Empirical Evaluation of the Hypothesis of Food Competition in Salamanders of the Genus Plethodon

Abstract

Two species of salamander, Plethodon cinereus, and Plethodon hoffmani were used in experiments designed to test the hypothesis that food is the object of competition. Plethodon hoffmani occurs in the Appalachian Ridge and Valley Province where it appears to exclude the closely related and contiguously allopatric P. cinereus. Detailed field observations and a laboratory experiment confirm Jaeger's (1972) hypothesis that the food of salamanders could be limited in availability during dry weather and suggest that the cause of the low availability is the reduced mobility of the salamanders rather than a reduced food supply. However, because stomach content data and behavioral observations indicate that salamanders do not forage when the surface is dry, it was reasoned that food competition could occur under only two restricted conditions: (1) when more than one animal is isolated under damp refugia, such as rocks and logs, during dry weather, and (2) when many animals emerge onto the surface to forage when wet weather follows a prolonged dry period. Empirical evidence suggests that salamanders do not clump in refugia as the habitat dries out and that they do not surface simultaneously to forage after a dry period. Thus, even though food is periodically unavailable, the staggered feeding schedule prevents the density of salamanders from ever reaching competitive levels. Interference mechanisms are not ruled out as mechanisms of the observed spacing patterns. Competition for space is suggested as an alternative to the food competition hypothesis.