Colony size and reproduction in the western harvester ant, Pogonomyrmex occidentalis

Summary: We report data from a four-year field study on the relationship between colony size and reproduction in the western harvester ant, Pogonomyrmex occidentalis. In all years, the likelihood of reproduction significantly increased with increasing size in both field censuses during naturally-occurring mating flights and experimentally-watered colonies whose entire reproductive output was collected. However, the total amount of reproductive biomass was unrelated to colony size. We describe the size threshold for reproduction in P. occidentalis and show that it varies across years. Once colonies become reproductively mature, they reproduce consistently although not in every year. We describe a method for collecting the entire reproductive output for desert ants whose reproductive flights are cued by rainfall.