Ecosystems (short for ecological systems) are functional units that result from the interactions of abiotic, biotic, and cultural (anthropogenic) components. Like all systems they are a combination of interacting, interrelated parts that form a unitary whole. All ecosystems are "open" systems in the sense that energy and matter are transferred in and out. The Earth as a single ecosystem constantly converts solar energy into myriad organic products, and has increased in biological complexity over time.

Natural ecosystems, made up of abiotic factors (air, water, rocks, energy) and biotic factors (plants, animals, and microorganisms). The Earth’s biosphere, including the atmosphere (air), hydrosphere (water), and litosphere (land), constitutes a feedback of cybernatic system that reflects what Rene Dubos referred to as "a co-evolutionary process" between living things and their physical and chemical environments. Ecosystem is made up of many smaller ecosystems interlocked through cycles of energy and chemical elements. The flow of energy and matter through ecosystems, therefore, is regulated by the complex interactions of the energy, water, carbon, oxygen, nitrogen, phosphorus, sulfur, and other cycles that are essential to the functioning of the biosphere. (Eblen and Eblen, 1994, p. 185)

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Rudolf Husar Last updated 10/26/94.