| Contents Notes |
A system of generalizations was formulated about the organization, development and persistence, adaptation, and productivity of ecological systems and their response to toxic substances. Laboratory ecosystems composed of persistent populations of guppies, amphipods, snails and various micro-invertebrates were used in examining the generalizations for their utility and conformity with field observation. Guppy populations in the ecosystems were exploited at different rates to simulate fishing, and the systems were provided with different levels of habitat availability and energy input rates. The laboratory communities developed different steady-state structures (population densities) at different guppy exploitation rates and different levels of habitat availability and energy input. One part per billion (ppb) of dieldrin was continuously introduced into four ecosystems, one at each guppy exploitation rate, at the low level of habitat availability and energy input. It was determined in ancillary experiments that 1 ppb of dieldrin probably directly affected only the guppy populations. As exploitation rates increased, guppies exhibited increased growth and reproduction. Dieldrin altered life history patterns by reducing survival, growth, and reproduction. Thus, the toxicant may have caused the extinction of the heavily exploited population by effectively preventing it from exhibiting the life history pattern that adapted it to persist at high exploitation rates. In aquarium experiments conducted in conjunction with the laboratory ecosystem studies, concentrations of dieldrin similar to those used in the laboratory ecosystems had effects on life history patterns similar to those observed in the ecosystems. It is less evident how the diversity of effects on guppy populations observed in the ecosystems; ranging from perturbation and recovery to extinction - could have been predicted from the aquarium experiments. |
