Ant (Hymenoptera : Formicidae) responses to environmental stressors in thenorthern Chihuahuan Desert

We studied responses of ant communities to shrub removal and intense pulse seasonal grazing by domestic livestock for four consecutive years. Weighted relative abundance and percent of traps in which an ant species occurred w ere analyzed using randomized complete block design. split in time analysis of variance to test for significant differences between means of ant group s. The ant community in the Chihuahuan Desert grassland is dominated by sma ll, liquid-feeding ants, Conomurma insana (Buckley), and large seed harvest ing ants, Pogonomyrmex desertorum Wheeler. The weighted relative abundance of C. isana was significantly reduced on the plots without shrubs. The rela tive abundance of P, desertorum was significantly lower on grazed plots wit hout shrubs than on the ungrazed plots without shrubs. There were no detect able effects of shrub removal or intense, pulse grazing on the less abundan t ant species. These results suggest that the recent encroachment of shrubs into Chihuahuan Desert grasslands has increased the relative abundance of the dominant ant species in these communities. Intensive grazing by livesto ck has had an adverse effect on the most abundant seed-harvester, P. desert orum.