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General ecological principles have been used to hypothesize community stress responses. A review of responses of microcosms, mesocosms, and ecosystems to chemical stressors indicated that changes in taxonomic and standing crop measures of community structure were usually reliable and sensitive indicators of stress responses. Changes in process rates showed less frequent response to chemical stressors. Ecosystem experiments have not demonstrated some predicted changes even at extreme levels of stress. Problems in demonstrating community and ecosystem responses may be a result of present methodologies or may identify failures of ecologists to accurately predict stress effects. Many ecosystem processes are substrate limited and robust even under severe stress. Although additional information is needed on the natural variability of measures of both structure and process, stress measures based on the composition of biological communities seem to have the greatest promise for evaluating ecosystem conditions.
stress, community, ecological effects, microcosm, mesocosm, aquatic toxicology
Assistant Professor of Aquatic Ecology, School of Forest Resources, The Pennsylvania State University, University Park, PA