Recent articles in Ecological Applications and a response by Painter and Belsky (this issue) illustrate the controversy over theories of plant response to grazing, such as herbivore optimization and overcompensation. Observations of elk grazing in Yellowstone National Park and mixed cattle and elk grazing in the Southwest are presented as case studies to test these theories. Heavy grazing by elk in Yellowstone caused some areas to be dominated by exotic grasses, while shrubby species were heavily browsed. High—elevation rangeland conditions deteriorated in the Southwest where elk and cattle both grazed. Theories of herbivore optimization and overcompensation do not appear to be supported by the response of western rangelands to grazing by native herbivores.