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Grand Teton National Park and Yellowstone National Park

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Ecosystems that possess physical, chemical and biological elements interacting in ways necessary for sustainability are said to have integrity. While conceptually appealing, measuring the condition of ecosystems has proven difficult. Ecosystems are thought to respond to stressors (e.g. detrimental or disorganizing influences) through changes in functional attributes such as energy flow and nutrient cycling and through changes in community structure as well as general system-level changes (Margalef 1981; Odum 1985; Kay and Schneider 1993). Attempts to assess ecosystem condition have rarely considered energy flow and focused instead on either community structure or nutrient cycling (Karr 1993). Although energy flow has not been widely used as a tool in assessing and monitoring ecosystems, its importance to ecosystem integrity is recognized (Ricklefs 1979). All systems require energy and altering the nature (quantity, flow, flux) of that energy supply alters the quality of the ecosystem. In spite of this knowledge few, if any, agency programs devote attention to balancing energy sources (Karr 1993). Recent research suggests that positive relationships between biodiversity and energy flow within ecosystems may exist (Tillman 1996).