Rangeland Relations and Harvester Ants in Northcentral Wyoming

This study was conducted in northcentral Wyoming to evaluate the relationships of harvester ant (Pogonomyrmex owyheei) abundance and activity with grazing intensity, vegetation cover and composition and edaphic factors. Ant colony density, percent of soil surface denuded by ants, and average area denuded per ant colony were used as indices of ant abundance and activity. The study area, located in a Nuttall saltbush range type, was a pasture system of 600 acres involving four grazing intensities with distinct variations in vegetational cover and composition values. After 10 years of grazing at four intensities of use, harvester ant abundance was positively correlated with some plants, the correlations appeared incidental to the ability of a species to establish and grow in specific soil conditions and were not related to any ant preference for available food source. Soil texture was the most important factor influencing harvester ant abundance. If harvester ant abundance is affected by grazing and range condition, then such responses are very slow, requiring more than ten years in the area of this study.