In recent decades, the biosphere has become increasingly stressed, often beyond the point where the internal structure and function of ecosystems are sustained. We have experienced an intensified "exploration" of natural system resources to support agricultural and forest production, to provide water for human consumption, to supply the needs of industrial processes, and to provide, in addition, attractive, diverse landscapes for recreation and tourism. Exceeding thresholds via anthropogenic disturbance that results in degradation of ecosystems is dangerous, since the system-level effects and...