Temperature-mediated coexistence in temperate forest ant communities

Patterns of ant species diversity are well documented and yet the mechanisms promoting species coexistence among communities are often elusive. Two emerging hypotheses that account for coexistence in ant communities are the discovery-dominance tradeoff and the dominance-thermal tolerance tradeoff. Here we used behavioural assays and community-level sampling from ant assemblages in the southern Appalachians, USA to test for the discovery-dominance and dominance-thermal tolerance tradeoffs. Species that were behaviorally dominant during interspecific interactions tended to forage in a narrow window of generally warmer temperatures, whereas subordinate species tended to forage in a wide range of temperatures, including colder temperatures. Species that foraged at lower temperature tended to be behaviourally subordinate, suggesting that a dominance-thermal tolerance tradeoff promotes coexistence in this system. Species richness was positively related to site average annual temperature and within-site variation in ground temperature, suggesting that temperature also shapes the structure of ant communities and regulates diversity. There was no relationship between the ability of a species to discover food resources and its behavioural dominance, contrary to the predictions of the discovery-dominance tradeoff hypothesis. In sum, our results show that temperature plays numerous roles in promoting regional coexistence in this system.