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 issu e in population ecology, both fundamentally and applied to important i ssues such as the maintenance of biodiversity, species conservation an d the biocontrol of pests. Empirical support for mechanisms with the a pparent potential to provide stability or persistence has hitherto bee n weak. Here, by contrast, long-term, replicated population data show that a demonstrable 'refuge' for prey (hosts) from parasitoid attack l eads to the persistence of an otherwise unstable parasitoid-host inter action, as predicted by theory. However, the unequivocal demonstration of that refuge, and distinguishing it from a habitat with simply a lo wer parasitoid attack rate, is not straightforward, emphasizing the da ngers of assuming the existence of a refuge too readily. The resultant parasitoid-host dynamics follow host generation length cycles, anothe r prediction hitherto lacking convincing empirical support. Here, the support, while superficially strong, is misleading: host populations e xhibit similar cycles even in the absence of parasitoids.