Habitat relationships among grasshoppers (Orthoptera : Acrididae) at the western limit of the Great Plains in Colorado

We measured grasshopper densities on 66 shortgrass, mixed grass, tallgrass and hayfield plots on Boulder, Colorado, open space in 1995-1996. Grasshopp ers as a group, and most species individually, were more abundant on relati vely sparse short and mixed grass plots than on lusher hayfields and tallgr ass plots-a result consistent with the hypothesis that most species require warm and sunny open ground for survival and reproduction. Band-winged gras shoppers (Oedipodinae) were particularly associated with open ground in sho rtgrass vegetation, whereas spur-throated grasshoppers (Melanoplinae) were most abundant in mixed grass plots with a high percentage of forb vs. grami noid cover. Slant-faced grasshoppers (Gomphocerinae) were the most uniforml y distributed among habitats, but were generally associated with plots incl uding relatively high proportions of grass rs. forb cover. While 20 of the 25 most common grasshopper species on Boulder open space occurred in all fo ur grassland types, each habitat was dominated by a distinctive set of spec ies. However, numerically dominant grasshoppers on short, mixed and tallgra ss plots only loosely resembled groups of dominant species in the same habi tats elsewhere on the Great Plains. While most Great Plains grasshoppers ar e widely distributed, they are apparently numerically responsive to combina tions of environmental conditions expressed at local scales. Common species of grasshoppers on Boulder open space in 1995-1996 were the same as those collected in the region in the 1950s. Our results suggest these protected g rasslands, although invaded by alien vegetation and fragmented by suburbani zation, are still effectively conserving this particular insect group.