The ecology of Plethodontid salamanders in acidic headwater streams in Virginia

The abiotic environment can be a strong factor shaping the structure and function of stream communities. Salamanders are key taxa in stream food webs because they feed at multiple trophies levels and constitute a large pool of biomass for other predators. I hypothesized that the indirect effects from a salamander's physiological tolerance to acidity would alter its competitive and predatory abilities. I demonstrated that acid sensitivity varied between stream salamander species and between life states. In acute, acidic laboratory conditions (pH < 4.25), the survival rates of Eurycea cirrigera, Gyrinophilus porphyriticus, and Pseudotriton ruber larvae were higher than larvae of Desmognathus quadramaculatus. The survival E. cirrigtera and D. quadramaculatus adults was greater than that of larvae under similar laboratory conditions. To consider how these physiological difference in acid tolerance affect stream communities, I placed larvae of three salamander species in artificial streams at either chronically low (pH 4.7) or nearly neutral pH (6.3): two large-bodied predators, Desmognathus quadramaculatus and Gyrinophilus porphyriticus; and a common prey, Eurycea cirrigera. Survive al of G. porphyriticus and E. cirrigera larvae was not reduced by acidity. The activity of D.quadramaculatus individuals was adversely affected by its acid sensitivity, resulting in less growth in E. cirrigera in the presence of both salamander predators and acidic conditions. The broader impacts of the physiological and community responses to acidity were investigated in surveys of 58 headwater streams. The abundance of Desmognathus monticola was higher in streams characterized with low acid-neutralizing capacity (low ANC). Overall body sizes of D. fuss, D. quadramaculatus, and G. porphyriticus were larger in low ANC streams and among streams with different salamander assemblages. These changes to the distributions and sizes of stream salamanders cannot be attributed to other habitat variables, indicating that the acidification of headwater streams has become an important factor regulating the structure of stream communities.