Masters Thesis

Density, Diversity, and Diet of Shortgrass Steppe Grasshoppers in Response to Cattle and Prairie Dog Grazing

Agriculture has transformed the western Great Plains of North America from a heterogeneous landscape generated and maintained by natural disturbances to homogeneous patches of uniformly managed rangelands and croplands, with negative impacts on regional biodiversity. In an effort to reduce or reverse biodiversity loss, rangeland managers have employed novel strategies that integrate processes such as alternative cattle ranching regimes and prairie dog activity into traditional land-use practices. I sought to determine the effects of cattle and prairie dog grazing on grasshopper communities in a semiarid shortgrass steppe in north-central Colorado. I used quadrat counts, sweep net sampling, and stable isotope analysis to compare grasshopper assemblage density, diversity, and diet in ungrazed livestock exclosures, cattle-grazed pastures, and cattle-grazed prairie dog colonies. Overall grasshopper density was not affected by cattle or prairie dogs, but these grazers did influence earlyand late-season grasshopper diversity at the subfamily and species level. Cattle and prairie dog grazing also influenced diet in two of the five grasshopper species examined. My results suggest that, in semiarid grasslands, cattle and prairie dogs alter the landscape in ways that support different grasshopper assemblages, and that the diets of some grasshopper species also shift under these different grazing conditions.

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