Environmental fluctuations and predation modulate community dynamics and diversity

Abstract

Predation, environmental fluctuations, and immigration are commonly expected to affect community dynamics and diversity. However, interactions between these factors are largely unknown. A further complication is that rapid evolution of species interactions potentially alters ecological community dynamics. The role of environmental fluctuations in ecological dynamics of competitive communities was explored in a simulation study. We explored how the patterns of species diversity are affected by the frequency spectrum of stochastic environmental variations and density independent immigration rates in a competition model. Next, three microcosm experiments were conducted where heterotrophic aquatic bacteria were exposed to different resource fluctuation regimes and / or a protozoan predator Tetrahymena thermophila. Both the simulation study and the experiments revealed that fluctuating environments can promote diversity. Furthermore, diversity patterns produced by fluctuations are altered by immigration and predation. These results suggest that the environmental fluctuations and predation jointly affect community dynamics and diversity. In experiments with predation, the bacteria evolved to resist predation better. These changes altered the ecological properties of the predator-prey interaction. For example, an increase in prey grazing resistance may explain the observed strong decrease in predator densities during experiments. Thus, the ecological consequences of predator-induced rapid evolution need more attention.