Effects of an asynchronous alien host on a native host-parasitoid system

We present a discrete-generation model to study the effect of a seasonally asynchronous alien host on the population dynamics of a native host/parasitoid system. We assume that i) the native host and parasitoid are seasonally synchronous; ii) there is no direct competition for resources between the two host species (one native, one alien); and iii) the introduced alien host population (the alternative host) is in an invasive stage and, consequently, it is not subject to any density-dependent regulation. In our model, variations in the annual number of generations (voltinism) of the alien host greatly alter the dynamics of the native host/parasitoid interaction. When the alien host is synchronous with the native host, the parasitoid is favoured, and the native host population decreases until reaching a new, lower equilibrium or becoming extinct. By contrast, when alien and native hosts are asynchronous with each other, there are population oscillations of the native community members compatible with the pulsating availability of the alien host and, under specific conditions, the parasitoid may rapidly become extinct.