CRITICAL THERMAL LIMITS IN MEDITERRANEAN ANT SPECIES - TRADE-OFF BETWEEN MORTALITY RISK AND FORAGING PERFORMANCE

1. In Mediterranean ant communities, a close relationship has been fou nd between activity rhythm in the period of maximum activity and posit ion in the dominance hierarchy: subordinate species are active during the day, when conditions are more severe, while dominants are active d uring the afternoon and the night. 2. Results obtained in this study c onfirmed that the species foraging at higher temperatures were closer to their critical thermal limits than the species foraging at lower te mperatures. 3. This enabled two extreme strategies of foraging in rela tion to temperature to be distinguished: (1) heat-intolerant ant speci es behaved as risk-averse species, foraging at temperatures very far f rom their critical thermal limits; and (2) heat-tolerant ant species b ehaved as risk-prone species, foraging very near their critical therma l limits and running a high heat mortality risk, 4. Heat-tolerant spec ies benefited from this strategy by having better foraging performance at high temperatures. 5. This wide range of thermal niches may be one reason why Mediterranean ant faunas are so diverse in the face of lim ited diversity in vegetation and habitat structure: the daily range of temperature may be sufficiently great to meet the requirement both of heat-adapted and cold-adapted species as well as a spectrum of interm ediate forms.