The importance of inter- and intraspecific variation in critical thermal limits for estimating the distribution of ant species in the eastern U.S

Understanding the factors that limit the distribution of species and patterns of biodiversity is at the core of ecological and biogeographical research. The complex relationship between environmental conditions and biogeographical distributions often relies on large-scale climatic information and macroecological data from museum records and field guides. Few studies, however, incorporate actual physiological mechanisms and measurements of the studied organisms to understand patterns of diversity and predict the distributions of species in a changing world. In this study, we examined trait-based physiological responses to varying thermal regimes to better predict the effects of a changing climate on ant distributions and community structure.  Through controlled laboratory experiments coupled with field-collected data on the distributions of ants, we investigated critical thermal minima and maxima of ant species along elevational and latitudinal gradients in the eastern U.S.  Ants were collected in Great Smoky Mountains National Park (400m-1800m) as well as 25 sites from Florida to Maine, spanning approximately 15 degrees latitude. Interestingly, we documented considerable intraspecific variation in thermal tolerance in several ant species, including one of the most common and ecologically important genera of forest ants in eastern deciduous forests (Aphaenogaster). Generally, we have found that populations from high elevations and latitudes exhibit more variation in thermal tolerance and lower critical thermal minima than populations from low elevations.  These results suggest that species distribution models may benefit from a more mechanistic approach when estimating the distributions of ant species, which may be critical in predicting the response of biodiversity to ongoing climatic changes.