Population synchrony induced by resource fluctuations and dispersal in an aquatic microcosm

Two of the principal explanations for regional population synchrony, largescale environmental variability and dispersal, have received considerable theoretical attention. Although time series analysis has helped to validate the relative importance of these two explanations, very little of this theory has been confirmed by experiment. Here, we demonstrate the dual synchronizing effect of dispersal and temporal environmental variation. We used an experimental model system based on the rotifer Brachionus calyciflorus and its algal prey Chlorella vulgaris. We constructed temporal prey fluctuations with two periodic components that matched the generation time and life span of the rotifer. By varying the amplitude of these two periods we created prey variability with "white" (both periods had equal power) and "red" (the longest period had greatest power) spectra. In the absence of dispersal only the red fluctuations induced synchrony in the population dynamics of the rotifer. Dispersal had a strong and rapid synchronizing effect. The combination of red (but not white) fluctuations and dispersal resulted in the highest levels of synchrony. These results confirm the predictions of recent theory, but they also suggest that the temporal structure of environmental variability determines its capacity to synchronize population dynamics over large spatial scales.