Response of rangeland grasshopper communities to cattle and prairie dog grazing

Novel rangeland management strategies seek to benefit ecosystem services and biodiversity in semiarid grasslands by manipulating the distributions and densities of herbivorous ecosystem engineers, such as cattle and black-tailed prairie dogs, to increase habitat heterogeneity. We investigated the impacts of these two grazers on grasshopper populations by counting and collecting grasshoppers from May to August 2010 on plots in three northern shortgrass steppe habitats: ungrazed exclosures, long-term cattle-grazed pastures, and grazed prairie dog colonies. We also measured habitat structure and plant species composition in each plot, and assessed the proportion of C₃ and C₄ plants in the diets of grasshoppers using stable isotope analysis. While total grasshopper density and species richness were higher later in the season, both were largely unaffected by cattle and prairie dog grazing. However, we did observe responses in grasshopper diversity to both grazers at the subfamily and species level, with bandwinged and spur-throated grasshoppers being most abundant on prairie dog colonies and slant­-faced grasshoppers having the highest densities in cattle grazed pastures. The different grazing patterns also affected plant species composition and habitat structure, and we found several plant species that correlated strongly to changes in grasshopper species assemblages. The diets of late-season, but not early-season, grasshopper species were influenced by the presence of grazers. Our results suggest that in shortgrass steppe, grasshopper diversity responds more strongly than density to cattle and prairie dog grazing, and that these responses may be associated with changes in plant species composition and linked to alterations in feeding habits.