Coexistence of Three Congeneric Salamanders: The Importance of Habitat and Body Size

In the southern Appalachians three congeneric salamanders–Desmognathus quadramaculatus, D. monticola, and D. ochrophaeus–are broadly sympatric. D. monticola is intermediate to the others species in body size and in degree of terrestrial habit. This study analyzed the roles of competition, predation, and habitat conditions in limiting the abundance of this "ecologically intermediate" species and in directing its evolution. In field observations, D. monticola regularly used both stream—bank and forest—floor habitats; experimental exclusion from either of these habitats resulted in poor survival. Field enclosure experiments also showed that growth, survival, and habitat selection of D. monticola were altered by the presence of congeners. Interference from conspecifics and from congeners of equal size decreased growth and reduced survival of D. monticola. Predation by large D. quadramaculatus sharply reduced survival of juveniles and caused shifts in activity and habitat selection. I suggest that predation has controlled the evolution of body size and habitat selection in D. monticola and that populations of this intermediate species are limited by the availability of streambank cover as a refuge from predation. Competition may also be important among species of similar size when food is limited.