THE PERSISTENCE OF HOST-PARASITOID ASSOCIATIONS IN PATCHY ENVIRONMENTS .1. A GENERAL CRITERION

In this article we show that, for host-parasitoid interactions in a heterogeneous environment and with discrete generations, the dynamic effects of any patterns of distribution of searching parasitoids can be assessed within a common, simple framework. The populations are regulated if the distribution of searching parasitoids is sufficiently heterogeneous. Specifically, the square of the coefficient of variation (CV2) of the searching parasitoids per host must exceed unity. This criterion is demonstrated to apply approximately, in general and also in several specific cases. We further show that CV2 may be partitioned into a density-dependent component caused by the response of parasitoids to host density per patch and a density-independent component. Population regulation is enhanced as much by density-independent as by density-dependent heterogeneity.