Density Dependence in Host-Parasitoid Models
SUMMARY (1) Insect populations frequently suffer some density dependent effect in addition to mortality from insect parasitoids. This paper follows Wang & Gutierrez (1981) in examining the question: 'Does the ordering of density dependence and parasitism in the host life cycle have a significant effect on the dynamics of the interaction?' (2) The properties of three models in which density dependence either acts before or after parasitism are displayed in terms of the hosts' rate of increase and the extent to which parasitism depresses the host equilibrium below its carrying capacity. (3) From this analysis, we conclude that the sequence of these events in the host life cycle can indeed have a marked affect on the population dynamics. In particular, the model with parasitism acting before density dependence stands apart in permitting a stable host-parasitoid interaction with the host population above its parasite-free carrying capacity. (4) These conclusions have implications for the use of parasitoids as biological control agents.