Rangeland Ecology in a Changing World

Millions of people in rangelands depend directly on livestock for their livelihoods, but the management of these regions is mired in controversy (see the figure). Early colonial efforts imposed economic management models based on equilibrium carrying capacities. In the 1990s, however, “the new ecology” took hold and challenged equilibrium models by exploring the variability and flux inherent in most ecological and social systems (1). Such models (2) described a disequilibrium rangeland system, in which animal numbers were limited by drought events, thereby preventing an impact on vegetation (3). Since then, a variety of rangeland responses have been described, in which environmental variation and density-dependent effects on animal numbers are observed to a greater or lesser extent.