Climate but Not Land Use Influences Body Size of Fowler's Toad (Anaxyrus fowleri)

Anthropogenic changes to the environment have been associated with changes in body size of multiple organisms. However, although climate and land use influences on body size have been examined separately, the simultaneous effects and potential interactions of these two factors on body size have rarely been studied. We examined the size and mass of a common North American toad (Fowler's toad, Anaxyrus fowleri) using museum specimens from 1931 to 1998 to quantify the potential interactive effects of climate change (temperature and precipitation) and land use change (forested area) on body size. We found that snout-vent length (SVL) and mass declined over time, and that size was negatively related to both temperature and precipitation (smaller size at higher values of temperature and precipitation). We did not find evidence of an effect of forest cover on size or mass. Our results suggest that Fowler's toad body size is affected by climate but not land use, and we encourage further examination of additional species and land cover variables (such as urbanization) to determine whether our results are representative of ectotherms more broadly. This work highlights the strength of climate in determining anuran body size and contrasts with existing studies showing interactive effects of climate and land use on animal body size.