Effects of three species of Chihuahuan Desert ants on annual plants and soil properties

We tested the hypothesis that ant species, which occupy the same nest for a decade or longer, would modify nest soils by increasing soil nutrients and microorganisms resulting in increased biomass, density, cover and species richness of annual plants. We measured soil properties and annual plants on nest soils of three species of Chihuahuan Desert ants (Pogonomyrmex rugosus-seed harvester, Aphaenogaster cockerelli-generalist forager, and Myrmecocystus depilis-liquid collector-insect scavenger) in comparison to paired reference soils at several locations. There were no differences in nest and reference total soil nitrogen of M. depilis and of P. rugosus on three catena soils. Total soil nitrogen of nest-modified soils was higher than of reference soils of A. cockerelli and P. rugosus in a desert grassland site. Soil microbial biomass and respiration were not significantly different among ant species at most locations with the exception of P. rugosus at the base of the catena. Annual plant biomass was higher on M. depilis and A. cockerelli nest soils than on the reference soils. Annual plant biomass was higher on P. rugosus nest soils than on reference soils at the base of the catena and in the grassland but not at the mid-slope and top of the catena. The effects of long-lived ant colony nests on soil properties and vegetation vary in time and space but are independent of the feeding behavior of the ant species.