DISSERTATION RESEARCH: Putting the Relationship Between Species Diversity and Ecosystem Functioning into Context.

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With the rate of global species extinction rapidly increasing, there is an intensifying debate among scientists as to whether or not a high diversity of species is required to maintain ecological processes that are important for the functioning of ecosystems (processes like primary productivity, decomposition, and the cycling of nutrients). Limited evidence suggests that the certain types of ecosystems may require more species than others. For example, recent experimental work has led to the hypothesis that decreasing species diversity in ecosystems characterized by periodic disturbances leads to greater changes in ecological processes than decreasing species diversity in ecosystems less characterized by disturbance. The current research will test this hypothesis by relating species diversity to the rates of 3 ecological processes in stream ecosystems that differ in flooding regime (=disturbance metric). Using records from the US Geological Survey, 200 randomly selected streams from the eastern United States will be ranked according to their frequency and predictability of bank-full flooding. The 25 streams most characterized by flooding and 25 streams least characterized by flooding will be sampled to determine the rates of three ecological processes (primary productivity, leaf decomposition, and removal of suspended particles from the water), and the diversity of species that influence these processes (primary producers, invertebrate detritivores, and invertebrate filter feeders). To test the hypothesis, the relationships between (1) algal diversity and primary productivity, (2) invertebrate detritivore diversity and leaf decomposition, and (3) invertebrate filter-feeder diversity and retention of suspended particulate matter, will be statistically compared between streams most and least characterized by flooding. The results will help determine whether species diversity is more or less important for conserving biological processes in ecosystems that are naturally or anthropogenically disturbed. This study will also provide much needed, basic information about the factors that potentially regulate the contribution of species diversity to ecosystem-level processes.