Empirical evidence for predator-prey source-sink dynamics

Theory suggests that a source-sink structure for a prey species can promote the persistence of an otherwise nonpersisting predator-prey interaction. Using a heliozoan protist predator, Actinosphaerium nucleofilum, and a ciliated protozoan prey species, Tetrahymena pyriformis, we tested this prediction in laboratory microcosms. We created subdivided microcosms, each consisting of a 30-mL bottle containing predators and prey connected to a 30-mL bottle containing prey only. Prey dispersed freely through this connection, but predators did not disperse for hundreds of prey generations. The predators and prey in the subdivided microcosms persisted for over three times as long as they did in undivided 30-mL and 60-mL bottles. Our results suggest that prey rescue effects and spatial asynchrony in prey dynamics, characteristic metapopulation features, enhanced persistence in the subdivided microcosms. However, the details by which persistence was achieved closely resemble source-sink dynamics, not classic metapopulation dynamics. Evidence suggests that continuous prey immigration into predator-prey bottles from extinction-invulnerable prey-only bottles may have weakened the coupling between predator and prey dynamics and contributed to the increase in persistence. In showing that source-sink dynamics enhanced predator-prey persistence, our experiments support conclusions of metapopulation theory that point to the importance of immigration between spatially discrete populations.