Too cold to handle: Climatic constraints on arboreal ants in temperate forests.

The macroscale at which we measure, model and predict climate change does not align with the microscale at which small ectotherms experience climate. To understand climate's influence on biodiversity and potential ecological effects of climate change, more work is needed to understand how ectotherm physiology relates to microclimatic temperatures. Tree canopies are an example of a habitat that produces extreme microclimates, and arthropods in tropical forest canopies are threatened by extreme heat and warming. The situation in temperate canopies, however, is less clear. Conventional wisdom suggests that winter cold limits arboreal arthropod diversity in temperate forests, but because the canopy is less buffered from extreme temperatures, summer heat could also play a role. Heat- and cold-limited communities will respond differently to climate change, so this distinction is critical. Using the frameworks of the thermal adaptation hypothesis and thermal niche asymmetry, we asked whether arboreal ants were physiologically adapted to their extreme environment and whether summer heat or winter cold was more stressful. We tracked internal microclimates of ant nests in the canopy and on the ground over the seasonal cycle in temperate forests in North Carolina, USA. Then, we measured the heat (CT