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Insect Ecology - An Ecosystem Approach 2nd ed - Chapter 8

SECTION III COMMUNITY ECOLOGY SPECIES CO-OCCURRING AT A SITE INTERACT TO VARIOUS degrees, both directly and indirectly, in ways that have intrigued ecologists since earliest times. These interactions represent mechanisms that control population dynamics, hence community structure, and also control rates of energy and matter fluxes. | SECTION III COMMUNITY ECOLOGY SPECIES CO-OCCURRING AT A SITE INTERACT TO VARIOUS degrees both directly and indirectly in ways that have intrigued ecologists since earliest times. These interactions represent mechanisms that control population dynamics hence community structure and also control rates of energy and matter fluxes hence ecosystem function. Some organisms engage in close direct interactions as consumers and their hosts whereas others interact more loosely and indirectly. For example predation on mimics depends on the presence of their models and herbivores are affected by their host s chemical or other responses to other herbivores. Direct interactions i.e. competition predation and symbioses have been the focus of research on factors controlling community structure and dynamics but indirect interactions also control community organization. Species interactions are the focus of Chapter 8. A community is composed of the plant animal and microbial species occupying a site. Some of these organisms are integral and characteristic components of the community and help define the community type whereas others occur by chance as a result of movement across a landscape or through a watershed. For example certain combinations of species e.g. ruderal competitive or stress-tolerant distinguish desert grassland or forest communities. Different species assemblages are found in turbulent water stream versus standing water lake or eutrophic versus oligotrophic systems. The number of species and their relative abundances define species diversity a community attribute that is the focus of a number of ecological issues. Chapter 9 addresses the various approaches to describing community structure and factors determining geographic patterns of community structure. Communities change through time as populations respond differently to changing environmental conditions especially to disturbances. Just as population dynamics reflect the net effects of individual natality .