and Population Ageing in a Two-Sector Growth Model

    NARCIS (Netherlands)

    van Groezen, B.J.A.M.; Meijdam, A.C.; Verbon, H.A.A.

    2002-01-01

    This paper analyses the effects of reducing unfunded social security and population ageing on economic growth and welfare, both for a small open economy and for a closed economy.The economy consists of a service sector and a commodity sector.Productivity growth only occurs in the latter sector and

  18. Social security reform and population ageing in a two-sector growth model

    NARCIS (Netherlands)

    Groezen, Bas van; Meijdam, L.; Verbon, H.

    2002-01-01

    This paper analyses the e¤ects of reducing unfunded social security and population ageing on economic growth and welfare, both for a small open economy and for a closed economy. The economy consists of a service sector and a commodity sector. Productivity growth only occurs in the latter sector

  19. Population studies of echinoderms and growth and mortality of sea cucumbers

    International Nuclear Information System (INIS)

    Ebert, T.A.

    1979-01-01

    Progress is reported on the following studies: methods of collecting sea cucumbers; determination of growth rates of plates of the calcareous ring; use of growth parameters and a length-frequency distribution to estimate mortality and population turnover; movement of materials through the atoll ecosystem; and autoradiographic studies on spines of sea urchins

  20. Do social grants contribute to the jobless population growth in the former South African homelands?

    CSIR Research Space (South Africa)

    Geyer, H

    2018-05-01

    Full Text Available migration. A possible reason could be the high level of dependency on social grants in the former homelands. The article analyses population growth rates, economic growth rates and the ratio of social grant recipients within former homeland settlements...

  1. Global water resources: vulnerability from climate change and population growth.

    Science.gov (United States)

    Vörösmarty, C J; Green, P; Salisbury, J; Lammers, R B

    2000-07-14

    The future adequacy of freshwater resources is difficult to assess, owing to a complex and rapidly changing geography of water supply and use. Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrate that (i) a large proportion of the world's population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question.

  2. Stochastic population dynamics of a montane ground-dwelling squirrel.

    Directory of Open Access Journals (Sweden)

    Jeffrey A Hostetler

    Full Text Available Understanding the causes and consequences of population fluctuations is a central goal of ecology. We used demographic data from a long-term (1990-2008 study and matrix population models to investigate factors and processes influencing the dynamics and persistence of a golden-mantled ground squirrel (Callospermophilus lateralis population, inhabiting a dynamic subalpine habitat in Colorado, USA. The overall deterministic population growth rate λ was 0.94±SE 0.05 but it varied widely over time, ranging from 0.45±0.09 in 2006 to 1.50±0.12 in 2003, and was below replacement (λ<1 for 9 out of 18 years. The stochastic population growth rate λ(s was 0.92, suggesting a declining population; however, the 95% CI on λ(s included 1.0 (0.52-1.60. Stochastic elasticity analysis showed that survival of adult females, followed by survival of juvenile females and litter size, were potentially the most influential vital rates; analysis of life table response experiments revealed that the same three life history variables made the largest contributions to year-to year changes in λ. Population viability analysis revealed that, when the influences of density dependence and immigration were not considered, the population had a high (close to 1.0 in 50 years probability of extinction. However, probability of extinction declined to as low as zero when density dependence and immigration were considered. Destabilizing effects of stochastic forces were counteracted by regulating effects of density dependence and rescue effects of immigration, which allowed our study population to bounce back from low densities and prevented extinction. These results suggest that dynamics and persistence of our study population are determined synergistically by density-dependence, stochastic forces, and immigration.

  3. "Peer Review: Nonroad (NR) Updates to Population Growth, Compression Ignition (CI) Criteria, Toxic Emission Factors and Speciation Profiles"

    Science.gov (United States)

    This report focuses on the methodology for estimating growth in NR engine populations as used in the MOVES201X-NONROAD emission inventory model. MOVES NR growth rates start with base year engine populations and estimate growth in the populations of NR engines, while applying cons...

  4. The between-population genetic architecture of growth, maturation, and plasticity in Atlantic salmon.

    Science.gov (United States)

    Debes, Paul Vincent; Fraser, Dylan John; Yates, Matthew; Hutchings, Jeffrey A

    2014-04-01

    The between-population genetic architecture for growth and maturation has not been examined in detail for many animal species despite its central importance in understanding hybrid fitness. We studied the genetic architecture of population divergence in: (i) maturation probabilities at the same age; (ii) size at age and growth, while accounting for maturity status and sex; and (iii) growth plasticity in response to environmental factors, using divergent wild and domesticated Atlantic salmon (Salmo salar). Our work examined two populations and their multigenerational hybrids in a common experimental arrangement in which salinity and quantity of suspended sediments were manipulated to mimic naturally occurring environmental variation. Average specific growth rates across environments differed among crosses, maturity groups, and cross-by-maturity groups, but a growth-rate reduction in the presence of suspended sediments was equal for all groups. Our results revealed both additive and nonadditive outbreeding effects for size at age and for growth rates that differed with life stage, as well as the presence of different sex- and size-specific maturation probabilities between populations. The major implication of our work is that estimates of the genetic architecture of growth and maturation can be biased if one does not simultaneously account for temporal changes in growth and for different maturation probabilities between populations. Namely, these correlated traits interact differently within each population and between sexes and among generations, due to nonadditive effects and a level of independence in the genetic control for traits. Our results emphasize the challenges to investigating and predicting phenotypic changes resulting from between-population outbreeding.

  5. Population Density Modulates Drug Inhibition and Gives Rise to Potential Bistability of Treatment Outcomes for Bacterial Infections.

    Directory of Open Access Journals (Sweden)

    Jason Karslake

    2016-10-01

    Full Text Available The inoculum effect (IE is an increase in the minimum inhibitory concentration (MIC of an antibiotic as a function of the initial size of a microbial population. The IE has been observed in a wide range of bacteria, implying that antibiotic efficacy may depend on population density. Such density dependence could have dramatic effects on bacterial population dynamics and potential treatment strategies, but explicit measures of per capita growth as a function of density are generally not available. Instead, the IE measures MIC as a function of initial population size, and population density changes by many orders of magnitude on the timescale of the experiment. Therefore, the functional relationship between population density and antibiotic inhibition is generally not known, leaving many questions about the impact of the IE on different treatment strategies unanswered. To address these questions, here we directly measured real-time per capita growth of Enterococcus faecalis populations exposed to antibiotic at fixed population densities using multiplexed computer-automated culture devices. We show that density-dependent growth inhibition is pervasive for commonly used antibiotics, with some drugs showing increased inhibition and others decreased inhibition at high densities. For several drugs, the density dependence is mediated by changes in extracellular pH, a community-level phenomenon not previously linked with the IE. Using a simple mathematical model, we demonstrate how this density dependence can modulate population dynamics in constant drug environments. Then, we illustrate how time-dependent dosing strategies can mitigate the negative effects of density-dependence. Finally, we show that these density effects lead to bistable treatment outcomes for a wide range of antibiotic concentrations in a pharmacological model of antibiotic treatment. As a result, infections exceeding a critical density often survive otherwise effective treatments.

  6. Density dependence in flower visitation rates of cockroach-pollinated Clusia blattophila on the Nouragues inselberg, French Guiana

    Czech Academy of Sciences Publication Activity Database

    Vlasáková, Blanka

    2015-01-01

    Roč. 31, Part 1 (2015), s. 95-98 ISSN 0266-4674 R&D Projects: GA ČR GPP505/12/P039 Institutional support: RVO:67985939 Keywords : Clusia * ockroach * density dependence Subject RIV: EF - Botanics Impact factor: 0.975, year: 2015

  7. Population growth of Mexican free-tailed bats (Tadarida brasiliensis mexicana predates human agricultural activity

    Directory of Open Access Journals (Sweden)

    Cox Murray P

    2011-04-01

    Full Text Available Abstract Background Human activities, such as agriculture, hunting, and habitat modification, exert a significant effect on native species. Although many species have suffered population declines, increased population fragmentation, or even extinction in connection with these human impacts, others seem to have benefitted from human modification of their habitat. Here we examine whether population growth in an insectivorous bat (Tadarida brasiliensis mexicana can be attributed to the widespread expansion of agriculture in North America following European settlement. Colonies of T. b. mexicana are extremely large (~106 individuals and, in the modern era, major agricultural insect pests form an important component of their food resource. It is thus hypothesized that the growth of these insectivorous bat populations was coupled to the expansion of agricultural land use in North America over the last few centuries. Results We sequenced one haploid and one autosomal locus to determine the rate and time of onset of population growth in T. b. mexicana. Using an approximate Maximum Likelihood method, we have determined that T. b. mexicana populations began to grow ~220 kya from a relatively small ancestral effective population size before reaching the large effective population size observed today. Conclusions Our analyses reject the hypothesis that T. b. mexicana populations grew in connection with the expansion of human agriculture in North America, and instead suggest that this growth commenced long before the arrival of humans. As T. brasiliensis is a subtropical species, we hypothesize that the observed signals of population growth may instead reflect range expansions of ancestral bat populations from southern glacial refugia during the tail end of the Pleistocene.

  8. Impact of spin-orbit density dependent potential in heavy ion reactions forming Se nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Rajni; Sharma, Ishita; Sharma, Manoj K. [Thapar University, School of Physics and Materials Science, Patiala (India); Jain, Deepika [Mata Gujri College, Department of Physics, Fatehgarh Sahib (India)

    2017-10-15

    The Skyrme energy density formalism is employed to explore the effect of spin-orbit interaction potential by considering a two nucleon transfer process via various entrance channels such as {sup 23}Na + {sup 49}V, {sup 25}Mg + {sup 47}Ti, {sup 27}Al + {sup 45}Sc, {sup 29}Si + {sup 43}Ca and {sup 31}P + {sup 41}K, all forming the same compound system {sup 72}Se*, using both spherical as well as quadrupole deformed (β{sub 2}) nuclei. For spherical nuclei, the spin-orbit density part V{sub J} of nuclear potential remains unaffected with the transfer of two nucleons from the target to the projectile, however, show notable variation in magnitude after inclusion of deformation effects. Likewise, deformations play an important role in the spin-orbit density independent part V{sub P}, as the fusion pocket start appears, which otherwise diminish for the spherical nuclei. Further, the effect of an increase in the N/Z ratio of Se is explored on V{sub J} as well as V{sub P} and results are compared with transfer channels. In addition to this, the role of double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}) with relative contribution of the isoscalar and isovector parts of spin-orbit strength is explored in view of SkI2, SkI3 and SkI4 Skyrme forces. Beside this, the decay path of {sup 72}Se* nucleus formed in {sup 27}Al + {sup 45}Sc reaction is investigated within the framework of dynamical cluster decay model (DCM), where the nuclear proximity potential is obtained by both Skyrme energy density formalism (SEDF) and proximity pocket formula. The fusion hindrance in the {sup 27}Al + {sup 45}Sc reaction is also addressed via the barrier lowering parameter ΔV{sub B}. Finally, the contribution of spin-orbit density dependent interaction potential is estimated for the {sup 27}Al + {sup 45}Sc reaction using single (W{sub 0} or W{sub 0}{sup '}) and double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}). (orig.)

  9. Studies of Health and Long-Term Care Expenditure Growth in Aging Populations

    NARCIS (Netherlands)

    C.A.M. de Meijer (Claudine)

    2012-01-01

    textabstractIn recent decades, elderly populations in most developed countries have increased considerably, both in absolute and relative terms. This growth of the elderly share of the population is mainly attributable to two demographic transitions: the (simultaneous) increase in longevity and

  10. Growth and physiological responses to varied environments among populations of Pinus ponderosa

    Science.gov (United States)

    Jianwei Zhang; Bert M. Cregg

    2005-01-01

    We investigated population responses in physiology, morphology, and growth of mature Pinus ponderosa trees to an environmental gradient across Nebraska, USA. Ten populations from western Nebraska and eastern Wyoming were grown in three 26-year-old provenance tests from the warmest and wettest site in the east (Plattsmouth) to the intermediate site in...

  11. The effects of declining population growth on the demand for housing.

    Science.gov (United States)

    Thomas C. Marcin

    1974-01-01

    Declining population growth and unprecedented changes in the age structure of the population in the next several decades will profoundly affect housing demand in the next 50 years. A decline in housing demand and substantial change in the type of housing in demand are likely to occur by 1990.

  12. Rapid population growth and fragile environments: the sub-Saharan African and south Asian experience.

    Science.gov (United States)

    Caldwell, J C; Caldwell, P

    1994-02-18

    Case studies of the world's two poorest regions, sub-Saharan Africa and South Asia, were used to illustrate the compromised standard of living of the poor and environmental damage due to continued rapid population growth. The conclusion was that the livelihoods of the poor should not be endangered for preserving the living standards of richer people. Nations must not ignore the challenges of reducing population growth as fast as can be achieved. The transitional period over the next 50 years is the main concern, because population growth rates will be slowing. Rural population growth is expected to decline from 60% of total population growth in South Asia to 7% between 2000 and 2025; similarly the decline in sub-Saharan Africa would be from 50% to 15%. Over the past 30 years, food production in South Asia has kept pace with population growth. Sub-Saharan Africa has adopted food importation to meet demand. African problems are a low resource base, faster population growth, and the fact that governments and individuals are too poor to maintain soil fertility. Long-term studies of how much soil depletion will occur are not available for these regions, and local area studies are not as pessimistic. Transition policies are needed to put "people first in terms of engineered or directed population and ecological change." The six main issues are the following: 1) the Brundtland Commission appropriately identified poverty as the main cause and effect of environmental degradation because of the threat to survival; 2) the verdict is still out about whether food production will keep pace with population growth through economic growth and investment in agriculture; 3) empirical research is needed to examine local social and regulatory institutions and the possibility of reinforcing these mechanisms rather than instituting central controls; 4) central coercion or modernizing economic policies can destroy local level controls; 5) famine is a complex ecological phenomenon and the

  13. Control of density-dependent, cell state-specific signal transduction by the cell adhesion molecule CEACAM1, and its influence on cell cycle regulation

    International Nuclear Information System (INIS)

    Scheffrahn, Inka; Singer, Bernhard B.; Sigmundsson, Kristmundur; Lucka, Lothar; Oebrink, Bjoern

    2005-01-01

    Growth factor receptors, extracellular matrix receptors, and cell-cell adhesion molecules co-operate in regulating the activities of intracellular signaling pathways. Here, we demonstrate that the cell adhesion molecule CEACAM1 co-regulates growth-factor-induced DNA synthesis in NBT-II epithelial cells in a cell-density-dependent manner. CEACAM1 exerted its effects by regulating the activity of the Erk 1/2 MAP kinase pathway and the expression levels of the cyclin-dependent kinase inhibitor p27 Kip1 . Interestingly, both inhibitory and stimulatory effects were observed. Confluent cells continuously exposed to fetal calf serum showed little Erk activity and DNA synthesis compared with sparse cells. Under these conditions, anti-CEACAM1 antibodies strongly stimulated Erk activation, decreased p27 expression, and induced DNA synthesis. In serum-starved confluent cells, re-addition of 10% fetal calf serum activated the Erk pathway, decreased p27 expression, and stimulated DNA synthesis to the same levels as in sparse cells. Under these conditions anti-CEACAM1 antibodies de-activated Erk, restored the level of p27, and inhibited DNA synthesis. These data indicate that CEACAM1 mediates contact inhibition of proliferation in cells that are constantly exposed to growth factors, but co-activates growth-factor-induced proliferation in cells that have been starved for growth factors; exposure to extracellular CEACAM1 ligands reverts these responses

  14. [Fifty years of population growth and absorbing manual labor in Brazil, 1950-2000].

    Science.gov (United States)

    Paiva, P D

    1986-01-01

    The economically active population has grown rapidly in Brazil, resulting either from population growth or increased female participation in the work force. This rhythm of growth will continue at least until the end of this century. The authors suggest that the impact of the recent decline in fertility will be moderate and will only affect the younger age groups. Despite the rapid growth of employment in the processing industry, the relative size of the so-called informal sector has remained stable since 1950. It is further predicted that, given the economically active population's rate of growth and the decrease in employment in agriculture, there will be a great demand for urban employment in the next 20 years.

  15. A new ODE tumor growth modeling based on tumor population dynamics

    International Nuclear Information System (INIS)

    Oroji, Amin; Omar, Mohd bin; Yarahmadian, Shantia

    2015-01-01

    In this paper a new mathematical model for the population of tumor growth treated by radiation is proposed. The cells dynamics population in each state and the dynamics of whole tumor population are studied. Furthermore, a new definition of tumor lifespan is presented. Finally, the effects of two main parameters, treatment parameter (q), and repair mechanism parameter (r) on tumor lifespan are probed, and it is showed that the change in treatment parameter (q) highly affects the tumor lifespan

  16. Comparisons of Growth and Survival Performance Among Selected Families and Wild Populations of Fenneropenaeus chinensis

    Science.gov (United States)

    Luo, Kun; Kong, Jie; Meng, Xianhong; Luan, Sheng; Cao, Baoxiang; Chen, Baolong

    2018-04-01

    In this study, families of selected population for growth (SP_BWT), selected population for white spot syndrome virus (WSSV) resistance (SP_RW), Bohai wild population (WP_BH) and Huanghai wild population (WP_HH) of F. chinensis were constructed through artificial insemination and with the standardized procedure of larvae rearing. Growth and survival performance were studied among four populations after a 70 days common test. The results showed that the maximum least square mean of body weight was 17.50 g in SP_BWT while the minimum was 13.03 g in WP_HH. Compared with WP_BH, body weight of SP_BWT increased by 23.41% ( P 0.05). Body weights of SP_BWT and SP_RW were significantly higher than that of WP_HH, which increased by 34.31% ( P populations was 0.19, 0.18, 0.17 and 0.16 g d-1, respectively. Coefficient of variation of body weight among four populations was high, which ranged from 32.67% to 35.25%. Such a range showed that there was the potentiality for further improvement in selected populations. Coefficient of variation of survival rate among four populations was low, varying between 3.20% and 5.90%. The difference of survival was highly significant ( P populations ( P growth performances were also observed among different families in each population. The body weight of 798F family was the highest. The absolute growth rate (AGR) was 0.25 g d-1, 150% higher than that of the lowest one, 0.1 g d-1 in 807F family. Survival rate of families among four populations was different. The highest was 94.74%, and the lowest was 71.88%.

  17. A new ODE tumor growth modeling based on tumor population dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Oroji, Amin; Omar, Mohd bin [Institute of Mathematical Sciences, Faculty of Science University of Malaya, 50603 Kuala Lumpur, Malaysia amin.oroji@siswa.um.edu.my, mohd@um.edu.my (Malaysia); Yarahmadian, Shantia [Mathematics Department Mississippi State University, USA Syarahmadian@math.msstate.edu (United States)

    2015-10-22

    In this paper a new mathematical model for the population of tumor growth treated by radiation is proposed. The cells dynamics population in each state and the dynamics of whole tumor population are studied. Furthermore, a new definition of tumor lifespan is presented. Finally, the effects of two main parameters, treatment parameter (q), and repair mechanism parameter (r) on tumor lifespan are probed, and it is showed that the change in treatment parameter (q) highly affects the tumor lifespan.

  18. The ocean blues. Navigating the course of population growth.

    Science.gov (United States)

    Sarkar, D

    1996-01-01

    Oceans and their role in environmental balance are discussed in this article. Coastal waters within 200 miles from land are identified as providing over half the ocean's total biological productivity and supply of nearly all of the world's fish catch. Almost 3.6 billion people live in coastal areas or within 90 miles of coastal waters, which accounts for about 66% of world population. Coastal land areas account for about 8% of the earth's total land area. 8.3 billion people are expected by 2025 to live in coastal areas. 9 of the 10 largest cities in the world are located on coasts. 7 of the 10 largest cities in the US are coastal cities (54% of the US population or 142 million people). Almost all of the marine pollution is derived from land-based sources, such as sewage, nutrients, sediments, litter, and plastics. Mangroves in coastal waters have been reduced by about 50% to about 90,000 sq. miles worldwide. Global consumption of fish is responsible for depleting fish supplies and the loss of mangroves due to aquaculture of shrimp or other seafood. The US National Fisheries Service is cited for its report that 67 of the 156 fish stocks are overexploited. About 1 billion people, mostly in developing countries, rely on fish as their main food source. If imbalances in demand and supply continue, the rising price of fish and seafood will threaten the lives of about 1 billion or more people. Numerous international and national actions have been taken in order to protect supplies and reduce pollution. Sound resource management practices need to be instituted. Small and large fisheries can begin by reducing the 27 million tons of unintentional fish captures and by converting 29 million tons of fish used for animal feed into food for human consumption. Management of US coastal lands in most coastal states, with the exception of California and Rhode Island, is weak. Maryland has adopted a community-level approach for management of the Chesapeake Bay. Other environmental

  19. Population size structure indices and growth standards for Salmo (trutta trutta Linnaeus, 1758 in Central Italy

    Directory of Open Access Journals (Sweden)

    Pedicillo G.

