Modeling the effects of precipitation on salamander demography for conservation planning
Howard, Jillian Sloper
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Integrative conservation recognizes that conservation of natural resources is a complex process because most, if not all, systems are coupled human and natural systems. Conservation planning requires conceptual tools that transcend disciplines and understanding of the ecological and human aspects of a system. For example, Southern Appalachia is a region of exceptional biodiversity which provides a number of ecosystem services within and across the broader southeastern United States. It is also a rapidly exurbanizing landscape with associated cultural and social pressures and is expected to experience significant climate change in the future. A key issue in this region is increasing residential development on steep mountain slopes and how it will impact social and economic development, public safety, and the integrity of terrestrial and aquatic ecosystems. In order for communities to conserve and manage their natural systems, we need rigorous models to identify and prioritize areas of high current and future suitability for sensitive taxa. However, for many of those species, we lack the rigorous demographic data needed for such models. At the same time, we must have an understanding of local stakeholder perspectives and values regarding issues like steep slope development that may affect conservation priorities. In this dissertation, I address these needs in the context of salamander ecology and conservation. First, I conducted a literature review to assess current knowledge of demographic rates available for parameterizing models of population dynamics for direct-developing North American salamanders in the family Plethodontidae. I determined that some rates, such as clutch size and frequency are well-documented and reasonably transferrable across species, but there are very few published estimates of survival, and nearly half of those published rates may not be realistic despite being estimated from field data. I found that there were few expected patterns in estimated survival rates among methodologies or environments that could be used to predict variation in survival among taxa and contexts from published studies. Next, I developed a Bayesian model for an eight-year robust design, capture-mark-recapture dataset of Plethodon in the Coweeta Basin in western North Carolina to estimate salamander survival rates and their sensitivity to precipitation. I used several hundred observations of live and preserved mature female salamanders to develop a novel algorithm to estimate final clutch size from ovarian follicle counts made at different points in the female reproductive cycle. I also used N-mixture models of repeated counts of salamanders across a spatial precipitation gradient to estimate size-class specific abundance and reproductive rates as a function of mean annual precipitation. I used the survival and reproductive rate estimates to project salamander population growth across the extent of the Coweeta Basin and Macon County, North Carolina, under current [past 30 years] climate and future drought frequency and severity scenarios. Model projections suggest that only a small proportion of the region likely supports consistent positive salamander population growth. Many areas occupied by salamanders likely have limited abundance and depend on limited source habitats such as coves to support local salamander populations. Finally, I used archival research, targeted interviews and participatory mapping to identify the primary concerns of stakeholders in Macon County regarding the regional environment and forest land use. I found that people are generally concerned about steep slope development, but their primary focus is on the economic impacts and regulation of development, not on its ecological impacts. These local priorities differ from the foci of scientists working in the region who are primarily concerned with impacts of steep slope development on biodiversity and natural resources. Nonetheless, while artifacts suggest a non-ecological focus on steep slope development, participants in the mapping study consistently placed conservation land use priorities at higher elevations than development priorities, suggesting some intrinsic connection between steep slopes and conservation. A combined, spatially-explicit map of stakeholder land use priorities and projected salamander population growth rates identified consistencies between areas people prioritized for conservation and areas likely to sustain salamander populations under current and future precipitation scenarios.