The Coexistence of Competing Parasites. Part II-Hyperparasitism and Food Chain Dynamics.

Hyperparasitism is a widespread interaction in natural communities, but has to date received little attention in the theoretical literature. In this paper, we compared canonical models for food chains (resource-prey-predator systems) and host-parasite-hyperparasite interactions. We focus on microparasites, so the dynamical variables are the abundances of host individuals in different classes (e.g. with or without a particular parasite), and assume that the parasite is the only factor regulating a host population. Analysis of a "donor-controlled" model in which the primary parasite regulates host population growth, but with no additional demographic impact of the hyperparasite, suggests that intrinsic growth rate r of the host population is a fundamental parameter governing persistence of the hyperparasite. We then examine a model in which the hyperparasite can affect host births, deaths, and rate of recovery from the primary parasite. A wide range of outcomes are possible. For instance, hyperparasites can stabilize inherently unstable host-parasite systems, or destabilize stable systems. Persistence at a stable equilibrium often requires that the host intrinsic growth rate 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 conclude by sketching directions for future work, and suggesting some possible practical implications of our results.Copyright 1998 Academic Press