Soils of the ant nest plots have been substantially modified by harvester ant activity (Fig. 6). This is borne out by the cluster analysis (Fig. 7), which completely separated ant nest soils from those of the control plots. Soil pH was significantly lower (difference = 0.43; Z = 6.00, P < 0.0001) than in the control plots, and this was reflected by a corresponding lack of carbonate (difference = 3.3; Z = 6.07, P < 0.0001).