Mechanisms of Succession in Natural Communities and Their Role in Community Stability and Organization

Abstract

The sequence of species observed after a relatively large space is opened up is a consequence of the following mechanisms. Opportunist species with broad dispersal powers and rapid growth to maturity usually arrive first and occupy empty space. These species cannot invade and grow in the presence of adults of their own or other species. Several alternative mechanisms may then determine which species replace these early occupants. Three models of such mechanisms have been proposed. The first facilitation model suggests that the entry and growth of the later species is dependent upon the earlier species preparing the ground; only after this can later species colonize. Evidence in support of this model applies mainly to certain primary successions and in heterotrophic succession. A second tolerance model suggests that a predictable sequence is produced by the existence of species that have evolved different strategies for exploiting resources. Later species will be those able to tolerate lower levels...