Doctor of Philosophy, University of Toledo, 2011, Biology (Ecology)

Understanding what factors drive an organism's population fluctuations in time and space can be very difficult in complex ecosystems due to changing environmental conditions and issues with spatial scale. In this dissertation, I examined the effect of soft-sediment Dreissena (D. polymorpha and D. rostriformis bugensis) clusters, an invasive ecosystem engineer, on a native burrowing mayfly (Hexagenia limbata and H. rigida). Specifically, at the small-scale, I examined the effect of Dreissena clusters on Hexagenia: 1) habitat preference, 2) availability as prey, and 3) behavior during changing abiotic (low oxygen) and biotic (presence of a predator) conditions. At the large scale I examined: 1) the spatial association of Hexagenia and Dreissena and 2) the abiotic and biotic factors influencing Hexagenia spatial distribution and temporal fluctuations. I conducted experiments, spatial mapping and statistics, and generalized additive models to examine these objectives. Hexagenia were found to prefer sediment covered with both live and artificial clusters over bare sediment, likely due to decreased fish predation when under Dreissena clusters in turbid conditions. Hexagenia also received benefit from Dreissena clusters during hypoxic conditions; Hexagenia were able to exit anoxic burrows to seek well-oxygenated waters while staying within the Dreissena cluster as refuge from predation. At the large scale, Hexagenia density was not related to Dreissena density, however Hexagenia were more likely to occur where Dreissena were also present. Similarly, Dreissena density was not a good predictor of Hexagenia density in western Lake Erie, but abiotic factors, such as percent silt, organic carbon, depth, and distance from western shore did significantly influence Hexagenia distribution. Sites with high average Hexagenia density were clustered near the western shoreline of Lake Erie and exhibited a two-year density cycle, likely a density-dependent regulation. Overall, abiotic fa (open full item for complete abstract)

Committee: Christine Mayer PhD (Advisor); Jonathan Bossenbroek PhD (Committee Member); Thomas Bridgeman PhD (Committee Member); Lynda Corkum PhD (Committee Member); Kenneth Krieger PhD (Committee Member) Subjects: Aquatic Sciences; Ecology; Environmental Studies; Limnology

Master of Science, University of Toledo, 2006, Biology (Ecology)

It is well known that invasive species, such as the dreissenid mussels in the Great Lakes, play significant roles in changing the substrate, community species composition, and habitat. This study examined the role of Dreissena, (zebra mussel, D. polymorpha and quagga mussel, D. bugensis) as an invasive “paver”, which compacts the sediment, and its effects on two native bioturbators, Hexagenia (burrowing mayflies; H. limbata and H. rigida) and unionid bivalve mollusks. Resulting consequences on sediment properties, infaunal invertebrates, and microbial community composition were analyzed. I further examined the spatial relationship between Dreissena and Hexagenia. Experiments showed that Hexagenia density increased in the presence of Dreissena, nematodes decreased, and oligochaetes and microbes were unaltered. In the absence of Dreissena, bioturbating species altered sediment water content and increased infaunal invertebrate densities, microbial activity, and microbial functional diversity. In further exploration of the relationship between Dreissena and Hexagenia, Hexagenia preferred habitat with 50-100% spatial coverage of live Dreissena clusters. These experiments thus revealed habitat facilitation by an invasive ecosystem engineer on a native ecosystem engineer, Hexagenia, with opposite effects on invertebrates, microbes, and sediment properties.

Committee: Christine Mayer (Advisor) Subjects: