Interactive Effects of Sublethal Nematodes and Nutritional Status on Snowshoe Hare Vulnerability to Predation

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. We studied the effect of parasitism on snowshoe hare (Lepus americanus) survival through a field experiment that reduced natural burdens of sublethal nematodes in a free-ranging hare population. We treated half the hares on each of six study areas year-round with an anthelminthic drug, and the other half with a placebo. Potential interactive effects of parasitism and nutrition were examined by supplementing the natural food supply on three of the six study areas during two winters. Survival was measured by radio-collaring a total of 612 hares with mortality-sensitive transmitters and monitoring survival daily between April 1991 and June 1993. Overall, nematode burdens in hares were highest between March and October, andObeliscoides cuniculi was the most abundant of the five species present. The proximate cause of 95% of mortalities (n = 318) during the study was predation. Predators killed hares with heavy burdens of 0. cuniculi disporportionately during May-June, but burdens of the four other species (Nematodirus triangularis, Trichuris leporis, Dirofilaria scapiceps, Protostrongylus boughtoni) were similar between predator-killed hares and the live population. 3. During May-October 1991, the anthelminthic treatment did not affect hare survival, but during May-October 1992 survival of parasite-reduced hares was 2-4times higher than that of controls. During November 1991-April 1992 survival of food supplemented hares was 21% higher than food-normal animals, but survival was similar during November 1992-April 1993. 4. The effect of parasite-reduction on hare survival was apparently contingent on overwinter food supplies between November 1991 and April 1992, with survival being highest in hares subjected to both treatments, intermediate in those receiving only food supplementation, and lowest in unfed hares. We conclude that the effect of sublethal nematode parasitism on hare survival can be important if interactive with predation, and that synergistic effects of parasitism and nutrition may affect hares if food availability is limited.

Independent and Competing Disease Risks: Implications for Host Populations in Variable Environments

“…Since then, a number of laboratory studies (e.g., Anderson and Crombie 1984;Scott 1987) and one field study of gastrointestinal worm infections in grouse (Dobson and Hudson 1992;Hudson et al 1992b have shown that vertebrate populations can also be regulated by parasites, suggesting independent disease effects. On the other hand, several field studies have found interactions between disease and predation (Hudson et al 1992a;Murray et al 1997;Joly and Messier 2004a) or among diseases (Joly and Messier 2004b), indicating synergistic effects. Given the limited number of studies on disease effects in natural populations and their mixed results, it is still far from clear whether disease effects are typically independent, competing, or synergistic or whether such a generalization can legitimately be made at all.…”

Serological survey of virus infection among wild house mice (Mus domesticus) in the UK

“…However, these infections may cause significant population effects through alterations in fecundity (Hudson 1986, Feore et al 1997, vulnerability to predation (Hudson et al 1992, Murray et al 1997 or potentiation of other stressors such as poor nutritional status (Beck & Levander 2000). Several endemic diseases of wild rodents may affect reproducibility of results in behavioural, physiological or clinical research using laboratory rodents (Baker 1998), and a limited number pose a zoonotic risk to personnel, notably lymphocytic choriomeningitis virus (LCMV) (Rousseau et al 1997).…”

Beyond population regulation and limitation

“…Intrinsic processes operating through territorial behavior could thus result in predation being judged to be the regulating or limiting factor for this population. Parasites and diseases are often considered to be debilitating conditions that may expose individuals to a higher probability of mortality from starvation, predation, or exposure to bad weather (Murray et al 1997). These interactions between the factors listed in Fig.…”