An Altitudinal Comparison of Oxygen Consumption Rates in Three Species of Pogonomyrmex Harvester Ants (Hymenoptera: Formicidae)

The oxygen consumption rates at 30 C and the temperature sensitivity of the rates were compared for member groups (larvae, pupae, callows, workers, females, and males) of three species of harvester ants which occur at different altitudes in southern California. Developmental changes in both rates and temperature sensitivity were found. There is an abrupt doubling or tripling of the respiratory rates of males prior to the mating flights. No similar changes were found in the respiratory rates of the females. The males are dimorphic, with each size having different respiratory rates. In general, Pogonomyrmex montanus MacKay, the harvester ant from the highest altitude, had the highest respiratory rates and demonstrated the greatest temperature sensitivity. The mid-altitude species, P. subnitidus Emery, had intermediate respiratory rates. The lowest-altitude species, P. rugosus Emery, had the lowest respiratory rates and demonstrated the least temperature sensitivity. These differences are important as the ants are exposed to different temperature ranges; the higheraltitude species are exposed to lower temperatures. This physiological adaptation may be necessary to allow each of the species to be active at similar rates in the three different habitats. Although a physiological adaptation involving higher respiratory rates in ants from higher altitudes was determined in the three species investigated, it may not be a general phenomenon in ants. It is suggested that further investigation is needed to determine the parameters which have an effect on the important physiological process of respiration and to provide ecological interpretations for the differences observed.