Habitat reconstruction results in increased abundance, density, reproduction, and recruitment of endangered Eurycea sosorum, the Barton Springs Salamander

Background/Question/Methods

Endangered species management often is constrained by lack of knowledge of the natural history of the target species and by past and present human activities. Eurycea sosorum, the Barton Springs Salamander, is a federally endangered species of solely aquatic, neotenic, lungless salamanders whose range is limited to four Edwards Aquifer karst springs located in Austin, Texas. Major human alteration of three of these springs began roughly 100 years ago and consists of various impoundments of natural water flow. The largest spring is within Barton Creek, which was permanently dammed in 1929 to create a public swimming area, Barton Springs Pool. Regular monitoring data indicate E. sosorum is rare; from 1993–2002 average salamander abundance and density in all sites combined was 14.9 and 0.3 salamanders/sq.m. At the time of federal listing in 1997, little was known about the natural history of this species; efforts to protect the species focused on increasing survival of wild salamanders. Yet, avoidance of extinction also requires reproduction and recruitment to increase long-term effective population size (N_e). To understand what changes in habitat might foster reproduction and recruitment in the wild, I examined available scientific information on E. sosorum natural history. Although there are some data on survival and reproduction in captive salamanders, information on life history, ecology, and population dynamics of E. sosorum in the wild is scant. Consequently, I relied on phylogenetic history and ecology of other Eurycea species, and limnological and hydrogeological information from other springs to infer likely characteristics of the habitat under which Eurycea sosorum evolved.

Results/Conclusions

From these inferences I reconstructed habitat in Eliza Spring, where average salamander abundance pre-reconstruction (1992-2002) was 9.0, and density was 0.02 salamanders/sq.m. Data were collected on salamander number and life-stage, physical habitat, and prey before and after reconstruction. Average E. sosorum abundance in Eliza Spring post-reconstruction (2004-2010) was 411, density was 5.5/sq.m., both statistically significant increases.  There were also significant and lasting increases in both juveniles and adults, suggesting continued reproduction and recruitment, leading to a lasting increase in N_e. Similar reconstruction in the other three springs could help E. sosorum take one step back from the edge of extinction.