ENERGY COST OF LOCOMOTION: VALIDATION OF LABORATORY DATA BY IN SITU RESPIROMETRY

Abstract

The energy cost of activities central to overall fitness in most animals, such as pedestrian locomotion, is traditionally measured in the laboratory and then extrapolated to field conditions for modeling or hypothesis-testing purposes. However, no accurate, direct, in situ validation of these extrapolations has been made on undisturbed animals. We present the first such validation here, on harvester ants (Messor pergandei). After measuring their energy parameters in the laboratory using a running tube, we measured the metabolic rate (MR) of a natural, undisturbed ant trail foraging through a respirometer chamber in the field. From temperature, ant numbers, ant masses, and foraging speeds (obtained through video analysis), we predicted trail MRs from separately obtained laboratory data and compared them to measured field trail MRs. No significant difference was found between actual field values and values predicted from equations produced from data acquired in the laboratory. Our results therefore serve to validate two unusual findings in ants, which would otherwise be troubling to extrapolate to field conditions: that their extrapolated MR at zero running speed does not differ from standard (resting) metabolic rate, and that their costs of transport are far lower than predicted on the basis of current allometric equations.