Abstract

We used an occupancy modeling framework to test the relative importance of upland habitat composition (proportion of different types of vegetation and development) and pond characteristics (water chemistry and vegetation) in determining the occurrence of two species of pond-breeding salamanders, the Marbled Salamander (Ambystoma opacum) and Mabee's Salamander (Ambystoma mabeei), in an urban nature reserve in southeastern Virginia, USA. Of 55 ponds surveyed in 2009, we found A. opacum larvae in 17 (30.9%) ponds and A. mabeei larvae in seven (12.7%) ponds. We found a strong positive relationship between A. opacum larval occupancy probability and pH; salamanders were more likely to occupy less acidic waters. Sampled ponds were highly acidic, with pH values ranging between 3.36 and 4.41, but A. opacum occupied only ponds with pH values >3.66. Ambystoma mabeei was more tolerant of the highly acidic conditions and was more likely to occupy larger ponds with fewer trees and scrubs. Landscape-level models were not well supported. Although pond acidification is generally dismissed as a cause of amphibian declines, our results suggest that pH can be an important, species-specific factor in determining occupancy of pond-breeding amphibians.