ABSTRACT
The impracticality of studying all species, or even all important species, in any community forces most ecologists to focus their studies on a taxonomic or functional subset of the community such as the fur bearers of a woodland or the zooplankton in a lake. The ecosystem concept incorporates the biotic community and abiotic environment into an organized unit. Toxicant-induced alterations of slightly more complex species interactions can impact ecological communities. Several community or species assemblage qualities are routinely measured to assess toxicant effect. The number of species inhabiting a contaminated site may be compared to the number found at a reference site. The most frequently used indices of community change are species richness, evenness, and diversity. Measures of community structure and function were then discussed relative to toxicant effects. Such changes were placed into the context of community successional regression, functional redundancy theory, and the law of frequencies.
