The shortgrass prairie is an ecosystem located in the Great Plains of North America. The two most dominant grasses in the shortgrass prairie are blue grama (Bouteloua gracilis) and buffalograss (Bouteloua dactyloides), the two less dominant grasses in the prairie are greasegrass (Tridens flavus) and sideoats grama (Bouteloua curtipendula). The prairie was formerly maintained by grazing pressure of American bison, which is the keystone species. Due to its semiarid climate, the shortgrass prairie receives on average less precipitation than that of the tall and mixed grass prairies to the east.