Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

It is well known that many species show strong temporal variation in diet. Long-term dietary trends may be important in assessing the effects of ecological change such as global warming, land use change, or introductions of invasive species. Short-term variation in food sources or prey selection may be crucial for understanding population dynamics in poorly understood species. The Barton Springs Salamander ( Eurycea sosorum ) is an endangered species endemic to four small spring outflows in downtown Austin, Texas. This species remains aquatic throughout life and inhabits benthic rocky substrate. While little is known about its foraging ecology, E. sosorum is assumed to be a generalist predator with the abundant amphipod Hyalella azteca as its primary food source. The salamander’s secretive behavior and obscure microhabitat make direct foraging observations impossible. Thus, stable isotope applications may be the only feasible means of estimating diet in these animals. Measurements of [delta]^13^C and [delta]^15^N for wild-caught Eurycea sosorum and a suite of potential invertebrate prey (amphipods, chironomids and planarians) were taken in November 2007, February 2008, May 2008 and August 2008. Quantitative invertebrate censuses track seasonal changes in invertebrate relative abundance. A multi-source mixing model is applied to field isotope data, and a distribution of likely prey item contributions to salamander diet is obtained for each season. Measurement of [delta]^13^C and [delta]^15^N from captive-bred E. sosorum raised on a constant diet indicate minimal fractionation of [delta]^13^C (