Dietary Similarity of Some Primary Consumers

The dry—weight composition of the diets of richardson ground squirrels (Citellus richardsonii), mormon crickets (Anabrus simplex), and six species of grasshoppers (Xanthippus corallipes, Circotettix rabula, Aeropedellus clavatus, Melanoplus infantalis, Melanoplus bruneri, and Melanoplus alpinus), collected at Prairie Divide, Colorado, was determined. Many food plants were shared by these herbivores. Vetch (Astragalus spp.), sandwort (Arenaria fendleri), fungi, parry oatgrass (Danthonia parryi), bluegrass (Poa spp.), fringed sagebrush (Artemisia frigida), dandelion (Taraxacum officinale), and sedge (Carex spp.) were major foods. Bluegrasses, vetch, and sandwort would probably become limiting if population peaks of several of these herbivores coincided. The ranking of the food niches of these herbivores from specialized to generalized based on mean indices of dietary similarities is X. corallipes, A. clavatus, C. rabula, M. alpinus, A. simplex, M. bruneri, C. richardsonii, and M. infantalis. Males ate fewer species of food plants than females of the same orthopteran species, and the diets of males and females of the same orthopteran species were occasionally less similar than were the overall diets of different species on the same date.