PREDATOR-PREY CYCLES WITH PERIOD SHIFTS BETWEEN 2-SPECIES AND 3-SPECIES SYSTEMS

POPULATION ecology typically focuses on particular species or pairs of species within webs of interacting species to understand variations i n their abundance. Classical theory(1-3) predicts multigeneration cycl es in predator and prey abundance. These cycles have received consider able attention(3-6), although there is an alternative possibility, of prey generation-length cycles in predator-prey interactions(7-9). Does observation of either of these patterns depend on how firmly predator s and prey are embedded in their web of interactions? Concurrent inves tigations of predator-prey dynamics both in isolation and within a lar ger web have been lacking. Here we report observations of the populati on dynamics of a simple predator-prey system, and also of a three-spec ies system including predator and prey. The dynamic patterns exhibited by both systems are cyclic, but the increase from two to three specie s gives rise to a marked shift in cycle peroid from one to several hos t generation lengths.