The persistence of host-parasitoid associations in patchy environments. II. Evaluation of field data

Introduces a method for estimating the parameters of simple host-parasitoid models from field data relating percent parasitism to local host density per patch. By using these parameters, the coefficient of variation (CV²) of the density of searching parasitoids can be calculated. This quantity is important because a general criterion for heterogeneity to regulate discrete-generation host-parasitoid models is that CV² >1 (see 92L/04394). The method further allows one to partition CV² into a host-density-dependent component caused by nonzero covariance between the spatial distributions of the host and parasitoid (HDD), and a component that is independent of host density (HDI). The authors analyzed 34 sets of published data. Heterogeneity is sufficient to regulate the populations (CV² >1) in a third of the cases. In c90% of the cases in which CV² >1, the density-independent component of CV² is considerably more important for population regulation than the direct or inverse density-dependent components. -Authors