PedersenGreives2008 - Journal of Animal Ecology 2008, 77,...

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Journal of Animal Ecology 2008, 77 , 370–377 doi: 10.1111/j.1365-2656.2007.01321.x © 2007 The Authors. Journal compilation © 2007 British Ecological Society Blackwel Publishing Ltd The interaction of parasites and resources cause crashes in a wild mouse population Amy B. Pedersen 1 * and Timothy J. Greives 2 1 Department of Biology, University of Virginia, Charlottesville, VA 22904, USA; and 2 Department of Biology and Center for the Integrative Study of Animal Behaviour, Indiana University, 1001 E. 3rd Street, Bloomington, IN 47401, USA Summary 1. Populations of white-footed mice Peromyscus leucopus and deer mice Peromyscus maniculatus increase dramatically in response to food availability from oak acorn masts. These populations subsequently decline following this resource pulse, but these crashes cannot be explained solely by resource depletion, as food resources are still available as population crashes begin. 2. We hypothesized that intestinal parasites contribute to these post-mast crashes; Peromyscus are infected by many intestinal parasites that are often transmitted by density-dependent contact and can cause harm to their hosts. To test our hypothesis, we conducted a factorial experiment in natural populations by supplementing food to mimic a mast and by removal of intestinal nematodes with the drug, ivermectin. 3. Both food supplementation and the removal of intestinal nematodes lessened the rate and magnitude of the seasonal population declines as compared with control populations. However, the combination of food supplementation and removal of intestinal nematodes prevented seasonal population crashes entirely. 4. We also showed a direct effect on the condition of individuals. Faecal corticosterone levels, an indicator of the stress response, were signi±cantly reduced in populations receiving both food supplementation and removal of intestinal nematodes. This effect was observed in autumn, before the overwinter crash observed in control populations, which may indicate that stress caused by the combination of food limitation and parasite infection is a physiological signal that predicts low winter survival and reproduction. 5. This study is one of the few to demonstrate that the interaction between resource availability and infectious disease is important for shaping host population dynamics and emphasizes that multiple factors may drive oscillations in wild animal populations. Key-words: glucocorticoids, host–pathogen interactions, macroparasites, Quercus , resource pulses. Introduction Relatively few empirical studies have attempted to assess the role of infectious disease in natural populations. This is despite the fact that diseases often exhibit density-dependent transmission and have harmful effects on host ±tness (Anderson & May 1992). Theoretical models suggest that macroparasites can cause oscillations in abundance (Anderson & May 1979; Anderson 1980), and a manipulative ±eld experiment has strongly supported this hypothesis as an explanation for population cycles in red grouse Lagopus lagopus scoticus (L.) (Hudson, Dobson & Newborn 1998). It
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This note was uploaded on 09/22/2009 for the course ECOL 4150 taught by Professor Prin during the Spring '08 term at University of Georgia Athens.

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PedersenGreives2008 - Journal of Animal Ecology 2008, 77,...

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