The interaction of parasites and resources cause crashes in a wild mouse population

Abstract

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 significantly 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.

Food provisioning alters infection dynamics in populations of a wild rodent

“…Nevertheless, voles in food supplemented populations generally displayed better body condition than voles in non-supplemented populations prior to B. bronchiseptica introduction. This indicates that the ability to mount an immune response against infection may be enhanced by the availability of resources, in line with research that has demonstrated higher disease associated mortality in resource-limited populations [7,47]. We found that although non-specific inflammatory cell recruitment occurred following the introduction of B. bronchiseptica (increase in neutrophils and decrease in lymphocytes); its magnitude was not influenced by resource levels.…”

“…A small but growing body of research has identified more subtle effects of pathogens on host reproduction and survival [3][4][5][6]. However, experimental evidence for pathogen-induced population limitation in natural settings is rare (but see [3,7]). …”

The relationship between physiological stress and wildlife disease: consequences for health and conservation

“…For example, Owen et al (2012) found that experimentally elevated plasma corticosterone can reduce the survival of northern cardinals (Cardinalis cardinalis) infected with West Nile virus (Owen et al 2012). Similarly, Pedersen and Greives (2008) demonstrated experimentally that stress, parasitism and malnutrition drive winter population crashes in white-footed mice (Peromyscus leucopus). In addition, improving our understanding of the relationship between stress and the incidence, prevalence, intensity, recrudescence and severity of disease in wildlife could benefit biodiversity conservation and One Health (Zinsstag et al 2011).…”

“…The bi-directional relationship between stress and infection poses a challenge to establishing causality in observation studies. Experimental approaches can be used to investigate causality and the multi-dimensional nature of the stress-disease relationship, including experimental stressors (Oppliger et al 1998), experimental infections (Warne et al 2011;Kindermann et al 2012;Marino et al 2014) and parasite treatment experiments (Goldstein et al 2005;Raouf et al 2006;Pedersen and Greives 2008;Monello et al 2010). However, experimental approaches have numerous logistical and ethical challenges, particularly when working with small populations of free-ranging endangered species.…”

Fecal antibody levels as a noninvasive method for measuring immunity to gastrointestinal nematodes in ecological studies

“…2002; Cattadori et al. 2005; Pedersen and Greives 2008). Among‐individual differences in the prevalence and burden of such parasites are therefore likely to have important downstream consequences for life‐history traits and fitness.…”