Ecology and conservation of the endangered Barton Springs Salamander (Eurycea sosorum)
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Amphibian decline is a major concern worldwide, and a lack of basic ecological and life history information for many species significantly limits our ability to evaluate the degree and possible causes of such declines, and to develop effective conservation strategies for threatened and endangered species. Not only is there a shortage of adequate long-term datasets necessary for robust analyses of population variability, but the elusive nature and obscure microhabitats of many species make it difficult to collect even the most basic natural history data. In a series of observational and experimental studies, I employed both traditional and novel ecological methodologies to examine environmental correlates of temporal population variability, foraging ecology and anti-predator behavior in endangered Barton Springs Salamander (Eurycea sosorum) from Austin (Travis County), Texas. Though headwater springs are typically thought of as habitats with relatively stable environmental conditions, I discovered that E. sosorum population abundance was strongly influenced by periodic extremes of rainfall that affect cycles in spring flow rates, water temperature, and other physico-chemical variables. I also found that population dynamics in E. sosorum are highly consistent with those expected for organisms with a storage effect life-history strategy, in which a few long-lived females capable of high fecundity and prolonged survival in subterranean habitat during adverse environmental conditions may be sufficient for population persistence. In addition, juveniles may use subterranean habitat as a thermal refuge. Using stable isotope analyses and macroinvertebrate prey censuses, I determined that at the population level, adult E. sosorum exhibits high electivity for planarian flatworms (Dugesia sp.). This would not have been detectable using traditional methods of dietary analysis such as stomach or fecal content analysis because Dugesia are soft-bodied animals. Additionally, stable isotope analyses revealed that adult E. sosorum exhibits inter-individual diet variation and is capable of diet switching. Finally, I discovered that anti-predator behavior in E. sosorum is influenced more strongly by visual and bioelectric cues from potential predators, but not olfactory cues. This is the first known demonstration of anti-predatory response mediated only by bioelectric stimuli in an amphibian, and one of very few to observe this phenomenon among aquatic vertebrates.