THE EFFECT OF LIVESTOCK GRAZING ON THE RAINBOW GRASSHOPPER: POPULATION DIFFERENCES AND ECOLOGICAL CORRELATES

Abstract

This study examined the effect of livestock grazing on a common herbivore in semiarid grasslands of the Southwest: the rainbow grasshopper, Dactylotum variegatum. Population attributes and key environmental variables were compared between sites on active cattle ranches and sites on a 3160-ha ungrazed sanctuary. Although density of D. variegatum nymphs did not differ significantly between grazed and ungrazed sites, adult density was significantly lower on grazed sites, and sex ratios differed between grazed and ungrazed sites over time. Grazed sites had higher percentages of bare ground and fewer Baccharis pteronioides, a common shrub. However, only bare ground was highly correlated with adult D. variegatum density; lower adult densities were associated with more bare ground. At a smaller scale, D. variegatum tended to be more abundant in areas with B. pteronioides on grazed sites and less abundant in areas on un-grazed sites. This study suggests that cattle grazing influences ecological variables important in determining density, sex ratio, and spatial distribution of D. variegatum at both large and small spatial scales.