Succession in Particular

Most ecologists would now regard succession as a community or local ecosystem process, and consider the general processes to include auto-genic mechanisms constrained or mediated by allogenic environmental contexts. They would agree that organisms occurring in early stages are generally unsuited for the later stages of development (for various reasons specific to the different organisms involved), that much depends on availability of colonists, that organizational complexity of local systems increases during succession, and that systems left undisturbed for long periods of time usually come to be dominated by one or a few supercompeti-tors. At least small-scale disturbance is needed to open space or relinquish resources to less successful competitors and thereby bolster diversity. This means that the most diverse ecosystems are those experiencing intermediate levels of disturbance or small-scale disruptions, allowing coexistence of many species.

There are two modern ways of thinking about true succession. Ecosystem ecologists tend to see it as involving an orderly process of development of the trophic (food) relationships from simple pathways to more complicated weblike interactions, change from rapid to slow flow rates of nutrients, and increase in homeostasis (self-regulated stability) over time. The maturation of systems appears to be mostly a manifestation of the thermodynamic properties of interacting population systems. Systems are predicted to self-organize to increase efficiency of energy and chemical transfers, build up pools of biomass and nutrients, and reduce entropy. This model stresses deterministic themes. By comparison, population ecologists are inclined to see succession as an organism-by-organism replacement process. Some outcomes are more likely than others, depending on several variables: potential for recruitment from adjacent patches; properties of component populations, including tradeoffs between reproductive biology, growth rates, competitive abilities, and methods of resource capture and utilization; and the importance of chance events like spatial patterning of disruptions, the timing of those disruptions, and previous conditions in the ecosystem. The population approach is strongly influenced by probabilistic consider ations. In both approaches, communities or local ecosystems are now seen as successional mosaics, often consisting of neighboring patches at different stages of recovery at the same time.

—William Miller III

See also: Benthos; Climatology; Coevolution; Communities; Conservation Biology; Ecological Niches; Ecology; Ecosystems; Evolution; Extinction, Direct Causes of; Food Webs and Food Pyramids; Geological Time Scale; Global Climate Change; Habitat Tracking; Mass Extinction; Paleontology; Positive Interactions

Bibliography

Connell, Joseph H. 1978. "Diversity in Tropical Rain Forests and Coral Reefs." Science 199:1302-1310; Connell, Joseph H., and Ralph O. Slatyer. 1977. "Mechanisms of Succession in Natural Communities and Their Role in Community Stability and Organization." American Naturalist 111:1119-1144; Horn, Henry S. 1975. "Forest Succession." Scientific American 232, no. 5:90-98; Miller, William, III. 1991. "Hierarchical Concept of Reef Development." Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 182:21-35; Miller, William, III. 1996. "Ecology of Coordinated Stasis." Palaeogeography, Palaeoclimatol-ogy, Palaeoecology 127:177-190; Odum, Eugene P. 1969. "The Strategy of Ecosystem Development." Science 164:262-270; Pickett, S. T. A., and P. S. White. 1985. The Ecology of Natural Disturbance and Patch Dynamics. Orlando, FL: Academic; Rees, Mark, et al. 2001. "Long-term Studies of Vegetation Dynamics." Science 293:650-655.

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