PERSISTENCE OF A PARASITOID-HOST SYSTEM - REFUGES AND GENERATION CYCLES

The elaboration and quantification of the mechanisms lending stability and persistence to biological populations is perhaps the central issue in population ecology, both fundamentally and applied to important issues such as the maintenance of biodiversity, species conservation and the biocontrol of pests. Empirical support for mechanisms with the apparent potential to provide stability or persistence has hitherto been weak. Here, by contrast, long-term, replicated population data show that a demonstrable 'refuge' for prey (hosts) from parasitoid attack leads to the persistence of an otherwise unstable parasitoid-host interaction, as predicted by theory. However, the unequivocal demonstration of that refuge, and distinguishing it from a habitat with simply a lower parasitoid attack rate, is not straightforward, emphasizing the dangers of assuming the existence of a refuge too readily. The resultant parasitoid-host dynamics follow host generation length cycles, another prediction hitherto lacking convincing empirical support. Here, the support, while superficially strong, is misleading: host populations exhibit similar cycles even in the absence of parasitoids.