The competitive interactions of closely-related and ecologically similar species have long been considered an important topic in evolutionary ecology. These species interactions can have considerable effects on community composition and species distributions. Furthermore, ecological, behavioral, and morphological traits of species can be influenced by interactions with competitors. Throughout Ohio, two closely related and ecologically similar salamander species, Plethodon cinereus and P. electromorphus, occur in similar habitats and can be found in sympatry. Interestingly, the contact zone of these two species is much broader than has been observed in other pairs of Plethodon species that competitively interact. However, when these distributions are viewed at a finer scale, the two species do not always co-occur.

I examined the interactions of P. cinereus and P. electromorphus through a variety of methods to better understand how the interactions between these two species lead to their distributions in Ohio. I found that in sympatry, both species were more aggressive towards individuals of the other species than when each was found in allopatry, indicating that the process of alpha-selection may have led to the evolution of enhanced aggressive behavior in sympatry. Within some sympatric areas, P. cinereus may be excluding P. electromorphus through these interference mechanisms. In addition, disturbance processes, such as flooding, may have sped up this process of competitive exclusion in areas where flooding occurred. These two species were using the same resources, both refuge sites and prey resources, which suggests that if these resources are limiting, they would compete for them. At different sympatric sites, morphology is evolving in different ways, such that these two species become more divergent at some sites, more similar at some sites, and do not seem to be changing at other sites. Furthermore, morphological differences are associated with differences in food use across all the sites that were examined.

The distribution and persistence patterns of sympatric localities between P. cinereus and P. electromorphus suggest that these species respond to community processes in complex ways. It appears that competitive interactions between these two species in sympatry can lead to the evolution of character displacement or competitive exclusion of one species (likely P. electromorphus). Additionally, at least one sympatric site appears to be stable where intense aggression may have resulted in interspecific territoriality. In this system, complex interactions of competition and disturbance are shaping the observed distribution patterns of these two species. While the results of my research have shed light on these species interactions, further studies could reveal the potential impacts that additional competitors or predators may have on these distributions.