Application Of Stable Isotope Analysis To Study Temporal Changes In Foraging Ecology In A Highly Endangered Amphibian

Background -- Understanding dietary trends for endangered species may be essential to assessing the effects of ecological disturbances such as habitat modification, species introductions or global climate change. Documenting temporal variation in prey selection may also be crucial for understanding population dynamics. However, the rarity, secretive behaviours and obscure microhabitats of some endangered species can make direct foraging observations difficult or impossible. Furthermore, the lethality or invasiveness of some traditional methods of dietary analysis (e.g. gut contents analysis, gastric lavage) makes them inappropriate for such species. Stable isotope analysis facilitates non-lethal, indirect analysis of animal diet that has unrealized potential in the conservation of endangered organisms, particularly amphibians. Methodology/findings -- I determined proportional contributions of aquatic macroinvertebrate prey to the diet of an endangered aquatic salamander Eurycea sosorum over a two-year period using stable isotope analysis of 13/12C and 15/14N and the Bayesian stable isotope mixing model SIAR. I calculated Strauss’ dietary electivity indices by comparing these proportions with changing relative abundance of potential prey species through time. Stable isotope analyses revealed that a previously unknown prey item (soft-bodied planarian flatworms in the genus Dugesia) made up the majority of E. sosorum diet. Results also demonstrate that E. sosorum is an opportunistic forager capable of diet switching to include a greater proportion of alternative prey when Dugesia populations decline. There is also evidence of intra-population dietary variation. Conclusions/significance -- Effective application of stable isotope analysis can help circumvent two key limitations commonly experienced by researchers of endangered species: the inability to directly observe these species in nature and the invasiveness or lethality of traditional methods of dietary analysis. This study illustrates the feasibility of stable isotope analysis in identifying preferred prey species that can be used to guide conservation management of both wild and captive food sources for endangered species.This work was generously funded by a Sigma Xi Grant-In-Aid of Research (http://www.sigmaxi.org/programs/giar/ind​ex.shtml), a Howard McCarley Student Research Award from the Southwestern Association of Naturalists (http://biosurvey.ou.edu/swan/stuaeng.htm​#_HOWARD_MCCARLEY), a grant from the Barton Springs Salamander Conservation Fund (administered by the City of Austin and Austin Community Foundation; http://www.austincommunityfoundation.org​/?nd=news#Salamander) and grants from the Zoology Scholarship Endowment for Excellence, Dorothea Bennett Memorial Graduate Fellowship and Terrell H. Hamilton Endowed Graduate Fellowship at the University of Texas at Austin (http://www.biosci.utexas.edu/graduate/ee​b/current.aspx). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Biological Sciences, School o

Food Webs in Caves

Energy (carbon) availability is considered the primary mechanism influencing both evolutionary and ecological processes in cave ecosystems, and both experimental and observational studies broadly support this hypothesis. However, we suggest that this conceptual model overlooks several factors that also influence cave community dynamics. In this chapter we explore these additional factors in two types of cave food webs, those supported by energy from detritus (dead animal or plant matter) and chemolithoautotrophic bacteria. We begin by examining the origin of each energy source and then explore what factors influence the input and/or productivity rates of each energy source, including the strength of surface connectivity, the productivity of surface habitats, and the compounds available for oxidation. We then explore how several factors are influencing cave community dynamics, including resource quantity and quality, size of resource surpluses, spatial distribution of resources, consumer-resource stoichiometry, top-down forces, and the relative harshness of certain cave environments. We hope this discussion both provides a broad overview of how food web dynamics influence cave community structure and highlights areas of future research.No Full Tex