Linking the coevolutionary and population dynamics of host-parasitoid interactions

The interplay between coevolutionary and population or community dynamics i s currently the focus of much empirical and theoretical consideration. Here , we develop a simulation model to study the coevolutionary and population dynamics of a hypothetical host-parasitoid interaction. In the model, host resistance and parasitoid virulence are allowed to coevolve. We investigate how trade-offs associated with these traits modify the system's coevolutio nary and population dynamics. The most important influence on these dynamic s comes from the incorporation of density-dependent costs of resistance abi lity. We find three main outcomes. First, if the costs of resistance are hi gh, then one or both of the players go extinct. Second, when the costs of r esistance are intermediate to low, cycling population and coevolutionary dy namics are found, with slower evolutionary changes observed when the costs of virulence are also low. Third, when the costs associated with resistance and virulence are both high, the hosts trade-off resistance against fecund ity and invest little in resistance. However, the parasitoids continue to i nvest in virulence, leading to stable host and parasitoid population sizes. These results support the hypothesis that costs associated with resistance and virulence will maintain the heritable variation in these traits found in natural populations and that the nature of these trade-offs will greatly influence the population dynamics of the interacting species.