Fluctuation-independent mechanisms are
those that function independently of the presence of fluctuations over
time in population
densities and environmental factors. They may be affected by the
presence of fluctuations, but do not require them for their operation,
and in general still function in the presence of fluctuations. A
classic example is resource partitioning (Chesson 1991). When the
population dynamics with resource partitioning are modeled according
the Lotka-Volterra competition model, then presence of fluctuations
over time in terms of a disturbance to the population per capita growth
rate, has no effect what so ever on species coexistence (Chesson 1994).
Naturally, fluctuation-independent mechanisms are to be contrasted with
mechanisms. This distinction was first presented in Chesson
(1994), and discussed in more detail in Chesson (2000). Note that
both fluctuation-dependent and fluctuation-independent mechanisms may
well operate together in a given ecological system (Chesson 1994,
related concepts to do with spatial variation are termed
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
1990. MacArthur's consumer-resource model.
Theoret. Pop. Biol., 37, 26-38.
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.