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An ecosystem is a natural system consisting of all plants, animals and microorganisms (biotic factors) in an area functioning together with all the non-living physical (abiotic) factors of the environment.
The term ecosystem was coined in 1930 by Roy Clapham, to denote the physical and biological components of an environment considered in relation to each other as a unit. British ecologist Arthur Tansley later refined the term, describing it as the interactive system established between biocoenosis (a group of living creatures) and their biotope (the environment in which they live).
Central to the ecosystem concept is the idea that living organisms are continually engaged in a set of relationships with every other element constituting the environment in which they exist. The human ecosystem concept is then grounded in the deconstruction of the human/nature dichotomy, and the emergent premise that all species are ecologically integrated with each other, as well as with the abiotic constituents of their biotope.
Ecosystems can be bounded and discussed with tremendous variety of scope, and describe any situation where there is relationship between organisms and their environment. A system as small as a household or university, or as large as a nation state, may then be suitably discussed as a human ecosystem. While they may be bounded and individually discussed, (human) ecosystems do not exist independently, but interact in a complex web of human and ecological relationships connecting all (human) ecosystems to make up the biosphere. As virtually no surface of the earth today is free of human contact, all ecosystems can be more accurately considered as human ecosystems.
- Community: The organisms (plants and animals) in an ecosystem.
- Ecosystem hotspots: These are ecosystems where the species they support are at risk or endangered.
- Habitat: The type of environment that the organisms have adapted to and live in.
The term ecosystem, while originally used in an ecology context, has also been adapted and applied in other disciplines:
The Study Of Ecosystems
Introduction of new elements, whether biotic or abiotic, 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; i.e. how far the ecosystem is away from its steady state.
Ecosystems are primarily governed by stochastic (chance) events, the reactions they provoke on non-living materials and the responses by organisms to the conditions surrounding them. Thus, an ecosystem results from the sum of myriad 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 events. As the number of species in an ecosystem is higher, the number of stimuli is also higher. Since the beginning of life, in this vision, organisms have survived continuous change through natural selection of successful feeding, reproductive and dispersal behaviour. Through natural selection 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. 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.
If ecosystems are indeed governed primarily 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.
The Millennium Ecosystem Assessment
In 2005, the largest ever assessment  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 multi volume Millennium Ecosystem Assessment, which concluded that in the past 50 years humans have altered the earth's ecosystems more than any other time in our history.
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 be achieved most effectively by using a physiognomic-ecological classification system, as ecosystems are easily recognizable in the field as well as on satellite images. They argued that the structure and seasonality of the associated vegetation, complemented with ecological data (such as elevation, humidity, drainage, salinity of water and characteristics of water bodies), are each 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 classification systems are available: Physiognomic-Ecological Classification of Plant Formations of the Earth (a system based on the 1974 work of Mueller-Dombois and Heinz Ellenberg, and developed by UNESCO), and the Land Cover Classification System (LCCS), developed by the Food and Agriculture Organization (FAO). Several aquatic classification systems are available, and an effort is being made by the United States Geological Survey (USGS) and the Inter-American Biodiversity Information Network (IABIN) to design a complete ecosystem classification system that will cover both terrestrial and aquatic ecosystems. An ecosystem also consists of all the organisms living in an area and the nonliving features of the environment.
Ecosystem services are “fundamental life-support services upon which human civilization depends,”i and can be direct or indirect. Example of direct ecosystem services are: pollination, wood, erosion prevention etc. Indirect services could be considered climate moderation, nutrient cycles, detoxifying natural substances and many more.
Ecosystem legal rights
The borough of Tamaqua, Pennsylvania passed a law giving ecosystems legal rights. The ordinance establishes that the municipal government or any Tamaqua resident can file a lawsuit on behalf of the local ecosystem.  Other townships, such as Rush, followed suit and passed their own laws.
This is part of a growing body of legal opinion proposing 'wild law'. Wild law, a term coined by Cormac Cullinan (a lawyer based in South Africa), would cover birds and animals, rivers and deserts.
Function and biodiversity
Biodiversity in an ecosystem helps it to stay resilient, “the magnitude of disturbance that can be absorbed or accommodated by an ecosystem before its structure is fundamentally changed to a different state”ii . As well as resistant, or resist change that would alter the ecosystem. From an anthropological viewpoint it also gives a greater number of ecosystem services to draw upon and depend on, such a medicinal plants and rich soils. Studies show that, “Many observational, experimental, and theoretical studies have found that species-rich communities have higher values of some ecosystem functioning than species in poor communities.”iii
- Christopherson, Robert W. (1997). Geosystems: An Introduction to Physical Geography (in english), 3rd. Upper Saddle River, NJ, USA: Prentice Hall Inc.. ISBN 0-13-505314-5.
- Wilson, Edward O. (1992). The Diversity of Life (in english). New York, NY, USA: W.W. Norton & Company Inc.. ISBN 0-393-31047-7.