Time to competitive exclusion

A predictive theory of population extinction for natural populations requires integrating the effects of stochasticity with the interactions engaged in with populations of other species. The theory of competitive exclusion predicts that inferior competitors for a limiting resource will be driven to extinction, but the effects of resource competition on time to extinction have not been examined. We studied a stochastic version of Tilman's resource competition model to examine two species competition-driven extinction. Simulations showed that competitive imbalance, population size and demographic rates of the inferior'' competitor were the most important determinants of mean extinction time, while factors including resource supply and nutrient uptake had negligible influence. However, when competitors were more evenly matched and had small initial population sizes the superior'' competitor often went extinct. In these cases the distribution of extinction times shifted from the familiar exponential tail towards a heavy-tailed distribution with characteristically longer extinction times that may be indicative of the transition between exclusion and coexistence. These results provide new insight into the quantitative effects of competition and demographic stochasticity on extinction risk. Further work is needed to understand how extinction of superior competitors affects coexistence and extinction in natural communities.