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The influence of prevailing environmental conditions on population and community responses to chronic toxicant perturbation was addressed in a 36-month laboratory ecosystem study. A series of 16 aquatic communities incorporating guppy, amphipod, snail, planaria, algal, and microbial populations were established in 750-L (200-gal) fiberglass tanks and were monitored monthly for changes in population biomasses. The environmental variables were the exploitation levels of the fish populations and the energy input and habitat availability. The development and resultant near steady states of the predator, prey, and competitor populations were presented graphically using phase plane analysis. Both the density-dependent and the time-dependent responses of the laboratory ecosystems to “established” sublethal dieldrin exposure varied according to the prevailing levels of environmental conditions. The ecologically different outcomes ranged from substantial perturbation, including mortalities but with eventual recovery to the preexposure population densities and community structure, to the extinction of a major population as a result of sublethal effects.
model ecosystem, microcosm, aquatic toxicology, ecological effects, community structure, predator-prey interactions, competition, dieldrin, hazard assessment
Aquatic biologist, Environmental Safety Department, Procter & Gamble Co., Ivorydale Technical Center, Cincinnati, OH