On models for assembling ecological communities

Previous numerical studies of community assembly have found (1) that invasion resistance increases with time, and (2) that different assembly sequences typically result in different community endpoints. The algorithm used in these studies involved sequential introductions of species coupled with tests for existence of feasible equilibria with local asymptotic stability. In this paper the algorithm is tested against a method based on numerical integration. We show that the algorithm contains serious technical flaws. The algorithm gives the incorrect outcome in many iterations, and correct assembly sequences diverge rapidly from those it predicts. In the light of this, we reassess the earlier work and suggest that results (1) and (2) above should be treated with caution. A more reliable method of community assembly is clearly needed. Numerical integration, although useful for investigating the outcome over small numbers of iterations, is too slow to deal with large, highly replicated, assembly sequences. We suggest that an alternative, based on a criterion of coexistence known as permanence, would be appropriate, as this is relatively fast and reliable.

Duke Scholars

Author Stuart L. Pimm Environmental Sciences and Policy