Coexistence theory

Coexistence theory is a framework to understand how competitor traits can maintain species diversity and stave-off competitive exclusion even among similar species living in ecologically similar environments. Coexistence theory explains the stable coexistence of species as an interaction between two opposing forces: fitness differences between species, which should drive the best-adapted species to exclude others within a particular ecological niche, and stabilizing mechanisms, which maintains diversity via niche differentiation. For many species to be stabilized in a community, population growth must be negative density-dependent, i.e. all participating species have a tendency to increase in density as their populations decline. In such communities, any species that becomes rare will experience positive growth, pushing its population to recover and making local extinction unlikely. As the population of one species declines, individuals of that species tend to compete predominantly with individuals of other species. Thus, the tendency of a population to recover as it declines in density reflects reduced interspecific competition (between-species) relative to intraspecific competition (within-species), the signature of niche differentiation (see Lotka-Volterra competition). Coexistence theory is a framework to understand how competitor traits can maintain species diversity and stave-off competitive exclusion even among similar species living in ecologically similar environments. Coexistence theory explains the stable coexistence of species as an interaction between two opposing forces: fitness differences between species, which should drive the best-adapted species to exclude others within a particular ecological niche, and stabilizing mechanisms, which maintains diversity via niche differentiation. For many species to be stabilized in a community, population growth must be negative density-dependent, i.e. all participating species have a tendency to increase in density as their populations decline. In such communities, any species that becomes rare will experience positive growth, pushing its population to recover and making local extinction unlikely. As the population of one species declines, individuals of that species tend to compete predominantly with individuals of other species. Thus, the tendency of a population to recover as it declines in density reflects reduced interspecific competition (between-species) relative to intraspecific competition (within-species), the signature of niche differentiation (see Lotka-Volterra competition). Two qualitatively different processes can help species to coexist: a reduction in average fitness between species or an increase in niche differentiation between species. These two factors have been termed equalizing and stabilizing mechanisms, respectively. A general way of measuring the effect of stabilizing mechanisms is by calculating the growth rate of species i in a community as r i ^ = b i ( k i − k ^ + A ) {displaystyle {hat {r_{i}}}=b_{i}(k_{i}-{hat {k}}+A)}