An Experimental Approach to the Production Dynamics and Structure of Freshwater Animal Communities1

The effects of three levels of inorganic nutrients and two predator densities on aquatic animal communities were examined in a series of twenty 0.07‐ha freshwater ponds. The treatments were cross‐classified in a randomized block design and continued over 3 years. Analyses of the responses include community composition, secondary production, and demographic description of the dominant species of both zooplankton and benthos. The fish populations and their feeding behavior are described in detail. Ancillary data on water chemistry and primary production were available. Nutrients generally increased production of the zooplankton but had little effect on community composition. Fish predation had profound effects on the diversity and size distribution of the zooplankton but only affected production at lower nutrient levels. The benthos responded markedly to nutrients during the first year, but this was not apparent the second and third years. The response of the benthos to both nutrients and predation was best shown by changes in the distribution of body size. Both zooplankton and benthic communities showed complementary responses between large‐ and small‐bodied organisms. Differences in the physical structure of the environment (i.e., macrophytes) also produced significant changes in production and composition of both systems. The biomass production of the fish populations was clearly related to nutrient level. Both fish and invertebrate predators were size selective, but the fish had a much greater influence on the prey populations.