The Experts below are selected from a list of 6378 Experts worldwide ranked by ideXlab platform
Samuel M. Flaxman - One of the best experts on this subject based on the ideXlab platform.
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Quantitative tests of multitrophic Ideal Free Distribution theory
Animal Behaviour, 2013Co-Authors: Amanda C. Williams, Sean E. Flaherty, Samuel M. FlaxmanAbstract:Ideal Free Distribution (IFD) theory is often used to explain small-scale spatial Distributions of organisms. However, few studies have rigorously tested predictions of IFD models in situations involving multiple species and trophic levels. We fully parameterized and tested predictions of a general interference IFD model for both predators and prey in a tritrophic system: seven-spotted lady beetles (Coccinella septempunctata L., Coleoptera: Coccinellidae), pea aphids (Acyrthosiphon pisum (Harris), Hemiptera: Aphididae), and tic bean plants (Vicia faba L., Fabaceae). We used habitat selection treatments having both predators and prey in the presence and absence of one another. We also performed experiments to quantify the strength of interspecific competition, the functional response of predators and several measures of fitness for the prey. Our results show that whether prey were present or not, predators followed IFD predictions and aggregated most strongly in the patch with the highest-quality resource. Prey in the presence of predators followed the predicted IFD, which was similar to a uniform Distribution. However, prey in the absence of predators moved infrequently and were far from Ideal Free, suggesting that predators instigated habitat selection behaviour. Our results underscore the importance of considering trophic interactions and multiple measures of patch quality in studies of habitat selection. The observed departures from theoretical predictions also usefully suggest promising extensions for future theory and experiments.
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different modes of resource variation provide a critical test of Ideal Free Distribution models
Behavioral Ecology and Sociobiology, 2007Co-Authors: Samuel M. Flaxman, Christina A DeroosAbstract:Ideal Free Distribution (IFD) models are perhaps the group of mathematical models of behavior that have been the most widely and successfully applied by empiricists. These models can be applied to nearly any situation in which consumers compete—by any mechanism—for resources that are patchily distributed in their environment. Although IFD models have come to be broadly accepted, experiments that simultaneously test more than a single prediction are rare. Instead, investigators normally either test (1) for a relationship between the Distribution of consumers and the Distribution of resources or (2) whether average fitnesses are equal across resource patches. We conducted experiments with pea aphids (Acyrthosiphon pisum Harris) feeding on two patches of fava beans (Vicia faba L.) to fully independently parameterize an IFD model with interference competition and then test quantitative predictions about aphid spatial Distributions and the payoffs of patch choice. We found a precise fit between aphids’ predicted and observed reproductive successes. Furthermore, by varying patch “quality” in two ways, we were able to show that aphid Distributions vary with the mode of resource variation in the predicted manner: aphids (1) matched resources when patches varied in size but not quality and (2) overmatched the good patch when patches varied in quality but not size (predicted as a consequence of weak interference). The close correspondence between quantitative predictions of the model with observed behaviors suggests that IFD theory is a framework with more explanatory power than is generally appreciated.
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Putting competition strategies into Ideal Free Distribution models: habitat selection as a tug of war.
Journal of theoretical biology, 2006Co-Authors: Samuel M. Flaxman, H. Kern ReeveAbstract:When resources are patchily distributed in an environment, behavioral ecologists frequently turn to Ideal Free Distribution (IFD) models to predict the spatial Distribution of organisms. In these models, predictions about Distributions depend upon two key factors: the quality of habitat patches and the nature of competition between consumers. Surprisingly, however, no IFD models have explored the possibility that consumers modulate their competitive efforts in an evolutionarily stable manner. Instead, previous models assume that resource acquisition ability and competition are fixed within species or within phenotypes. We explored the consequences of adaptive modulation of competitive effort by incorporating tug-of-war theory into payoff equations from the two main classes of IFD models (continuous input (CI) and interference). In the models we develop, individuals can increase their share of the resources available in a patch, but do so at the costs of increased resource expenditures and increased negative interactions with conspecifics. We show how such models can provide new hypotheses to explain what are thought to be deviations from IFDs (e.g., the frequent observation of fewer animals than predicted in "good" patches of habitat). We also detail straightforward predictions made uniquely by the models we develop, and we outline experimental tests that will distinguish among alternatives.
Carlos Bernstein - One of the best experts on this subject based on the ideXlab platform.
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Predator Migration Decisions, the Ideal Free Distribution, and Predator-Prey Dynamics.