    2010-10-01

    Full Text Available The purpose of this study was to provide reference data on the growth and population structure of brown trout Salmo (trutta trutta Linnaeus, in Central Italy. Standards for growth (percentiles and a standard growth model were developed from the von Bertalanffy growth model by using length-at-age data obtained from 122 sampling sites in the River Tiber basin. Length-frequency indices provide a numeric estimation for deviations of the population structure from a balanced population. We adapted the traditional North American Relative Stock Density (RSD and Proportional Stock Density (PSD indices to brown trout populations in Central Italy by means of two methods. In the first method, the benchmarks of length categories were established by using percentages applied to the largest individual in the dataset. In the second method, asymptotic length and size at maturity were used to define the length categories for index calculation. Both methods were tested on length-frequency data from 263 sampling sites in the River Tiber basin. The results showed that the PSD calculated by the first method provided a better insight into the population structures of brown trout. These results provide tools that will help ichthyologists and fish managers to compare the growth and population structure of brown trout throughout Central Italy.

  20. Population growth and environment as a self-organizing system

    Directory of Open Access Journals (Sweden)

    Peter M. Allen

    1999-01-01

    Full Text Available Over recent years a new understanding of complex systems, and their dynamics and evolution has emerged, and these have been shown to provide a new basis for models of the changing patterns of population and economic activities that shape the landscape. In this paper we make clear the necessarily partial description that any particular model must provide, and show the importance of a multidisciplinary, holistic understanding, linking any particular model to the co-evolution of its environment. In addition, we show how evolutionary processes link the microscopic level of molecules through successive scales of structure and organization ultimately to the biosphere itself, to issues of climatic change, of biomes at the continental scale and atmospheric and oceanic circulation patterns. Some very recent results will be shown which demonstrate that the world climate has already been modified considerably by human activities, particularly agriculture, underlining the vital need to understand better the on-going interaction between human activities and the biosphere.

  1. Influence of Cell-Cell Interactions on the Population Growth Rate in a Tumor

    Science.gov (United States)

    Chen, Yong

    2017-12-01

    The understanding of the macroscopic phenomenological models of the population growth at a microscopic level is important to predict the population behaviors emerged from the interactions between the individuals. In this work, we consider the influence of the population growth rate R on the cell-cell interaction in a tumor system and show that, in most cases especially small proliferative probabilities, the regulative role of the interaction will be strengthened with the decline of the intrinsic proliferative probabilities. For the high replication rates of an individual and the cooperative interactions, the proliferative probability almost has no effect. We compute the dependences of R on the interactions between the cells under the approximation of the nearest neighbor in the rim of an avascular tumor. Our results are helpful to qualitatively understand the influence of the interactions between the individuals on the growth rate in population systems. Supported by the National Natural Science Foundation of China under Grant Nos. 11675008 and 21434001

  2. [Is it necessary to control the population growth of national minorities].

    Science.gov (United States)

    Tian, X Y

    1981-02-01

    In the process of Socialist construction and modernization, the development of the population of national minorities deserves our attention because it is directly related to the economic and cultural development in the areas inhabited by such national minorities, and it has a great impact on the welfare and future of those people. Moreover, the population growth of the minorities is a key factor in the national population control strategy. A rapid population growth among the minorities has caused serious problems in distribution of farm land and food supply, low personal income, a rise in the unemployment rate, and a rise in the illiteracy rate. This has prevented a rise in the living standard among the minority population. In order to prevent and solve population problems among the minorities, we must take appropriate measures according to local conditions to control population increases. Through popularization of education, population growth may be put under control. For those people who volunteer to practice family planning, the government should provide all kinds of assistance. At the same time, an effort is needed to introduce the necessity of improving birth quality, to popularize new methods of child birth, and to develop health and medical care for the general public, so that the quality of the minority population may be gradually improved.

  3. A spatial analysis of patterns of growth and concentration of population based on homogeneous population censuses: Spain (1877-2001

    Directory of Open Access Journals (Sweden)

    Xavier Franch Auladell

    2013-01-01

    Full Text Available This work constitutes a contribution to the analysis of long term patterns of population concentration applied to the case of Spain. The proposed methodology is based on the homogenisation of both data and administrative units which takes the municipal structure of the 2001 census as its base reference. This work seeks to show how applying spatial analysis techniques to this type of homogeneous data series allows us to make more detailed studies of population patterns within a given territory. The most important conclusions that we reached was that, in Spain, sustained population growth has followed a spatial pattern that has become increasingly consolidated over time. The tendencies observed have produced an uneven distribution of population within the national territory marked by the existence of a series of well-defined, and often very localised, areas that spread beyond the limits of the official administrative boundaries.

  4. Adult survival and population growth rate in Colorado big brown bats (Eptesicus fuscus)

    Science.gov (United States)

    O'Shea, T.J.; Ellison, L.E.; Stanley, T.R.

    2011-01-01

    We studied adult survival and population growth at multiple maternity colonies of big brown bats (Eptesicus fuscus) in Fort Collins, Colorado. We investigated hypotheses about survival using information-theoretic methods and mark-recapture analyses based on passive detection of adult females tagged with passive integrated transponders. We constructed a 3-stage life-history matrix model to estimate population growth rate (??) and assessed the relative importance of adult survival and other life-history parameters to population growth through elasticity and sensitivity analysis. Annual adult survival at 5 maternity colonies monitored from 2001 to 2005 was estimated at 0.79 (95% confidence interval [95% CI] = 0.77-0.82). Adult survival varied by year and roost, with low survival during an extreme drought year, a finding with negative implications for bat populations because of the likelihood of increasing drought in western North America due to global climate change. Adult survival during winter was higher than in summer, and mean life expectancies calculated from survival estimates were lower than maximum longevity records. We modeled adult survival with recruitment parameter estimates from the same population. The study population was growing (?? = 1.096; 95% CI = 1.057-1.135). Adult survival was the most important demographic parameter for population growth. Growth clearly had the highest elasticity to adult survival, followed by juvenile survival and adult fecundity (approximately equivalent in rank). Elasticity was lowest for fecundity of yearlings. The relative importances of the various life-history parameters for population growth rate are similar to those of large mammals. ?? 2011 American Society of Mammalogists.

  5. Physical growth of the shuar: Height, Weight, and BMI references for an indigenous amazonian population.

    Science.gov (United States)

    Urlacher, Samuel S; Blackwell, Aaron D; Liebert, Melissa A; Madimenos, Felicia C; Cepon-Robins, Tara J; Gildner, Theresa E; Snodgrass, J Josh; Sugiyama, Lawrence S

    2016-01-01

    Information concerning physical growth among small-scale populations remains limited, yet such data are critical to local health efforts and to foster basic understandings of human life history and variation in childhood development. Using a large dataset and robust modeling methods, this study aims to describe growth from birth to adulthood among the indigenous Shuar of Amazonian Ecuador. Mixed-longitudinal measures of height, weight, and body mass index (BMI) were collected from Shuar participants (n = 2,463; age: 0-29 years). Centile growth curves and tables were created for each anthropometric variable of interest using Generalized Additive Models for Location, Scale, and Shape (GAMLSS). Pseudo-velocity and Lambda-Mu-Sigma curves were generated to further investigate Shuar patterns of growth and to facilitate comparison with United States Center for Disease Control and Prevention and multinational World Health Organization growth references. The Shuar are small throughout life and exhibit complex patterns of growth that differ substantially from those of international references. Similar to other Amazonians, Shuar growth in weight compares more favorably to references than growth in height, resulting in BMI curves that approximate international medians. Several additional characteristics of Shuar development are noteworthy, including large observed variation in body size early in life, significant infant growth faltering, extended male growth into adulthood, and a markedly early female pubertal growth spurt in height. Phenotypic plasticity and genetic selection in response to local environmental factors may explain many of these patterns. Providing a detailed reference of growth for the Shuar and other Amazonian populations, this study possesses direct clinical application and affords valuable insight into childhood health and the ecology of human growth. © 2015 Wiley Periodicals, Inc.

  6. Current demographics suggest future energy supplies will be inadequate to slow human population growth.

    Science.gov (United States)

    DeLong, John P; Burger, Oskar; Hamilton, Marcus J

    2010-10-05

    Influential demographic projections suggest that the global human population will stabilize at about 9-10 billion people by mid-century. These projections rest on two fundamental assumptions. The first is that the energy needed to fuel development and the associated decline in fertility will keep pace with energy demand far into the future. The second is that the demographic transition is irreversible such that once countries start down the path to lower fertility they cannot reverse to higher fertility. Both of these assumptions are problematic and may have an effect on population projections. Here we examine these assumptions explicitly. Specifically, given the theoretical and empirical relation between energy-use and population growth rates, we ask how the availability of energy is likely to affect population growth through 2050. Using a cross-country data set, we show that human population growth rates are negatively related to per-capita energy consumption, with zero growth occurring at ∼13 kW, suggesting that the global human population will stop growing only if individuals have access to this amount of power. Further, we find that current projected future energy supply rates are far below the supply needed to fuel a global demographic transition to zero growth, suggesting that the predicted leveling-off of the global population by mid-century is unlikely to occur, in the absence of a transition to an alternative energy source. Direct consideration of the energetic constraints underlying the demographic transition results in a qualitatively different population projection than produced when the energetic constraints are ignored. We suggest that energetic constraints be incorporated into future population projections.

  7. Current demographics suggest future energy supplies will be inadequate to slow human population growth.

    Directory of Open Access Journals (Sweden)

    John P DeLong

    Full Text Available Influential demographic projections suggest that the global human population will stabilize at about 9-10 billion people by mid-century. These projections rest on two fundamental assumptions. The first is that the energy needed to fuel development and the associated decline in fertility will keep pace with energy demand far into the future. The second is that the demographic transition is irreversible such that once countries start down the path to lower fertility they cannot reverse to higher fertility. Both of these assumptions are problematic and may have an effect on population projections. Here we examine these assumptions explicitly. Specifically, given the theoretical and empirical relation between energy-use and population growth rates, we ask how the availability of energy is likely to affect population growth through 2050. Using a cross-country data set, we show that human population growth rates are negatively related to per-capita energy consumption, with zero growth occurring at ∼13 kW, suggesting that the global human population will stop growing only if individuals have access to this amount of power. Further, we find that current projected future energy supply rates are far below the supply needed to fuel a global demographic transition to zero growth, suggesting that the predicted leveling-off of the global population by mid-century is unlikely to occur, in the absence of a transition to an alternative energy source. Direct consideration of the energetic constraints underlying the demographic transition results in a qualitatively different population projection than produced when the energetic constraints are ignored. We suggest that energetic constraints be incorporated into future population projections.

  8. Settlement, mortality and growth of the asari clam (Ruditapes philippinarum) for a collapsed population on a tidal flat in Nakatsu, Japan

    Science.gov (United States)

    Tezuka, Naoaki; Kamimura, Satomi; Hamaguchi, Masami; Saito, Hajime; Iwano, Hideki; Egashira, Junichi; Fukuda, Yuichi; Tawaratsumida, Takahiko; Nagamoto, Atsushi; Nakagawa, Koichi

    2012-04-01

    suggests that density-dependent processes such as predation or competition may affect population levels. In the center of the flat, the initial density of settlement was more stable than the rate of decrease after settlement. These results suggest that the clam population on this tidal flat is probably suppressed by variable but high mortality rates after settlement, not by recruitment limitation.

  9. [Effect of the population density on growth and regeneration in the snail Achatina fulica].

    Science.gov (United States)

    Sidel'nikov, A P; Stepanov, I I

    2000-01-01

    In the laboratory, the growth rate of the giant African snail Achatina fulica, as estimated by the weight and shell length was shown to decrease when the population density increased from 10 to 60 snails/m2 of the total terrarium area for five months. In the second experiment, when the population density increased from 48 to 193 snails/m2, the growth rate had already decreased by six weeks. In the groups with a high population density the feeding behavior was weakened, expressed by a greater amount of nonconsumed food, according to visual observations, than in the groups with lower population densities. At the population density of 10 to 60 snails/m2, the proliferative activity in the course of the optic tentacle regeneration, as expressed by the mitotic index, did not differ reliably within five months. In the second experiment, the mitotic indices at the population densities of 96 and 193 snails/m2 within 1.5 months exceeded that of 48 snails/m2. Recommendations are given concerning the population density from the viewpoint of commercial growth of the snails. It was proposed that, based on the analysis of the mechanism underlying the inhibition of feeding behavior in populations with extra high densities, one may develop a new approach to the production of chemical agents to control land snails as agricultural pests.

  10. Quantifying long-term population growth rates of threatened bull trout: challenges, lessons learned, and opportunities

    Science.gov (United States)

    Budy, Phaedra; Bowerman, Tracy; Al-Chokhachy, Robert K.; Conner, Mary; Schaller, Howard

    2017-01-01

    Temporal symmetry models (TSM) represent advances in the analytical application of mark–recapture data to population status assessments. For a population of char, we employed 10 years of active and passive mark–recapture data to quantify population growth rates using different data sources and analytical approaches. Estimates of adult population growth rate were 1.01 (95% confidence interval = 0.84–1.20) using a temporal symmetry model (λTSM), 0.96 (0.68–1.34) based on logistic regressions of annual snorkel data (λA), and 0.92 (0.77–1.11) from redd counts (λR). Top-performing TSMs included an increasing time trend in recruitment (f) and changes in capture probability (p). There was only a 1% chance the population decreased ≥50%, and a 10% chance it decreased ≥30% (λMCMC; based on Bayesian Markov chain Monte Carlo procedure). Size structure was stable; however, the adult population was dominated by small adults, and over the study period there was a decline in the contribution of large adults to total biomass. Juvenile condition decreased with increasing adult densities. Utilization of these different information sources provided a robust weight-of-evidence approach to identifying population status and potential mechanisms driving changes in population growth rates.

  11. Carrier-density dependence of photoluminescence from localized states in InGaN/GaN quantum wells in nanocolumns and a thin film

    Energy Technology Data Exchange (ETDEWEB)

    Shimosako, N., E-mail: n-shimosako@sophia.jp; Inose, Y.; Satoh, H.; Kinjo, K.; Nakaoka, T.; Oto, T. [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan); Kishino, K.; Ema, K. [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan); Sophia Nanotechnology Research Center, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)

    2015-11-07

    We have measured and analyzed the carrier-density dependence of photoluminescence (PL) spectra and the PL efficiency of InGaN/GaN multiple quantum wells in nanocolumns and in a thin film over a wide excitation range. The localized states parameters, such as the tailing parameter, density and size of the localized states, and the mobility edge density are estimated. The spectral change and reduction of PL efficiency are explained by filling of the localized states and population into the extended states around the mobility edge density. We have also found that the nanocolumns have a narrower distribution of the localized states and a higher PL efficiency than those of the film sample although the In composition of the nanocolumns is higher than that of the film.

  12. Population growth and economic development: two new U.S. perspectives.

    Science.gov (United States)

    Wulf, D; Klitsch, M

    1986-01-01

    This report compares the research paths of economic development reports by the US National Academy of Sciences (NAS) and the American Assembly of Columbia University. The NAS group, made up principally of economists and demographers, refrained from recommending population reduction targets, in contrast to the stronger terms of its 1971 report. A 1965 report by the Assembly spoke of population as a serious negative influence for economic development, political stability, and world peace, while the new report speaks of negative socioeconomic effects, and of the limiting of a person's right to control family size. The NAS agenda was established before the US delegation to the UN population conference in Mexico City retreated from declaring population growth to be a necessarily negative influencer of socioeconomic progress. The Assembly took the position that possible benefits of population growth would be far outweighed by factors such as resource depletion and women's health. The NAS maintained that growth might provide incentives for institutional adjustments (market development, investment in education) and control of growth should not be considered a substitute for such interventions. Both reports agree that control of fertility is a human right, but the NAS report examined the question of the acceptable degree of compulsion to be used to encourage couples. The Assembly objected to limiting access to family planning by defunding abortion programs oversease. Differences exist between the 2 reports in questins such as the negative impact of 1950's population growth, the synergistic effect of growth on many areas of human activity, the extent to which welfare of future generations is considered relevant today, and the adequacy of pure economic analysis in assessing need. Much study of population/development linkages is still required.

  13. Influence of Plant Population and Nitrogen-Fertilizer at Various Levels on Growth and Growth Efficiency of Maize

    Directory of Open Access Journals (Sweden)

    M. I. Tajul

    2013-01-01

    Full Text Available Field experiments were conducted to evaluate plant population and N-fertilizer effects on yield and yield components of maize (Zea mays L.. Three levels of plant populations (53000, 66000, and 800000 plants ha−1 corresponding to spacings of 75 × 25, 60 × 25, and 50 × 25 cm and 4 doses of N (100, 140, 180, and 220 kg ha−1 were the treatment variables. Results revealed that plant growth, light interception (LI, yield attributes, and grain yield varied significantly due to the variations in population density and N-rates. Crop growth rate (CGR was the highest with the population of 80,000 ha−1 receiving 220 kg N ha−1, while relative growth rate (RGR showed an opposite trend of CGR. Light absorption was maximum when most of densely populated plant received the highest amount of N (220 kg N ha−1. Response of soil-plant-analysis development (SPAD value as well as N-content to N-rates was found significant. Plant height was the maximum at the lowest plant density with the highest amount of N. Plants that received 180 kg N ha−1 with 80,000 plants ha−1 had larger foliage, greater SPAD value, and higher amount of grains cob−1 that contributed to the maximum yield (5.03 t ha−1 and the maximum harvest index (HI compared to the plants in other treatments.

  14. A necessary condition for dispersal driven growth of populations with discrete patch dynamics.

    Science.gov (United States)

    Guiver, Chris; Packman, David; Townley, Stuart

    2017-07-07

    We revisit the question of when can dispersal-induced coupling between discrete sink populations cause overall population growth? Such a phenomenon is called dispersal driven growth and provides a simple explanation of how dispersal can allow populations to persist across discrete, spatially heterogeneous, environments even when individual patches are adverse or unfavourable. For two classes of mathematical models, one linear and one non-linear, we provide necessary conditions for dispersal driven growth in terms of the non-existence of a common linear Lyapunov function, which we describe. Our approach draws heavily upon the underlying positive dynamical systems structure. Our results apply to both discrete- and continuous-time models. The theory is illustrated with examples and both biological and mathematical conclusions are drawn. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  15. Uropathogenic Escherichia coli Express Type 1 Fimbriae Only in Surface Adherent Populations Under Physiological Growth Conditions

    DEFF Research Database (Denmark)

    Stærk, Kristian; Kolmos, Hans Jørn; Khandige, Surabhi

    2016-01-01

    were correlated with the ability to adhere to and invade cultured human bladder cells. RESULTS:  Although inactive during planktonic growth in urine, T1F expression occurs when UPEC settles on and infects bladder epithelial cells or colonizes catheters. As a result, UPEC in these sessile populations...... with increased expression during surface growth adaptation and infection of uroepithelial cells. This leads to separation of UPEC into low-expression planktonic populations and high-expression sessile populations....... enhances bladder cell adhesion and invasion potential. Only T1F-negative UPEC are subsequently released to the urine, thus limiting T1F expression to surface-associated UPEC alone. CONCLUSION:  Our results demonstrate that T1F expression is strictly regulated under physiological growth conditions...

  16. Dynamics of individual growth in a recovering population of lake trout (Salvelinus namaycush)

    Science.gov (United States)

    Fabrizio, Mary C.; Dorazio, Robert M.; Schram, Stephen T.

    2001-01-01

    In 1976, the Wisconsin Department of Natural Resources established a refuge for a nearly depleted population of lake trout (Salvelinus namaycush) at Gull Island Shoal, Lake Superior. The refuge was intended to reduce fishing mortality by protecting adult lake trout. We examined the growth dynamics of these lake trout during the period of recovery by comparing estimates of ndividual growth before and after the refuge was established. Our estimates are based on an annual mark-recapture survey conducted at the spawning area since 1969. We developed a model that allowed mean growth rates to differ among individuals of different sizes and that accommodated variation in growth rates of individuals of the same size. Likelihood ratio tests were used to determine if the mean growth increments of lake trout changed ater the refuge was established. Our results suggest that growth of mature lake trout (particularly wild fish) decreased significantly in the postrefuge period. This decreased growth may have been associated with a reduction in food availability. We also observed reductions in growth as wild fish grew older and larger, which suggests that the growth of these fish may be adequately approximated by a von Bertalanffy growth model if it becomes possible to obtain accurate ages.

  17. On the growth of primary industry and population of China’s counties

    Science.gov (United States)

    Xie, Wen-Jie; Gu, Gao-Feng; Zhou, Wei-Xing

    2010-09-01

    The growth dynamics of complex organizations have attracted much interest of econophysicists and sociophysicists in recent years. However, most of the studies are done for developed countries. We investigate the growth dynamics of the primary industry and the population of 2079 counties in mainland China using the data from the China County Statistical Yearbooks from 2000 to 2006. We find that the annual growth rates are distributed according to Student’s t distribution with the tail exponent less than 2. We find power-law relationships between the sample standard deviation of the growth rates and the initial size. The scaling exponent is less than 0.5 for the primary industry and close to 0.5 for the population.

  18. Density dependence of a positron annihilation and positronium formation in H2 gas at temperatures between 77 and 297 K

    International Nuclear Information System (INIS)

    Laricchia, G.; Charlton, M.; Beling, C.D.; Griffith, T.C.

