The influence of natural and human-induced environmental change on the community composition of temporary ponds

The influence of environmental change on biodiversity has received a significant amount of attention in recent years. Typically, environmental change is modeled in terms of changes in the physical environment that drive shifts in the species composition of ecosystems. Such shifts in the physical environment can result from both natural and human-induced processes. Anthropogenic modifications of the environment are of particular concern, as human-induced environmental change is believed to be accelerating rates of species loss.; Of the systems impacted by urbanization, wetlands appear particularly sensitive. As amphibians commonly use wetlands for breeding habitat, and given the concern over their ongoing global declines, there is a need to quantify the effects of urbanization on the breeding distribution of amphibians. Thus, I conducted a survey of the larval amphibian community in central Pennsylvania (U.S.A.) wetlands along an urbanization gradient. Wetlands in urban areas had less surrounding forest and wetlands and greater road density than rural wetlands. Urbanization was also associated with increases in hydroperiod (i.e., wetland permanency) and the presence of fish predators. Moreover, urban wetlands had lower larval amphibian species richness than rural wetlands. This decrease in richness was due to a decrease in occurrence of wood frogs (Rana sylvatica) and ambystomatid salamanders (Ambystoma maculatum and A. jeffersonianum) in urban sites. Wood frogs and ambystomatid salamanders were positively associated with the amount of forest surrounding sites and negatively associated with hydroperiod. As a result, I hypothesize that these species are sensitive to the effects of urban development. The remaining species in this study appear fairly resilient to the effects of urbanization. These data demonstrate the importance of quantifying both local and landscape attributes when describing the factors that limit the breeding distribution of amphibians.; Human-induced environmental change need not always be as obvious as urbanization. For example, the temperate deciduous forest of the northeastern US is believed to be undergoing a shift from mixed-oak (Quercus sp.) to red maple (Acer rubrum) dominated; a shift termed "The Red Maple Paradox". This subtle shift in the composition of the forest is believed to be the result of human activities such as fire suppression. Such a change in the structure of the forest has the potential to affect ecosystems within the forest that utilize leaf-litter as an energy source. To assess the impact of "The Red Maple Paradox" on detrital food webs, we conducted a mesocosm experiment investigating the influence of red maple litter on the food web of temporary woodland ponds. (Abstract shortened by UMI.)...