The influence of local mate competition on host–parasitoid dynamics

The influence of local mate competition on the dynamics of host–parasitoid systems was investigated with three models in which parasitoid sex ratios change according to the predictions of local mate competition and differ in their host and parasitoid distributions. In the first model, local parasitoid density is uniform across host patches and the density of patches (number of patches per unit area) is constant. In the second, local parasitoid density is uniform across patches and the density of patches is a function of host density. The third model assumes that local parasitoid density is heterogeneous across patches and that the density of patches is constant. Despite their differences, the three models show a limited stabilizing influence of local mate competition. This result differs from those of previous models (J. Anim. Ecol. 52 (1983)) that consider density dependent changes in sex ratio but allow for male-biased sex ratios beyond the predictions of local mate competition. Those models are more stable than the models presented here. This difference shows the importance of including realistic descriptions of changes in life history traits when analyzing the influence of these changes on population dynamics. The differences in results also suggest that factors leading to a further decrease in the number of females emerging from a parasitized host (such as differential mortality and parasitoid larval scramble competition) may have an important stabilizing role on host–parasitoid systems.