Seasonal and diurnal activity patterns in ant communities in a vegetation transition region of southeastern New Mexico (Hymenoptera : Formicidae)

The densities of active ant colonies were estimated in three habitats: creo sotebush shrubland, grassland, and shinnery-oak mesquite dunes. Diurnal for aging patterns were studied at bait boards. Species richness of ant communi ties in this transitional region (8-12 species) was considerably lower than Chihuahuan Desert ant communities in an area with lower annual average rai nfall. The numerically dominant species was Forelius pruinosus. Crematogast er spp. was subdominant in all of the habitats and exhibited relatively con stant activity throughout the growing season. Harvester ants, Pogonomyrmex spp. exhibited different seasonal activity patterns in the three habitats. One species, Trachymyrmex septentrionalis, was not recorded until October, when its nests were conspicuous with discarded leaf fragments around the en trances. Several species of ants feeding at bait board extended their forag ing times in comparison to colonies of the same species too distant from th e bait boards for foragers to reach the baits. Only one species (Pogonomyrm ex apache) exhibited a high-tolerance foraging behavior, by initiating fora ging at the bait boards after soil surface temperatures exceeded 40 degrees C and other species had ceased foraging. Foraging activity of most species continued throughout the day when cloud cover reduced soil surface tempera tures to 40 degrees C during midday.