I. Short-Term Change in Community Structure
II. Successional Change in Community Structure
A. Patterns of Succession
B. Factors Affecting Succession
C. Models of Succession
IV. Diversity versus Stability
A. Components of Stability
B. Stability of Community Variables
COMMUNITY STRUCTURE CHANGES THROUGH TIME AS SPECIES abundances change, altering the network of interactions. Short-term (e.g., seasonal or annual) changes in community structure represent responses to environmental changes that favor some species or affect interaction strength (see Chapter 8). Longer-term (e.g., successional) changes in community structure often reflect relatively predictable trends during community development on newly available or disturbed sites. Finally, changes in community structure over evolutionary time reflect responses to long-term trends in environmental conditions.
Among the major environmental issues facing governments worldwide is the effect of anthropogenic activities (e.g., altered atmospheric or aquatic chemistry, land use, species redistribution) on the composition of natural communities and the ecosystem services they provide to humans. How might changes in community structure affect epidemiology of human diseases? How stable is community structure, and how sensitive are communities and ecosystems to changes in species composition? Our perception of communities as self-organizing entities or random assemblages has significant implications for our sensitivity to species loss and our approach to management of ecosystem resources.
As with population dynamics, study of changes in community structure requires long periods of observation. Few studies have continued over sufficiently long time periods to evaluate many of the factors presumed to affect community structure. However, paleoecological evidence and studies of community recovery following disturbance have provided useful data. Research on factors affecting community structure over a range of temporal scales can enhance understanding of the degree of stability in community structure and anticipation of responses to environmental changes.
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