The American naturalist, 1999Co-Authors: Carlos Bernstein, Pierre Auger, Jean-christophe PoggialeAbstract:abstract: The aim of the present work is to analyze the influence of optimal predator emigration decisions that can lead to the Ideal Free Distribution (IFD) on the stability of predator‐prey systems. The assumption of optimal decisions is then relaxed to analyze the possible influence of different degrees of deviation from the IFD. The first migration rule we analyze is based on the marginal‐value theorem and assumes perfect knowledge of capture rate in the patch of residence and in the environment as a whole. When migration rates are high, this rule leads the predator population to the IFD. The results suggest that under these conditions predator migration plays no major role in the stability of the system. This is so because the systems naturally merge into a single patch. This result is independent of the particular functional response used. The other two rules we analyze take into account lower migration rates, the limitations in making optimal decisions by predators, and the possible constraints in ...
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The Ideal Free Distribution and predator-prey populations
Trends in ecology & evolution, 1992Co-Authors: Alejandro Kacelnik, John R. Krebs, Carlos BernsteinAbstract:The Ideal Free Distribution, a theoretical model of the Distribution of competitors between habitat patches, has recently undergone a number of modifications and extensions. These fall into two main categories: those that assume that equilibrium is attained, and those that establish whether it is attained. The modifications suggest ways in which behavioural properties of individuals might affect the Distribution of competitors, and clear a path for further empirical tests.
Vlastimil Křivan - One of the best experts on this subject based on the ideXlab platform.
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The Allee-type Ideal Free Distribution.
Journal of mathematical biology, 2013Co-Authors: Vlastimil KřivanAbstract:The Ideal Free Distribution (IFD) in a two-patch environment where individual fitness is positively density dependent at low population densities is studied. The IFD is defined as an evolutionarily stable strategy of the habitat selection game. It is shown that for low and high population densities only one IFD exists, but for intermediate population densities there are up to three IFDs. Population and Distributional dynamics described by the replicator dynamics are studied. It is shown that Distributional stability (i.e., IFD) does not imply local stability of a population equilibrium. Thus Distributional stability is not sufficient for population stability. Results of this article demonstrate that the Allee effect can strongly influence not only population dynamics, but also population Distribution in space.
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the Ideal Free Distribution as an evolutionarily stable state in density dependent population games
Oikos, 2010Co-Authors: Ross Cressman, Vlastimil KřivanAbstract:In classical games that have been applied to ecology, individual fitness is either density independent or population density is fixed. This article focuses on the habitat selection game where fitness depends on the population density that evolves over time. This model assumes that changes in animal Distribution operate on a fast time scale when compared to demo graphic processes. Of particular interest is whether it is true, as one might expect, that resident phenotypes who use density-dependent optimal foraging strategies are evolutionarily stable with respect to invasions by mutant strategies. In fact, we show that evolutionary stability does not require that residents use the evolutionarily stable strategy (ESS) at every population density; rather it is the combined resident–mutant system that must be at an evolutionary stable state. That is, the separation of time scales assumption between behavioral and ecological processes does not imply that these processes are independent. When only consumer population dynamics in several habitats are considered (i.e. when resources do not undergo population dynamics), we show that the existence of optimal foragers forces the resident-mutant system to approach carrying capacity in each habitat even though the mutants do not die out. Thus, the Ideal Free Distribution (IFD) for the single-species habitat selection game becomes an evolutionarily stable state that describes a mixture of resident and mutant phenotypes rather than a strategy adopted by all individuals in the system. Also discussed is how these results are affected when animal Distribution and demographic processes act on the same time scale.
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The Ideal Free Distribution as an evolutionarily stable state in density‐dependent population games
Oikos, 2010Co-Authors: Ross Cressman, Vlastimil KřivanAbstract:In classical games that have been applied to ecology, individual fitness is either density independent or population density is fixed. This article focuses on the habitat selection game where fitness depends on the population density that evolves over time. This model assumes that changes in animal Distribution operate on a fast time scale when compared to demo graphic processes. Of particular interest is whether it is true, as one might expect, that resident phenotypes who use density-dependent optimal foraging strategies are evolutionarily stable with respect to invasions by mutant strategies. In fact, we show that evolutionary stability does not require that residents use the evolutionarily stable strategy (ESS) at every population density; rather it is the combined resident–mutant system that must be at an evolutionary stable state. That is, the separation of time scales assumption between behavioral and ecological processes does not imply that these processes are independent. When only consumer population dynamics in several habitats are considered (i.e. when resources do not undergo population dynamics), we show that the existence of optimal foragers forces the resident-mutant system to approach carrying capacity in each habitat even though the mutants do not die out. Thus, the Ideal Free Distribution (IFD) for the single-species habitat selection game becomes an evolutionarily stable state that describes a mixture of resident and mutant phenotypes rather than a strategy adopted by all individuals in the system. Also discussed is how these results are affected when animal Distribution and demographic processes act on the same time scale.
