Nonequilibrium Ecology and Resilience Theory

Abstract

Nonequilibrium ecology and resilience theory have transformed rangeland ecology and management by challenging the traditional assumptions of ecological stability and linear successional dynamics. These alternative interpretations indicate that ecosystem dynamics are strongly influenced by disturbance, heterogeneity, and existence of multiple stable states. The nonequilibrium persistent model indicates that plant production and livestock numbers are seldom in equilibrium in pastoral systems because reoccurring drought maintains livestock number below the ecological carrying capacity. However, it has recently been demonstrated that live- stock are often in equilibrium with key dry-season resources, even though they may only be loosely coupled to abundant wet-season resources. Similarly, state- and- transition models were initially influenced by nonequilibrium ecology, but they have subsequently been organized around resilience theory to represent both equilibrial dynamics within states and existence of multiple states. Resilience the- ory was introduced to describe how ecosystems can be dynamic, but still persist as self- organized systems. It envisions that community structure is maintained by ecological processes representing feedback mechanisms and controlling variables to moderate community fluctuation in response to disturbance. Appropriate qualifica- tion of equilibrium ecology within resilience theory, rather than its complete replacement by nonequilibrium models, provides more realistic interpretations for both plant–herbivore interactions and vegetation dynamics than does complete reli- ance on disturbance-driven events. Resilience thinking represents a “humans-in- nature” perspective that emphasizes human values and goals and it seeks to guide change in social-ecological systems by creating opportunities for multiple stakeholders to adaptively design management strategies and policies.