Thermal disruption of transitive hierarchies in Mediterranean ant communities

1. Ants are known to compete in transitive hierarchies, where the superior competitors behaviourally exclude subordinate species. Nevertheless, in Mediterranean communities, where environmental factors show important daily and seasonal variations, the limited thermal tolerance of behaviourally dominant species compared with that of subordinates disrupts the expected transitive hierarchies. 2. This thermal tolerance allows a far greater dominance in the ecosystem by subordinate species than might be expected from their relative abundance and fighting abilities. 3. In the studied areas, activity curves of dominants and subordinates did not overlap because the latter were less temperature-limited and active during the day, while the former were more temperature-limited and active during the afternoon and night periods. 4. The lower thermal limitation of subordinate activity not only increased their exploitative ability, but also altered the outcome of interspecific interactions at food resources, i.e. modified the interference hierarchy. 5. These temporal changes in the foraging abundance of species lead to increasing diversity: more competing species may co exist as a result of changes in the environment that periodically reverse the order of competitive prevalence among the species.