Animals 'on the move' stabilize host-parasitoid systems

In host-parasitoid systems occurring in a patchy environment, travelling between breeding sites can result in spatial heterogeneity in the birth and death rates of individuals either because the environment is heterogeneous or because individuals do not distribute evenly in space. A second effect of dispersal is that at any one time, a fraction of the individuals of a population is in transit between breeding sites. While population models have focused on the first effect of dispersal to analyse the consequences of spatial heterogeneity for population dynamics, we develop models to investigate the effects of dispersal per se, i.e. the absence of individuals from breeding sites, on stability in host-parasitoid systems. We show that the existence of a 'pool' of dispersing hosts and/or parasitoids can stabilize otherwise unstable population models.