Thermal Responses and Temperature Tolerance in a Diurnal Desert Ant, Ocymyrmex barbiger

Abstract

Foragers were active on the insolated surface between sand surface temperatures (Ts) of 27–67 C. At Ts > 51 C foragers periodically paused in relatively cooler thermal refuges, such as by remaining in the shade or by climbing above the desert floor on any available object. The frequency and length of pauses in thermal refuges increased with increasing Ts. Workers, because of their small size (∼4 mg live mass), had low thermal inertia, as evidenced by high cooling rates in a range of air speeds, and were therefore efficient heat exchangers, equilibrating rapidly to ambient temperature. Through measurements of operative environmental temperature (Te) in pertinent positions in the ant's habitat and a knowledge of wind-related cooling rates, it was possible to estimate the body temperature (Tb) Of foraging ants. Foragers experienced periods when Tb would have equaled or exceeded their critical thermal maximum (CTM) of 51.5 C. Laboratory experiments indicated that ants could tolerate temperatures >CTM for short periods and that short but frequent thermal respites facilitated ant survival at temperatures = CTM.