A dynamic refuge model and population regulation by insect parasitoids

Abstract

1. The population dynamic effects of refuges, which hosts enter and leave by diffusive movement, in host–parasitoid interactions are explored using simple models in continuous time. 2. This type of refuge has a stabilizing effect on a host–parasitoid interaction, which is contrary to the implications of some previous models. 3. Stability can be explained by considering how depletion processes lead to a refuge proportion (proportion of hosts protected at a given instant) that increases as parasitoid density increases. This effect is synonymous with pseudointerference in the context of the model. 4. Very high rates of movement of host larvae largely destroy this stability process. Stability is greatest at intermediate levels of movement. 5. Density‐dependent host movement can alter the effect of these refuges such that they are either more stabilizing, or tend to destabilize, the dynamics of host–parasitoid systems, depending on the type of density dependence assumed. The conclusion that intermediate movement rates are likely to generate stability with this general type of refuge is not altered in the presence of any type of density dependence, unless the density dependence is at levels which we consider unrealistically high and unlikely to be encountered in nature. 6. It is the assumption that larvae do not move into the refuge prior to becoming vulnerable to parasitism that ensures top‐down population control in the model. Thus, parasitoids attacking very early instars make good candidates for biological control when faced with a structural refuge.