Abstract
Parasites have been shown to reduce host density and to induce host population extinction in some cases but not in others. Epidemiological models suggest that variable effects of parasites on individual hosts can explain this variability on the population level. Here, we aim to support this hypothesis with a specific epidemiological model using a cross-parasite species approach. We compared the effect of six parasites on host fecundity and survival to their effects on density and risk of extinction of clonal host populations. We contrast our empirical results of population density with predictions from a deterministic model and contrast our empirical results of host and parasite extinction rates with those predicted by a stochastic model. Five horizontally transmitted microparasites (two bacteria: white bacterial disease, Pasteuria ramosa; two microsporidia: Glugoides intestinalis, Ordospora colligata; one fungus: Metschnikowiella biscuspidata); and six strains of a vertically transmitted microsporidium (Flabelliforma magnivora) of the planktonic crustacean Daphnia magna were used. In life table experiments, we quantified fecundity and survival in individual parasitized and healthy hosts and compared these with the effect of the parasites on host population density and on the likelihood of host population extinction in microcosm populations. Parasite species varied strongly in their effects on host fecundity, host survival, host density reduction, and the frequency with which they drove host populations to extinction. The fewer offspring an infected host produced, the lower the density of an infected host population. This effect on host density was relatively stronger for the vertically transmitted parasite strains than for the horizontally transmitted parasites. As predicted by the stochastic simulations, strong effects of a parasite on individual host survival and fecundity increased the risk of host population extinction. The same was true for parasite extinctions. Our results have implications for the use of microparasites in biological control programs and for the role parasites play in driving small populations to extinction.
Highlights
Parasites have been shown to reduce host density and to induce host population extinction in some cases but not in others
Mathematical models predict different population dynamics for hosts infected with microparasites that reduce host fecundity versus parasites that reduce host survival (Anderson 1979, 1982)
We used five species of horizontally transmitted microparasites that varied in their effects on their host, the planktonic crustacean Daphnia magna, to test whether the predicted relationship between individual effects and population effects hold across parasites
Summary
Abstract: Parasites have been shown to reduce host density and to induce host population extinction in some cases but not in others. Parasite species varied strongly in their effects on host fecundity, host survival, host density reduction, and Keywords: experimental epidemiology, microparasites, Daphnia magna, host regulation, host extinction, individual and population level effects. The aim of this study was to test whether the extent to which a parasite reduces the fecundity and survival of individual infected hosts can be used to predict the ability of a parasite to regulate its host population. When host populations are small, density fluctuations are expected to increase the chance of host extinction because host density is more likely to drop to 0 during population bottlenecks (May 1974; McCallum and Dobson 1995) Epidemiological models, such as those cited above, are often used to explain empirical results where parasites reduce the density or lead to the extinction of their host populations. We used five species of horizontally transmitted microparasites that varied in their effects on their host, the planktonic crustacean Daphnia magna, to test whether the predicted relationship between individual effects and population effects hold across parasites
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
