The question of how biodiversity affects the stability of population and community properties has long interested ecologists. While early conceptual ideas emphasized positive effects of biodiversity on stability, later theoretical work indicates that increasing biodiversity tends to promote stability at the community level but reduce stability at the population level. Accumulating empirical evidence generally supports positive relationships between biodiversity and community stability, but few studies have reported findings supporting negative relationships between biodiversity and population stability. Notably, most empirical studies that reported positive or neutral effects of biodiversity on population stability were conducted in systems with more than one trophic level. We thus suggest that increasing biodiversity may promote population and community stability in multi-trophic systems, possibly via the weak interaction effect (McCann et al. 1998). We tested this hypothesis with an aquatic protist microcosm experiment, which used a two-way factorial design with the presence/absence of a predatory ciliate (Lacrymaria sp.) and prey species richness (1, 2, or 3 species from a pool of three bacterivorous ciliate species: Colpidium striatum, Halteria sp., and Tetrahymena pyriformis) as the two factors.

Results/Conclusions

The strength of the interaction of the three prey species with the predator differed, as indicated by their similar population dynamics in the absence of predators and substantially different dynamics in the presence of predators. Predation affected the relationships between prey diversity and population temporal stability; in particular, the diversity-stability relationship for Tetrahymena was negative in the absence of predators and positive in the presence of predators. Temporal stability of total prey biomass increased with prey diversity in the presence of predators, but was unaffected by prey diversity in the absence of predators. These results indicate that predators have the potential to alter relationships between biodiversity and stability at both population and community levels.