Spatial and temporal niche partitioning in grassland ants

Species coexistence can reflect niche partitioning at several spatial and t emporal scales. We measured patterns of spatial and temporal niche overlap in an Oklahoma grassland ant assemblage. Ant species foraging on a 400-m(2) grid of 25 tuna-fish baits were censused hourly for one 24-h period each m onth for 1 year. We used partial correlations to analyze pairwise associati ons of the four commonest species, and a null model analysis to quantify ni che overlap among all seven species present. On a seasonal (monthly) time s cale, niche overlap and pairwise species associations were random or aggreg ated, probably due to thermal constraints on ectotherms foraging in a seaso nal environment. Within the warmer months of the year, there was some evide nce of diurnal (24 h) niche partitioning: the variance in niche overlap was often greater than expected, and common species displayed both negative an d positive associations with each other and with ambient air temperature. T he strongest evidence for niche partitioning was at the spatial scale of in dividual baits. Species occurrences at baits were dynamic, with considerabl e turnover in composition and significantly less spatial niche overlap than expected by chance. These results are consistent with other studies sugges ting that ant species partition resources at fine spatial and temporal scal es.