This research focuses on several issues emerging from recent research on relations between biodiversity and ecosystem functioning. Recent studies have fueled a growing controversy about whether species richness, the number of functional groups, or the biomass of dominant species best explains variation in ecosystem function. A series of independent manipulations of species richness, numbers of functional groups, and biomass of dominant species within functional groups will be conducted to separate effects of these factors on variation in several ecosystem processes. Other manipulations of species composition will explore causes of limited community membership, specifically by exploring whether simple assembly rules provide an adequate explanation of r differences in community composition along a productivity gradient. Finally, manipulations of environmental variation will test whether responses of simple and complex communities to environmental change depend on the extent of temporal autocorrelation in changing temperature regimes. An important goal of this research is the rigorous identification of links between population dynamics, community structure, and ecosystem function. Such links are best explored in systems where population dynamics, community structure, and ecosystem processes are simultaneously measured. This level of integration is quite tractable in microbial communities established in experimental microcosms, which are particularly amenable to manipulations of various aspects of biodiversity and environmental change.
