Abstract :
A general model of competition between several species in a variable environment is presented and analyzed using a general method that unifies treatment of different specific models. This method yields broad conclusions that are independent of the details of a model. It is used here to show that mechanisms of coexistence and competitive exclusion are largely restricted to three broad categories. One of these categories includes classical mechanisms that do not depend on fluctuations over time. Another category includes mechanisms which may be referred to collectively as the storage effect. These mechanisms involve species-specific responses to environmental fluctuations, a relationship between fluctuations in competition and fluctuations in the environment, and an interaction between environment and competition. The final category depends on fluctuating competition and nonlinear responses to competition that differ between species. These general results are illustrated with analyses of several specific models, including a Lotka-Volterra model, a model of nonlinear resource consumption, and models of recruitment fluctuations for iteroparous organisms and for annual plants.
