From Balance of Nature to Hierarchical Patch Dynamics: A Paradigm Shift in Ecology
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Abstract
A common assumption historically in ecology is evident in the term "balance of nature." The phrase usually implies that undisturbed nature is ordered and harmonius, and that ecological systems return to a previous equilibrium after disturbances. The more recent concepts of point equilibrium and static stability, which characterize the classical equilibrium paradigm in ecology, are traceable to the assumptions implicit in "balance of nature." The classical equilibrium view, however, has failed not only because equilibrium conditions are rare in nature, but also because of our past inability to incorporate heterogeneity and scale multiplicity into our quantitative expresssions for stability. The theories and models built around these equlibrium and stability principles have misrepresented the foundations of resource management, nature conservation, and environemtnal protection. In this paper, we sysntesize recent developments that advance our understandings of equilibrium vs. nonequilibrium, homogeneity vs. heterogeneity, determinism vs. stochasticity, and single-sclae phenomenon vs. hierarchical linkages in ecological systems. The integration of patch dynamics with hierarchy theory has led to new perspectives in spatial and temporal dynamics, with explicit linkage between scale and heterogeneity. The major elements of the hierarchical patch dynamics paradigm include the idea of nested hirarchies of patch mosaics, ecosystem dynamics as a composite of patch changes in time and space, the pattern-process-scale perspecitve, the nonequilibrium perspective, and the concepts of incorporation and metastability. Both enviromental stochasticities and biotic feedback interactions can cause instability and contribute to the dynamcis observed a various scales. Stabilizing mechanisms that dampen these destabilizing forces include spatial incorporation, environmental disturbances, biological compensatory mechanisms, and heterogeneity absorpion. Hierarchical patch dynamics incorporates certain "emergent properties" of ecological system, such as metastabilityor persistence at the meta-scale, as opposed to the transient dynamics that usually characterize local phenomena. In contrast to the stability that derives from an assumed self-regulation in a closed system, the concepts of incorporation and metastability deal explicity with multiple-scale processes and the consequences of heterogeneity. The most imporatant contribution of hierarchical patch dynamics lies in the framework provided for explicitly incorporating heterogeneity and scale, and for integrating equilibrium, multiple equilibrium, and nonequilibrium perspectives.