HERBIVORE OPTIMIZATION AND OVERCOMPENSATION - DOES NATIVE HERBIVORY ON WESTERN RANGELANDS SUPPORT THESE THEORIES

Recent articles in Ecological Applications and a response by Painter a nd Belsky (this issue) illustrate the controversy over theories of pla nt response to grazing, such as herbivore optimization and overcompens ation. Observations of elk grazing in Yellowstone National Park and mi xed cattle and elk grazing in the Southwest are presented as case stud ies to test these theories. Heavy grazing by elk in Yellowstone caused some areas to be dominated by exotic grasses, while shrubby species w ere heavily browsed. High-elevation rangeland conditions deteriorated in the Southwest where elk and cattle both grazed. Theories of herbivo re optimization and overcompensation do not appear to be supported the response of western rangelands to grazing by native herbivores.