Fluctuation-Dependent Mechanisms

Fluctuation-dependent mechanisms are those that require fluctuations over time either in population densities or environmental factors for their operation.  In the study of species coexistence, the storage effect and nonlinear competitive variance are fluctuation-dependent mechanisms of species coexistence.  Naturally, these are to be contrasted with fluctuation-independent mechanisms.  This distinction was first presented in Chesson (1994), and discussed in more detail in Chesson (2000).  The related concepts to do with spatial variation are termed variation-dependent, and variation-independent mechanisms.  The old distinction between equilibrium and nonequilibrium, as discussed in Chesson and Case (1986), has become the modern distinction between fluctuation-dependent and fluctuation-independent mechanisms.  The reason for the change in terminology is discussed in Chesson (2000): equilibrium means different things to different people. In Chesson and Case (1986), the equilibrium was a point equilibrium, but some people point out that limit cycles and stationary probability distributions are in a certain sense equilibria too. So the terms were changed to contain common words with less labile meaning. 


Chesson, P.L., Case, T.J. 1986.  Nonequilibrium community theories: chance, variability, history, and coexistence. Pp 229-239 in J. Diamond and T. Case, eds, "Community Ecology," Harper and Row

Chesson, P. 2000. Mechanisms of maintenance of species diversity. Annual Review of Ecology and Systematics 31, 343-66.