Biological, Geological, and Environmental Sciences

B. Michael Walton Research Interests

 1. Effects of terrestrial salamander within food webs of the forest floor.
Salamanders of the family Plethodontidae are among the most abundant organisms, and are certainly the most abundant vertebrates, in temperate forests of eastern North America, where they are hypothesized to play a critical role in the regulation of invertebrate communities and nutrient processing of the forest floor. My students and I are investigating the role that plethodontid salamanders within forest-floor food webs, as well as factors that may alter that role in space and time. Our recent studies have demonstrated that the red-backed salamander, Plethodon cinereus, can have substantial impacts on the species composition of forest-floor invertebrate communities, including both direct and indirect effects (see Walton and Steckler 2005). In experimental microcosms, numbers of large invertebrate detritivores decline in the presence of salamanders, but small detritivores, e.g., mites and Collembola, increase. We hypothesize that small detritivores benefit from reduced competition and/or a nutrient subsidy to bacteria and fungi supplied by salamander wastes and secretions. However, the nature of these effects in terms of their strength and through which invertebrate taxa they are exerted is related to complex interactions among abiotic and biotic factors within the forest-floor environment, including age (and perhaps nutrient quality) of leaf litter (Walton and Steckler 2005), seasonal variation in temperature, litter moisture, and litter thickness (Walton, in review), and species composition and size distribution of invertebrate prey communities (Walton, Tsatiris, and Rivera-Sostre, in review). Our on-going studies are investigating the interactive effects of plethodontids and arthropod predators on the forest-floor, the potential for size-selective predation by plethodontid salamanders to buffer the impact of non-native arthropods in forest-floor communities, and the role of semi-aquatic plethodontid salamanders in transferring material and nutrients between stream habitats and the adjacent forest-floor.



 2. Effects of urbanization on ecological communities of small stream watersheds.


My research group is also interested in the effects of human-disturbance, especially the effects of urbanization on the ecological dynamics of riparian forest-small stream ecosystems. Our work in this area includes a multivariate analysis of the effects of land use/land cover, human population and housing density, and stream habitat on the quality of fish communities in urbanized and suburbanized NE Ohio (Walton, Salling, Wyles, and Wolin, in review). This analysis emphasizes the variation in value of forest cover in urban vs less urbanized areas, and the importance of both geological and human-development histories in determining regional patterns of the impact of urbanization on ecological integrity. We are currently extending these analyses to a state-wide comparison of urbanization-biological integrity relationships among five urban regions in Ohio. Additinal work includes studies of the relationship between biological quality of stream communities and that of the adjacent riparian zone, and investigations of the extent to which urbanization disrupts reciprocal exchanges of energy and nutrients between in-stream and terrestrial food webs.

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