The role of feeding strategy in the tolerance of a terrestrial salamander (Plethodon cinereus) to biogeochemical changes in northern hardwood forests

Abstract

We investigated whether the trophic ecology of an apex predator is influenced by ecosystem-level nutrient depletion. The feeding behavior and nutrient assimilation of a terrestrial salamander, Eastern Red-backed Salamander (Plethodon cinereus (Green, 1818)), was surveyed along a gradient of forest biogeochemistry. Recent studies have documented populations of these salamanders in forests with low-pH soils that were long thought to be fatal. One mechanism that may enable P. cinereus to tolerate acid-impaired habitats is its generalist life history. We sampled diet, invertebrate prey abundance, and tissue composition of P. cinereus from sites that range in calcium availability and soil pH in northern forests of North America. We found that P. cinereus consistently exhibited a generalist feeding strategy, having diverse diets closely representing resource availability. Prey abundances were unrelated to the biogeochemical gradient (excluding gastropods), indicating relatively intact food webs. Although P. cinereus at the two most acid-impaired sites consumed more prey, overall trophic strategies were consistent across the gradient. Salamander tissue composition was unrelated to variation in forest biogeochemistry, although manganese levels were elevated in the most acid-impaired forests. We suggest that a generalist feeding strategy, combined with diverse and compositionally stable food webs, facilitates tolerance by this abundant predator of the challenges imposed by acid-impaired habitats.