COS 235-3 - Impacts of Climate Change on the Range Expansion Potential of the Green Treefrog (Hyla cinerea): Implications of Native Species Redistributions

Abstract: Species distribution shifts due to climate alterations have been increasingly well documented over the last century. Amphibian species are one of the most sensitive groups of animals to environmental perturbations due to climate change, however, no studies have offered any evidence of poleward distribution shifts in response to climate warming and increased precipitation. Green treefrogs (Hyla cinerea) have recently been observed to expand their range northward and eastward in the midwestern United States, which provides an ideal system to study amphibian species' range shifts in response to increased temperature and precipitation. In this study, we hypothesized that there would be a latitudinal gradient in thermal tolerance among populations of H. cinerea sampled from historical and expanded range locations. We first used a species distribution model to project H. cinerea’s habitat suitability across the United States and predicted their distribution shift under the scenario of warming temperature. We then conducted fieldwork to measure thermal tolerance - critical thermal maximum (CT_max) and minimum (CT_min) in historical and recently colonized populations of H. cinerea. The prediction of the suitability of H. cinerea occurrence suggested that the most suitable environment is in the Southeastern United States, and H. cinerea had the potential to continue expanding poleward in the Midwest. Our field work further found that CT_min significantly decreased with latitude in both groups (expansion and historical), while historical-range frogs had lower CT_min compared to expanded range frogs. These findings are in accord with the prior hypothesis of northward and eastward shifts in native amphibian species distribution ranges due to climate warming and are potentially the first documented evidence of climate-driven poleward distribution shifts in an amphibian species.