HARVESTER ANTS (POGONOMYRMEX SPP.): Their Community and Ecosystem Influences

We summarize the influences of harvester ants of the genus Pogonomyrmex on communities and ecosystems. Because of nest densities, the longevity of nests, and the amount of seed harvested and soil handled, harvester ants have significant direct and indirect effects on community structure and ecosystem functioning. Harvester ants change plant species composition and diversity near their nests. These changes result from differential seed predation by the ants, their actions as seed dispersers and competitors with other granivores, and the favorable soil conditions they create through their digging. Their nest building creates islands of increased nutrient density. In some areas, the effects of their activities may be so pervasive that plant community structure is strongly influenced. Ant removal studies, which would reveal their total impact, have generally not been done. Granivore removals have been conducted in North America where ants are of lesser importance than small mammals, in contrast to other areas (except Israel) where ants are dominant granivores. We review the influence of harvester ants on their competitors, predators, and nest associates, and catalog the factors that influence their foraging patterns and consequently their local distribution.