Impact of noise on bistable ecological systems

The existence and implications of alternative stable states in ecological systems have been studied extensively within deterministic models. In this paper, we study the influence of random fluctuations in environmental parameters (e.g. nutrient input and rainfall) on the behavior of two simple bistable, ecological models with a single dynamical variable. We describe the changes in the bifurcation diagram of the bistable system: we find that the region of bistability is reduced for small amounts of noise while for noise beyond a critical width bistability vanishes completely. In the regime where bistability is eliminated by the noise, the time series of the solution shows that the system can undergo frequent catastrophic regime shifts. We also discuss how some of the results depend on model-specific details. We comment on the robustness of our results to changes in the noise characteristics and the implications for modeling real systems.