Ecosystem

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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 behavior of some defined subset of the biosphere. Elements of an ecosystem may include flora, fauna, lower life forms, water and soil.

Contents 1 Ecosystem dynamics 2 Classification 3 History of the term 4 The Millennium Ecosystem Assessment 5 Hotspots 6 Ecosystem examples 7 Definitions outside ecology 8 See also 9 References 10 External links

[edit] Ecosystem dynamics

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 (chance) 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 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 behavior. 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 behavior 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.

[edit] Classification

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.

[edit] History of the term

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.

[edit] 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 multivolume Millennium Ecosystem Assessment, which concluded that in the past 50 years humans have altered the earth's ecosystems more than at any other time in our history.

[edit] Hotspots

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

[edit] Ecosystem examples

• Aquatic ecosystem
  
• Coral reef
  
• Greater Yellowstone Ecosystem
  
• Human ecosystem
  
• Large marine ecosystem
  
• Marine ecosystem
  
• Subsurface Lithoautotrophic Microbial Ecosystem
  
• Taiga
  
• Tundra
  
• Urban ecosystem
  

[edit] Definitions outside ecology

• Anthroposystem
• Business ecosystem
• Corporate Ecosystem
• Digital ecosystem
• Knowledge Ecosystem
• Media ecosystem

[edit] See also

• Biodiversity Action Plan
• Biogeochemical cycle
• Biome
• Biosphere
• Biosphere 2
• Ecological economics
• Ecological yield
• Ecoregion
• Ecosystem diversity
• Ecosystem ecology
• Ecosystem engineer
• Ecosystem model
• Ecosystem services
• Ecosystem valuation
• Edge effect
• Eugene Odum
• Food chain
• Invasive species
• Landscape ecology
• Leaf
• List of biogeographic provinces
• Long-term Ecosystem Observatory
• Overfishing
• Principles of Intelligent Urbanism
• Systems ecology
• The Ecosystem Approach
• Trophic level

[edit] References

[edit] External links

• The ecosystems
• Teaching about Ecosystems
• Millennium Ecosystem Assessment (2005)
• A popularized version of the Millennium Ecosystem Assessment by GreenFacts.
• Bering Sea Climate and Ecosystem: current status
• Arctic Climate and Ecosystem: current status
• The State of the Nation's Ecosystems