Biomass and habitat partitioning of salamanders on wet rock faces in the southern Appalachian Mountains

Background/Question/Methods

The importance of plethodontid salamanders in forested ecosystems has been recognized for decades and studies aimed at quantifying salamander biomass have become more common. Although population and biomass estimates are becoming more precise for plethodontid salamanders, these estimates only account for salamanders on the forest floor (i.e., stream, riparian, and upland habitat). Currently, there is a lack of knowledge on the contribution of vertical structures (e.g., wet rock faces) to total salamander biomass within a forested ecosystem. Within the southern Appalachian Mountains the steep topography, high rainfall, erosion-resistant rock, and construction of roads has exposed masses of rock on the sides of mountains and gorges. Exposed rock faces with a constant supply of water can provide suitable habitat for certain species of stream salamanders. The objectives of our study were to characterize the population density, biomass, and habitat use of a wet rock face by a stream salamander assemblage in a southern Appalachian forested ecosystem. Mark-recapture surveys were conducted approximately once every five nights for a total of fifteen sampling periods (May-July) and data were analyzed with open population models using Jolly-Seber estimation in Program Mark (version 4.2).

Results/Conclusions

The total estimated population size of the assemblage (Desmognathus monticola, D. ocoee, and D. quadramaculatus) on the 33.75 m² study area was 496 salamanders (95% C.I. = 374–619), which yielded a biomass of 916.56 g (95% C.I. = 670.90–1166.27). We estimated the population density of the wet rock face salamander assemblage to be 74,600 ha^-1 (95% CI = 66,400–100,400 ha^-1), which leads to a total biomass estimate of 203.8 kg ha^-1 (95% CI = 169.4–294.4 kg ha^-1). Although this biomass estimate is more than two times greater than any previously reported salamander biomass in the eastern U.S., the estimates for two of the three species in our assemblage (D. quadramaculatus and D. ocoee) are similar to other studies. Accompanying the large biomass of the wet rock face was a significant spatial structure in the salamander assemblage (F_{2, 208} = 10.107, P < 0.001) where D. ocoee inhabited significantly higher reaches of the wet rock face than both D. monticola and D. quadramaculatus. Although the salamanders are likely protected from non-caudate predators, the spatial structuring on the assemblage still follows the predation gradient seen in horizontal habitats.