    1987-01-01

    Positron lifetime experiments have been performed on H 2 gas at temperatures between 77 and 297 K and in the density range from 12-160 Amagat. The extracted parameters are discussed in terms of current models. In the case of the positronium fraction it has been found that the observed density dependence can, in part, be interpreted using a combined Ore and spur model. (author)

  19. Population growth and development of Liposcelis pearmani (Psocoptera: Liposcelididae) at constant temperatures and relative humidities.

    Science.gov (United States)

    Aminatou, B A; Gautam, S G; Opit, G P; Talley, J; Shakya, K

    2011-08-01

    Psocids of genus Liposcelis are now considered serious pests of stored products. We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0°C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis pearmani Lienhard. L. pearmani did not survive at 37.5 and 40.0°C, at all relative humidities tested; at 43% RH, at all temperatures tested; and at 55% RH, at 32.5 and 35°C. The greatest population growth was recorded at 32.5°C and 75% RH (32-fold growth). L. pearmani males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 17, 63, and 20%, respectively. Female L. pearmani have two to five instars, and the percentages of females with two, three, four, and five instars were 5, 39, 55, and 1%, respectively. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. Based on 30-d population growth, L. pearmani cannot survive at temperatures >35.0°C; does not thrive at low relative humidities (55%), at temperatures above 25°C; and has a high optimum relative humidity for population growth (75%). Therefore, we expect it to have a more limited distribution compared with other Liposcelis species. These data provide a better understanding of how temperature and RH may influence L. pearmani population dynamics and can be used in population growth models to help develop effective management strategies for this psocid, and to predict its occurrence.

  20. Human population and atmospheric carbon dioxide growth dynamics: Diagnostics for the future

    Science.gov (United States)

    Hüsler, A. D.; Sornette, D.

    2014-10-01

    We analyze the growth rates of human population and of atmospheric carbon dioxide by comparing the relative merits of two benchmark models, the exponential law and the finite-time-singular (FTS) power law. The later results from positive feedbacks, either direct or mediated by other dynamical variables, as shown in our presentation of a simple endogenous macroeconomic dynamical growth model describing the growth dynamics of coupled processes involving human population (labor in economic terms), capital and technology (proxies by CO2 emissions). Human population in the context of our energy intensive economies constitutes arguably the most important underlying driving variable of the content of carbon dioxide in the atmosphere. Using some of the best databases available, we perform empirical analyses confirming that the human population on Earth has been growing super-exponentially until the mid-1960s, followed by a decelerated sub-exponential growth, with a tendency to plateau at just an exponential growth in the last decade with an average growth rate of 1.0% per year. In contrast, we find that the content of carbon dioxide in the atmosphere has continued to accelerate super-exponentially until 1990, with a transition to a progressive deceleration since then, with an average growth rate of approximately 2% per year in the last decade. To go back to CO2 atmosphere contents equal to or smaller than the level of 1990 as has been the broadly advertised goals of international treaties since 1990 requires herculean changes: from a dynamical point of view, the approximately exponential growth must not only turn to negative acceleration but also negative velocity to reverse the trend.

  1. Population growth, economic development and carrying capacity of the environment - are they compatible or in conflict?

    Directory of Open Access Journals (Sweden)

    A. E. F. Heydom

    1996-07-01

    Full Text Available In South Africa, as in many other countries, human population growth is currently reaching levels which render competition for basic human needs such as land and water, inevitable. Concurrent to population growth is the absolute necessity for economic development and job opportunities which, in turn, make tremendous demands upon the environment and natural resource base. As a consequence ever greater emphasis is placed by the news media on apparent conflicts between industrial development and social needs on the one hand, and conservation of the environment and natural resources on the other.

  2. Population increase, economic growth, educational inequality, and income distribution: some recent evidence.

    Science.gov (United States)

    Ram, R

    1984-04-01

    The relationship between population increase, economic growth, education and income inequality was examined in a cross-section study based on data from 26 developing and 2 developed countries. As other studies have noted, high population growth is associated with a less equal income distribution. A 1 percentage point reduction in the rate of population growth tends to raise the income share of the poorest 80% in the less developed world by almost 5 percentage points and is associated with a 1.7 percentage point increase in the income share of the poorest 40%. The relationship between short-run income growth and equality, on the other hand, is strong and positive. Estimates suggest that a 1 percentage point increase in the short-run rate of growth of the gross domestic product (GDP) increases the income share of the bottom 80% by about 2 percentage points and that of the poorest 40% by almost 1 percentage point. Although higher mean schooling appears to be a mild equalizer, educational inequality does not appear to have an adverse effect on income distribution. Overall, these results challenge the widely held belief that there must be a growth-equity trade-off. Moreover, they suggest that the impact of educational inequality on income distribution may be different from that observed in earlier studies, implying a need for caution in using these earlier results as a basis for educational policy development.

  3. Causes of mortality in California sea otters during periods of population growth and decline

    Science.gov (United States)

    Estes, J.A.; Hatfield, B.B.; Ralls, K.; Ames, J.

    2003-01-01

    Elevated mortality appears to be the main reason for both sluggish growth and periods of decline in the threatened California sea otter population. We assessed causes of mortality from salvage records of 3,105 beach-cast carcasses recovered from 1968 through 1999, contrasting two periods of growth with two periods of decline. Overall, an estimated 40%-60% of the deaths were not recovered and 70% of the recovered carcasses died from unknown causes. Nonetheless, several common patterns were evident in the salvage records during the periods of population decline. These included greater percentages of (1) prime age animals (3-10 yr), (2) carcasses killed by great white shark attacks, (3) carcasses recovered in spring and summer, and (4) carcasses for which the cause of death was unknown. Neither sex composition nor the proportion of carcasses dying of infectious disease varied consistently between periods of population increase and decline. The population decline from 1976 to 1984 was likely due to incidental mortality in a set-net fishery, and the decline from 1995 to 1999 may be related to a developing live-fish fishery. Long-term trends unrelated to periods of growth and decline included a decrease in per capita pup production and mass/length ratios of adult carcasses over the 31-yr study. The generally high proportion of deaths from infectious disease suggests that this factor has contributed to the chronically sluggish growth rate of the California sea otter population.

  4. Genetic variation facilitates seedling establishment but not population growth rate of a perennial invader.

    Science.gov (United States)

    Li, Shou-Li; Vasemägi, Anti; Ramula, Satu

    2016-01-01

    Assessing the demographic consequences of genetic variation is fundamental to invasion biology. However, genetic and demographic approaches are rarely combined to explore the effects of genetic variation on invasive populations in natural environments. This study combined population genetics, demographic data and a greenhouse experiment to investigate the consequences of genetic variation for the population fitness of the perennial, invasive herb Lupinus polyphyllus. Genetic and demographic data were collected from 37 L. polyphyllus populations representing different latitudes in Finland, and genetic variation was characterized based on 13 microsatellite loci. Associations between genetic variation and population size, population density, latitude and habitat were investigated. Genetic variation was then explored in relation to four fitness components (establishment, survival, growth, fecundity) measured at the population level, and the long-term population growth rate (λ). For a subset of populations genetic variation was also examined in relation to the temporal variability of λ. A further assessment was made of the role of natural selection in the observed variation of certain fitness components among populations under greenhouse conditions. It was found that genetic variation correlated positively with population size, particularly at higher latitudes, and differed among habitat types. Average seedling establishment per population increased with genetic variation in the field, but not under greenhouse conditions. Quantitative genetic divergence (Q(ST)) based on seedling establishment in the greenhouse was smaller than allelic genetic divergence (F'(ST)), indicating that unifying selection has a prominent role in this fitness component. Genetic variation was not associated with average survival, growth or fecundity measured at the population level, λ or its variability. The study suggests that although genetic variation may facilitate plant invasions by

  5. Density-dependent recruitment rates in great tits : the importance of being heavier

    NARCIS (Netherlands)

    Both, C; Visser, ME; Verboven, N

    1999-01-01

    In birds, individuals with a higher mass at fledging have a higher probability of recruiting into the breeding population. This can be because mass is an indicator of general condition and thereby of the ability to survive adverse circumstances, and/or because fledging mass is positively related to

  6. Density-dependent recruitment rates in great tits: the importance of being heavier

    NARCIS (Netherlands)

    Both, C.; Visser, M.E.; Verboven, N.

    1999-01-01

    In birds, individuals with a higher mass at fledging have a higher probability of recruiting into the breeding population. This can be because mass is an indicator of general condition and thereby of the ability to survive adverse circumstances, and/or because fledging mass is positively related to

  7. Modeling the pre-industrial roots of modern super-exponential population growth.

    Science.gov (United States)

    Stutz, Aaron Jonas

    2014-01-01

    To Malthus, rapid human population growth-so evident in 18th Century Europe-was obviously unsustainable. In his Essay on the Principle of Population, Malthus cogently argued that environmental and socioeconomic constraints on population rise were inevitable. Yet, he penned his essay on the eve of the global census size reaching one billion, as nearly two centuries of super-exponential increase were taking off. Introducing a novel extension of J. E. Cohen's hallmark coupled difference equation model of human population dynamics and carrying capacity, this article examines just how elastic population growth limits may be in response to demographic change. The revised model involves a simple formalization of how consumption costs influence carrying capacity elasticity over time. Recognizing that complex social resource-extraction networks support ongoing consumption-based investment in family formation and intergenerational resource transfers, it is important to consider how consumption has impacted the human environment and demography--especially as global population has become very large. Sensitivity analysis of the consumption-cost model's fit to historical population estimates, modern census data, and 21st Century demographic projections supports a critical conclusion. The recent population explosion was systemically determined by long-term, distinctly pre-industrial cultural evolution. It is suggested that modern globalizing transitions in technology, susceptibility to infectious disease, information flows and accumulation, and economic complexity were endogenous products of much earlier biocultural evolution of family formation's embeddedness in larger, hierarchically self-organizing cultural systems, which could potentially support high population elasticity of carrying capacity. Modern super-exponential population growth cannot be considered separately from long-term change in the multi-scalar political economy that connects family formation and

  8. The temporal and spatial dynamics of income and population growth in Ohio, 1950-1990.

    Science.gov (United States)

    Fan, C C

    1994-01-01

    "This paper focuses on spatial variation of growth within a state. Using Ohio as a case study, two hypotheses are extracted from the literature. First, the theories of polarization and polarization reversal suggest that in the old industrial core the leading sector role of manufacturing has diminished in old manufacturing poles, and that income growth trends differ substantially between these old poles and new centres of development. Second, the theories of suburbanization and migration reversals suggest that population growth is contingent upon level of urbanization, and that the relationship has changed drastically between the pre-1970s, 1970s, and post-1970s periods." (SUMMARY IN FRE AND GER) excerpt

  9. Analysis of single hyphal growth and fragmentation in submerged cultures using a population model

    DEFF Research Database (Denmark)

    Krabben, Preben; Nielsen, Søren; Michelsen, Michael Locht

    1997-01-01

    Descriptions of population dynamics in submerged cultures are important when studying the mechanisms of growth and fragmentation of filamentous microorganisms. Population models are traditionally formulated as population balance equations. Population models of filamentous morphology are difficult...... to solve because of random fragmentation, which introduces an integral term into the population balance equations. Balances for the systemic properties, e.g. concentration of hyphal elements, substrate concentration, average total hyphal length, and average number of growing tips, are set up. Based...... on these balances one can solve the inverse problem, i.e. determination of kinetic parameters directly from measurements of the hyphal morphology. Both a Monte Carlo method and a discretization method have been used to calculate the steady-state population distribution. The two methods are compared and the Monte...

  10. An application of Pontrjagin's principle to the study of the optimal growth of population

    International Nuclear Information System (INIS)

    Spinadel, V. de

    1976-01-01

    This paper examines the consequences of an optimal control of population growth and allows to derive criteria referring to the economic basis of expenditure on population control and to obtain optimal paths for a model in which such a control is possible. By means of very simple assumptions one can reduce the problem to a two-state variable control problem and, in consequence, apply Pontrjagin's maximum principle to solve it. (author)

  11. Nonylphenol stimulates fecundity but not population growth rate (λ) of Folsomia candida

    DEFF Research Database (Denmark)

    Widarto, T. H.; Krogh, P. H.; Forbes, V. E.

    2007-01-01

    of NP on these traits did not result in a statistically significant increase in population growth rate (λ). Decomposition analysis indicated that fecundity was the main contributor to the (non-significant) changes observed in λ However, since the elasticity of fecundity was very low, large changes...... at the population level and that λ is an appropriate endpoint for ecotoxicological studies. © 2007 Elsevier B.V. All rights reserved...

  12. Density-dependent benefits in ant-hemipteran mutualism? The case of the ghost ant Tapinoma melanocephalum (Hymenoptera: Formicidae and the invasive mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae.

    Directory of Open Access Journals (Sweden)

    Aiming Zhou

    Full Text Available Although density-dependent benefits to hemipterans from ant tending have been measured many times, few studies have focused on integrated effects such as interactions between ant tending, natural enemy density, and hemipteran density. In this study, we tested whether the invasive mealybug Phenacoccus solenopsis is affected by tending by ghost ants (Tapinoma melanocephalum, the presence of parasitoids, mealybug density, parasitoid density and interactions among these factors. Our results showed that mealybug colony growth rate and percentage parasitism were significantly affected by ant tending, parasitoid presence, and initial mealybug density separately. However, there were no interactions among the independent factors. There were also no significant interactions between ant tending and parasitoid density on either mealybug colony growth rate or percentage parasitism. Mealybug colony growth rate showed a negative linear relationship with initial mealybug density but a positive linear relationship with the level of ant tending. These results suggest that benefits to mealybugs are density-independent and are affected by ant tending level.

  13. India in the Twenty-first Century: The Challenge of Population Growth. Fulbright-Hays Summer Seminars Abroad, 1997 (India).

    Science.gov (United States)

    La Fleur, Mary Ann

    This paper contains a course outline for a five-hour graduate class focusing on the issue of population in India. Students examine contributing factors to population growth, along with studying characteristics of, and efforts to, control population growth. The significance of ethnic diversity in India also is addressed. Group discussion and group…

  14. Effects of temperature and population density on von Bertalanffy growth parameters in Atlantic herring: a macro-ecological analysis

    NARCIS (Netherlands)

    Brunel, T.P.A.; Dickey-Collas, M.

    2010-01-01

    The effect of temperature and population density on the growth of Atlantic herring Clupea harengus was studied using a comparative approach applied to 15 North Atlantic populations. The von Bertalanffy (VB) equation was applied to describe mean growth of individuals in each population, both averaged

  15. Analysis of Urban Growth in Edwardsville Illinois Using Remote Sensing and Population Change

    Science.gov (United States)

    Onuoha, Hilda U.

    Rapid urbanization is one of the many critical, global issues. This very significant social and economic phenomenon has brought about much debate in the past twenty years and has become a very important policy issue. Understanding its dynamics and patterns is important to develop appropriate policies and make more informed planning decisions. Many dimensions to the urban land growth have been identified in related literature including drivers, relationship with other factors like population, impacts, and methods of measurement. In this study, urban growth in the Edwardsville area (composed of Edwardsville and Glen Carbon, Illinois) is analyzed spatio-temporally using remote sensing and population change from 1990 to 2015. The objectives of this study are (a) identifying the major land use changes in the Edwardsville area from 1990 to 2015, (b) analyzing the rate of urban growth and its relationship to population change in the area from 1990 to 2015, (c) identifying the general pattern and direction of urban growth in the study area. Using multi-temporal satellite images to classify and derive changes in land cover classes during the study period, results showed that the land cover classes with major changes are the urban/built-up land and agricultural/grassland, with a steady increase in the former and steady decrease in the later. Results also show the highest rate of increase in urban land was between 2000 and 2010. In comparison to population, the both show increase over the study years but urban land shows a higher rate of increase indicating dispersion. To analyze urban growth pattern in the area, the study area was divided into three zones: NE, SE, and W. The SE zone showed the highest amount of the growth and from the results, the infill type of growth was inferred.

  16. Density-dependent reproductive and vegetative allocation in the aquatic plant Pistia stratiotes (Araceae

    Directory of Open Access Journals (Sweden)

    Flávia Freitas Coelho

    2005-09-01

    Full Text Available Pistia stratiotes is an aquatic macrophyte that grows in temporary-ponds in the southern Pantanal, Brazil. It reproduces both sexually and asexually and is usually observed forming dense mats on the water surface, a condition favored by the plant’s vegetative reproduction coupled with an ability for rapid growth. In this study we examined the effect of densely crowded conditions on the production of reproductive and vegetative structures. In addition, we verified whether there is a trade-off between clonal growth and investment in sexual reproductive structures, and whether there is an allocation pattern with plant size. Individual plant biomass and the number of the rosettes producing sexual reproductive structures and vegetative growth structures both increased with density. Increase in plant size resulted in increased proportional allocation to sexual reproductive structures and vegetative growth structures. Allocation of biomass to reproduction did not occur at the expense of clonal growth. Thus, the density response appears as a increase of rosettes producing sexual reproductive structures and vegetative growth structures. Therefore, long leaves and stolons may be adaptive under densely crowded conditions where competition for light is intense. An important aspect in the study of trade-offs is the size-dependency of the allocation patterns .Usually, larger plants produce more biomass. Therefore, larger plants can allocate more biomass to both vegetative and sexual reproduction than smaller plants and thus show a positive correlation between both traits rather than the expected negative one. Rev. Biol. Trop. 53(3-4: 369-376. Epub 2005 Oct 3.Pistias strariotes es una macrófita acuática que crece en charcas estacionales en el Pantanal sureño de Brasil. Se reproduce tanto sexual como asexualmente y se obsrva generalmente que forma densas parches sobre la superficie del agua, una condicion que favorecida por la reproduccion vegetativa de la

  17. Ability of matrix models to explain the past and predict the future of plant populations.

    Science.gov (United States)

    McEachern, Kathryn; Crone, Elizabeth E.; Ellis, Martha M.; Morris, William F.; Stanley, Amanda; Bell, Timothy; Bierzychudek, Paulette; Ehrlen, Johan; Kaye, Thomas N.; Knight, Tiffany M.; Lesica, Peter; Oostermeijer, Gerard; Quintana-Ascencio, Pedro F.; Ticktin, Tamara; Valverde, Teresa; Williams, Jennifer I.; Doak, Daniel F.; Ganesan, Rengaian; Thorpe, Andrea S.; Menges, Eric S.

    2013-01-01

    Uncertainty associated with ecological forecasts has long been recognized, but forecast accuracy is rarely quantified. We evaluated how well data on 82 populations of 20 species of plants spanning 3 continents explained and predicted plant population dynamics. We parameterized stage-based matrix models with demographic data from individually marked plants and determined how well these models forecast population sizes observed at least 5 years into the future. Simple demographic models forecasted population dynamics poorly; only 40% of observed population sizes fell within our forecasts' 95% confidence limits. However, these models explained population dynamics during the years in which data were collected; observed changes in population size during the data-collection period were strongly positively correlated with population growth rate. Thus, these models are at least a sound way to quantify population status. Poor forecasts were not associated with the number of individual plants or years of data. We tested whether vital rates were density dependent and found both positive and negative density dependence. However, density dependence was not associated with forecast error. Forecast error was significantly associated with environmental differences between the data collection and forecast periods. To forecast population fates, more detailed models, such as those that project how environments are likely to change and how these changes will affect population dynamics, may be needed. Such detailed models are not always feasible. Thus, it may be wiser to make risk-averse decisions than to expect precise forecasts from models.

  18. Ability of matrix models to explain the past and predict the future of plant populations.

    Science.gov (United States)

    Crone, Elizabeth E; Ellis, Martha M; Morris, William F; Stanley, Amanda; Bell, Timothy; Bierzychudek, Paulette; Ehrlén, Johan; Kaye, Thomas N; Knight, Tiffany M; Lesica, Peter; Oostermeijer, Gerard; Quintana-Ascencio, Pedro F; Ticktin, Tamara; Valverde, Teresa; Williams, Jennifer L; Doak, Daniel F; Ganesan, Rengaian; McEachern, Kathyrn; Thorpe, Andrea S; Menges, Eric S

    2013-10-01

    Uncertainty associated with ecological forecasts has long been recognized, but forecast accuracy is rarely quantified. We evaluated how well data on 82 populations of 20 species of plants spanning 3 continents explained and predicted plant population dynamics. We parameterized stage-based matrix models with demographic data from individually marked plants and determined how well these models forecast population sizes observed at least 5 years into the future. Simple demographic models forecasted population dynamics poorly; only 40% of observed population sizes fell within our forecasts' 95% confidence limits. However, these models explained population dynamics during the years in which data were collected; observed changes in population size during the data-collection period were strongly positively correlated with population growth rate. Thus, these models are at least a sound way to quantify population status. Poor forecasts were not associated with the number of individual plants or years of data. We tested whether vital rates were density dependent and found both positive and negative density dependence. However, density dependence was not associated with forecast error. Forecast error was significantly associated with environmental differences between the data collection and forecast periods. To forecast population fates, more detailed models, such as those that project how environments are likely to change and how these changes will affect population dynamics, may be needed. Such detailed models are not always feasible. Thus, it may be wiser to make risk-averse decisions than to expect precise forecasts from models. © 2013 Society for Conservation Biology.

