Heterogeneity in host-parasitoid interactions: 'Aggregation of risk' and the 'CV(2) > 1 Rule'.

In host-parasitoid interactions the coefficient of variation (CV) of the risk of parasitism measures, at least approximately, the stabilizing influence of many forms of heterogeneity. This realization emphasizes the underlying similarity of these heterogeneities, and should end two decades of confusion about how to study them in nature. The first applications of this approach suggest that roughly one-third of systems studied show substantial measurable heterogeneity. Proper use of the CV measure, however, requires that the density-dependent processes linking this static phenomenon to temporal population dynamics also be examined; this has yet to be done for any system.