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Prey Dynamics (prey + dynamics)
Selected AbstractsThe anatomy of predator,prey dynamics in a changing climateJOURNAL OF ANIMAL ECOLOGY, Issue 6 2007CHRISTOPHER C. WILMERS Summary 1Humans are increasingly influencing global climate and regional predator assemblages, yet a mechanistic understanding of how climate and predation interact to affect fluctuations in prey populations is currently lacking. 2Here we develop a modelling framework to explore the effects of different predation strategies on the response of age-structured prey populations to a changing climate. 3We show that predation acts in opposition to temporal correlation in climatic conditions to suppress prey population fluctuations. 4Ambush predators such as lions are shown to be more effective at suppressing fluctuations in their prey than cursorial predators such as wolves, which chase down prey over long distances, because they are more effective predators on prime-aged adults. 5We model climate as a Markov process and explore the consequences of future changes in climatic autocorrelation for population dynamics. We show that the presence of healthy predator populations will be particularly important in dampening prey population fluctuations if temporal correlation in climatic conditions increases in the future. [source] Predator behaviour and prey density: evaluating density-dependent intraspecific interactions on predator functional responsesJOURNAL OF ANIMAL ECOLOGY, Issue 1 2001Nilsson P. Anders Abstract 1In models of size-structured predator,prey systems, the effects are evaluated of gape-size limited predation on prey population growth and density when predators are non-interacting, cannibalistic, interfering, and cannibalistic and interfering. 2Predation from non-interacting predators markedly reduces prey density, compared with prey densities in the absence of predation. When density-dependent cannibalism between predators is introduced, predator density and therefore total functional response decrease, resulting in a decrease in predation pressure and higher prey densities. 3Size- and density-dependent interference between predators substantially decreases functional responses in the predators, and the prey population is thus allowed to grow more dense. Allowing for cannibalism between interfering predators also decreases predator density, but here the decreased number of predators does not have the releasing effect seen in solely cannibalistic predators. The interference between predators decreases with predator density, and per capita functional responses increase and compensate for the decrease in predator density. 4These theoretical results are compared with results from natural systems with pikeperch and northern pike. Both species are cannibalistic, and pike are also kleptoparasitic, mirroring the models. Results from introductions of the different piscivores into natural systems corroborate the outcome of the models, since introduction or increased densities of pikeperch have shown to have severe and long-lasting effects on prey, while pike have only initial, decreasing over time effects on prey stock. Thus, predator behaviour may seriously affect predator impact on prey, and size- and density-dependent interactions between predators may be a major key to the understanding of predator,prey dynamics and community composition in lakes. [source] Insect pests and natural enemies in two varieties of quinua (Chenopodium quinoa) at Cusco, PeruJOURNAL OF APPLIED ENTOMOLOGY, Issue 6 2002E. Yábar The quinua varieties differ, among other traits, in their content of saponins (secondary metabolites associated to plant resistance) late in the season. Whereas Agromyzidae and Cicadellidae were abundant only in the early season, both Chrysomelidae and Aphididae populations showed fluctuations. Likewise, Araneae and Braconidae showed fluctuating numbers during the season. The abundance of Coccinellidae peaked at mid-season whereas that of Syrphidae was high only in the late season. Although the overall abundance of insects was very similar in both varieties of quinua, there were different patterns depending on the season. In the early season there was a tendency towards greater insect numbers on Blanca, but in contrast, in the late season Amarilla (the high-saponin variety) had a higher load of insect pests. This suggests that saponins do not play a major role in quinua resistance against insects. In the early season, no significant relationship between pests and natural enemies held across quinua varieties. In the late season, Aphididae and Coccinellidae were negatively and significantly correlated in both varieties. The temporal population dynamics of Aphididae and both Coccinellidae and Braconidae resembled the traditional predator,prey dynamics. [source] Changes in survivorship, behavior, and morphology in native soft-shell clams induced by invasive green crab predatorsMARINE ECOLOGY, Issue 3 2010W. Lindsay Whitlow Abstract Many studies on invasive species show reduced native densities, but few studies measure trait-mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft-shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait-mediated effects to investigate predator,prey dynamics. [source] Habitat-dependent foraging in a classic predator,prey system: a fable from snowshoe haresOIKOS, Issue 2 2005Douglas W. Morris Current research contrasting prey habitat use has documented, with virtual unanimity, habitat differences in predation risk. Relatively few studies have considered, either in theory or in practice, simultaneous patterns in prey density. Linear predator,prey models predict that prey habitat preferences should switch toward the safer habitat with increasing prey and predator densities. The density-dependent preference can be revealed by regression of prey density in safe habitat versus that in the riskier one (the isodar). But at this scale, the predation risk can be revealed only with simultaneous estimates of the number of predators, or with their experimental removal. Theories of optimal foraging demonstrate that we can measure predation risk by giving-up densities of resource in foraging patches. The foraging theory cannot yet predict the expected pattern as predator and prey populations covary. Both problems are solved by measuring isodars and giving-up densities in the same predator,prey system. I applied the two approaches to the classic predator,prey dynamics of snowshoe hares in northwestern Ontario, Canada. Hares occupied regenerating cutovers and adjacent mature-forest habitat equally, and in a manner consistent with density-dependent habitat selection. Independent measures of predation risk based on experimental, as well as natural, giving-up densities agreed generally with the equal preference between habitats revealed by the isodar. There was no apparent difference in predation risk between habitats despite obvious differences in physical structure. Complementary studies contrasting a pair of habitats with more extreme differences confirmed that hares do alter their giving-up densities when one habitat is clearly superior to another. The results are thereby consistent with theories of adaptive behaviour. But the results also demonstrate, when evaluating differences in habitat, that it is crucial to let the organisms we study define their own habitat preference. [source] | ||||||||||