Thermal constraints to ant activity in six communities along a latitudinal gradient

While gradients of diversity and abundance of ants (Hymenoptera: Formicidae) are well-established, global patterns in their activity are not. In this age of rapid environmental changes it is necessary to know the temperature tolerance of such an ecologically important group of insects. Here we explore how the activity of common ants in six ecosystems, from 44° to 9° N latitude, co-varies with surface temperature. We tested two hypotheses. Thermal Adaptation predicts thermal optimum which tracks average temperatures and that those populations from variable environments are able to exploit a wider range of temperatures, yielding flatter temperature performance curves. Nutrition-Performance assumes that predators are better nourished than herbivores, and that this allows them to be active at a broader range of temperature. Ant communities collectively foraged at wide range of temperatures 12 - 45 °C.  There was little evidence of a single metabolic optimum shared by all ant species; thermal performance curves varied in shape across common species and ecosystems. Ants varied widely in stable isotope signatures, and the shape and mode of thermal activity will be used to test the Nutrition-Performance hypothesis.