9520882 Smith A wide variety of mechanisms have been proposed to explain the ways by which energy flow regulates the biodiversity of ecological communities. However, there has been relatively little experimental work aimed at discriminating among these competing hypotheses. These investigators will conduct direct experimental tests of the most plausible hypotheses relating eutrophication to biodiversity in aquatic communities. These experiments will be conducted in a series of mesocosms which provide three important advantages: (1) both nutrient loading and trophic structure can be independently manipulated, (2) other potentially confounding factors can be controlled, and (3) the expected biological responses can be easily measured and evaluated. Additional, experimental enclosures will be established in ponds to test these hypotheses under more natural conditions. Finally, extensive analyses of controls on biodiversity in natural ponds will be conducted, as well. The results of this study will confirm or reject four competing hypotheses that are believed to explain patterns of biodiversity in natural systems. Moreover, the research will assess the relative importance of "bottom-up" versus "top-down" factors in the regulation of plankton diversity. This knowledge is particularly important if future environmental policies directed at the protection of biodiversity are to be based on valid scientific premises. Finally, this work will provide an increased understanding of the potentially detrimental effects of eutrophication on biodiversity in natural wetland communities.
