Stochastic Processes in Ecology

Chance events (such as lightning strikes or floods) occur commonly in nature. In ecology, random events that can affect population and community dynamics are called stochastic processes. Although ecologists recognize that stochastic processes occur, their importance in shaping populations and communities has been controversial. Determining when and how stochastic processes are important ecologically is critical for predicting extinction events or responses to climate change and explaining tropical biodiversity. Many population dynamics appears to be stochastic, particularly when the environment fluctuates or the population is small. For example, environmental variation that can reduce population size can increase the likelihood of stochastic extinction, because a small population is prone to go extinct due to random fluctuation in population size. Chance colonization and random order of immigration/emigration can influence the dynamics of populations and communities if early-arriving species outcompete later-arriving species. Stochastic processes can also create environmental fluctuations that favor species that could otherwise go extinct, if such fluctuations can allow for coexistence when species benefit from different environmental conditions. Modern ecologists generally agree that dynamics of populations and communities have both deterministic and stochastic components that operate simultaneously. The author wishes to thank Stacey Halpern for comments.