THE COEXISTENCE OF COMPETING PARASITES - PART II - HYPERPARASITISM AND FOOD-CHAIN DYNAMICS

Hyperparasitism is a widespread interaction in natural communities, bu t has to date received little attention in the theoretical literature. In this paper, we compare canonical models for food chains (resource- prey-predator systems) and host-parasite-hyperparasite interactions. W e focus on microparasites, so the dynamical variables are the abundanc es of host individuals in different classes (e.g. with or without a pa rticular parasite), and assume that the parasite is the only factor re gulating a host population. Analysis of a ''donor-controlled'' model i n which the primary parasite regulates host population growth, but wit h no additional demographic impact of the hyperparasite, suggests that intrinsic growth rate r of the host population is a fundamental param eter governing persistence of the hyperparasite. We then examine a mod el in which the hyperparasite can affect host births, deaths, and rate of recovery from the primary parasite. A wide range of outcomes are p ossible. For instance, hyperparasites can stabilize inherently unstabl e host-parasite systems, or destabilize stable systems. Persistence at a stable equilibrium often requires that the host intrinsic growth ra te r lie within defined bounds; at low r, the hyperparasite may not be able to persist (in stable systems), whereas at high r the system is unstable and the host population grows in an unbounded fashion. We con clude by sketching directions for future work, and suggesting some pos sible practical implications of our results. (C) 1998 Academic Press.