Sorbonne Université, Université Paris Diderot, Université Paris-Est Créteil, CNRS, INRA, IRD, Institute of Ecology and Environmental Science - Paris (iEES-Paris), Campus Pierre et Marie Curie, 4 place Jussieu, Paris 75005, France.
J Theor Biol. 2018 Dec 7;458:68-77. doi: 10.1016/j.jtbi.2018.09.004. Epub 2018 Sep 7.
Parasites are important components of food webs. Although their direct effects on hosts are well-studied, indirect impacts on trophic networks, thus on non-host species, remain unclear. In this study, we investigate the consequences of parasitism on coexistence and stability within a simple trophic module: one predator consuming two prey species in competition. We test how such effects depend on the infected species (prey or predator). We account for two effects of parasitism: the virulence effect (parasites affect the infected species intrinsic growth rate through direct effects on fecundity or mortality) and the interaction effect (increased vulnerability of infected prey or increased food intake of infected predators). Results show that coexistence is favored when effects have intermediate intensity. We link this result to modifications of direct and apparent competitions among prey species. Given a prey infection, accounting for susceptible-infected population structure highlights that coexistence may also be reduced due to predator-parasite competition. Parasites affect stability by modulating energy transfer from prey to predator. Predator infection therefore has a stabilizing effect due to increased energy fluxes and/or predator mortality. Our results suggest that parasites potentially increase species coexistence. Precise predictions however require an assessment of various parasite effects. We discuss the implications of our results for the functioning of trophic networks.
寄生虫是食物网的重要组成部分。虽然它们对宿主的直接影响已经得到了充分研究，但它们对营养网络的间接影响，从而对非宿主物种的影响仍不清楚。在这项研究中，我们研究了寄生对简单营养模块内共存和稳定性的影响：一种捕食者消耗两种竞争的猎物物种。我们测试了这些影响如何取决于受感染的物种（猎物或捕食者）。我们考虑了寄生的两种效应：毒力效应（寄生虫通过对繁殖力或死亡率的直接影响来影响感染物种的内在增长率）和相互作用效应（增加受感染猎物的脆弱性或增加受感染捕食者的食物摄入量）。结果表明，当影响强度处于中等水平时，共存更有利。我们将这一结果与猎物物种之间直接和明显竞争的变化联系起来。考虑到猎物感染，易感-感染种群结构表明，由于捕食者-寄生虫竞争，共存也可能减少。寄生虫通过调节从猎物到捕食者的能量转移来影响稳定性。因此，由于能量通量增加和/或捕食者死亡率增加，捕食者感染具有稳定作用。我们的结果表明，寄生虫可能会增加物种共存。然而，准确的预测需要评估各种寄生虫的影响。我们讨论了我们的研究结果对营养网络功能的影响。
