Ecosystem

From Palaeos

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.

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."

[edit] 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 Howard T. Odum, sometimes called the 'father' of ecosystems ecology, in founding the transdiscipline known as systems ecology.

[edit] Description

The ecosystem is composed of two entities, the entirety of life, the biocoenosis and the medium that life exists in, the biotope. Within the ecosystem, species are connected by food chains or food webs. Energy from the sun, captured by primary producers via photosynthesis, flows upward through the chain to primary consumers (herbivores), and then to secondary and tertiary consumers (carnivores), before ultimately being lost to the system as waste heat. In the process, matter is incorporated into living organisms, which return their nutrients to the system via decomposition, forming biogeochemical cycles such as the carbon and nitrogen cycles.

The concept of an ecosystem can apply to units of variable size, such as a pond, a field, or a piece of deadwood. A unit of smaller size is called a microecosystem. For example, an ecosystem can be a stone and all the life under it. A mesoecosystem could be a forest, and a macroecosystem a whole ecoregion, with its drainage basin.

The main questions when studying an ecosystem are:

• Whether the colonization of a barren area could be carried out
• Investigation the ecosystem's dynamics and changes
• The methods of which an ecosystem interacts at local, regional and global scale
• Whether the current state is stable
• Investigating the value of an ecosystem and the ways and means that interaction of ecological systems provide benefit to humans, especially in the provision of healthy water.

Ecosystems are often classified by reference to the biotopes concerned. The following ecosystems may be defined:

• As continental ecosystems, such as forest ecosystems, meadow ecosystems such as steppes or savannas), or agro-ecosystems
• As ecosystems of inland waters, such as lentic ecosystems such as lakes or ponds; or lotic ecosystems such as rivers
• As oceanic ecosystems.

Another classification can be done by reference to its communities, such as in the case of an human ecosystem.

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.

[edit] 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.

[edit] 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

[edit] Credits