Experimental study of diffuse competition in harvester ants

Experiments carried out over a 5-yr period in the Chihuahuan Desert support the a priori prediction of diffuse competition between two species 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.