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.

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.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.

1979. Reproductivechangein the 10-yearcycleofsnowshoe hares.Can. J. Zool. 57: 375-390.Rep~*dcxluctian was monirored during : r. 16-year qtudy uf s n o w h w hure (Lrprrs urneriunt~tts~ popu1;ltions near Rochester. Alberta. Pregnancv race. ovularion rate. and litter size changed markedly between succebsive lirtes w i t h~n the breeding ceason; t h e~e pa~xrneters were thus funher categurized by litter i n our an;llyfes. Mtlsr reproduc~ive c o m p n r n t s varied significantly between yearc: a signihcanl ' 10-year' periodiciry w a h rhe dominim! wurce of this varkation. The cyclic flucitlations of reprorluctivt: parametem were broadly synchronous and tended to precede Ihe popufation cycle hv ahuut 3 ye:irs. thereby prwlucinga range i n pnten~ial narality annualty of 7.5 to 17.9 young per Female. The year-to-year v;rri,lhilit y of pregnancy rate, OVU~~IIIO~ rate. and litter ~i z e wa$ rni~rkedly larger in the larer Ittters than In the early ones. Paunched weight. mean age. incidence of enJopa~.ac~tcs. liver and spteen weights, and mi~lwinter-to-

No abstract

No abstract

No abstract

No abstract

We evaluated the hypothesis that the effects of parasitism on animal body condition are accentuated when host nutritional status is compromised. In a field experiment we manipulated natural burdens of five nematode species via anthelmintic treatment in onehalf the free-ranging snowshoe hares (Lepus americanus) on each of six study areas and supplemented overwinter food level on three areas, to assess whether treatments interacted synergistically. We predicted that the effects of parasitism would be aggravated in malnourished hares (i.e., hares not administered supplemental food), and that animals receiving both treatments would have (1) lower parasite burdens, and (2) higher body mass, fat storage, and reproduction, than those receiving only one or no treatments. Mean numbers of Trichuris leporis were lower in hares subjected to food supplementation, suggesting that nutritional status affected immunity to that species. Obeliscoides cuniculi, Nematodirus triangularis, Dirofilaria scapiceps, and Protostrongylus boughtoni numbers were not directly affected by supplementation. Body mass of parasite-normal controls (i.e., not administered the anthelmintic treatment) was negatively correlated to nematode abundance during May-June, implying that parasitism had a deleterious effect on hare mass at that time. However, the anthelmintic treatment failed to directly affect hare body mass, fat storage, or reproduction. Food supplementation had a positive effect on body mass, fat storage, and reproduction, although effects of food were neither strong nor consistent among study areas and body condition parameters being measured. Only 2 of 22 analyses of hare production yielded marginally significant (i.e., 0.05 Ͻ P Ͻ 0.10) interactions between food and parasitism; therefore, we concluded that the two factors were not strongly linked. However, because our snowshoe hare population was at low densities and likely exposed to neither severe food shortage nor high rates of nematode parasitism, failure to detect an interaction between treatments may not comprise a general refutation of the hypothesis. Rather, hare populations subject to more serious food limitation (i.e., during a cyclic peak in numbers) may be apt to display stronger interactions between nutrition and parasitism.