J.a. Beecham - One of the best experts on this subject based on the ideXlab platform.
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how do grazers achieve their Distribution a continuum of models from random diffusion to the Ideal Free Distribution using biased random walks
The American Naturalist, 1999Co-Authors: Keith D. Farnsworth, J.a. BeechamAbstract:abstract: A conceptual model is described for generating Distributions of grazing animals, according to their searching behavior, to investigate the mechanisms animals may use to achieve their Distributions. The model simulates behaviors ranging from random diffusion, through taxis and cognitively aided navigation (i.e., using memory), to the optimization extreme of the Ideal Free Distribution. These behaviors are generated from simulation of biased diffusion that operates at multiple scales simultaneously, formalizing ideas of multiple‐scale foraging behavior. It uses probabilistic bias to represent decisions, allowing multiple search goals to be combined (e.g., foraging and social goals) and the representation of suboptimal behavior. By allowing bias to arise at multiple scales within the environment, each weighted relative to the others, the model can represent different scales of simultaneous decision‐making and scale‐dependent behavior. The model also allows different constraints to be applied to the...
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Beyond the Ideal Free Distribution: More General Models of Predator Distribution
Journal of Theoretical Biology, 1997Co-Authors: Keith D. Farnsworth, J.a. BeechamAbstract:Abstract The Ideal Free Distribution model which relates the spatial Distribution of mobile consumers to that of their resource is shown to be a limiting case of a more general model which we develop using simple concepts of diffusion. We show how the Ideal Free Distribution model can be derived from a more general model and extended by incorporating simple models of social influences on predator spacing. First, a Free Distribution model based on path switching rules, with a power-law interference term, which represents instantaneous biased diffusion is derived. A social bias term is then introduced to represent the effect of predator aggregation on predator fitness, separate from any effects which act through intake rate. The social bias term is expanded to express an optimum spacing for predators and example solutions of the resulting biased diffusion models are shown. The model demonstrates how an empirical interference coefficient, derived from measurements of predator and prey densities, may include factors expressing the impact of social spacing behaviour on fitness. We conclude that empirical values of log predator/log prey ratio may contain information about more than the relationship between consumer and resource densities. Unlike many previous models, the model shown here applies to conditions without continual input.
Winfried Lampert - One of the best experts on this subject based on the ideXlab platform.
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Vertical Distribution of zooplankton: density dependence and evidence for an Ideal Free Distribution with costs
BMC biology, 2005Co-Authors: Winfried LampertAbstract:Background In lakes with a deep-water algal maximum, herbivorous zooplankton are faced with a trade-off between high temperature but low food availability in the surface layers and low temperature but sufficient food in deep layers. It has been suggested that zooplankton (Daphnia) faced with this trade-off distribute vertically according to an "Ideal Free Distribution (IFD) with Costs". An experiment has been designed to test the density (competition) dependence of the vertical Distribution as this is a basic assumption of IFD theory.
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Trade-offs in the vertical Distribution of zooplankton: Ideal Free Distribution with costs?
Proceedings. Biological sciences, 2003Co-Authors: Winfried Lampert, Edward Mccauley, Bryan F. J. ManlyAbstract:Zooplankton vertical migratory patterns are a classic example of optimal habitat choice. We hypothesize that zooplankton distribute themselves vertically in the water column according to an Ideal Free Distribution (IFD) with costs such as to optimize their fitness. In lakes with a deep-water chlorophyll maximum, zooplankton are faced with a trade-off, either experiencing high food (high reproductive potential) but low temperature (slow development) in the hypolimnion or high temperature and low food in the epilimnion. Thus, in the absence of fish predation (e.g. at night) they should allocate the time spent in the different habitats according to fitness gain dependent on the temperature gradient and Distribution of food. We tested this hypothesis with a Daphnia hyalina x galeata clone in large indoor columns (Plon Plankton Towers) and with a dynamic energy budget model. In the tower experiments, we simulated a deep-water algal maximum below the thermocline with epilimnetic/hypolimnetic temperature differences of 2, 5 and 10 degrees C. Experimental data supported the model. We found a significantly larger proportion of daphniids in the hypolimnion when the temperature difference was smaller. Our results are consistent with the concept of IFD with costs originally developed for stream fishes. This concept can be applied to predict the vertical Distribution of zooplankton in habitats where fish predation is of minor importance.
