Jaramillo, V.J. and Detling, J.K. 1988. Grazing history, defoliation, and competition: Effects on shortgrass production and nitrogen accumulation. Ecology 69. pp 1599-1608.
Plants of Bouteloua gracilis were collected from heavily grazed prairie dog (Cynomys ludovicianus) colonies (ON-colony) and lightly grazed uncolonized sites (OFF-colony) in Wind Cave National Park, South Dakota. Results support the hypothesis that genetically based morphological and physiological differentiation has occurred in B. gracilis as a result of strong selection pressure from grazing mammals on prairie dog colonies. We suggest the ON-colony population displays a strategy that reduces grazing severity rather than a 'grazing tolerance' response to aboveground herbivory.