Effects of an exotic invasive plant and microtopography on terrestrial salamander populations

Abstract

Plant invasions can have strong, negative effects on some amphibians and represent a substantial challenge to conserving native biodiversity. However, invasive plant species do not always impose an immediate threat to amphibian populations and in some cases may facilitate increased abundance and provide additional habitat. The objective of my study was to determine how habitats invaded with pale swallowwort (Vincetoxicum rossicum) affected Plethodon cinereus and P. glutinosus salamander populations, their forest floor microclimate, and prey availability, and to determine if these parameters differed across a microtopographic gradient. I focused on these two plethodontid species because they were the most abundant within my study area at Oatka Creek County Park in Wheatland, New York during 2019 and 2020, and their many important roles within forested ecosystems have been widely studied. Plethodon glutinosus relative abundance peaked early during late summer 2019, while P. cinereus peaked during early fall. In 2020 P. cinereus relative abundance peaked in early April and late August, while P. glutinosus peaked in late summer. Peaks in the surface activity of both species corresponded to their documented life history patterns. P. cinereus relative abundance was significantly higher in uninvaded habitat during 2019 but did not differ between habitat types in 2020. There was no difference in P. glutinosus abundance between habitat types in either year. Plethodon cinereus relative abundance was highest in uphill topography types during both years, but P. glutinosus differed only during 2019. Generalized linear models predicting relative abundance showed positive relationships with the presence of the other Plethodon species, leaf litter depth, relative humidity, soil moisture, swallowwort cover, and arthropod abundance. There was also a negative relationship with temperature. Topography was an important factor in predicting relative salamander abundance, with more of an effect on P. cinereus relative to P. glutinosus, which may result from differences in microhabitat preference and morphology. Patterns in relative salamander abundance and distribution, as well as variation in abiotic parameters may be related to indirect effects of plant cover and microtopography. Ultimately, my findings suggest that swallowwort invasion does not directly and negatively impact P. cinereus and P. glutinosus and instead, may provide favorable microclimate and habitat features during periods of extreme weather, especially as dry spells and elevated temperatures become increasingly prevalent.