  19. Rapid Population Growth and Human Carrying Capacity: Two Perspectives. World Bank Staff Working Papers No. 690 and Population and Development Series No. 15.

    Science.gov (United States)

    Mahar, Dennis J., Ed.; And Others

    Two perspectives on carrying capacity and population growth are examined. The first perspective, "Carrying Capacity and Rapid Population Growth: Definition, Cases, and Consequences" (Robert Muscat), explores the possible meanings of the idea of carrying capacity under developing country conditions, looks at historical and present-day cases of…

  20. An exponential growth model with decreasing r captures bottom-up effects on the population growth of Aphis glycines Matsumura (Hemiptera: Aphididae)

    NARCIS (Netherlands)

    Costamagna, A.C.; Werf, van der W.; Bianchi, F.J.J.A.; Landis, D.A.

    2007-01-01

    1 There is ample evidence that the life history and population dynamics of aphids are closely linked to plant phenology. Based on life table studies, it has been proposed that the growth of aphid populations could be modeled with an exponential growth model, with r decreasing linearly with time.

  1. Generation time, net reproductive rate, and growth in stage-age-structured populations

    DEFF Research Database (Denmark)

    Steiner, Uli; Tuljapurkar, Shripad; Coulson, Tim

    2014-01-01

    examples to show how reproductive timing Tc and level R0 are shaped by stage dynamics (individual trait changes), selection on the trait, and parent-offspring phenotypic correlation. We also show how population structure can affect dispersion in reproduction among ages and stages. These macroscopic...... to age-structured populations. Here we generalize this result to populations structured by stage and age by providing a new, unique measure of reproductive timing (Tc) that, along with net reproductive rate (R0), has a direct mathematical relationship to and approximates growth rate (r). We use simple...

  2. Growth rates and variances of unexploited wolf populations in dynamic equilibria

    Science.gov (United States)

    Mech, L. David; Fieberg, John

    2015-01-01

    Several states have begun harvesting gray wolves (Canis lupus), and these states and various European countries are closely monitoring their wolf populations. To provide appropriate perspective for determining unusual or extreme fluctuations in their managed wolf populations, we analyzed natural, long-term, wolf-population-density trajectories totaling 130 years of data from 3 areas: Isle Royale National Park in Lake Superior, Michigan, USA; the east-central Superior National Forest in northeastern Minnesota, USA; and Denali National Park, Alaska, USA. Ratios between minimum and maximum annual sizes for 2 mainland populations (n = 28 and 46 yr) varied from 2.5–2.8, whereas for Isle Royale (n = 56 yr), the ratio was 6.3. The interquartile range (25th percentile, 75th percentile) for annual growth rates, Nt+1/Nt, was (0.88, 1.14), (0.92, 1.11), and (0.86, 1.12) for Denali, Superior National Forest, and Isle Royale respectively. We fit a density-independent model and a Ricker model to each time series, and in both cases we considered the potential for observation error. Mean growth rates from the density-independent model were close to 0 for all 3 populations, with 95% credible intervals including 0. We view the estimated model parameters, including those describing annual variability or process variance, as providing useful summaries of the trajectories of these populations. The estimates of these natural wolf population parameters can serve as benchmarks for comparison with those of recovering wolf populations. Because our study populations were all from circumscribed areas, fluctuations in them represent fluctuations in densities (i.e., changes in numbers are not confounded by changes in occupied area as would be the case with populations expanding their range, as are wolf populations in many states).

  3. Nutritional status and growth of children on macrobiotic diets : a population-based study

    NARCIS (Netherlands)

    Dagnelie, P.C.

    1988-01-01

    This thesis reports on the relationship between diet, growth, blood chemistry, psychomotor development, and clinical findings in the Dutch population of children on macrobiotic diets.- The macrobiotic diet mainly consisted of cereals, pulses and vegetables with small additions of seaweeds,

  4. The Effect of Population Growth upon the Quantity of Education Children Receive.

    Science.gov (United States)

    Simon, Julian L.; Pilarski, Adam M.

    1979-01-01

    There is indeed some negative effect of population growth on the amount of education in developing nations, but the effect is less severe than has been thought. This finding is in sharp contrast to previous conclusions drawn from similar cross-national data. Available from Review of Economics and Statistics, M-8 Littauer Center, Cambridge, MA…

  5. Growth strategy of heterotrophic bacterial population along successional sequence on spoil of brown coal colliery substrate

    Czech Academy of Sciences Publication Activity Database

    Krištůfek, Václav; Elhottová, Dana; Chroňáková, Alica; Dostálková, I.; Picek, T.; Kalčík, Jiří

    2005-01-01

    Roč. 50, č. 5 (2005), s. 427-435 ISSN 0015-5632 R&D Projects: GA ČR(CZ) GA526/03/1259 Institutional research plan: CEZ:AV0Z60660521 Keywords : growth strategy * heterotrophic bacterial population * brown coal colliery spoil Subject RIV: EH - Ecology, Behaviour Impact factor: 0.918, year: 2005

  6. Effects of population density on the growth and egg-laying capacity ...

    African Journals Online (AJOL)

    The effects of the population density of adult African giant land snail, Archachatina marginata on the egg-laying capacity and the growth of the brooders and hatchlings were investigated for 9 months. Ten culture pens were stocked with snails at 20%, 40%, 60%, 80% and 100% capacity with each group in 2 replicates.

  7. Teaching Population Growth Using Cultures of Vinegar Eels, "Turbatrix aceti" (Nematoda)

    Science.gov (United States)

    Wallace, Robert L.

    2005-01-01

    A simple laboratory exercise is presented that follows the population growth of the common vinegar eel, "Turbatrix aceti" (Nematoda), in a microcosm using a simple culture medium. It lends itself to an exercise in a single semester course. (Contains 4 figures.)

  8. Calculating second derivatives of population growth rates for ecology and evolution

    NARCIS (Netherlands)

    Shyu, E.; Caswell, H.

    2014-01-01

    Second derivatives of the population growth rate measure the curvature of its response to demographic, physiological or environmental parameters. The second derivatives quantify the response of sensitivity results to perturbations, provide a classification of types of selection and provide one way

  9. Population Growth Rates: Connecting Mathematics to Studies of Society and the Environment

    Science.gov (United States)

    Ninbet, Steven; Hurley, Gabrielle; Weldon, Elizabeth

    2006-01-01

    This article reports on the teaching of a unit of lessons which integrates mathematics with studies of society and the environment. The unit entitled "Population Growth Rates" was taught to a double class of Year 6 students by a team of three teachers. The objectives of the unit were: (1) to provide students with a real-world context in…

  10. Growth of the human lens in the Indian adult population: Preliminary observations

    Directory of Open Access Journals (Sweden)

    Ashik Mohamed

    2012-01-01

    Full Text Available Context: The eye lens grows throughout life by the addition of new cells inside the surrounding capsule. How this growth affects the properties of the lens is essential for understanding disorders such as cataract and presbyopia. Aims: To examine growth of the human lens in the Indian population and compare this with the growth in Western populations by measuring in vitro dimensions together with wet and dry weights. Settings and Design: The study was conducted at the research wing of a tertiary eye care center in South India and the study design was prospective. Materials and Methods: Lenses were removed from eye bank eyes and their dimensions measured with a digital caliper. They were then carefully blotted dry and weighed before being placed in 5% buffered formalin. After 1 week fixation, the lenses were dried at 80 °C until constant weight was achieved. The constant weight was noted as the dry weight of the lens. Statistical Analysis Used: Lens parameters were analyzed as a function of age using linear and logarithmic regression methods. Results: Data were obtained for 251 lenses, aged 16-93 years, within a median postmortem time of 22 h. Both wet and dry weights increased linearly at 1.24 and 0.44 mg/year, respectively, throughout adult life. The dimensions also increased continuously throughout this time. Conclusions: Over the age range examined, lens growth in the Indian population is very similar to that in Western populations.

  11. Effects of growth curve plasticity on size-structured population dynamics

    DEFF Research Database (Denmark)

    Zhang, Lai; Lin, Zhigui; Pedersen, Michael

    2011-01-01

    The physiological-structured population models assume that a fixed fraction of energy intake is utilized for individual growth and maintenance while the remaining for adult fertility. The assumption results in two concerns: energy loss for juveniles and a reproduction dilemma for adults. The dile...

  12. Population growth and the decline of natural Southern yellow pine forests

    Science.gov (United States)

    David B. South; Edward R. Buckner

    2004-01-01

    Population growth has created social and economic pressures that affect the sustainability of naturally regenerated southern yellow pine forests. Major causes of this decline include (1) a shift in public attitudes regarding woods burning (from one favoring it to one that favors fire suppression) and (2) an increase in land values (especially near urban centers). The...

  13. Female strobili incidence in a Minnesota population of black spruce: heritability and correlation with height growth

    Science.gov (United States)

    C. Dana Nelson; C. A. Mohn

    1989-01-01

    Significant family variation in female strobili incidence, ripeness-to-flower and production were found in a Minnesota black spruce (Picea mariana (Mill.) B.S.P.) population tested at four locations. Heritability estimates indicated that gain in early flowering from selection would be possible. Height growth through age 12 years was positively correlated (genetic and...

  14. Connecting phenological predictions with population growth rates for mountain pine beetle, an outbreak insect

    Science.gov (United States)

    James A. Powell; Barbara J. Bentz

    2009-01-01

    It is expected that a significant impact of global warming will be disruption of phenology as environmental cues become disassociated from their selective impacts. However there are few, if any, models directly connecting phenology with population growth rates. In this paper we discuss connecting a distributional model describing mountain pine beetle phenology with a...

  15. Does pollen limitation affect population growth of the endangered Dracocephalum austriacum L.?

    Czech Academy of Sciences Publication Activity Database

    Castro, Sílvia; Dostálek, Tomáš; van der Meer, S.; Oostermeijer, G.; Münzbergová, Zuzana

    2015-01-01

    Roč. 57, č. 1 (2015), s. 105-116 ISSN 1438-3896 R&D Projects: GA ČR GP13-10850P; GA ČR GAP505/10/0593 Institutional support: RVO:67985939 Keywords : Dracocephalum austriacum * pollination ecology * population growth rate Subject RIV: EF - Botanics Impact factor: 1.698, year: 2015

  16. Population growth in a wild bird is buffered against phenological mismatch

    NARCIS (Netherlands)

    Reed, T.; Grotan, V.; Jenouvrier, S.; Saether, B.E.; Visser, M.E.

    2013-01-01

    road-scale environmental changes are altering patterns of natural selection in the wild, but few empirical studies have quantified the demographic cost of sustained directional selection in response to these changes. We tested whether population growth in a wild bird is negatively affected by

  17. Meeting the Sustainable Development Goals leads to lower world population growth.

    Science.gov (United States)

    Abel, Guy J; Barakat, Bilal; Kc, Samir; Lutz, Wolfgang

    2016-12-13

    Here we show the extent to which the expected world population growth could be lowered by successfully implementing the recently agreed-upon Sustainable Development Goals (SDGs). The SDGs include specific quantitative targets on mortality, reproductive health, and education for all girls by 2030, measures that will directly and indirectly affect future demographic trends. Based on a multidimensional model of population dynamics that stratifies national populations by age, sex, and level of education with educational fertility and mortality differentials, we translate these goals into SDG population scenarios, resulting in population sizes between 8.2 and 8.7 billion in 2100. Because these results lie outside the 95% prediction range given by the 2015 United Nations probabilistic population projections, we complement the study with sensitivity analyses of these projections that suggest that those prediction intervals are too narrow because of uncertainty in baseline data, conservative assumptions on correlations, and the possibility of new policies influencing these trends. Although the analysis presented here rests on several assumptions about the implementation of the SDGs and the persistence of educational, fertility, and mortality differentials, it quantitatively illustrates the view that demography is not destiny and that policies can make a decisive difference. In particular, advances in female education and reproductive health can contribute greatly to reducing world population growth.

  18. Growth Indicators of a 48-Clone Sugar Cane Population (Saccharum spp. with Forage Potential

    Directory of Open Access Journals (Sweden)

    Yoslen Fernández Gálvez

    2016-09-01

    Full Text Available The aim of this paper was to determine growth indicators in a 48-clone sugar cane population, with promising phenotypical features for forage production. The following indicators were assessed: leaf area (A, leaf area index (LA1; leaf area ratio (LAR; specific leaf area (SLA; leaf weight ratio (LWR; crop growth rate (CGR; net assimilation rate (NAR; relative growth rate in weight (RGR; biomass production speed (G; leaf area duration (LAD; and biomass duration (Z, monthly (187 - 370 days. The minimum, the mean, the maximum values, and the population variance were determined for all cutting ages and the variables assessed. The results achieved have provided quantitative values that can be used as reference for selection and assessment of forage genotypes for ruminant nutrition.

  19. Individualism in plant populations: using stochastic differential equations to model individual neighbourhood-dependent plant growth.

    Science.gov (United States)

    Lv, Qiming; Schneider, Manuel K; Pitchford, Jonathan W

    2008-08-01

    We study individual plant growth and size hierarchy formation in an experimental population of Arabidopsis thaliana, within an integrated analysis that explicitly accounts for size-dependent growth, size- and space-dependent competition, and environmental stochasticity. It is shown that a Gompertz-type stochastic differential equation (SDE) model, involving asymmetric competition kernels and a stochastic term which decreases with the logarithm of plant weight, efficiently describes individual plant growth, competition, and variability in the studied population. The model is evaluated within a Bayesian framework and compared to its deterministic counterpart, and to several simplified stochastic models, using distributional validation. We show that stochasticity is an important determinant of size hierarchy and that SDE models outperform the deterministic model if and only if structural components of competition (asymmetry; size- and space-dependence) are accounted for. Implications of these results are discussed in the context of plant ecology and in more general modelling situations.

  20. A density-dependent switch drives stochastic clustering and polarization of signaling molecules.

    Directory of Open Access Journals (Sweden)

    Alexandra Jilkine

    2011-11-01

    Full Text Available Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered "off" state is desired? And, what limits the spread of clusters when an "on" state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the "neutral drift polarity model." Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization.

  1. Uncertainty in population growth rates: determining confidence intervals from point estimates of parameters.

    Directory of Open Access Journals (Sweden)

    Eleanor S Devenish Nelson

    Full Text Available BACKGROUND: Demographic models are widely used in conservation and management, and their parameterisation often relies on data collected for other purposes. When underlying data lack clear indications of associated uncertainty, modellers often fail to account for that uncertainty in model outputs, such as estimates of population growth. METHODOLOGY/PRINCIPAL FINDINGS: We applied a likelihood approach to infer uncertainty retrospectively from point estimates of vital rates. Combining this with resampling techniques and projection modelling, we show that confidence intervals for population growth estimates are easy to derive. We used similar techniques to examine the effects of sample size on uncertainty. Our approach is illustrated using data on the red fox, Vulpes vulpes, a predator of ecological and cultural importance, and the most widespread extant terrestrial mammal. We show that uncertainty surrounding estimated population growth rates can be high, even for relatively well-studied populations. Halving that uncertainty typically requires a quadrupling of sampling effort. CONCLUSIONS/SIGNIFICANCE: Our results compel caution when comparing demographic trends between populations without accounting for uncertainty. Our methods will be widely applicable to demographic studies of many species.

  2. JOB DISCRIMINATION AGAINST WOMEN AND ENDOGENOUS POPULATION CHANGE IN A GENERALIZED SOLOW GROWTH MODEL

    Directory of Open Access Journals (Sweden)

    Wei-Bin ZHANG

    2017-06-01

    Full Text Available This study examines economic growth and population change with discrimination against women in the labor market within the analytical framework of Solow’s neoclassical growth model. The study models dynamic interactions between wealth accumulation, time distribution between work, children caring, and leisure, population change with endogenous birth and mortality rates with gender discrimination. The production technology and markets are built on Solow’s neoclassical growth model. The basic mechanisms for population changes in the Barro-Becker fertility choice model and the Haavelmo population model are integrated to model the population change. This study also takes account of discrimination against woman in the labor market. We synthesize these dynamic forces in a compact framework by applying Zhang’s utility function. The model properties are studied by simulation. We find equilibrium points and illustrate motion of the dynamic system. We also examine the effects of changes in the discrimination against woman, the propensity to save, woman’s propensity to pursue leisure activities, the propensity to have children, woman’s human capital and man’s emotional involvement in children caring.

  3. Effect of Cadmium on the population growth of the marine diatom Chaetoceros gracilis Schutt

    Directory of Open Access Journals (Sweden)

    Giovana Vera

    2014-06-01

    Full Text Available Phytoplankton constitutes the base of the trophic webs in the marine environment, so it is important to know the possible effects of pollutants on the algal populations. In the present paper the effect of cadmium on the population growth of the diatom Chaetoceros gracilis was assessed. The microalgae were cultured in the a modified “f/2” Guillard medium, and were exposed to different concentrations of cadmium between 50 and 100000 µg.–1, which produced an inhibitory effect from 20% to 99% on the population growth of Chaetoceros gracilis. Based on the dose (cadmium-response (inhibition relationship, a mean effective concentration (EC50% equal to 591 µg.L–1 of cadmium was obtained.

  4. Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa

    DEFF Research Database (Denmark)

    Brandt, Martin Stefan; Rasmussen, Kjeld; Peñuelas, Josep

    2017-01-01

    The rapidly growing human population in sub-Saharan Africa generates increasing demand for agricultural land and forest products, which presumably leads to deforestation. Conversely, a greening of African drylands has been reported, but this has been difficult to associate with changes in woody...... an increase in woody cover largely in drylands, and 11% had a decrease (2,150,000 km2), mostly in humid zones. Increases in woody cover were associated with low population growth, and were driven by increases in CO2 in the humid zones and by increases in precipitation in drylands, whereas decreases in woody...... cover were associated with high population growth. The spatially distinct pattern of these opposing trends reflects, first, the natural response of vegetation to precipitation and atmospheric CO2, and second, deforestation in humid areas, minor in size but important for ecosystem services...

  5. Population dynamics of bowfin in a south Georgia reservoir: latitudinal comparisons of population structure, growth, and mortality

    Science.gov (United States)

    Porter, Nicholas J.; Bonvechio, Timothy F.; McCormick, Joshua L.; Quist, Michael

    2014-01-01

    The objectives of this study were to evaluate the population dynamics of bowfin (Amia calva) in Lake Lindsay Grace, Georgia, and to compare those dynamics to other bowfin populations. Relative abundance of bowfin sampled in 2010 in Lake Lindsay Grace was low and variable (mean±SD; 2.7±4.7 fish per hour of electrofishing). Total length (TL) of bowfin collected in Lake Lindsay Grace varied from 233–683 mm. Age of bowfin in Lake Lindsay Grace varied from 0–5 yr. Total annual mortality (A) was estimated at 68%. Both sexes appeared to be fully mature by age 2 with gonadosomatic index values above 8 for females and close to 1 for males. The majority of females were older, longer, and heavier than males. Bowfin in Lake Lindsay Grace had fast growth up to age 4 and higher total annual mortality than the other populations examined in this study. A chi-square test indicated that size structure of bowfin from Lake Lindsay Grace was different than those of a Louisiana population and two bowfin populations from the upper Mississippi River. To further assess bowfin size structure, we proposed standard length (i.e., TL) categories: stock (200 mm, 8 inches), quality (350 mm, 14 inches), preferred (460 mm, 18 inches), memorable (560 mm, 22, inches), and trophy (710 mm, 28 inches). Because our knowledge of bowfin ecology is limited, additional understanding of bowfin population dynamics provides important insight that can be used in management of bowfin across their distribution.

  6. Dynamics of urban population growth in Nigeria: The role of repeated migration.

    Science.gov (United States)

    Adepoju, A

    1976-02-01

    The paper examines the direct contribution of migration to the growth of the urban population both in terms of its mobility and stability components with special reference to Western Nigeria. The basis of the paper is a survey of urban migration conducted by the author in 1971-1972; the findings are supplemented where necessary by the 1952-1953 and 1963 census figures. Migration is a major factor in the growth of the urban population. The direct contribution by migrants to such growth can be traced to the following groups: the initial streams of migrants, the follow-up migrants and the potentially mobile migrants attracted from the migrants' communities of origin to the towns. Repeated migration by some migrants, particularly the young, the educated and the white collar-workers, are also major factors in the urban population growth. Such repeated migrations are predominantly urban to urban or turnover moves. The high mobility rate among a group of migrants tends to conceal the relative stability among the migrant population as a whole. Repeated migrants usually stay between 3 and 5 years at each destination, before moving on. A substantial proportion of migrants, mainly farmers, the less educated and the old, are relatively stable in the survey towns (Ife and Oshogho). The urban residence ration indices also indicate an increase in the rate of immigration, mainly of young persons, to the towns. The youthful age structure, the age selectivity in migration and the marital status of the young migrants tend to exacerbate the masculinity in the form of unbalanced sex ratio prevailing in most urban centers. The urban population is unlikely to be stable. The tendency for old migrants of rural origin to return to their villages at the end of their migration career and for contemporary migrants to consist predominantly of youths, will for the next generation or 2 lead to a young and unstable urban population.

