Patch exploitation strategies of parasitoids: The role of sex ratio and forager's interference in structuring metapopulations

We use a mathematical model to explore the effects of parasitoid reproductive strategies and foraging behavior in response to spatio-temporal variations in the patch quality of a host–parasitoid metapopulation system. The variations of patch quality over the landscape were measured by the presence of parasitoid competitors and the density of hosts. The parasitoid responses to patch quality are given by three different foraging behaviors: (i) the decision to remain in or leave the current patch; (ii) the control of progeny's sex ratio and (iii) competitive abilities, measured by changes in the potential to attack hosts due to interference from conspecifics in the exploited patch. We study the dynamics of host and parasitoid populations characterized by different levels of density-dependent sex ratio adjustment and interference competition. Our results show that population stability increases when parasitoid growth is correlated with patch conditions. The effect of sex ratio adjustment alone does not account for qualitative changes to system dynamics or to the distribution patterns of species. In contrast, the degree of competitive interference among the parasitoids plays a crucial role in constraining the parasitoids’ potential to reduce host populations and in determining the species’ distribution in the landscape. We found that high levels of interference competition disrupt the population dynamics within a patch and allows hosts to completely dominate the landscape. This study shows that the inclusion of life history traits and the co-evolutionary aspects of host–parasitoid interaction can help researchers to understand species distribution patterns in the landscape.