FORAGING IN THE SEED-HARVESTER ANT GENUS POGONOMYRMEX - ARE ENERGY COSTS IMPORTANT

Energy intake and expenditure on natural foraging trips were estimated for the seed-harvester ants, Pogonomyrmex maricopa and P. rugosus. Du ring seed collection, P. maricopa foraged individually, whereas P. rug osus employed a trunk-trail foraging system. Energy gain per trip and per minute were not significantly different between species. There was also no interspecific difference in energy cost per trip, but energy cost per minute was lower for P. maricopa foragers because they spent on average 7 min longer searching for a load on each trip. Including b oth unsuccessful and successful foraging trips, average energy gain pe r trip was more than 100 times the energy cost per trip for both speci es. Based on this result, we suggest that time cost incurred during in dividual foraging trips is much more important than energy cost in ter ms of maximizing net resource intake over time. In addition, because e nergy costs are so small relative to gains, we propose that energy cos ts associated with foraging may be safely ignored in future tests of f oraging theory with seed-harvesting ant species.