Harvester ants gather seeds and other foods and store them in underground nests. The ants feed on the seeds, process the food and deposit waste in and around the nest area. Ant activity can have a profound impact on soil chemistry and biota. Collecting seeds from adjacent areas removes nutrients such as nitrates and phosphorous and impoverishes soils nutritionally. Depositing seeds in the nest enriches the soil for nitrates and phosphorous.
Over time, soil of the ant mound can become more fertile for a variety of plants and micro-organisms. What at first glance may appear to be a uniform field of grass, can have significant heterogeneity in nutrient availability. Ants may also affect soil humidity and water content, both by aerating the soil to penetration by water and by adding more organic material that has better water retention than the inorganic soil particles.
Diane Wagner, Mark J. F. Brown, Deborah M. Gordon. Harvester ant nests, soil biota and soil chemistry. Oecologia October 1997, 112:pp 232-236.