The term
ecosystem refers to the combined physical
and biological components of an environment. An ecosystem is
generally an area within the
natural
environment in which physical (
abiotic)
factors of the environment, such as rocks and soil, function
together along with interdependent (
biotic)
organisms, such as plants and animals,
within the same habitat. Ecosystems can be permanent or temporary.
Ecosystems usually form a number of
food
webs.
Overview
Central to the ecosystem concept is the idea that
living organisms interact with every other
element in their local
environment. Eugene Odum, a
founder 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." The human ecosystem concept is
then grounded in the deconstruction of the human/nature
dichotomy and the premise that all species are
ecologically integrated with each other, as well as with the
abiotic constituents of their
biotope.
Etymology
The term ecosystem was coined in 1930 by
Roy
Clapham to mean the combined physical and biological components
of an environment. 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". Tansley regarded ecosystems
not simply as natural units, but as mental isolates. Tansley later
defined the spatial extent of ecosystems using the term
ecotope.
Examples of ecosystems
Biomes
Biomes are similar to ecosystems, and are
climatic 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.
Ecosystem topics
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 a commitment of 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 efficiently. 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, and drainage), 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 seasonal 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. This
classificatie "describes the above-ground or underwater vegetation
structures and cover as observed in the field, described as plant
life forms. This classification is fundamentally a
species-independent physiognomic, hierarchical vegetation
classification system which also takes into account ecological
factors such as climate, elevation, human influences such as
grazing, hydric regimes, and survival strategies such as
seasonality. The system was expanded with a basic classification
for open water formations".
- Land Cover Classification System (LCCS), developed by the
Food and Agriculture
Organization (FAO).
- Forest-Range
Environmental Study Ecosystems (FRES) developed by the United States Forest Service
for use in the United
States.
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.
From a
philosophy of science
perspective, ecosystems are not discrete units of nature that
simply can be identified using "the right" classification approach.
In agreement with the definition by Tansley ("mental isolates"),
any attempt to delineate or classify ecosystems should be explicit
about the
observer/
analyst input in the classification including its
normative rationale.
Ecosystem services
Ecosystem services are “fundamental life-support services upon
which human civilization depends,”
i and can be direct or
indirect. Examples of direct ecosystem services are:
pollination,
wood, and
erosion prevention. Indirect services could
be considered
climate moderation,
nutrient cycles, and detoxifying natural
substances.
Ecosystem legal rights
Ecuador's new
constitution of 2008 is the first in the world to recognize legally
enforceable Rights of Nature, or ecosystem 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
From an anthropological point of view, some people perceive
ecosystems as production units that produce goods and services,
such as wood by forest ecosystems and grass for cattle by natural
grasslands. Meat from wild animals, often referred to as bush meat
in Africa, has proven to be extremely successful under
well-controlled management schemes in South Africa and Kenya. Much
less successful has been the discovery and commercialization of
substances of wild organism for pharmaceutical purposes. Services
derived from ecosystems are referred to as ecosystem services. They
may include (1) facilitating the enjoyment of nature, which may
generate many forms of income and employment in the tourism sector,
often referred to as eco-tourisms, (2) water retention, thus
facilitating a more evenly distributed release of water, (3) soil
protection, open-air laboratory for scientific research, etc.
A greater degree of species or biological diversity - popularly
referred to as
Biodiversity - of an
ecosystem may contribute to greater resilience of an ecosystem,
because there are more species present at a location to respond to
change and thus "absorb" or reduce its effects. This reduces the
effect before the ecosystem's structure is fundamentally changed to
a different state. This is not universally the case and there is no
proven relationship between the species diversity of an ecosystem
and its ability to provide goods and services on a sustainable
level: Humid tropical forests produce very few goods and direct
services and are extremely vulnerable to change, while many
temperate forests readily grow back to their previous state of
development within a lifetime after felling or a forest fire. Some
grasslands have been sustainably exploited for thousands of years
(Mongolia, Africa, European peat and mooreland communities).
The study of ecosystems
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
within the ecosystem. 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 these events provoke on non-living materials, and the
responses by organisms to the conditions surrounding them. Thus, an
ecosystem results from the sum of individual responses of organisms
to stimuli from 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
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 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 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 governed primarily by
stochastic processes, through which its
subsequent state would be determined by both predictable and random
actions, they may be more resilient to sudden change than each
species 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 infrequent 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.
- See also: Relational
order theories, as to fundamentals of life
organization
Ecosystem ecology
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.
See also
References
- which show the (1996) Geosystems: An Introduction to
Physical Geography. Prentice Hall Inc.
- Odum, EP (1971) Fundamentals of ecology, third edition,
Saunders New York
- Tansley, AG (1935) The use and abuse of vegetational terms and
concepts. Ecology 16, 284-307.
- Tansley, AG (1939) The British islands and their vegetation.
Volume 1 of 2. Cambridge University Press, United. Kingdom. 484
pg.
- United Nations Environment Programme. Convention on Biological
Diversity. June 1992. UNEP Document no. Na.92-78. Reprint
- Möller-Dombois & Ellenberg: "A Tentative
Physiognomic-Ecological Classification of Plant Formations of the
Earth".
- Map of the ecosystems of Central America, WICE
2005. Retrieved 30 August 2008.
- Antonio Di Gregorio & Louisa J.M. Jansen (2000). Land Cover Classification System (LCCS):
Classification Concepts and User Manual. Retrieved 30
August 2008.
- Garrison, George A.; Bjugstad, A. J.; Duncan, D. A.; Lewis, M.
E.; and Smith, D. R. (1977) Vegetation and environmental features of forest
and range ecosystems (Forest Service Handbook Number 465)
United States Department
of Agriculture, Washington, D.C., OCLC
3359594
- The Community Environmental Legal Defense Fund: about the New
Constitution 2008 The
Community Environmental Legal Defense Fund, Retrieved
2009-09-07
- Tamaqua Law Recognizes Rights of Nature
- Rush Township Strips Sludge Corporation
"Rights"
- On Thin Ice
- Earthly rights
- Andrewatha, HG and LC Birch (1954) The distribution and
abundance of animals. University of Chicago
Press, Chicago, IL
- Robert Ulanowicz (1997). Ecology, the Ascendant
Perspective. Columbia Univ. Press. ISBN 0-23-110828-1.
Further reading
- 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, 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 August 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.
- Patten, B.C. 1959. An Introduction to the Cybernetics of the
Ecosystem: The Trophic-Dynamic Aspect. Ecology 40, no. 2.:
221-231.
- Ranganathan, J & Irwin, F. (2007, May 7). Restoring Nature's Capital: An Action Agenda to Sustain
Ecosystem Services
- 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.
External links