Abstract
Experiments carried out over 5 yr in the Chihuahuan Desert [Mexico] support the a priori prediction of diffuse competition between 2 spp. of harvester ants. Despite dietary overlap between a large species (Pogonomyrmex rugosus) and a small species (Pheidole xerophila), the large species facilitates the small species indirectly by suppressing populations of an intermediate-size species (Pogonomyrmex desertorum). Although similar indirect interactions may occur frequently in natural communities and be predictable on the basis of body size, very long-term studies may be necessary to demonstrate their effects experimentally.