Modeling the current and future roles of stream salamanders in headwater streams
Milanovich, Joseph Ross
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Communities are shaped by environmental conditions and the interactions within those environments, and changes in community composition or dynamics will in turn affect the environment through alteration of ecosystem processes. With humans rapidly altering ecosystems, predicting how environmental changes may lead to species losses, and how those biotic changes will feedback on ecosystem processes has emerged as a critical challenge. The southern Appalachian Mountains are a global hotspot for stream plethodontids, which are the numerically dominant vertebrate predators of high-elevation first order streams, and as such are hypothesized to be influential in a number of ecosystem processes. The objectives of this dissertation were to determine how projected shifts in salamander-community composition resulting from climate change may affect the retention of nutrients within first-and second-order streams. To meet this objective, elemental mass and excretion rates of salamanders was quantified to estimate the amount of nutrients captured and exported by a stream-salamander community, predictive models of species loss under climate-change scenarios were generated, and experiments were used to determine whether predicted species losses altered nutrient retention or whether compensation by other salamander species may occur. Research was conducted within the Coweeta Hydrological Laboratory basin (NC, USA). Plethodontids showed variation in elemental stoichiometry and relationships between body stoichiometry, body size, and excretion stoichiometry. Larval plethodontids were significant nutrient reservoirs when compared to other stream taxa, which implies that they are important to stream nutrient retention and nutrient cycling within streams. Excretion rates were low, but densities were high, and preliminary evidence indicates that plethodontids play a large role in re-release of nutrients. Models project a decline in suitable habitat associated with climate change scenarios for most currently dominant salamander species within the Coweeta basin, potentially affecting their role in nutrient retention. Furthermore, our results suggest that subordinate plethodontid species are able to compensate for species losses with respect to nutrient retention if their densities increase. Since plethodontids exhibit high diversity in the region and are significant contributors to a number of ecosystem processes, these projections identify a significant potential change to ecosystem function in southern Appalachian headwater streams.