The Ecological Concept of Disturbance and Its Expression at Various Hierarchical Levels

Abstract

Current definitions ofdisturbance are intuitive, narrow, and only implicitly based on system structure. This is because the concepts are based on experience at particular levels of organization or on systems whose structure is well known. The definitions are thus inadequate for the development of a general theory of ecological disturbance. A universally applicable definition would 1) identify the object disturbed; 2) distinguish between change in the object that is disturbance versus change that is not; and 3) distinguish between direct and indirect consequences of disturbance. To meet these requirements, we formally link the hierarchical organization of ecological objects and the concept of disturbance. Any persistent ecological object will have a minimal structure, or system of lower level entities that permit its persistence. Disturbance is a change in the minimal structure of an object caused by a factor external to the level of interest. Using these definitions, disturbancean be unequivocally identified and associated with various specific ecological levels of organization. Because of the dependence of the concept of disturbance on recognizing the minimal structure of ecological systems, application of the concept will advance as refined models of the hierarchical structure of ecological systems are elaborate.