Factors influencing the spatial distribution of the Red-backed salamander, Plethodon cinereus

Background/Question/Methods

A fundamental goal of community ecology is determining the processes that contribute to species’ presence or absence in local landscapes. While much is known about factors influencing the regional distribution of species, we know much less about how populations within a local habitat are arranged spatially. Evidence of non-random microhabitat selection could have implications for both population and community dynamics, as biased distributions would influence the subset of individuals a conspecific or community member is likely to encounter. This study searched for both environmental and competitive effects that could affect within-habitat distribution in a polymorphic population of Red-backed salamanders, Plethodon cinereus. We hypothesized that a combination of forest characteristics (i.e. tree type, tree size) and traits of neighboring salamanders (i.e. size, sex, color morphology) would influence a given individual’s microhabitat choice. Weekly field surveys of an established coverboard transect were used to determine salamander location, abundance, and color morphology across seasons. Several of these surveys recorded the size and sex of individual salamanders in order to identify any effects attributable to intraspecific competition. Evidence for such competition would take the form of individuals altering microhabitat selection based on key characteristics (morph, sex, or size) of neighboring salamanders.

Results/Conclusions

A variety of environmental variables were correlated with the abundance of P. cinereus. ANOVA indicated that abundance increased during the spring and fall seasons, in deciduous microhabitats, and in areas with larger average tree diameter (independent of forest type). Groups of salamanders in deciduous areas were smaller than those in coniferous or mixed locations, perhaps indicating crowding of individuals as abundance in preferred areas increases. Contrary to our hypothesis, path analysis revealed no evidence that microhabitat selection of individual salamanders was affected by the characteristics of neighboring conspecifics. In this system, then, broad-scale environmental variables are the major drivers of salamander abundance and site selection. Aside from potential crowding in areas of high abundance, as well as a disparity in size between color morphs, there is no evidence for intraspecific processes shaping salamander distribution. This possibility, however, will receive more long-term attention in a mark-recapture initiative started during the study presented here. Understanding the distribution of individuals within a habitat is an important task, as non-random patterns may influence both population and community dynamics. Here we support the role of environmental factors in such structuring, but highlight the need for further research to identify additional mechanisms driving spatial segregation.