Dispersal-induced instabilities in host-parasitoid metapopulations

We present a general host-parasitoid metapopulation model and, using analyt ical techniques (supported by numerical simulations), investigate the effec ts of dispersal on the equilibrium stability of local populations. As has b een demonstrated previously, if the intrinsic dynamics of local populations are unstable, then passive dispersal cannot stabilise. Extreme asymmetry i n the dispersal fractions between the two species can, however, destabilise the metapopulation equilibrium state. Our key conclusion is that the preci se effects of dispersal on stability depend critically on the underlying ec ology 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 dispers al-induced instabilities. Indeed, if the stabilising effects are sufficient ly 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 li mitation) amplify the destabilising effects of dispersal. (C) 1999 Academic Press.