  7. Inelastic collisions and density-dependent excitation suppression in a 87Sr optical lattice clock

    International Nuclear Information System (INIS)

    Bishof, M.; Martin, M. J.; Swallows, M. D.; Benko, C.; Lin, Y.; Quemener, G.; Rey, A. M.; Ye, J.

    2011-01-01

    We observe two-body loss of 3 P 0 87 Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 μK that are prepared either in a single nuclear-spin sublevel or with equal populations in two sublevels. The measured temperature and nuclear-spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the 1 S 0 - 3 P 0 transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system.

  8. Effects of climate change on long-term population growth of pronghorn in an arid environment

    Science.gov (United States)

    Gedir, Jay V.; Cain, James W.; Harris, Grant; Turnbull, Trey T.

    2015-01-01

    Climate often drives ungulate population dynamics, and as climates change, some areas may become unsuitable for species persistence. Unraveling the relationships between climate and population dynamics, and projecting them across time, advances ecological understanding that informs and steers sustainable conservation for species. Using pronghorn (Antilocapra americana) as an ecological model, we used a Bayesian approach to analyze long-term population, precipitation, and temperature data from 18 populations in the southwestern United States. We determined which long-term (12 and 24 months) or short-term (gestation trimester and lactation period) climatic conditions best predicted annual rate of population growth (λ). We used these predictions to project population trends through 2090. Projections incorporated downscaled climatic data matched to pronghorn range for each population, given a high and a lower atmospheric CO2 concentration scenario. Since the 1990s, 15 of the pronghorn populations declined in abundance. Sixteen populations demonstrated a significant relationship between precipitation and λ, and in 13 of these, temperature was also significant. Precipitation predictors of λ were highly seasonal, with lactation being the most important period, followed by early and late gestation. The influence of temperature on λ was less seasonal than precipitation, and lacked a clear temporal pattern. The climatic projections indicated that all of these pronghorn populations would experience increased temperatures, while the direction and magnitude of precipitation had high population-specific variation. Models predicted that nine populations would be extirpated or approaching extirpation by 2090. Results were consistent across both atmospheric CO2 concentration scenarios, indicating robustness of trends irrespective of climatic severity. In the southwestern United States, the climate underpinning pronghorn populations is shifting, making conditions increasingly

  9. Density-dependent clustering: I. Pulling back the curtains on motions of the BAO peak

    Science.gov (United States)

    Neyrinck, Mark C.; Szapudi, István; McCullagh, Nuala; Szalay, Alexander S.; Falck, Bridget; Wang, Jie

    2018-05-01

    The most common statistic used to analyze large-scale structure surveys is the correlation function, or power spectrum. Here, we show how `slicing' the correlation function on local density brings sensitivity to interesting non-Gaussian features in the large-scale structure, such as the expansion or contraction of baryon acoustic oscillations (BAO) according to the local density. The sliced correlation function measures the large-scale flows that smear out the BAO, instead of just correcting them as reconstruction algorithms do. Thus, we expect the sliced correlation function to be useful in constraining the growth factor, and modified gravity theories that involve the local density. Out of the studied cases, we find that the run of the BAO peak location with density is best revealed when slicing on a ˜40 h-1 Mpc filtered density. But slicing on a ˜100 h-1 Mpc filtered density may be most useful in distinguishing between underdense and overdense regions, whose BAO peaks are separated by a substantial ˜5 h-1 Mpc at z = 0. We also introduce `curtain plots' showing how local densities drive particle motions toward or away from each other over the course of an N-body simulation.

  10. Stickleback Population

    Directory of Open Access Journals (Sweden)

    Ulrika Candolin

    2012-01-01

    Full Text Available Human-induced eutrophication has increased offspring production in a population of threespine stickleback Gasterosteus aculeatus in the Baltic Sea. Here, we experimentally investigated the effects of an increased density of juveniles on behaviours that influence survival and dispersal, and, hence, population growth—habitat choice, risk taking, and foraging rate. Juveniles were allowed to choose between two habitats that differed in structural complexity, in the absence and presence of predators and conspecific juveniles. In the absence of predators or conspecifics, juveniles preferred the more complex habitat. The preference was further enhanced in the presence of a natural predator, a perch Perca fluviatilis (behind a transparent Plexiglas wall. However, an increased density of conspecifics relaxed the predator-enhanced preference for the complex habitat and increased the use of the open, more predator-exposed habitat. Foraging rate was reduced under increased perceived predation risk. These results suggest that density-dependent behaviours can cause individuals to choose suboptimal habitats where predation risk is high and foraging rate low. This could contribute to the regulation of population growth in eutrophicated areas where offspring production is high.

  11. A Room to Grow: The Residential Density-dependence of Childbearing in Europe and the United States

    Directory of Open Access Journals (Sweden)

    Nathanael Lauster

    2010-01-01

    Full Text Available I argue that cultural processes linked to the demographic transition produce new density-dependent fertility dynamics. In particular, childbearing becomes dependent upon residential roominess. This relationship is culturally specific, and I argue that the cultural nature of this relationship means that professional and managerial classes are likely to be particularly influenced by residential roominess, while immigrants are less likely to be influenced. I test hypotheses linking residential roominess to the presence of an “own infant” in the household using census data from the Austria, Greece, Portugal, Spain, and the United States. Roominess predicts fertility in all countries, but to differing degrees.

  12. Symmetry energy of the nucleus in the relativistic Thomas-Fermi approach with density-dependent parameters

    Science.gov (United States)

    Haddad, S.

    2017-11-01

    The symmetry energy of a nucleus is determined in a local density approximation and integrating over the entire density distribution of the nucleus, calculated utilizing the relativistic density-dependent Thomas-Fermi approach. The symmetry energy is found to decrease with increasing neutron excess in the nucleus. The isovector coupling channel reduces the symmetry energy, and this effect increases with increased neutron excess. The isovector coupling channel increases the symmetry energy integral in ^{40}Ca and reduces it in ^{48}Ca, and the interplay between the isovector and the isoscalar channels of the nuclear force explains this isotope effect.

  13. Impact of population and economic growth on carbon emissions in Taiwan using an analytic tool STIRPAT

    Directory of Open Access Journals (Sweden)

    Jong-Chao Yeh

    2017-01-01

    Full Text Available Carbon emission has increasingly become an issue of global concern because of climate change. Unfortunately, Taiwan was listed as top 20 countries of carbon emission in 2014. In order to provide appropriate measures to control carbon emission, it appears that there is an urgent need to address how such factors as population and economic growth impact the emission of carbon dioxide in any developing countries. In addition to total population, both the percentages of population living in urban area (i.e., urbanization percentage, and non-dependent population may also serve as limiting factors. On the other hand, the total energy-driven gross domestic production (GDP and the percentage of GDP generated by the manufacturing industries are assessed to see their respective degree of impact on carbon emission. Therefore, based on the past national data in the period 1990–2014 in Taiwan, an analytic tool of Stochastic Impacts by Regression on Population, Affluence and Technology (STIRPAT was employed to see how well those aforementioned factors can describe their individual potential impact on global warming, which is measured by the total amount of carbon emission into the atmosphere. Seven scenarios of STIRPAT model were proposed and tested statistically for the significance of each proposed model. As a result, two models were suggested to predict the impact of carbon emission due to population and economic growth by the year 2025 in Taiwan.

  14. Genetic variation in Pinus strobiformis growth and drought tolerance from southwestern US populations.

    Science.gov (United States)

    Goodrich, Betsy A; Waring, Kristen M; Kolb, Thomas E

    2016-10-01

    The persistence of some tree species is threatened by combinations of novel abiotic and biotic stressors. To examine the hypothesis that Pinus strobiformis Engelm., a tree threatened by an invasive forest pathogen and a changing climate, exhibits intraspecific genetic variation in adaptive traits, we conducted a common garden study of seedlings at one location with two watering regimes using 24 populations. Four key findings emerged: (i) growth and physiological traits were low to moderately differentiated among populations but differentiation was high for some traits in water-stressed populations; (ii) seedlings from warmer climates grew larger, had higher stomatal density and were more water-use efficient (as measured by the carbon isotope ratio) than populations from colder climates; (iii) seedlings from the northern edge of the species' distribution had lower water-use efficiency, higher stomatal conductance, slower growth and longer survival in a lethal drought experiment compared with seedlings from more southern populations; and (iv) based on non-metric multidimensional scaling analyses, populations clustered into southern and northern groups, which did not correspond to current seed transfer zones. Our discovery of a clinal geographic pattern of genetic variation in adaptive traits of P. strobiformis seedlings will be useful in developing strategies to maintain the species during ongoing climate change and in the face of an invasive pathogen. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  15. Postdischarge growth and development in a predominantly Hispanic, very low birth weight population.

    Science.gov (United States)

    Powers, George C; Ramamurthy, Rajam; Schoolfield, John; Matula, Kathleen

    2008-12-01

    The goals were to assess postdischarge growth and developmental progress of very low birth weight (birth weight: population and to identify predictors for neurodevelopmental impairment at 3 years of age. A cohort of 135 very low birth weight infants (gestational age: 23 to 35 weeks) were monitored to 3 years of age. Maternal and neonatal characteristics, anthropometric z scores, and developmental performance (using corrected age until 24 months) were analyzed collectively and according to gestational age groups. Specific criteria for failure to thrive and microcephaly were used. A characteristic pattern of poor weight gain in the first 12 months was followed by accelerated weight gain starting at 18 months, whereas head growth decreased at 18 months, with recovery beginning at 30 months of age. Infants born at gestational age of growth-impaired at 3 years of age, whereas infants born at gestational age of >or=27 weeks achieved catch-up growth by 30 months of age. Mean developmental scores also decreased in infancy, with improvements in motor development emerging at 18 months and cognitive skills at 30 months. Growth z scores, particularly for head growth, correlated with developmental scores. Infants born at gestational age of growth patterns that coincided with developmental progress in the first 3 years of life. Birth at gestational age of

  16. Are whooping cranes destined for extinction? Climate change imperils recruitment and population growth.

    Science.gov (United States)

    Butler, Matthew J; Metzger, Kristine L; Harris, Grant M

    2017-04-01

    Identifying climatic drivers of an animal population's vital rates and locating where they operate steers conservation efforts to optimize species recovery. The population growth of endangered whooping cranes ( Grus americana ) hinges on juvenile recruitment. Therefore, we identify climatic drivers (solar activity [sunspots] and weather) of whooping crane recruitment throughout the species' life cycle (breeding, migration, wintering). Our method uses a repeated cross-validated absolute shrinkage and selection operator approach to identify drivers of recruitment. We model effects of climate change on those drivers to predict whooping crane population growth given alternative scenarios of climate change and solar activity. Years with fewer sunspots indicated greater recruitment. Increased precipitation during autumn migration signified less recruitment. On the breeding grounds, fewer days below freezing during winter and more precipitation during breeding suggested less recruitment. We predicted whooping crane recruitment and population growth may fall below long-term averages during all solar cycles when atmospheric CO 2 concentration increases, as expected, to 500 ppm by 2050. Species recovery during a typical solar cycle with 500 ppm may require eight times longer than conditions without climate change and the chance of population decline increases to 31%. Although this whooping crane population is growing and may appear secure, long-term threats imposed by climate change and increased solar activity may jeopardize its persistence. Weather on the breeding grounds likely affects recruitment through hydrological processes and predation risk, whereas precipitation during autumn migration may influence juvenile mortality. Mitigating threats or abating climate change should occur within ≈30 years or this wild population of whooping cranes may begin declining.

  17. Impact of Population Growth and Climate Change on the Freshwater Resources of Lamu Island, Kenya

    Directory of Open Access Journals (Sweden)

    Cornelius Okello

    2015-03-01

    Full Text Available Demand for freshwater is rising with factors, such as population growth, land use change and climate variations, rendering water availability in the future uncertain. Groundwater resources are being increasingly exploited to meet this growing demand. The aim of this study is to identify the influence of population growth induced by land use change and climate change on the future state of freshwater resources of Lamu Island in Kenya where a major port facility is under construction. The results of this study show that the “no industrial development” population scenario (assuming the port was not constructed would be expected to reach ~50,000 people by 2050, while the projected population upon completion is expected to reach 1.25 million in the same year when the Lamu Port-South Sudan-Ethiopia Transport Corridor Program (LAPSSET port reaches its full cargo-handling capacity. The groundwater abstraction in 2009 was 0.06 m3 daily per capita, while the demand is expected to raise to 0.1 m3 by 2050 according to the “LAPSSET development” projection. The modelling results show that the Shela aquifer in Lamu, which is the main source of water on the island, will not experience stress by 2065 for the “no industrial development” population scenario, whereas for the “LAPSSET development projection” population scenario, it will occur sooner (between 2020 and 2028. The modelling results show that the Representative Concentration Pathways (RCP climate change scenarios will have a smaller impact on the effective water volume reserves than Special Report on Emissions Scenarios (SRES for the “no industrial development”, while the impact is expected to be similar for the “LAPSSET development”, suggesting that population growth exacerbated by land use change will be a more significant driving force than climate change in affecting freshwater availability.

  18. Impacts of invasive fish removal through angling on population characteristics and juvenile growth rate.

    Science.gov (United States)

    Evangelista, Charlotte; Britton, Robert J; Cucherousset, Julien

    2015-06-01

    Exploitation can modify the characteristics of fish populations through the selective harvesting of individuals, with this potentially leading to rapid ecological and evolutionary changes. Despite the well-known effects of invasive fishes on aquatic ecosystems generally, the potential effects of their selective removal through angling, a strategy commonly used to manage invasive fish, are poorly understood. The aim of this field-based study was to use the North American pumpkinseed Lepomis gibbosus as the model species to investigate the consequences of selective removal on their population characteristics and juvenile growth rates across 10 populations in artificial lakes in southern France. We found that the maximal individual mass in populations decreased as removal pressure through angling increased, whereas we did not observed any changes in the maximal individual length in populations as removal pressure increased. Total population abundance did not decrease as removal pressure increased; instead, here was a U-shaped relationship between removal pressure and the abundance of medium-bodied individuals. In addition, population biomass had a U-shaped curve response to removal pressure, implying that invasive fish populations can modulate their characteristics to compensate for the negative effects of selective removals. In addition, individual lengths at age 2 and juvenile growth rates decreased as removal pressure through angling increased, suggesting a shift toward an earlier size at maturity and an overall slower growing phenotype. Therefore, these outputs challenge the efficiency of selective management methods, suggesting the use of more proactive strategies to control invasive populations, and the need to investigate the potential ecological and evolutionary repercussions of nonrandom removal.

  19. Fifty years of population growth and absorption of labor in Brazil: from 1950 to 2000.

    Science.gov (United States)

    Paiva, P D

    1997-01-01

    For a long time, the Brazilian population has grown at a relatively high rate, and only recently has the process of demographic transition intensified in the country. While the associated decline in fertility could result in a future decline in the size of the working-age population, it could also lead to an increase in female participation in the labor market. Brazil's economy is performing well, with gross domestic product (GDP) growing at an average annual rate of 7.1% during 1947-80. Marked growth in industrial employment opportunities has accompanied this growth in GDP. The size of the informal sector, however, has not decreased in similar proportion, while the 1981-83 economic crisis caused urban employment levels to drop, especially in industry and construction. Moreover, the level of rural-urban migration has increased and the agricultural employment index has fallen. The author evaluates past growth trends of the Economically Active Population (EAP) and of employment in Brazil, and assesses the potential growth of the labor force until the year 2000.

  20. Population structure, growth and production of a recent brachiopod from the Chilean fjord region

    KAUST Repository

    Baumgarten, Sebastian

    2013-12-04

    Magellania venosa, the largest recent brachiopod, occurs in clusters and banks in population densities of up to 416 ind m-2 in Comau Fjord, Northern Chilean fjord region. Below 15 m, it co-occurs with the mytilid Aulacomya atra and it dominates the benthic community below 20 m. To determine the question of why M. venosa is a successful competitor, the in situ growth rate of the brachiopod was studied and its overall growth performance compared with that of other brachiopods and mussels. The growth in length was measured between February 2011 and March 2012 after mechanical tagging and calcein staining. Settlement and juvenile growth were determined from recruitment tiles installed in 2009 and from subsequent photocensus. Growth of M. venosa is best described by the general von Bertalanffy growth function, with a maximum shell length (L∞) of 71.53 mm and a Brody growth constant (K) of 0.336 year-1. The overall growth performance (OGP index = 5.1) is the highest recorded for a rynchonelliform brachiopod and in the range of that for Mytilus chilensis (4.8-5.27), but lower than that of A. atra (5.74). The maximal individual production (PInd) is 0.29 g AFDM ind-1 year-1 at 42 mm shell length and annual production ranges from 1.28 to 89.25 g AFDM year-1 m-2 (1-57% of that of A. atra in the respective fjords). The high shell growth rate of M. venosa, together with its high overall growth performance may explain the locally high population density of this brachiopod in Comau Fjord. However, the production per biomass of the population (P/B--ratio) is low (0.535) and M. venosa may play only a minor role in the food chain. Settling dynamics indicates that M. venosa is a pioneer species with low juvenile mortality. The coexistence of the brachiopod and bivalve suggests that brachiopod survival is affected by neither the presence of potential brachiopod predators nor that of space competitors (i.e. mytilids).

  1. Development and population growth of Hydra viridissima Pallas, 1766 (Cnidaria, Hydrozoa in the laboratory

    Directory of Open Access Journals (Sweden)

    FC. Massaro

    Full Text Available Hydras, the most representative freshwater Cnidaria, are of common occurrence in bodies of water in every continent except Antarctica. This study was planned with the aim of maintaining a population of Hydra viridissima in laboratory culture to enable the determination of the individual and population growth-rates of this species, as well as its population doubling time and generation time, with a view to employing these common animals as test-organisms in ecotoxicological assays. The organisms were maintained in reconstituted water at 20 ± 2 °C, illuminated at 800 lux with a photoperiod of 12 hours light: 12 hours dark, and were fed on neonates of the cladoceran Ceriodaphnia silvestrii (3 or 4 neonates per hydra, 3 times a week. The individual growth-rate (k of the species was 0.43, the maximum length of the column 2.53 mm and the generation time 6.6 ± 1.5 days on average. The hydra population showed an intrinsic growth-rate (r of 0.0468, according to the fitted curve, and a doubling time of 14.8 ± 2.63 days. Hydra viridissima is easy to grow in the laboratory and performs well in the conditions used in this study. It is thus a promising candidate test-organism for ecotoxicological studies.

  2. Living bacteria rheology: Population growth, aggregation patterns, and collective behavior under different shear flows

    Science.gov (United States)

    Patrício, P.; Almeida, P. L.; Portela, R.; Sobral, R. G.; Grilo, I. R.; Cidade, T.; Leal, C. R.

    2014-08-01

    The activity of growing living bacteria was investigated using real-time and in situ rheology—in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus—strain COL and its isogenic cell wall autolysis mutant, RUSAL9—were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of the cultures of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the cultures of the two strains follows different and rich behaviors, with no counterpart in the optical density or in the population's colony-forming units measurements. While the viscosity of strain COL culture keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain culture decreases steeply, still in the exponential phase, remains constant for some time, and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviors, which were observed to be shear-stress-dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL culture, obtained with oscillatory shear, exhibit power-law behaviors whose exponents are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant culture have complex behaviors, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. Nevertheless, these behaviors reflect the bacteria growth stage.

  3. Trends in the growth of population and labour force in Pakistan.

    Science.gov (United States)

    Hashmi, S S

    1990-01-01

    Trends in the growth of the population and labor force in Pakistan are examined and future prospects for growth of population and labor, particularly agriculture, are estimated. The definition of labor force as employed or seeking work after a short period of employment has led to a great disparity in results for women in the labor force. Past trends in population growth reflected a growth rate of 1.6% for the 1950's, and 2.4% in 1960. The population rose to 84.3 million in 1981 from 42.6 million in 1961, which intercensally was an increase of 3.6% per annum for 1961-72 and 3.1% per annum for 1972-81. The estimated rate for 1981-86 was 2.9%/year. The rural population doubled and the urban tripled. There was a net migration of 2.123 million to urban areas reported in the 1981 census. There is also evidence of a high sex ratio. Balochistan (7.1%) and Sindh (3.6%) provinces have the highest growth rates. Although the largest population is in the Punjab, the growth is the lowest at 2.7%. The population is primarily young -- 44.5% 15 years in 1981, which is the highest in the world. Under high, medium, and low levels of fertility, prospective trends are estimated for 2006 and 2031, and by sex every 5 years from 1981. Population under high fertility is expected to reach 270 million by 2031, which is 3.39 persons/hectare. The population/hectare of land under cultivation was 4.25 in 1981 and is expected to rise to 13.49 persons/hectare in 2031. 11 million acres could be brought under cultivation to reduce the ratio. However, there are ecological considerations as well as an employment problem. The dependency ratio under the high variant will decline from 76.8 persons 0-14 and 65 years/100 persons 15-64 years in 1986 to 70.3 in 2006 which is still considerably higher than other developing countries. It is suggested that replacement level fertility be attained as soon as possible. Under low fertility, replacement level can be reached by 2011 with strong political commitment

  4. Increasing Dengue Incidence in Singapore over the Past 40 Years: Population Growth, Climate and Mobility.

    Directory of Open Access Journals (Sweden)

    Claudio Jose Struchiner

    Full Text Available In Singapore, the frequency and magnitude of dengue epidemics have increased significantly over the past 40 years. It is important to understand the main drivers for the rapid increase in dengue incidence. We studied the relative contributions of putative drivers for the rise of dengue in Singapore: population growth, climate parameters and international air passenger arrivals from dengue endemic countries, for the time period of 1974 until 2011. We used multivariable Poisson regression models with the following predictors: Annual Population Size; Aedes Premises Index; Mean Annual Temperature; Minimum and Maximum Temperature Recorded in each year; Annual Precipitation and Annual Number of Air Passengers arriving from dengue-endemic South-East Asia to Singapore. The relative risk (RR of the increase in dengue incidence due to population growth over the study period was 42.7, while the climate variables (mean and minimum temperature together explained an RR of 7.1 (RR defined as risk at the end of the time period relative to the beginning and goodness of fit associated with the model leading to these estimates assessed by pseudo-R2 equal to 0.83. Estimating the extent of the contribution of these individual factors on the increasing dengue incidence, we found that population growth contributed to 86% while the residual 14% was explained by increase in temperature. We found no correlation with incoming air passenger arrivals into Singapore from dengue endemic countries. Our findings have significant implications for predicting future trends of the dengue epidemics given the rapid urbanization with population growth in many dengue endemic countries. It is time for policy-makers and the scientific community alike to pay more attention to the negative impact of urbanization and urban climate on diseases such as dengue.

