Interspecific Aggression in Ohio Plethodon: Implications for Competition

Interspecific competition between closely-related and ecologically similar species may limit geographic ranges and fine-scale sympatry, especially when one species is aggressive toward another species. Throughout Ohio, two closely-related salamander species, Plethodon cinereus and P. electromorphus, can be found in similar habitats. While the distributions of the two species generally overlap through much of this region, a finer-scale examination of their distributions indicates that many areas within the zone of sympatry contain only one or the other species. This geographic pattern suggests that the two species are interacting. In this study, we examined the behavioral responses of individuals from allopatric populations of both species to provide an initial understanding of their interactions. This study represents interactions between ‘novel’ biotic stimuli, as individuals from allopatry have not previously encountered members of the congeneric species. We found that allopatric populations of P. electromorphus exhibited all typical behaviors recorded in other Plethodon species and that both species from Ohio exhibited aggressive behavior. We found that when animals were tested in intraspecific trails, P. cinereus was more aggressive than P. electromorphus and that P. electromorphus was more submissive than P. cinereus. However, these two species did not differ in behavior during interspecific trials, except that P. electromorphus spent more time in escape behavior (EDGE). Therefore, we conclude that P. electromorphus likely would act submissively if encountering P. cinereus for the first time in the field. These results imply that P. electromorphus may not be able to expand its range into areas occupied by P. cinereus, and, in turn, P. cinereus may be able to successfully expand its range into areas presently occupied by P. electromorphus.