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An ecosystem, a contraction of "ecological" and "system", refers to the collection of biotic and abiotic components and processes that comprise, and govern the behaviour of some defined subset of the biosphere.

The word ecosystem is generally understood as to the entire assemblage of organisms (plant, animal and other living beings—also referred to as a biotic community or biocoenosis) living together in a certain space with their environment (or biotope), functioning as a loose unit. Together, these components and their interactions with and relationships to each other form a dynamic and complex new whole, functioning as an "ecological unit", with additional characteristics that can't be found in the individual components. There are no conceptual restrictions on how large or small a space or an area must be, nor on the minimum numbers species or individual organisms to be present.

Early conceptions of an ecosystem were as a structured functional unit in equilibrium of energy and matter flows among constituent elements. Some considered this vision limited,and preferred to view an ecosystem in terms of cybernetics, which, like any other type of system, is governed by the rules of systems science and cybernetics, as applied specifically to collections of organisms and relevant abiotic components. The branch of ecology that gave rise to this view has become known as systems ecology.

To many ecologists, "regulationists", ecosystems are somehow regulated by some kind of control mechanism intrinsic to the system, that strives to achieve a certain "Steady state" in which all components are at some degree of equilibrium with each other, often referred to as the "balance of nature". Some scholars go as far as to consider the biosphere as a single new self-regulating organism: the "Gaia theory". The steady state is understood as the phase of an ecological system's evolution when the organisms are "balanced" with each other and their environment. This balance is regulated through various types of interactions, such as predation, parasitism, mutualism, commensalism, competition, and amensalism. Introduction of new elements, whether abiotic or biotic, into an ecosystem tend to have a disruptive effect. In some cases, this can lead to ecological collapse or "trophic cascading" and the death of many species belonging to the ecosystem in question. Under this deterministic vision, the abstract notion of ecological health attempts to measure the robustness and recovery capacity for an ecosystem; that is, how far the ecosystem is away from its steady state.

To others, (den Boer & Reddingius, 1996), ecosystems are primarily governed by stochastic events, the reactions they provoke on non-living materials and the responses by organisms to the conditions surrounding them. Thus, ecosystems result from the sums of infinite individual responses of organisms to stimuli from non-living and living elements in the environment. The presence or absence of populations merely depends on reproductive and dispersal success and population levels fluctuate in response to stochastic (chance) events. As the number of species in an ecosystem is higher, the number of stimuli is also higher.

In their vision, since the beginning of life, organisms have survived continuous change through natural selection of successful feeding, reproductive and dispersal behaviour by means of which the planet's species have continuously adapted to change through variation in their biological composition and distribution. Mathematically it can be demonstrated that greater numbers of different interacting factors, tend to dampen fluctuations in each of the individual factors. Given the great diversity among organisms on earth, most of the time, ecosystems only changed very gradually, as some species would disappear while others would move in or evolve. Locally, sub-populations continuously go extinct, to be replaced later through dispersal of other sub-populations. Stochastists do recognise that certain intrinsic regulating mechanisms occur in nature. Feedback and response mechanisms at the species level regulate population levels, most notably through territorial behaviour. Andrewatha and Birch (1954), suggest that territorial behaviour tends to keep populations at levels where food supply is not a limiting factor. Hence, stochastists see territorial behaviour as a regulatory mechanism at the species level but not at the ecosystem level. Thus, in their vision, ecosystems are not regulated by feedback and response mechanisms from the (eco)system itself and there is no such thing as a balance of nature and.

If ecosystems would primarily be governed by stochastic processes, they may be somewhat more resilient to sudden change, as each species would respond individually. In the absence of a balance of nature, the species composition of ecosystems would undergo shifts that would depend on the nature of the change, but entire ecological collapse would probably be less frequently occurring events.

Ecosystems have become particularly important politically, since the Convention on Biological Diversity (CBD) - ratified by more than 175 countries - defines "the protection of ecosystems, natural habitats and the maintenance of viable populations of species in natural surroundings" as one of the binding commitments of the ratifying countries. This has created the political necessity to spatially identify ecosystems and somehow distinguish among them. The CBD defines an "ecosystem" as a "dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit".

