Cover title. "PB84-141183." "January 1984." "EPA/600-3-84-013." "Cooperative agreement CR80745702." Final report. Includes bibliographical references (pages 84-86). Photocopy.

Sixteen aquatic communities composed of persistent populations of guppies (Poecilia reticulata), amphipods (Gammarus fasciatus), snails (family Planorbidae), planaria (Dugesia sp.), and various microinvertebrates were established under laboratory conditions. Eight of these communities received low energy input with low habitat availability while the remaining eight communities had high habitat availability and received high energy input. At each level of input, guppy populations in two systems were exploited at either 0, 10, 20, or 40 percent of the population biomass each month. Macroinvertebrates were also sampled monthly for population counts and biomass measurements. After each system reached near steady-state conditions, 1 [mu]g/l of dieldrin was introduced into one system of each treatment. These systems were allowed to reach new steady-state conditions. The response of the systems was dependent upon both the energy input/habitat and exploitation levels. The low energy input/habitat systems were more sensitive to dieldrin particularly at higher levels of exploitation. The influence of organization and environment on population persistence and system structure are explored theoretically with isocline models and the implications for aquatic ecology and environmental management strategies are discussed.