Host-Parasitoid Food Webs: Dynamics, Persistence, and Invasion

Abstract

We study the population dynamics of a model host-parasitoid community containing two hosts that interact only through a shared generalist parasitoid. Each host is also attacked by a specialist parasitoid, making a community of up to five species of insects. Information from host-parasitoid community ecology is used in deciding how these species interact. By considering both community stability and whether absent species can invade, we predict which communities occur in different regions of parameter space. A crucial determinant of community structure is the relative searching efficiencies of specialists and generalists and the nature of the density-dependent reduction in parasitoid searching efficiency. In some areas of parameter space, there is no dynamically stable end point, and complex cycles occur where the food web structure is constantly changing, species being added through invasion and lost through direct and indirect competitive interactions. We also find that whether a species is able to invade can depend on the interaction between its dynamics and that of the resident species. We conclude that some communities of hosts and parasitoids may display complex dynamic behavior determined by both local population interactions and the frequency of species invasions.