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. U sing a heliozoan protist predator, Actinosphaerium nucleofilum, and a cilia ted protozoan prey species, Tetrahymena pyriformis, we tested this predicti on in laboratory microcosms. We created subdivided microcosms, each consist ing of a 30-mL bottle containing predators and prey connected to a 30-mL bo ttle containing prey only. Prey dispersed freely through this connection, b ut predators did not disperse for hundreds of prey generations. The predato rs 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, character istic metapopulation features, enhanced persistence in the subdivided micro cosms. However, the details by which persistence was achieved closely resem ble source-sink dynamics, not classic metapopulation dynamics. Evidence sug gests that continuous prey immigration into predator-prey bottles from exti nction-invulnerable prey-only bottles may have weakened the coupling betwee n 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.