With the need of protecting ecosystems, the political need arose to describe and identify them within a reasonable time and cost-effectively. Vreugdenhil et al. argued that this could most effectively be achieved using a physiognomic-ecological classification systems, as they are easily recognizable in the field as well as on satellite images. They argued that the structure and seasonality of the vegetation, complemented with ecological data, such as elevation, humidity, drainage, salinity of water, characteristics of water bodies, each are determining modifiers that separate partially distinct sets of species. This is true not only for plant species, but also for species of animals, fungi and bacteria. The degree of ecosystem distinction is subject to the physiognomic modifiers that can be identified on an image and/or in the field. Where necessary, specific fauna elements can be added, such as periodic concentrations of animals and the distribution of coral reefs. Several physiognomic-ecological are available: the UNESCO system: Physiognomic-Ecological Classification of Plant Formations of the Earth, Mueller Dombois and Ellenberg, 1974, and its derivatives, develloped by the United States Vegetation Committee USVCS and the FAO develloped Land Cover Classification System, LCCS. Several systems aquatic systems are available and an effort is being made by the USGS and IABIN to design a complete ecosystem classification system that covers both terrestrial and aquatic ecosystems.

History

The term ecosystem first appeared in a 1935 publication by the British ecologist Arthur Tansley (1935). However, the term had been coined already in 1930 by Tansley's colleague Roy Clapham, who was asked if he could think of a suitable word to denote the physical and biological components of an environment as a single unit. Tansley expanded on the term in his later work, adding the ecotope concept to define the spatial context of ecosystems (Tansley, 1939). Modern usage of the term derives from the work done by Raymond Lindeman in his classic study of a Minnesota lake (Lindeman, 1942). Lindeman's central concepts were that of functional organisation and ecological energy efficiency ratios. This approach is connected to ecological energetics and might also be thought of as environmental rationalism. It was subsequently applied by H.T.Odum, sometimes called the 'father' of ecosystems ecology, in founding the transdiscipline known as systems ecology.

The Millennium Ecosystem Assessment

In 2005, the largest ever assessement of the earth's ecosystems was conducted by a research team of over 1,000 scientists. The findings of the assessment were published in the multivolume Millennium Ecosystem Assessment and concluded that in the past 50 years, humans have altered the earth's ecosystems more than at any other time in our history.

Hotspots

Ecosystem "hotspots" are ecosystems and the species they support that are considered at risk or endangered.

Canada

(Source: Canadian Geographic Online)

Types of ecosystems

Definitions outside ecology

Humans are not part of the ecosystems

See also

References

  • Andrewartha, H. G., and L. C. Birch. 1954. The distribution and abundance of animals. Univ. of Chicago Press, Chicago, IL.
  • Boer, P. J. den, and J. Reddingius. 1996. Regulation and stabilization paradigms in population ecology. Population and Community Biology Series 16. Chapman and Hall, New York. 397 pg.
  • Lindeman, R. L. 1942. The trophic-dynamic aspect of ecology. Ecology 23: 399-418.
  • Patten, B.C. 1959. An Introduction to the Cybernetics of the Ecosystem: The Trophic-Dynamic Aspect. Ecology 40, no. 2.: 221-231.
  • Tansley, A. G. 1935. The use and abuse of vegetational concepts and terms. Ecology 16: 284-307.
  • Tansley, A.G. 1939. The British Islands and their Vegetation. Volume 1 of 2. University Press, Cambridge, Cambridge, United Kingdom. 484 pg.
  • Vreugdenhil, D., Terborgh, J., Cleef, A.M., Sinitsyn, M., Boere, G.C., Archaga, V.L., Prins, H.H.T., 2003, Comprehensive Protected Areas System Composition and Monitoring, IUCN, Gland, Switzerland. 106 pg.

External links


Smallwikipedialogo.png This page uses content from Wikipedia. The original article was at Ecosystem. The list of authors can be seen in the page history. As with Paleontology Wiki, the text of Wikipedia is available under the GNU Free Documentation License.

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