  5. Non-linear density-dependent effects of an intertidal ecosystem engineer.

    Science.gov (United States)

    Harley, Christopher D G; O'Riley, Jaclyn L

    2011-06-01

    Ecosystem engineering is an important process in a variety of ecosystems. However, the relationship between engineer density and engineering impact remains poorly understood. We used experiments and a mathematical model to examine the role of engineer density in a rocky intertidal community in northern California. In this system, the whelk Nucella ostrina preys on barnacles (Balanus glandula and Chthamalus dalli), leaving empty barnacle tests as a resource (favorable microhabitat) for other species. Field experiments demonstrated that N. ostrina predation increased the availability of empty tests of both barnacle species, reduced the density of the competitively dominant B. glandula, and indirectly increased the density of the competitively inferior C. dalli. Empty barnacle tests altered microhabitat humidity, but not temperature, and presumably provided a refuge from wave action. The herbivorous snail Littorina plena was positively associated with empty test availability in both observational comparisons and experimental manipulations of empty test availability, and L. plena density was elevated in areas with foraging N. ostrina. To explore the effects of variation in N. ostrina predation, we constructed a demographic matrix model for barnacles in which we varied predation intensity. The model predicted that number of available empty tests increases with predation intensity to a point, but declines when predation pressure was strong enough to severely reduce adult barnacle densities. The modeled number of available empty tests therefore peaked at an intermediate level of N. ostrina predation. Non-linear relationships between engineer density and engineer impact may be a generally important attribute of systems in which engineers influence the population dynamics of the species that they manipulate.

  6. The Contribution of Population Health and Demographic Change to Economic Growth in China and India

    Science.gov (United States)

    Bloom, David E.; Canning, David; Hu, Linlin; Liu, Yuanli; Mahal, Ajay; Yip, Winnie

    2010-01-01

    We find that a cross-country model of economic growth successfully tracks the growth takeoffs in China and India. The major drivers of the predicted takeoffs are improved health, increased openness to trade, and a rising labor force-to-population ratio due to fertility decline. We also explore the effect of the reallocation of labor from low-productivity agriculture to the higher-productivity industry and service sectors. Including the money value of longevity improvements in a measure of full income reduces the gap between the magnitude of China's takeoff relative to India's due to the relative stagnation in life expectancy in China since 1980. PMID:20419074

  7. Population growth and the environment: Can we eat the cake and have it?

    Directory of Open Access Journals (Sweden)

    Shmuel Amir

    1999-01-01

    Full Text Available Continuous population growth and the concomitant maintenance of a growth sustaining environment are not in conflict only if the rates of both economic and biological processes are slowed down steadily. For this to happen, individual and social impatience-lowering adaptations should be adopted, and the capital of the system, both economic and natural, has to be redistributed among the system interacting components to result in an ever more complex organizational web. In addition, these factors have to corroborate with a third element, the incorporation of an arsenal of varied technological innovations that improves the use of existing stocks.

  8. Periodic matrix population models: growth rate, basic reproduction number, and entropy.

    Science.gov (United States)

    Bacaër, Nicolas

    2009-10-01

    This article considers three different aspects of periodic matrix population models. First, a formula for the sensitivity analysis of the growth rate lambda is obtained that is simpler than the one obtained by Caswell and Trevisan. Secondly, the formula for the basic reproduction number R0 in a constant environment is generalized to the case of a periodic environment. Some inequalities between lambda and R0 proved by Cushing and Zhou are also generalized to the periodic case. Finally, we add some remarks on Demetrius' notion of evolutionary entropy H and its relationship to the growth rate lambda in the periodic case.

  9. Beaver-mediated methane emission: The effects of population growth in Eurasia and the Americas.

    Science.gov (United States)

    Whitfield, Colin J; Baulch, Helen M; Chun, Kwok P; Westbrook, Cherie J

    2015-02-01

    Globally, greenhouse gas budgets are dominated by natural sources, and aquatic ecosystems are a prominent source of methane (CH(4)) to the atmosphere. Beaver (Castor canadensis and Castor fiber) populations have experienced human-driven change, and CH(4) emissions associated with their habitat remain uncertain. This study reports the effect of near extinction and recovery of beavers globally on aquatic CH4 emissions and habitat. Resurgence of native beaver populations and their introduction in other regions accounts for emission of 0.18-0.80 Tg CH(4) year(-1) (year 2000). This flux is approximately 200 times larger than emissions from the same systems (ponds and flowing waters that became ponds) circa 1900. Beaver population recovery was estimated to have led to the creation of 9500-42 000 km(2) of ponded water, and increased riparian interface length of >200 000 km. Continued range expansion and population growth in South America and Europe could further increase CH(4) emissions.

  10. Mutually catalyzed birth of population and assets in exchange-driven growth

    Science.gov (United States)

    Lin, Zhenquan; Ke, Jianhong; Ye, Gaoxiang

    2006-10-01

    We propose an exchange-driven aggregation growth model of population and assets with mutually catalyzed birth to study the interaction between the population and assets in their exchange-driven processes. In this model, monomer (or equivalently, individual) exchange occurs between any pair of aggregates of the same species (population or assets). The rate kernels of the exchanges of population and assets are K(k,l)=Kkl and L(k,l)=Lkl , respectively, at which one monomer migrates from an aggregate of size k to another of size l . Meanwhile, an aggregate of one species can yield a new monomer by the catalysis of an arbitrary aggregate of the other species. The rate kernel of asset-catalyzed population birth is I(k,l)=Iklμ [and that of population-catalyzed asset birth is J(k,l)=Jklν ], at which an aggregate of size k gains a monomer birth when it meets a catalyst aggregate of size l . The kinetic behaviors of the population and asset aggregates are solved based on the rate equations. The evolution of the aggregate size distributions of population and assets is found to fall into one of three categories for different parameters μ and ν : (i) population (asset) aggregates evolve according to the conventional scaling form in the case of μ⩽0 (ν⩽0) , (ii) population (asset) aggregates evolve according to a modified scaling form in the case of ν=0 and μ>0 ( μ=0 and ν>0 ), and (iii) both population and asset aggregates undergo gelation transitions at a finite time in the case of μ=ν>0 .

  11. Density-dependent quiescence in glioma invasion: instability in a simple reaction–diffusion model for the migration/proliferation dichotomy

    KAUST Repository

    Pham, Kara

    2012-01-01

    Gliomas are very aggressive brain tumours, in which tumour cells gain the ability to penetrate the surrounding normal tissue. The invasion mechanisms of this type of tumour remain to be elucidated. Our work is motivated by the migration/proliferation dichotomy (go-or-grow) hypothesis, i.e. the antagonistic migratory and proliferating cellular behaviours in a cell population, which may play a central role in these tumours. In this paper, we formulate a simple go-or-grow model to investigate the dynamics of a population of glioma cells for which the switch from a migratory to a proliferating phenotype (and vice versa) depends on the local cell density. The model consists of two reaction-diffusion equations describing cell migration, proliferation and a phenotypic switch. We use a combination of numerical and analytical techniques to characterize the development of spatio-temporal instabilities and travelling wave solutions generated by our model. We demonstrate that the density-dependent go-or-grow mechanism can produce complex dynamics similar to those associated with tumour heterogeneity and invasion.

  12. The Association between Natural Amenities, Rural Population Growth, and Long-Term Residents' Economic Well-Being

    Science.gov (United States)

    Hunter, Lori M; Boardman, Jason D.; Saint Onge, Jarron M.

    2005-01-01

    Population growth in rural areas characterized by high levels of natural amenities has recently received substantial research attention. A noted concern with amenity-driven rural population growth is its potential to raise local costs-of-living while yielding only low-wage service sector employment for long-term residents. The work presented here…

  13. Effects of Population Growth and Climate Variability on Sustainable Groundwater in Mali, West Africa

    Directory of Open Access Journals (Sweden)

    Alexandra Lutz

    2010-12-01

    Full Text Available Groundwater is increasingly relied on as a source of potable water in developing countries, but factors such as population growth, development, and climate variability, pose potential challenges for ongoing sustainable supply. The effect of these factors on the groundwater system was considered in four scenarios using a numerical model to represent the Bani area of Mali, West Africa. By 2040, population growth, climate variability, and development as urbanization, agriculture, and industry creates scenarios in which groundwater extraction is an increasingly larger percentage of the groundwater system. Consumption from agriculture and industry increases extraction rates from less than 1 to 3.8% of mean annual precipitation, which will likely affect the groundwater system. For instance, concentrated pumping in local areas may result in water level declines. The results of this study contribute to an ongoing evaluation of sustainable groundwater resources in West Africa.

  14. Fetal growth and risk of stillbirth: a population-based case-control study.

    Science.gov (United States)

    Bukowski, Radek; Hansen, Nellie I; Willinger, Marian; Reddy, Uma M; Parker, Corette B; Pinar, Halit; Silver, Robert M; Dudley, Donald J; Stoll, Barbara J; Saade, George R; Koch, Matthew A; Rowland Hogue, Carol J; Varner, Michael W; Conway, Deborah L; Coustan, Donald; Goldenberg, Robert L

    2014-04-01

    Stillbirth is strongly related to impaired fetal growth. However, the relationship between fetal growth and stillbirth is difficult to determine because of uncertainty in the timing of death and confounding characteristics affecting normal fetal growth. We conducted a population-based case-control study of all stillbirths and a representative sample of live births in 59 hospitals in five geographic areas in the US. Fetal growth abnormalities were categorized as small for gestational age (SGA) (90th percentile) at death (stillbirth) or delivery (live birth) using population, ultrasound, and individualized norms. Gestational age at death was determined using an algorithm that considered the time-of-death interval, postmortem examination, and reliability of the gestational age estimate. Data were weighted to account for the sampling design and differential participation rates in various subgroups. Among 527 singleton stillbirths and 1,821 singleton live births studied, stillbirth was associated with SGA based on population, ultrasound, and individualized norms (odds ratio [OR] [95% CI]: 3.0 [2.2 to 4.0]; 4.7 [3.7 to 5.9]; 4.6 [3.6 to 5.9], respectively). LGA was also associated with increased risk of stillbirth using ultrasound and individualized norms (OR [95% CI]: 3.5 [2.4 to 5.0]; 2.3 [1.7 to 3.1], respectively), but not population norms (OR [95% CI]: 0.6 [0.4 to 1.0]). The associations were stronger with more severe SGA and LGA (95th percentile). Analyses adjusted for stillbirth risk factors, subset analyses excluding potential confounders, and analyses in preterm and term pregnancies showed similar patterns of association. In this study 70% of cases and 63% of controls agreed to participate. Analysis weights accounted for differences between consenting and non-consenting women. Some of the characteristics used for individualized fetal growth estimates were missing and were replaced with reference values. However, a sensitivity analysis using individualized norms

  15. Population Growth Rate, Life Expectancy and Pension Program Improvement in China

    OpenAIRE

    Yang, Zaigui

    2008-01-01

    Applying an overlapping-generations model with lifetime uncertainty, we examine in this paper China’s partially funded public pension system. The findings show that the individual contribution rate does not affect the capital-labor ratio but the firm contribution rate does. The optimal firm contribution rate depends on the capital share of income, social discount factor, survival probability, and population growth rate. The simulation results indicate that the optimal firm contribution rate r...

  16. Growth Performance Of Mono-Sex And Mixed Sex Population Of ...

    African Journals Online (AJOL)

    The growth performance of all-male, all-female and mixed sex population of Oreochromis niloticus fed similar diet was carried out. The fingerlings used in the study were of relatively similar weight ranges (24.8 g – 26.6 g) with initial mean weight of 25.7±1.3 g and initial mean total length of 3.8 ± 1.5 cm. The mean increase ...

  17. Bot fly parasitism of the red-backed vole: host survival, infection risk, and population growth.

    Science.gov (United States)

    Lemaître, Jérôme; Fortin, Daniel; Montiglio, Pierre-Olivier; Darveau, Marcel

    2009-03-01

    Parasites can play an important role in the dynamics of host populations, but empirical evidence remains sparse. We investigated the role of bot fly (Cuterebra spp.) parasitism in red-backed voles (Myodes gapperi) by first assessing the impacts of the parasite on the probability of vole survival under stressful conditions as well as on the reproductive activity of females. We then identified the main factors driving both the individual risk of infection and the abundance of bot flies inside red-backed voles. Finally, we evaluated the impacts of bot fly prevalence on the growth rate of vole populations between mid-July and mid-August. Thirty-six populations of red-backed voles were sampled in the boreal forest of Québec, Canada. The presence and the abundance of parasites in voles, two host life history traits (sex and body condition), three indices of habitat complexity (tree basal area, sapling basal area, coarse woody debris volume), and vole abundance were considered in models evaluating the effects of bot flies on host populations. We found that the probability of survival of red-backed voles in live traps decreased with bot fly infection. Both the individual risk of infection and the abundance of bot flies in red-backed voles were driven mainly by vole abundance rather than by the two host life history traits or the three variables of habitat complexity. Parasitism had population consequences: bot fly prevalence was linked to a decrease in short-term growth rate of vole populations over the summer. We found that bot flies have the potential to reduce survival of red-backed voles, an effect that may apply to large portions of populations.

  18. Population growth, interest rate, and housing tax in the transitional China

    Science.gov (United States)

    He, Ling-Yun; Wen, Xing-Chun

    2017-03-01

    This paper combines and develops the models in Lastrapes (2002) and Mankiw and Weil (1989), which enables us to analyze the effects of interest rate and population growth shocks on housing price in one integrated framework. Based on this model, we carry out policy simulations to examine whether the housing (stock or flow) tax reduces the housing price fluctuations caused by interest rate or population growth shocks. Simulation results imply that the choice of housing tax tools depends on the kind of shock that housing market faces. In the situation where the housing price volatility is caused by the population growth shock, the flow tax can reduce the volatility of housing price while the stock tax makes no difference to it. If the shock is resulting from the interest rate, the policy maker should not impose any kind of the housing taxes. Furthermore, the effect of one kind of the housing tax can be strengthened by that of the other type of housing tax.

  19. Population Growth and Sprawl on the Pine Ridge Indian Reservation, South Dakota

    Science.gov (United States)

    Campbell, R. L.

    2006-05-01

    The most important impact on global land cover is human use and development. With the recent population growth occurring on the reservations in South Dakota, especially Pine Ridge Indian Reservation, the towns and agricultural areas of the reservation are undergoing a change. Although urban sprawl certainly is not a consideration on the reservations, the population explosion currently underway has seen a subsequent increase in rural sprawl. In this case, rural sprawl is defined as exponential population growth and geographic expansion of remote reservation communities. Using satellite imagery and software to render these images is a cost effective way to investigate this growth. Also, using remotely sensed data and a GIS (geographic information system) package can address different issues that concern people and communities in and around the Pine Ridge area. The objective of my project is to observe land use change on the Pine Ridge Indian reservation using Geographic Information Systems such as; ARCGis 9, ENVI, and Multispec, along with Landsat 4, 5, and 7 imagery over the past 20 years.

  20. Plant growth promoting rhizobacteria reduce aphid population and enhance the productivity of bread wheat.

    Science.gov (United States)

    Naeem, Muhammad; Aslam, Zubair; Khaliq, Abdul; Ahmed, Jam Nazir; Nawaz, Ahmad; Hussain, Mubshar

    2018-04-24

    Plant growth promoting rhizobacteria increase plant growth and give protection against insect pests and pathogens. Due to the negative impact of chemical pesticides on environment, alternatives to these chemicals are needed. In this scenario, the biological methods of pest control offer an eco-friendly and an attractive option. In this study, the effect of two plant growth promoting rhizobacterial strains (Bacillus sp. strain 6 and Pseudomonas sp. strain 6K) on aphid population and wheat productivity was evaluated in an aphid susceptible (Pasban-90) and resistant (Inqlab-91) wheat cultivar. The seeds were inoculated with each PGPR strain, separately or the combination of both. The lowest aphid population (2.1tiller -1 ), and highest plant height (85.8cm), number of spikelets per spike (18), grains per spike (44), productive tillers (320m -2 ), straw yield (8.6Mgha -1 ), and grain yield (4.8Mgha -1 ) were achieved when seeds were inoculated with Bacillus sp. strain 6+Pseudomonas sp. strain 6K. The grain yield of both varieties was enhanced by 35.5-38.9% with seed inoculation with both bacterial strains. Thus, the combine use of both PGPR strains viz. Bacillus sp. strain 6+Pseudomonas sp. strain 6K offers an attractive option to reduce aphid population tied with better wheat productivity. Copyright © 2018 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. All rights reserved.

  1. The relationship between population ageing and the economic growth in Asia

    Science.gov (United States)

    Brendan, Lo Rick; Sek, Siok Kun

    2017-08-01

    Asia has witnessed robust economic growth since the 1960s. Today, emerging markets in Asia have managed to maintain rapid growth even when the world's main economies suffer from debt and banking crises. However, declining total fertility rate, increasing life expectancy, continuous change of birth and death patterns, and increasing share of old age population in the age distribution in Asia exert significant pressure on its economies. This paper analyses the relationship between population ageing and economic growth using 2 different panels of countries; one Asian and another the from the oldest countries worldwide between 1970 and 2014. The analysis is based on the Auto Regression Distributed Lag models. The MG (Mean Group) and PMG (Pooled Mean Group) estimations are applied in this analysis. The Hausman Test is conducted to decide between the MG and PMG estimators. We find that ageing will negatively affect the economy in the long run. The growing number of youths will initially have a negative effect on the economy but would eventually lead to a positive growth in the future. The old age dependency ratio has yet to have affect the Asian economy but is expected eventually to impose a negative effect as seen in the oldest nations of the world.

  2. Perturbation analysis of nonlinear matrix population models

    Directory of Open Access Journals (Sweden)

    Hal Caswell

    2008-03-01

    Full Text Available Perturbation analysis examines the response of a model to changes in its parameters. It is commonly applied to population growth rates calculated from linear models, but there has been no general approach to the analysis of nonlinear models. Nonlinearities in demographic models may arise due to density-dependence, frequency-dependence (in 2-sex models, feedback through the environment or the economy, and recruitment subsidy due to immigration, or from the scaling inherent in calculations of proportional population structure. This paper uses matrix calculus to derive the sensitivity and elasticity of equilibria, cycles, ratios (e.g. dependency ratios, age averages and variances, temporal averages and variances, life expectancies, and population growth rates, for both age-classified and stage-classified models. Examples are presented, applying the results to both human and non-human populations.

  3. Using a laboratory-based growth model to estimate mass- and temperature-dependent growth parameters across populations of juvenile Chinook Salmon

    Science.gov (United States)

    Perry, Russell W.; Plumb, John M.; Huntington, Charles

    2015-01-01

    To estimate the parameters that govern mass- and temperature-dependent growth, we conducted a meta-analysis of existing growth data from juvenile Chinook Salmon Oncorhynchus tshawytscha that were fed an ad libitum ration of a pelleted diet. Although the growth of juvenile Chinook Salmon has been well studied, research has focused on a single population, a narrow range of fish sizes, or a narrow range of temperatures. Therefore, we incorporated the Ratkowsky model for temperature-dependent growth into an allometric growth model; this model was then fitted to growth data from 11 data sources representing nine populations of juvenile Chinook Salmon. The model fit the growth data well, explaining 98% of the variation in final mass. The estimated allometric mass exponent (b) was 0.338 (SE = 0.025), similar to estimates reported for other salmonids. This estimate of b will be particularly useful for estimating mass-standardized growth rates of juvenile Chinook Salmon. In addition, the lower thermal limit, optimal temperature, and upper thermal limit for growth were estimated to be 1.8°C (SE = 0.63°C), 19.0°C (SE = 0.27°C), and 24.9°C (SE = 0.02°C), respectively. By taking a meta-analytical approach, we were able to provide a growth model that is applicable across populations of juvenile Chinook Salmon receiving an ad libitum ration of a pelleted diet.

