Dispersal-induced instabilities in host-parasitoid metapopulations.

We present a general host-parasitoid metapopulation model and, using analytical techniques (supported by numerical simulations), investigate the effects of dispersal on the equilibrium stability of local populations. As has been demonstrated previously, if the intrinsic dynamics of local populations are unstable, then passive dispersal cannot stabilise. Extreme asymmetry in the dispersal fractions between the two species can, however, destabilise the metapopulation equilibrium state. Our key conclusion is that the precise effects of dispersal on stability depend critically on the underlying ecology of the interaction within each population. The presence of regulatory mechanisms, be they in the form of density-dependent host reproduction or the presence of host refugia, decreases the likelihood of observing dispersal-induced instabilities. Indeed, if the stabilising effects are sufficiently strong, then dispersal cannot be destabilising, no matter how asymmetric the dispersal fractions are. On the other hand, positive feedbacks arising from threshold effects in host reproduction or inversely density-dependent patterns of parasitism (due to, for example, long handling times or egg limitation) amplify the destabilising effects of dispersal. Copyright 1999 Academic Press.