Diversity patterns from ecological models at dynamical equilibrium

Abstract

We study a dynamic model of ecosystems where immigration plays an essential role both in assembling the species community and in mantaining its biodiversity. This framework is particularly relevant for insular ecosystems. Population dynamics is represented either as an individual based model or as a set of deterministic equations for population abundances. Local extinctions and immigrations balance in a statistically stationary state where biodiversity fluctuates around a constant mean value. At stationarity, biodiversity increases as a power law of the immigration rate. Our model yields almost power law species area relationships, with a range of effective exponents in agreement with that observed for biodiversity of whole archipelagos. We also observe broad distributions for species abundances and species lifetimes and a small number of trophic levels, limited by the immigration rate. These results are rather robust with respect to change of description level, as well as change of population dynamic equations, from prey dependent to ratio dependent.