HOST-PARASITOID METAPOPULATIONS - THE CONSEQUENCES OF PARASITOID AGGREGATION ON SPATIAL DYNAMICS AND SEARCHING EFFICIENCY

Recent studies of host-parasitoid metapopulations have shown how uniform dispersal, from a patch to its neighbouring patches, can result in the persistence of an otherwise non-persistent interaction. Here these models are extended to include density-dependent parasitoid aggregation. The fraction of dispersing hosts colonize the neighbouring patches equally, whereas parasitoid dispersal is related to the relative density of healthy hosts in each surrounding patch. Interestingly, this shows that the degree of parasitoid aggregation is associated with the self-organization of spatial structures and, in particular, spiral waves. Regions where spirals are most pronounced correspond to minimal variance in population densities. It is demonstrated, however, that parasitoid searching efficiency is highest (and mean host densities lowest) for levels of aggregation where the spatial dynamics consist of an even mixture of spirals and disordered patterns. Using an algorithmic complexity measure, it is verified that spatial transitions are also reflected in the temporal dynamics. Finally, it is demonstrated that multiple episodes of parasitoid dispersal, within a host generation, can inhibit persistence, particularly for large parasitoid movement rates.