Context-dependent aggression and ecological dominance in a Mediterranean ant community

Aggression plays a central role in structuring ecological communities, particularly in territorial and socially complex taxa such as ants, where conflicts within and between species are often resolved through overt aggression. Here, we combined field monitoring of ant nests over a six-month period with laboratory experiments to investigate the coexistence of three dominant ant species in an urban Mediterranean grassland: Aphaenogaster senilis, Messor barbarus, and Tapinoma darioi. We analysed behavioural asymmetries, dominance hierarchies, and the potential mechanisms that may facilitate coexistence. The three species were the most abundant in the study area (84% of nests), and nest surveys indicated their coexistence despite seasonal fluctuations in A. senilis and T. darioi, with some winter nests of the former taken over by the latter. Aggression was context-dependent and varied strongly among species and seasons. A. senilis displayed low aggression and frequent submissive behaviours; M. barbarus showed consistently higher aggression towards conspecifics; and T. darioi combined low aggression in laboratory assays with traits associated with supercoloniality, consistent with a “back-seat driver” strategy. Although native to the Mediterranean, its high occupation potential suggests that T. darioi may gradually reshape local communities through persistent interference. However, year-round monitoring and resource-based competition assays are required to distinguish persistent trends from seasonal dynamics. Overall, our findings highlight how behavioural plasticity, ecological context, and species-specific aggression contribute to community structure. They also underscore the importance of monitoring numerically dominant species, which can exert substantial long-term effects on community composition even when displaying low overt aggression.