  4. Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

    Directory of Open Access Journals (Sweden)

    Simone Vincenzi

    2014-09-01

    Full Text Available The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth and L∞ (asymptotic size. Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC, the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

  5. Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

    Science.gov (United States)

    Vincenzi, Simone; Mangel, Marc; Crivelli, Alain J; Munch, Stephan; Skaug, Hans J

    2014-09-01

    The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth) and L∞ (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

  6. The impact of population growth on environment: the debate heats up.

    Science.gov (United States)

    Shaw, R P

    1992-02-01

    A proposed framework, which was introduced at the 1989 meetings of the American Association for the Advancement of Science, included political constraints as well as population growth as a proximate cause with potentially important impacts on the environment in Paul and Ann Ehrlich's well-known PAT equation. PAT limitations are identified as the 1.2 billion people caught in the debt-poverty trap, less developed countries' balance of payments deficits, and "distortionary factors" that undermined economic incentives and contributed to mismanagement of resources. Such factors could be keeping farm prices low and have an impact on deterring use of environmentally sound traditional agricultural practices. Mismanagement of public lands occurs when large commercial enterprises or large scale mechanization displace population onto marginal or less productive lands. Intergroup warfare is a new form impacting on the environment. In Burma loggers are authorized to clear cut large tracts of teak forests in order to ferret out Karen guerrillas. Over 15 million refugees were thus displaced and forced to live in encampments that require trees for shelter, firewood for survival, and overgrazing of livestock. Social and economic environments are also undermined by "dependency" factors such as trade protectionism, brain drain, and limited foreign aid. The Group of 77 Non-Aligned Developing Countries proposed that discussions of the links between population and the environment be omitted from the agenda of the 1994 UN Conference on Population and Development. Basic clarifications are needed to distinguish ultimate versus proximate factors and current versus future concerns. The debate ignores distribution patterns, migration, or changing age structures. The debate blames unjustifiably rapid population growth as the ultimate cause of global environmental degradation and links population growth to a host of other social problems such as famine and refugees, while ignoring civil unrest

  7. REGIONAL COMPONENTS OF GROWTH THE QUALITY OF LIFE OF THE POPULATION (FOR EXAMPLE, VORONEZH REGION

    Directory of Open Access Journals (Sweden)

    N. A. Serebryakova

    2015-01-01

    Full Text Available At the present stage of development of economy there is a transformation of main objectives of the state from ensuring growth of welfare of citizens to ensuring continuous growth of quality of life. Ensuring growth of quality of life of the population is carried out not only on state, but also on regional levels. At the state level key tasks are formed, the state assumes a considerable share of functions on achievement of the designated purpose. In the real research the attention to consideration of the program documents directed on improvement of quality of life of the population on the example of the Voronezh region is paid. The program documents of a social orientation existing in the region are for this purpose studied. It is revealed that in the region a number of the programs and subprogrammes aimed at improvement of a demographic situation, improvement of a regional budgetary and tax policy, social support of citizens in general works. As tools which use regional authorities, are noted: social standards, address social help, social contracts. It is established that introduction of system of social contracts allows to save budget funds and, at the same time, to motivate the persons which are in a difficult life situation on change of the situation to the best, joint efforts with social security authorities. It is noted that as the leading principles of rendering the social help paramount value has detailed definition of degree of need of the help and a condition of granting. The last often generate dependant moods which are important for leveling, using levers of social interaction. The analysis of the contents of the realized programs for improvement of quality of life of the population allowed to reveal advantages and defects in these programs, and also to define reserves of growth of quality of life. So, it is specified that program documents of regional level in the prevailing majority have a narrow focus on ensuring the help and

  8. Spatial analysis of cattle and shoat population in Ethiopia: growth trend, distribution and market access.

    Science.gov (United States)

    Leta, Samson; Mesele, Frehiwot

    2014-01-01

    The livestock subsector has an enormous contribution to Ethiopia's national economy and livelihoods of many Ethiopians. The subsector contributes about 16.5% of the national Gross Domestic Product (GDP) and 35.6% of the agricultural GDP. It also contributes 15% of export earnings and 30% of agricultural employment. The livestock subsector currently support and sustain livelihoods for 80% of all rural population. The GDP of livestock related activities valued at 59 billion birr. Ethiopian livestock population trends, distribution and marketing vary considerably across space and time due to a variety of reasons. This study was aimed to assess cattle and shoat population growth trend, distribution and their access to market. Regression analysis was used to assess the cattle and shoat population growth trend and Geographic Information Systems (GIS) techniques were used to determine the spatial distribution of cattle and shoats, and their relative access to market. The data sets used are agricultural census (2001/02) and annual CSA agricultural sample survey (1995/96 to 2012/13). In the past eighteen years, the livestock population namely cattle, sheep and goat grew from 54.5 million to over 103.5 million with average annual increment of 3.4 million. The current average national cattle, sheep and goat population per km(2) are estimated to be 71, 33 and 29 respectively (excluding Addis Ababa, Afar and Somali regions). From the total livestock population the country owns about 46% cattle, 43% sheep and 40% goats are reared within 10 km radius from major livestock market centres and all-weather roads. On the other hand, three fourth of the country's land mass which comprises 15% of the cattle, 20% of the sheep and 21% of goat population is not accessible to market (greater than 30 km from major livestock market centres). It is found that the central highland regions account for the largest share of livestock population and also more accessible to market. Defining the

  9. Climate threats on growth of rear-edge European beech peripheral populations in Spain

    Science.gov (United States)

    Dorado-Liñán, I.; Akhmetzyanov, L.; Menzel, A.

    2017-12-01

    European beech ( Fagus sylvatica L.) forests in the Iberian Peninsula are a clear example of a temperate forest tree species at the rear edge of its large distribution area in Europe. The expected drier and warmer climate may alter tree growth and species distribution. Consequently, the peripheral populations will most likely be the most threatened ones. Four peripheral beech forests in the Iberian Peninsula were studied in order to assess the climate factors influencing tree growth for the last six decades. The analyses included an individual tree approach in order to detect not only the changes in the sensitivity to climate but also the potential size-mediated sensitivity to climate. Our results revealed a dominant influence of previous and current year summer on tree growth during the last six decades, although the analysis in two equally long periods unveiled changes and shifts in tree sensitivity to climate. The individual tree approach showed that those changes in tree response to climate are not size dependent in most of the cases. We observed a reduced negative effect of warmer winter temperatures at some sites and a generalized increased influence of previous year climatic conditions on current year tree growth. These results highlight the crucial role played by carryover effects and stored carbohydrates for future tree growth and species persistence.

  10. Effects of an invasive plant on population dynamics in toads.

    Science.gov (United States)

    Greenberg, Daniel A; Green, David M

    2013-10-01

    When populations decline in response to unfavorable environmental change, the dynamics of their population growth shift. In populations that normally exhibit high levels of variation in recruitment and abundance, as do many amphibians, declines may be difficult to identify from natural fluctuations in abundance. However, the onset of declines may be evident from changes in population growth rate in sufficiently long time series of population data. With data from 23 years of study of a population of Fowler's toad (Anaxyrus [ = Bufo] fowleri) at Long Point, Ontario (1989-2011), we sought to identify such a shift in dynamics. We tested for trends in abundance to detect a change point in population dynamics and then tested among competing population models to identify associated intrinsic and extrinsic factors. The most informative models of population growth included terms for toad abundance and the extent of an invasive marsh plant, the common reed (Phragmites australis), throughout the toads' marshland breeding areas. Our results showed density-dependent growth in the toad population from 1989 through 2002. After 2002, however, we found progressive population decline in the toads associated with the spread of common reeds and consequent loss of toad breeding habitat. This resulted in reduced recruitment and population growth despite the lack of significant loss of adult habitat. Our results underscore the value of using long-term time series to identify shifts in population dynamics coincident with the advent of population decline. © 2013 Society for Conservation Biology.

  11. Relativistic mean field theory with density dependent coupling constants for nuclear matter and finite nuclei with large charge asymmetry

    Energy Technology Data Exchange (ETDEWEB)

    Typel, S; Wolter, H H [Sektion Physik, Univ. Muenchen, Garching (Germany)

    1998-06-01

    Nuclear matter and ground state properties for (proton and neutron) semi-closed shell nuclei are described in relativistic mean field theory with coupling constants which depend on the vector density. The parametrization of the density dependence for {sigma}-, {omega}- and {rho}-mesons is obtained by fitting to properties of nuclear matter and some finite nuclei. The equation of state for symmetric and asymmetric nuclear matter is discussed. Finite nuclei are described in Hartree approximation, including a charge and an improved center-of-mass correction. Pairing is considered in the BCS approximation. Special attention is directed to the predictions for properties at the neutron and proton driplines, e.g. for separation energies, spin-orbit splittings and density distributions. (orig.)

  12. Effects of Density-Dependent Quark Mass on Phase Diagram of Color-Flavor-Locked Quark Matter

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Considering the density dependence of quark mass, we investigate the phase transition between the (unpaired) strange quark matter and the color-flavor-locked matter, which are supposed to be two candidates for the ground state of strongly interacting matter. We find that if the current mass of strange quark ms is small, the strange quark matter remains stable unless the baryon density is very high. If ms is large, the phase transition from the strange quark matter to the color-flavor-locked matter in particular to its gapless phase is found to be different from the results predicted by previous works. A complicated phase diagram of three-flavor quark matter is presented, in which the color-flavor-locked phase region is suppressed for moderate densities.

  13. Density-Dependent Formulation of Dispersion-Repulsion Interactions in Hybrid Multiscale Quantum/Molecular Mechanics (QM/MM) Models

    DEFF Research Database (Denmark)

    Curutchet, Carles; Cupellini, Lorenzo; Kongsted, Jacob

    2018-01-01

    embedding approaches, respectively, nonelectrostatic dispersion and repulsion interactions are instead commonly described through classical potentials despite their quantum mechanical origin. Here we present an extension of the Tkatchenko-Scheffler semiempirical van der Waals (vdWTS) scheme aimed......Mixed multiscale quantum/molecular mechanics (QM/MM) models are widely used to explore the structure, reactivity, and electronic properties of complex chemical systems. Whereas such models typically include electrostatics and potentially polarization in so-called electrostatic and polarizable...... at describing dispersion and repulsion interactions between quantum and classical regions within a QM/MM polarizable embedding framework. Starting from the vdWTSexpression, we define a dispersion and a repulsion term, both of them density-dependent and consistently based on a Lennard-Jones-like potential. We...

  14. On the calculation of the structure of charge-stabilized colloidal dispersions using density-dependent potentials

    International Nuclear Information System (INIS)

    Castañeda-Priego, R; Lobaskin, V; Mixteco-Sánchez, J C; Rojas-Ochoa, L F; Linse, P

    2012-01-01

    The structure of charge-stabilized colloidal dispersions has been studied through a one-component model using a Yukawa potential with density-dependent parameters examined with integral equation theory and Monte Carlo simulations. Partial thermodynamic consistency was guaranteed by considering the osmotic pressure of the dispersion from the approximate mean-field renormalized jellium and Poisson-Boltzmann cell models. The colloidal structures could be accurately described by the Ornstein-Zernike equation with the Rogers-Young closure by using the osmotic pressure from the renormalized jellium model. Although we explicitly show that the correct effective pair-potential obtained from the inverse Monte Carlo method deviates from the Yukawa shape, the osmotic pressure constraint allows us to have a good description of the colloidal structure without losing information on the system thermodynamics. Our findings are corroborated by primitive model simulations of salt-free colloidal dispersions. (paper)

  15. Separation of active and inactive fractions from starved culture of Vibrio parahaemolyticus by density dependent cell sorting.

    Science.gov (United States)

    Nayak, Binaya Bhusan; Kamiya, Eriko; Nishino, Tomohiko; Wada, Minoru; Nishimura, Masahiko; Kogure, Kazuhiro

    2005-01-01

    The co-existence of physiologically different cells in bacterial cultures is a general phenomenon. We have examined the applicability of the density dependent cell sorting (DDCS) method to separate subpopulations from a long-term starvation culture of Vibrio parahaemolyticus. The cells were subjected to Percoll density gradient and separated into 12 fractions of different buoyant densities, followed by measuring the cell numbers, culturability, respiratory activity and leucine incorporation activity. While more than 78% of cells were in lighter fractions, about 95% of culturable cells were present in heavier fractions. The high-density subpopulations also had high proportion of cells capable of forming formazan granules. Although this was accompanied by the cell specific INT-reduction rate, both leucine incorporation rates and INT-reduction rates per cell had a peak at mid-density fraction. The present results indicated that DDCS could be used to separate subpopulations of different physiological conditions.

  16. Integrating physiological and biomechanical drivers of population growth over environmental gradients on coral reefs.

    Science.gov (United States)

    Madin, Joshua S; Hoogenboom, Mia O; Connolly, Sean R

    2012-03-15

    Coral reefs exhibit marked spatial and temporal variability, and coral reef organisms exhibit trade-offs in functional traits that influence demographic performance under different combinations of abiotic environmental conditions. In many systems, trait trade-offs are modelled using an energy and/or nutrient allocation framework. However, on coral reefs, differences in biomechanical vulnerability have major demographic implications, and indeed are believed to play an essential role in mediating species coexistence because highly competitive growth forms are vulnerable to physical dislodgment events that occur with high frequency (e.g. annual summer storms). Therefore, an integrated energy allocation and biomechanics framework is required to understand the effect of physical environmental gradients on species' demographic performance. However, on coral reefs, as in most ecosystems, the effects of environmental conditions on organisms are measured in different currencies (e.g. lipid accumulation, survival and number of gametes), and thus the relative contributions of these effects to overall capacity for population growth are not readily apparent. A comprehensive assessment of links between the environment and the organism, including those mediated by biomechanical processes, must convert environmental effects on individual-level performance (e.g. survival, growth and reproduction) into a common currency that is relevant to the capacity to contribute to population growth. We outline such an approach by considering the population-level performance of scleractinian reef corals over a hydrodynamic gradient, with a focus on the integrating the biomechanical determinants of size-dependent coral colony dislodgment as a function of flow, with the effects of flow on photosynthetic energy acquisition and respiration.

  17. APPLICATION OF ELASTICITY ANALYSES AND PERTURBATION SIMULATIONS IN DETERMINING STRESSOR IMPACTS ON POPULATION GROWTH RATE AND EXTINCTION RISK

    Science.gov (United States)

    Population structure and life history strategies are determinants of how populations respond to stressor-induced impairments in individual-level responses, but a consistent and holistic analysis has not been reported. Effects on population growth rate were modeled using five theo...

  18. Population Growth and Its Expression in Spatial Built-up Patterns: The Sana’a, Yemen Case Study

    Directory of Open Access Journals (Sweden)

    Gunter Zeug

    2010-04-01

    Full Text Available In light of rapid global urbanisation, monitoring and mapping of urban and population growth is of great importance. Population growth in Sana’a was investigated for this reason. The capital of the Republic of Yemen is a rapidly growing middle sized city where the population doubles almost every ten years. Satellite data from four different sensors were used to explore urban growth in Sana’a between 1989 and 2007, assisted by topographic maps and cadastral vector data. The analysis was conducted by delineating the built-up areas from the various optical satellite data, applying a fuzzy-rule-based composition of anisotropic textural measures and interactive thresholding. The resulting datasets were used to analyse urban growth and changes in built-up density per district, qualitatively as well as quantitatively, using a geographic information system. The built-up area increased by 87 % between 1989 and 2007. Built-up density has increased in all areas, but particularly in the northern and southern suburban districts, also reflecting the natural barrier of surrounding mountain ranges. Based on long-term population figures, geometric population growth was assumed. This hypothesis was used together with census data for 1994 and 2004 to estimate population figures for 1989 and 2007, resulting in overall growth of about 240%. By joining population figures to district boundaries, the spatial patterns of population distribution and growth were examined. Further, urban built-up growth and population changes over time were brought into relation in order to investigate changes in population density per built-up area. Population densities increased in all districts, with the greatest density change in the peripheral areas towards the North. The results reflect the pressure on the city’s infrastructure and natural resources and could contribute to sustainable urban planning in the city of Sana’a.

  19. Bone growth, limb proportions and non-specific stress in archaeological populations from Croatia.

    Science.gov (United States)

    Pinhasi, R; Timpson, A; Thomas, M; Slaus, M

    2014-01-01

    The effect of environmental factors and, in particular, non-specific stress on the growth patterns of limbs and other body dimensions of children from past populations is not well understood. This study assesses whether growth of mediaeval and post-mediaeval children aged between 0-11.5 years from Adriatic (coastal) and continental Croatia varies by region and by the prevalence and type of non-specific stress. Dental ages were estimated using the Moorrees, Fanning and Hunt (MFH) scoring method. Growth of long bone diaphyses (femur, tibia, humerus, radius and ulna) was assessed by using a composite Z-score statistic (CZS). Clavicular length was measured as a proxy for upper trunk width, distal metaphyseal width of the femur was measured as a proxy for body mass and upper and lower intra-limb indices were calculated. Differences between sub-sets sampled by (a) region and (b) active vs healed non-specific stress indicators and (c) intra-limb indices were tested by Mann--Whitney U-tests and Analysis of Covariance (ANCOVA). Adriatic children attained larger dimensions-per-age than continental children. Children with healed stress lesions had larger dimensions-per-age than those with active lesions. No inter-regional difference was found in intra-limb indices. These findings highlight the complexity of growth patterns in past populations and indicate that variation in environmental conditions such as diet and differences in the nature of non-specific stress lesions both exert a significant effect on long bone growth.

  20. [The impact of population growth on Tamba Kosi, a Himalayan valley in Nepal].

    Science.gov (United States)

    Verliat, S

    1994-01-01

    Two several-month-long stays in the isolated Tamba Kosi valley in Nepal in 1983 and 1986 allowed an assessment of the importance of changes in rural societies. In about 50 years, the oldest inhabitants of some villages have seen the number of houses quadruple. In the absence of reliable statistical data, the inhabitants say that the Tamba Kosi valley population has doubled in the last 25 years. This population growth exacerbates the multiethnic fight for good land (i.e., ground of modest slope, hot, and humid). Many people have emigrated, which has somewhat eased problems relative to population growth. Soil degradation, which is becoming more and more acute, drives the inhabitants to cut down trees and clear the land for cultivation of new plots. These new plots are running up against steep slopes and high altitude. Most families have barely two hectares, which must suffice to feed 5-6 people on average. This fuels intensification of agricultural production, resulting in low efficacy. Livestock mutilate forests with their hooves and teeth. The marked increase in the variety of livestock accelerates this destruction. Three types of building materials are used in this high valley: thatch, shingles (fir tree), and bamboo matting. The disappearance of wild grasses used to make thatch roofs and people moving to higher and higher altitudes resulted in use of shingles to make roofs. Buildings made of shingles, which demanded changes in construction techniques, changed the conception of homes. They became the preferred building type, which increased the demand for fir trees and deforestation. This lead to a demand for roofing material made of bamboo matting and another change in construction techniques. The retreat of the forest and disappearance of the most wanted plant species are the most spectacular impacts of population growth. This environmental degradation exacerbates erosion at all bioclimatic altitudes.

  1. [The decline in the population growth rate--a priority issue in international politics].

    Science.gov (United States)

    Rhein, E

    1994-08-25

    The Third International UN Conference on Population and Development took place in Cairo in early September 1994 with the participation of 200 governments and 1000 nongovernmental organizations to discuss ways of stabilizing world population at the possible lowest level and how industrialized countries could contribute to this effort. As a consequence of the advances in reproductive medicine the use of contraceptives skyrocketed: in 1994 more than half of men and women were using contraception compared to only 5% in 1950. However, the demographic momentum would still increase world population for another 100 years, even if fertility would drop to 2.2 children per couple (compared to 4 children in 1990). Nevertheless, the present generation could be instrumental in deciding whether the world's population will remain around 8 billion or reach 12 billion between 2050 and 2150. Poor countries can no longer afford an annual growth rate of 2-4% while also trying to improve living standards; this would require an economic growth rate of 6-8%. For the control of population growth both a sustainable environmental policy in the North, with rapid transition to renewable energy and recycling, and a more effective population policy in the South are needed. Family planning (FP) is the precondition of stabilization. The global FP outlays are envisioned to double from the 1994 figure of $5 billion to over $10 billion in the year 2000, with donor contributions to increase from 20% to 40% of the total. The US contribution is to double from $500 million by 2000, while the European Commission decided to boost expenditures for FP from DM 30 million in 1994 to DM 600 million by 2000. Japan is also expending $3 billion during this period. Recent promising developments have emerged: national pronatalist policies have diminished sharply and the pronatalist influence of religions has also declined. Political commitment at the highest level is central to a successful population policy as

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

    Directory of Open Access Journals (Sweden)

    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

  3. 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.

