Energetics of Locomotion and Load Carriage and a Model of the Energy Cost of Foraging in the Leaf-Cutting Ant Atta colombica Guer

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Abstract
Standard rates of O₂ consumption ( ) and net, gross, and minimum costs of transport (NCOT, GCOT, and ) were measured in the leaf-cutting ant Atta colombica. Both closed (running wheel respirometer) and flow-through (treadmill) systems were used. The relation between body mass (.004-.035 g) and standard in workers was where is ml h⁻¹ at 28 C and M is mass in grams. When combined with published data for 30 ant species, at 20 C this equation becomes = . Equations that allow calculation of NCOT and GCOT from body mass and running speeds are presented. NCOT in A. colombica at 28 C was 18.6 ml O₂ g⁻¹ km⁻¹ (mass .015 g, running speed 5.2 cm s⁻¹). Both NCOT and GCOT decreased with increasing body mass. Load carriage decreased running speed and increased NCOT proportionally to the increase of body mass + load mass. Cost of transporting a unit of load and a unit of body mass were therefore equivalent. , was 10.1 ml O₂ g⁻¹ km⁻¹ (n = 11, mean mass .0314 g), which does not differ significantly from values predicted on the basis of published equations relating to body mass in vertebrates and insects. A model is developed to predict the energy costs of foraging and maintenance of an Atta colony. The cost of maintaining a 100-m trail with a traffic rate of 60 loaded and 60 unloaded workers min⁻¹ at 28 C was approximately 2.2 W.