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A coral reef near the Hawaiian islands is an example of a complex marine ecosystem.
A coral reef near the Hawaiian islands is an example of a complex marine ecosystem.
Arctic tundra on Wrangel Island, Russia.
Arctic tundra on Wrangel Island, Russia.

An ecosystem is a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment.[1]

Contents

Overview

Flora of Baja California Desert, Cataviña region, Mexico.
Flora of Baja California Desert, Cataviña region, Mexico.
Savanna at Ngorongoro Conservation Area, Tanzania.
Savanna at Ngorongoro Conservation Area, Tanzania.
Map of Terrestrial biomes classified by vegetation.
Map of Terrestrial biomes classified by vegetation.

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 whole system,… including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment".[2] Tansley regarded the ecosystems not simply as given natural units but as "mental isolates" [3]. Tansely later defined the spatial extent of ecosystems using the term "ecotope" in 1939.

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. Eugene Odum, one of the founders of the science of ecology, stated: "Any unit that includes all of the organisms (ie: the "community") in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (ie: exchange of materials between living and nonliving parts) within the system is an ecosystem."[4] 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.

A very similar term to an ecosystem is a biome , which is a climatically and geographically defined area of ecologically similar climatic conditions such as communities of plants, animals, and soil organisms, often referred to as ecosystems. Biomes are defined based on factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), plant spacing (forest, woodland, savanna), and climate. Unlike ecozones, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation.

Ecosystems can be bounded and discussed with tremendous variety of scope, and describe any situation where there is relationship between organisms and their environment. If humans are part of the organisms, one can speak of a 'human ecosystem'. As virtually no surface of the earth today is free of human contact, all ecosystems can be more accurately considered as human ecosystems, or more neutrally as human-influenced ecoystems.

Examples of ecosystems

=== Classification ===
=== Ecosystem services ===
=== Ecosystem legal rights ===
=== Function and biodiversity ===

The study of ecosystems

View of the home planet, taken in 1972 by the Apollo 17 crew. This image is the only photograph of its kind to date, showing a fully sunlit hemisphere of the Earth.
View of the home planet, taken in 1972 by the Apollo 17 crew. This image is the only photograph of its kind to date, showing a fully sunlit hemisphere of the Earth.

Ecosystem dynamics

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.

Often, however, ecosystems have the ability to rebound from a disruptive agent. The difference between collapse or a gentle rebound is determined by two factors -- the toxicity of the introduced element and the resiliency of the original ecosystem.

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 behavior. 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 recognize 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 theoretical ecologist Robert Ulanowicz has used information theory tools to describe the structure of ecosystems, emphasizing mutual information (correlations) in studied systems. Drawing on this methodology, and prior observations of complex ecosystems, Ulanowicz depicts approaches to determining the stress levels on ecosystems, and predicting system reactions to defined types of alteration in their settings (such as increased or reduced energy flow, and eutrophication.[5] See also Relational order theories, as to fundamentals of life organization.

Ecosystem ecology

Forest on San Juan Island
Forest on San Juan Island

Ecosystem ecology is the integrated study of biotic and abiotic components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals. Ecosystem ecology examines physical and biological structure and examines how these ecosystem characteristics interact]]

The relationship between systems ecology and ecosystem ecology is complex. Much of systems ecology can be considered a subset of ecosystem ecology. Ecosystem ecology also utilizes methods that have little to do with the holistic approach of systems ecology. However, systems ecology more actively considers external influences such as economics that usually fall outside the bounds of ecosystem ecology. Whereas ecosystem ecology can be defined as the scientific study of ecosystems, systems ecology is more of a particular approach to the study of ecological systems and phenomena that interact with these systems.

Systems ecology

An aerial view of a human ecosystem. Pictured is the city of Chicago
An aerial view of a human ecosystem. Pictured is the city of Chicago

Systems ecology is an interdisciplinary field of ecology, taking a holistic approach to the study of ecological systems, especially ecosystems. Systems ecology can be seen as an application of general systems theory to ecology. Central to the systems ecology approach is the idea that an ecosystem is a complex system exhibiting emergent properties. Systems ecology focuses on interactions and transactions within and between biological and ecological systems, and is especially concerned with the way the functioning of ecosystems can be influenced by human interventions. It uses and extends concepts from thermodynamics and develops other macroscopic descriptions of complex systems.

The Millennium Ecosystem Assessment

In 2005, the largest ever assessment[6] 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.

See also

Earth_sciences portal
Ecology portal
Environment portal

References

  1. ^ Robert W. Christopherson (1996). Geosystems: An Introduction to Physical Geography. Prentice Hall Inc.
  2. ^ A.G. Tansley (1935). "The use and abuse of vegetational terms and concepts". In: Ecology Vol 16 pp. 284-307.
  3. ^ Tansley, A.G. 1935. The use and abuse of vegetational concepts and terms. Ecology 16: 284-307
  4. ^ Odum EP (1971) Fundamentals of ecology, third edition, Saunders New York
  5. ^ Robert Ulanowicz (1997). Ecology, the Ascendant Perspective. Columbia Univ. Press. ISBN 0-23-110828-1.
  6. ^ http://www.maweb.org

Further reading

  • 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.
  • Ecological Society of America, Ecosytem Services, Ecological Society of America. 25 May 2007
  • Ehrlich, Paul; Walker, Brian “Rivets and Redundancy”.BioScience.vol.48.no.5. May 1998. pp. 387. American Institute of Biological Sciences.
  • Grime, J.P. "Biodiversity and Ecosystem Function: The Debate Deepens." Science Vol. 277. no. 533029 Aug 1997 pp. 1260 - 1261. 25 May 2007
  • Groom , Martha J., and Gary K. Meffe. Principles of Conservation Biology. 3. Sunderland, MA: Sinauer Associates, Inc, 2006.
  • Lawton, John H., What Do Species Do in Ecosystems?, Oikos, December, 1994. vol.71,no.3.
  • Lindeman, R.L. 1942. The trophic-dynamic aspect of ecology. Ecology 23: 399-418.
  • Ranganathan, J & Irwin, F. (2007, May 7). Restoring Nature's Capital: An Action Agenda to Sustain Ecosystem Services
  • 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.

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