  4. Crowded growth leads to the spontaneous evolution of semistable coexistence in laboratory yeast populations.

    Science.gov (United States)

    Frenkel, Evgeni M; McDonald, Michael J; Van Dyken, J David; Kosheleva, Katya; Lang, Gregory I; Desai, Michael M

    2015-09-08

    Identifying the mechanisms that create and maintain biodiversity is a central challenge in biology. Stable diversification of microbial populations often requires the evolution of differences in resource utilization. Alternatively, coexistence can be maintained by specialization to exploit spatial heterogeneity in the environment. Here, we report spontaneous diversification maintained by a related but distinct mechanism: crowding avoidance. During experimental evolution of laboratory Saccharomyces cerevisiae populations, we observed the repeated appearance of "adherent" (A) lineages able to grow as a dispersed film, in contrast to their crowded "bottom-dweller" (B) ancestors. These two types stably coexist because dispersal reduces interference competition for nutrients among kin, at the cost of a slower maximum growth rate. This tradeoff causes the frequencies of the two types to oscillate around equilibrium over the course of repeated cycles of growth, crowding, and dispersal. However, further coevolution of the A and B types can perturb and eventually destroy their coexistence over longer time scales. We introduce a simple mathematical model of this "semistable" coexistence, which explains the interplay between ecological and evolutionary dynamics. Because crowded growth generally limits nutrient access in biofilms, the mechanism we report here may be broadly important in maintaining diversity in these natural environments.

  5. Warming, soil moisture, and loss of snow increase Bromus tectorum’s population growth rate

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    Aldo Compagnoni

    2014-01-01

    Full Text Available Abstract Climate change threatens to exacerbate the impacts of invasive species. In temperate ecosystems, direct effects of warming may be compounded by dramatic reductions in winter snow cover. Cheatgrass (Bromus tectorum is arguably the most destructive biological invader in basins of the North American Intermountain West, and warming could increase its performance through direct effects on demographic rates or through indirect effects mediated by loss of snow. We conducted a two-year experimental manipulation of temperature and snow pack to test whether 1 warming increases cheatgrass population growth rate and 2 reduced snow cover contributes to cheatgrass’ positive response to warming. We used infrared heaters operating continuously to create the warming treatment, but turned heaters on only during snowfalls for the snowmelt treatment. We monitored cheatgrass population growth rate and the vital rates that determine it: emergence, survival and fecundity. Growth rate increased in both warming and snowmelt treatments. The largest increases occurred in warming plots during the wettest year, indicating that the magnitude of response to warming depends on moisture availability. Warming increased both fecundity and survival, especially in the wet year, while snowmelt contributed to the positive effects of warming by increasing survival. Our results indicate that increasing temperature will exacerbate cheatgrass impacts, especially where warming causes large reductions in the depth and duration of snow cover.

  6. Nonlinear dynamics in a business-cycle model with logistic population growth

    International Nuclear Information System (INIS)

    Brianzoni, Serena; Mammana, Cristiana; Michetti, Elisabetta

    2009-01-01

    We consider a discrete-time growth model of the Solow type where workers and shareholders have different but constant saving rates and the population growth dynamics is described by the logistic equation able to exhibit complicated dynamics. We show conditions for the resulting system having a compact global attractor and we describe its structure. We also perform a mainly numerical analysis using the critical lines method able to describe the strange attractor and the absorbing area, in order to show how cyclical or complex fluctuations may be produced in a business-cycle model. We study the dynamic behaviour of the model under different ranges of the main parameters, i.e. the elasticity of substitution between the two production factors and the one in the logistic equation (namely μ). We prove the existence of complex dynamics when the elasticity of substitution between production factors drops below one (so that capital income declines) or μ increases (so that the amplitude of movements in the population growth rate increases).

  7. An Assessment of Factors Affecting Population Growth of the Mountain Plover

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    Stephen J. Dinsmore

    2010-06-01

    Full Text Available Effective conservation measures should target the most sensitive life history attributes of a species, assuming they are responsive to potential management actions. The Mountain Plover (Charadrius montanus is a species of conservation concern with a patchy breeding distribution in western North America. Plovers prefer areas with short vegetation, bare ground, and disturbance for nesting. Current management tools, including grazing and burning, have been used to attract plovers and enhance nesting success. We used a stage-specific matrix model to study the influence of vital rates, e.g., juvenile and adult annual survival, on population growth rate in the Mountain Plover at two breeding sites in Colorado, South Park and Eastern Colorado, and one breeding site in Montana, USA. Our analysis was motivated by a need to 1 better understand the relationship between demographic rates and population growth rate, 2 assess current management tools for the plover by exploring their effect on population growth rate, and 3 identify areas of the plover's population biology where additional demographic work is needed. Stochastic population growth rate was most influenced by adult survival, especially in Montana and South Park, Colorado (elasticities > 0.60, and was least influenced by first-year reproduction (all elasticities < 0.20. The modeled relationships between lambda and each demographic rate were generally weak (r2 < 0.30 with the exception of number of eggs hatched per nest in Eastern Colorado (r2 = 0.63, chick survival in South Park (r2 = 0.40 and Montana (r2 = 0.38, and adult survival in Montana (r2 = 0.36. We examined the predicted increase in lambda that would result from increasing each demographic rate from its mean to the maximum value observed in our simulations. Chick and adult survival showed the greatest increase in lambda while eggs hatched per nest produced the smallest increase. Our results suggest that future conservation efforts should

  8. A fuzzy mathematical model of West Java population with logistic growth model

    Science.gov (United States)

    Nurkholipah, N. S.; Amarti, Z.; Anggriani, N.; Supriatna, A. K.

    2018-03-01

    In this paper we develop a mathematics model of population growth in the West Java Province Indonesia. The model takes the form as a logistic differential equation. We parameterize the model using several triples of data, and choose the best triple which has the smallest Mean Absolute Percentage Error (MAPE). The resulting model is able to predict the historical data with a high accuracy and it also able to predict the future of population number. Predicting the future population is among the important factors that affect the consideration is preparing a good management for the population. Several experiment are done to look at the effect of impreciseness in the data. This is done by considering a fuzzy initial value to the crisp model assuming that the model propagates the fuzziness of the independent variable to the dependent variable. We assume here a triangle fuzzy number representing the impreciseness in the data. We found that the fuzziness may disappear in the long-term. Other scenarios also investigated, such as the effect of fuzzy parameters to the crisp initial value of the population. The solution of the model is obtained numerically using the fourth-order Runge-Kutta scheme.

  9. Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa.

    Science.gov (United States)

    Brandt, Martin; Rasmussen, Kjeld; Peñuelas, Josep; Tian, Feng; Schurgers, Guy; Verger, Aleixandre; Mertz, Ole; Palmer, John R B; Fensholt, Rasmus

    2017-03-06

    The rapidly growing human population in sub-Saharan Africa generates increasing demand for agricultural land and forest products, which presumably leads to deforestation. Conversely, a greening of African drylands has been reported, but this has been difficult to associate with changes in woody vegetation. There is thus an incomplete understanding of how woody vegetation responds to socio-economic and environmental change. Here we used a passive microwave Earth observation data set to document two different trends in land area with woody cover for 1992-2011: 36% of the land area (6,870,000 km 2 ) had an increase in woody cover largely in drylands, and 11% had a decrease (2,150,000 km 2 ), mostly in humid zones. Increases in woody cover were associated with low population growth, and were driven by increases in CO 2 in the humid zones and by increases in precipitation in drylands, whereas decreases in woody cover were associated with high population growth. The spatially distinct pattern of these opposing trends reflects, first, the natural response of vegetation to precipitation and atmospheric CO 2 , and second, deforestation in humid areas, minor in size but important for ecosystem services, such as biodiversity and carbon stocks. This nuanced picture of changes in woody cover challenges widely held views of a general and ongoing reduction of the woody vegetation in Africa.

  10. Endogenous Population Dynamics and Economic Growth with Free Trade between Countries

    Directory of Open Access Journals (Sweden)

    Wei-Bin Zhang

    2016-05-01

    Full Text Available This paper builds a model to deal with dynamic interdependence between different countries' birth rates, mortality rates, populations, wealth accumulation, and time distributions between working, leisure and children caring. The model shows the role of human capital, technological and preference changes on national differences in birth rates, mortality rates, time distributions, population change, and wealth accumulation. The economic mechanisms of wealth accumulation, production and trade are based the Solow growth model and the Oniki-Uzawa trade model. We use the utility function proposed by Zhang to describe the behavior of households. We model national and gender differences in human capital, propensity to have children, propensity to use leisure time, and children caring efficiency. We describe the dynamics of global economic growth, trade patterns, national differences in wealth, income, birth rates, mortality rates, and populations with differential equations. We simulate the model to show the motion of the system and identify the existence of equilibrium point. We also examine the effects of changes in the propensity to have children, the propensity to save, woman's propensity to use leisure, woman's human capital, and woman's emotional involvement in children caring on the dynamics of the global and national economies.

  11. The hydrocarbon era, world population growth and oil use -- a continuing geological challenge

    International Nuclear Information System (INIS)

    Townes, H.L.

    1993-01-01

    The world's use of oil, the relationship of world population growth to this use, and what the energy situation might be in the future is a challenge to the geologist. The earth's population doubled between 1930 and 1975 and a comparison of world petroleum use and population growth show similar upward curves. Of the annual fossil fuel resources used in the world, crude oil supplies over 40 percent of the total resources. Petroleum is a finite resource and a projection of world oil production indicates it will peak early in the 21st century. Assuming an ultimate recovery range of 2600 to 3000 billion barrels of oil, 750 billion barrels have already been produced, there are 1000 billion barrels in proven reserves, and 1000 billion barrels remaining to be discovered. The challenge to the geologist will be to find these hidden oil reserves. Recovering this 1000 billion barrels of new oil reserves will require large capital expenditures and, currently, only 60 percent of the capital needed to discover this oil is being spent. With the world's demand for oil increasing, world-wide exploration expenditures are actually decreasing. Simple economics indicates that the reason for this drop in expenditures is that the price of oil is too low to encourage investment. Low oil prices also discourage investment in the development of alternative fuels. There is plenty of oil now, but the world must look to the future and realize present usage rate cannot continue forever. 23 refs., 10 figs

  12. Strong contribution of immigration to local population regulation: evidence from a migratory passerine.

    Science.gov (United States)

    Schaub, Michael; Jakober, Hans; Stauber, Wolfgang

    2013-08-01

    A mechanistic understanding of the dynamics of populations requires knowledge about the variation of the underlying demographic rates and about the reasons for their variability. In geographically open populations, immigration is often necessary to prevent declines, but little is known about whether immigration can contribute to its regulation. We studied the dynamics of a Red-backed Shrike population (Lanius collurio) over 36 years in Germany with a Bayesian integrated population model. We estimated mean and temporal variability of population sizes, productivity, apparent survival, and immigration. We assessed how strongly the demographic rates were correlated with population growth to understand the demographic reasons of population change and how strongly the demographic rates were correlated with population size to identify possible density-dependent mechanisms. The shrike population varied between 35 and 74 breeding pairs but did not show a significant trend in population size over time (growth rate 1.002 +/- 0.001 [mean +/- SD]). Apparent survival of females (juveniles 0.06 +/- 0.01; adults 0.37 +/- 0.03) was lower than that of males (juveniles 0.10 +/- 0.01; adults 0.44 +/- 0.02). Immigration rates were substantial and higher in females (0.56 +/- 0.02) than in males (0.43 +/- 0.02), and average productivity was 2.76 +/- 0.14. Without immigration, the Red-backed Shrike population would have declined strongly. Immigration was the strongest driver for the number of females while local recruitment was the most important driver for the number of males. Immigration of both sexes and productivity, but not local recruitment and survival, were subject to density dependence. Density-dependent productivity was not effectively regulating the local population but may have contributed to regulate shrike populations at larger spatial scales. These findings suggest that immigration is not only an important component to prevent a geographically open population from decline

  13. An application of the variable-r method to subpopulation growth rates in a 19th century agricultural population

    Directory of Open Access Journals (Sweden)

    Corey Sparks

    2009-07-01

    Full Text Available This paper presents an analysis of the differential growth rates of the farming and non-farming segments of a rural Scottish community during the 19th and early 20th centuries using the variable-r method allowing for net migration. Using this method, I find that the farming population of Orkney, Scotland, showed less variability in their reproduction and growth rates than the non-farming population during a period of net population decline. I conclude by suggesting that the variable-r method can be used in general cases where the relative growth of subpopulations or subpopulation reproduction is of interest.

  14. Local population extinction and vitality of an epiphytic lichen in fragmented old-growth forest.

    Science.gov (United States)

    Ockinger, Erik; Nilsson, Sven G

    2010-07-01

    The population dynamics of organisms living in short-lived habitats will largely depend on the turnover of habitat patches. It has been suggested that epiphytes, whose host plants can be regarded as habitat patches, often form such patch-tracking populations. However, very little is known about the long-term fate of epiphyte individuals and populations. We estimated life span and assessed environmental factors influencing changes in vitality, fertility, abundance, and distribution of the epiphytic lichen species Lobaria pulmonaria on two spatial scales, individual trees and forest patches, over a period of approximately 10 years in 66 old-growth forest fragments. The lichen had gone extinct from 7 of the 66 sites (13.0%) where it was found 10 years earlier, even though the sites remained unchanged. The risk of local population extinction increased with decreasing population size. In contrast to the decrease in the number of occupied trees and sites, the mean area of the lichen per tree increased by 43.0%. The number of trees with fertile ramets of L. pulmonaria increased from 7 (approximately 1%) to 61 (approximately 10%) trees, and the number of forest fragments with fertile ramets increased from 4 to 23 fragments. The mean annual rate of L. pulmonaria extinction at the tree level was estimated to be 2.52%, translating into an expected lifetime of 39.7 years. This disappearance rate is higher than estimated mortality rates for potential host trees. The risk of extinction at the tree level was significantly positively related to tree circumference and differed between tree species. The probability of presence of fertile ramets increased significantly with local population size. Our results show a long expected lifetime of Lobaria pulmonaria ramets on individual trees and a recent increase in vitality, probably due to decreasing air pollution. The population is, however, declining slowly even though remaining stands are left uncut, which we interpret as an

  15. Long-term growth of Desert Tortoises (Gopherus agassizii) in a southern Nevada population

    Science.gov (United States)

    Medica, P.A.; Nussear, Kenneth E.; Esque, Todd C.; Saethre, Mary B.

    2012-01-01

    Knowledge of growth rates, age at maturity, and longevity are important aspects of a species life history and are directly applicable to life table creation and population viability analyses. We measured the growth of a cohort of 17 semi-wild Desert Tortoises (Gopherus agassizii) located in Rock Valley, Nevada over a 47-yr period beginning in 1963. The tortoises were initially marked as hatchling and juvenile animals between the years 1963 and 1965 and ranged in size from 47 to 77 mm in plastron length. We assigned ages of 1-4 yr to the tortoises at initial capture based on their body size. These tortoises were recaptured, measured, and weighed approximately annually since their initial capture. Growth of male and female tortoises did not differ significantly until animals reached the age of 23-25 yr. Annual tortoise growth was correlated with the production of ephemeral vegetation, while accounting for size, sex, and repeated measurements of the animals as well as the interval between measurements. However, the production of ephemeral plants was likewise highly correlated (non-linearly) with winter rainfall. Stochastic predation events between 2003 and 2007 decimated this cohort of tortoises. The average age of the long-term surviving tortoises from this cohort was 43 yr with a range of 39-47 yr. Twelve of the tortoises survived to the age of 39 yr and 11 of the 12 reached 40 yr.

  16. Non-occupational exposure to paint fumes during pregnancy and fetal growth in a general population

    DEFF Research Database (Denmark)

    Sørensen, Mette; Andersen, Anne-Marie N; Raaschou-Nielsen, Ole

    2010-01-01

    in their residence during pregnancy. The mothers were also asked about smoking habits and alcohol consumption during pregnancy, pre-pregnancy weight, height, parity and occupation. Information on birth weight and gestational age was obtained from national registers. We found that 45% of the mothers had been exposed......Occupational exposure to organic solvents during pregnancy has been associated with reduced fetal growth. Though organic solvents in the form of paint fumes are also found in the home environment, no studies have investigated the effect of such exposure in a general population. We studied...... associations between residential exposure to paint fumes during pregnancy and fetal growth within the Danish National Birth Cohort which consecutively recruited pregnant women from 1996 to 2002 from all over Denmark. Around the 30th pregnancy week, 19,000 mothers were interviewed about use of paint...

  17. Fetal growth trajectory and risk for eczema in a Saudi population.

    Science.gov (United States)

    AlMakoshi, Amel; Ellahi, Awaiss; Sallout, Bala; Devereux, Graham; Turner, Steve

    2015-12-01

    Recent studies in Western cohorts have identified associations between increasing fetal abdominal circumference (AC) during mid-pregnancy and increased risk for eczema and atopy. We sought to replicate these findings in a Saudi population where antenatal environmental exposures are different compared with Western countries. A Saudi birth cohort was recruited to relate maternal dietary intake and fetal growth to wheeze, eczema, and rhinitis in the first 2 yrs. Fetal size was determined from routine ultrasound scan measurements in the second and third trimesters and birthweight was noted. Parent-reported outcomes during the first 2 yrs were acquired by telephone-administered questionnaire. There were 1076 mothers recruited. AC was determined in 562 for the second, in 632 for the third, and in 281 for both second and third trimesters. A history of eczema was determined in 814 children at 2 yrs of age. There was an inverse relationship between change in abdominal circumference between the second and third trimesters for eczema (OR 0.66 per z score increase in AC [95% CI 0.49, 0.89]), and the quartile with the greatest faltering growth were at increased risk compared with other groups (p ≤ 0.045). Change in fetal size between the third trimester and birth was not associated with altered eczema risk. There were no associations between fetal growth and wheeze at the age of 2 yrs. Our findings contrast observations made in Western populations but nonetheless suggest that factors associated with changing fetal growth trajectory in the second half of pregnancy are also relevant to atopy development on the global setting. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  18. Population growth, movements, and status of the Nushagak Peninsula Caribou Herd following reintroduction, 1988 - 2000

    Directory of Open Access Journals (Sweden)

    Gail H. Collins

    2003-04-01

    Full Text Available Barren ground caribou (Rangifer tarandus were reintroduced to the Nushagak Peninsula, Alaska in February of 1988 after an absence of more than 100 years. Since reintroduction, herd growth and population dynamics have been monitored closely. At this time, there has been no significant dispersal from the herds' core range. The Nushagak Peninsula Caribou Herd (NPCH grew rapidly from 146 reintroduced individuals to over 1000 in 13 years. Dramatic mean annual growth during the first 6 years (1988-1994 of 38% (r = 0.32 can be attributed to the high percentage of females in the initial reintroduction, high calf production and survival, exceptional range conditions, few predators, and no hunting. However, the populations' exceptional growth (peak counts of 1400 slowed and stabilized between 1996¬1998 and then decreased between 1998 and 2000. Size, body condition and weights of calves captured in 2000 were significantly lower than those captured in 1995 and 1997. Although calf production also decreased from close to 100% (1990-1995 to about 91% (1996-2000, overall calf survival continued to be high. Legal harvest began in 1995, and harvest reports have accounted for approximately 3% of population mortality annually. Although brown bears (Ursus arctos and wolves (Canis lupus are present, the extent of predation is unknown. Mean home range of the NPCH was 674 km2 and group sizes were greatest during post-calving aggregation in July (mean = 127. Caribou population density on the Nushagak Peninsula reached approximately 1.2 caribou/km2 in 1997 before declining to about 1.0 caribou/km2. A range survey in 1994 noted only trace utilization of lichens on the Nushagak Peninsula by caribou. A subsequent survey in 1999 found moderate to severe utilization in 46% of plots, suggesting the reintroduced herd was beginning to alter range condition. Between 1997 and 2000, both calf production and condition of 10-month-old calves declined. Calving has also been delayed

  19. Simultaneous inference of selection and population growth from patterns of variation in the human genome

    DEFF Research Database (Denmark)

    Williamson, Scott H.; Hernandez, Ryan; Fledel-Alon, Adi

    2005-01-01

    Natural selection and demographic forces can have similar effects on patterns of DNA polymorphism. Therefore, to infer selection from samples of DNA sequences, one must simultaneously account for demographic effects. Here we take a model-based approach to this problem by developing predictions fo......-specific methods, and (iii) strong evidence for very recent population growth....... for patterns of polymorphism in the presence of both population size change and natural selection. If data are available from different functional classes of variation, and a priori information suggests that mutations in one of those classes are selectively neutral, then the putatively neutral class can...... this method to a large polymorphism data set from 301 human genes and find (i) widespread negative selection acting on standing nonsynonymous variation, (ii) that the fitness effects of nonsynonymous mutations are well predicted by several measures of amino acid exchangeability, especially site...

  20. Population movements to a growth-pole: the case of Hosur, Tamil Nadu.

    Science.gov (United States)

    Heins, J J; Meijer, E N

    1990-08-01

    This study examines the characteristics of population growth in Hosur, a small town in Tamil Nadu, India. "A special feature of the population in Hosur is the phenomenon of bachelors living together, mostly young men who have migrated from big cities. Commuting is not important in the mobility pattern of Hosur, less than ten per cent of employees in the industrial areas travelling daily from outside. Only one-third of the non-migrant labour force has access to the more attractive jobs in the modern factories, while short-term wage labour plays an important role in the labour structure of commuters. The demographic future of Hosur is not connected strongly with commuting patterns, but more with the spatial behaviour of the bachelors." excerpt