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Ross A. Virginia* and Diana H. Wall†
*Dartmouth College; † Colorado State University


Development of the Ecosystem Concept Ecosystem Functioning and Ecosystem Services Important Ecosystem Functions Conclusions

ecosystem All the individuals, species, and populations in a spatially defined area and the interactions among them andwith the abiotic environment. ecosystem functioning The sum total of processes such as the cycling of matter, energy, and nutrients operating at the ecosystem level. functional group A group of species that perform similar roles in an ecosystem process. nutrient cycle (or biogeochemical cycle) The repeated pathway of mineral elements, such as carbon, nitrogen, phosphorus, and water, from theenvironment through organisms and back into the environment. succession The predictable change in species that occupy an area over time caused by a change in biotic or abiotic factors benefiting some species but at the expense of others.

their environment are represented in processes that are called ecosystem functions. The capture of solar energy (photosynthesis), the cycling of nutrients, and thestability of ecosystem functioning are influenced by biodiversity. An understanding of how biodiversity and ecosystem functioning are related is necessary for determining how to sustain human populations in the future.

The concept of the ecosystem as a functioning unit in the natural world is a relatively recent one. The term ecosystem was coined by theBritish ecologist Tansley in 1935 and has since become a common word in science and with the public. An ecosystem encompasses all the organisms of a given area and their relationships with one another and the physical or abiotic environment. The ecosystem contains the linkages and dynamic interactions between life and the environment, many of which are essential to society. A focus on the ecosystemas the unit of study represents a shift from studying the ecology and behavior of individual organisms and species (natural history) to the study of processes and how they influence or are influenced by organisms and their interactions with the environment. Dividing the complexity of nature into convenient units of study is required for scientific investigation but can present problems. Ecologicalsystems can be

ECOSYSTEMS ARE COMPOSED OF COMMUNITIES of organisms that interact with one another and the abiotic environment. The interactions of organisms and

Encyclopedia of Biodiversity, Volume 2 Copyright  2001 by Academic Press. All rights of reproduction in any form reserved.



Examples of the Biological and Physical Processesor Interactions That Contribute to Important Ecosystems Functions Process Photosynthesis Plant nutrient uptake Microbial respiration Soil and sediment food web dynamics Nitrification Denitrification Nitrogen fixation Plant transpiration Root activity Mineral weathering Soil bioturbation Vegetation succession Predator–prey interactions Ecosystem function Primary production Decomposition Nitrogencycling

organized in a hierarchy of increasing levels of organization and complexity: individual, population, species, community, ecosystem, landscape, and biome. The size (scale) of an ecosystem is defined by the purposes of the study. Ecosystems may have distinct boundaries as in the case of a lake or a watershed. More often, the boundaries of one ecosystem (a forest) may grade gradually intoanother (a meadow) across an intermediate area called an ecotone. The ecotone is often a zone of higher diversity because it may be a suitable habitat for species from each of the adjoining ecosystems. At one extreme of scale, the earth is sometimes treated as an ecosystem. At the other extreme, the complex symbiotic community of organisms inhabiting the gut of a termite has all the functional...
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