Dietary similarity and foraging range of two seed-harvester ants during resource fluctuations.

Diets of desert seed-harvester ants Veromessor pergandei and Pogonomyrmex rugosus were studied for 3 years at two habitats where they are common and sympatric. Diets of the two species were similar, consisting mainly (87% of 23,913 seeds) of three annual plant species (Schismus arabicus, Plantago insularis, and Pectocarya recurvata). Diets converged following a drought in Winter/Spring 1984 which reduced seed production during this time. Foraging range of P. rugosus almost doubled following the drought while foraging range of V. pergandei remained constant. Neither ant species move their nests once established rendering them effectively sessile granivores. This limits the dietary options of a given colony and may explain interspecific dietary convergence.