In laboratory experiments on complex microbial communities, comprising both predators (protozoa) and prey (bacteria), we observed correlated fluctuations in abundances between isolated replicates. As the reactor dilution rate increased, we observed a decrease in synchrony in the fluctuation in prey density but in not predator density. Increasing the reactor dilution rate corresponds to increasing the rate of input of external resources, which one might naïvely assume would increase, rather than decrease, synchrony. The dilution rate is also, however, a bifurcation parameter for the system, and by extending the Moran effect to multi-species communities with nonlinear dynamics experiencing stochastic fluctuations about equilibrium, we can qualitatively predict this phenomenon using a minimal mathematical model that assumes only noise, predator-prey dynamics and Michaelis-Mentin kinetics.

This is joint work with Emma J. Bowen, Thomas P. Curtis, Joshua B. Plotkin, and Christopher Quince