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  An ecosystem (Greek oikos, ‘home’ + system) is an interdependent community of living organisms, united by the environment in which they live. It is essentialy a human concept, useful for the study of the ecology of biological communities, but of limited use as a definition because no community lives entirely in isolation from others; the biosphere itself is probably the only complete ecosystem. However, in order to study the complex interactions which make up the web of life it is necessary to break down the biosphere into extremely simple units; thus an ecosystem may be a rotting log and the living organisms which base their lives around it, or the intestines of a cow and the various organisms that live within it. Ecosystems are best studied in terms of the interactions between individual organisms—these interactions can be described as energy and/or material exchange along the food chain. In this way ecosystems can be broken down into trophic levels, of which each is composed of individuals which derive nutrition in a certain basic way such as by harvesting sunlight or by hunting animals.

The basic trophic levels in any ecosystem are producers (the green plants), consumers (herbivores and carnivores) and reducers (bacteria, fungi and other organisms which reduce organic matter to an inorganic form. Material is transferred with energy and is thus cycled within the ecosystem, returning to the non-living environment where it becomes available once more to producers. The cycles of transfer of elements such as nitrogen and carbon can also reveal much about the characteristics of a given ecosystem. The environment is the non-living surroundings which support the biological community; in the case of terrestrial ecosystems it can be broken down into soil and climate. The environment provides physical support and is the reservoir for the basic materials which are required by the producers. The continuous nature of the environment illustrates how it is unrealistic to consider any ecosystem in isolation from those which surround it. RB

See also biome; conservation; food web.Further reading Joseph Moran, Introduction to Environmental Science.



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