Ecosystem

From Wikipedia, the free encyclopedia

An ecosystem, a contraction of "ecological" and "system", refers to the collection of components and processes that comprise, and govern the behavior of, some defined subset of the biosphere. The term is generally understood to refer to all biotic and abiotic components, and their interactions with each other, in some defined area, with no conceptual restrictions on how large or small that area can be. To many, ecosystems, like any other system, are governed by the rules of systems science and cybernetics, as applied specifically to collections of organisms and relevant abiotic components. To others, ecosystems are primarily governed by stochastic events, the reactions they provoke on non-living materials and the corresponding responses by organisms.

Overview

In general terms an ecological system can be thought of as an assemblage of organisms (plant, animal and other living organisms—also referred to as a biotic community or biocoenosis) living together with their environment (or biotope), functioning as a loose unit. That is, a dynamic and complex whole, interacting as an "ecological unit."

Ecosystems have become particularly important politically, since the Convention on Biological Diversity - 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". 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 define an ecosystem in terms of cybernetics. From this point of view an ecological system is a functional dynamic organization, or steady state. 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 would 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 and the death of many native species. The branch of ecology that gave rise to this view has become known as systems ecology. 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 steady state.

Other population ecologists, stochastists, (den Boer & Reddingius, 1996), view an ecosystem as an expression of stochastic events, and corresponding responses from organisms. 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. Mathematically it can be demonstrated that greater numbers of different interacting factors, tend to dampen fluctuations in each of the individual factors. In this vision, ecosystems are not regulated and there is no balance of nature. Stochastists do recognise that certain intrinsic regulating mechanisms occur in nature. In their vision they 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.

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.

Hotspots

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

Canada

• Atlantic coastal plain flora: Atlantic Coastal Plain Flora (ACPF)
• Carolinian forest
• Tall grass prairie
• South Okanagan’s antelope-brush ecosystem
• Coastal Douglas fir forest
• Eelgrass meadow

(Source: Canadian Geographic Online)

See also

• Biodiversity Action Plan
• Ecological Economics
• Biogeochemical cycle
• Biome
• Biosphere
• Biosphere 2
• Ecological yield
• Ecoregion
• Ecosystem ecology
• Edge effect
• Eugene Odum
• Food chain
• Invasive species
• Landscape ecology
• Overfishing
• Systems ecology
• Trophic level

Types of ecosystems

• Aquatic ecosystem
• Arctic Tundra
• Boreal Forest
• Urban ecosystem

Definitions outside ecology

• Anthroposystem
• Corporate Ecosystem
• Media ecosystem

References

External links

• 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