An ecosystem can be defined as a community made up of living organisms
and nonliving components such as air, water and mineral soil.
However, ecosystems can be defined in many ways. The biotic and
abiotic components interact through nutrient cycles and energy
flows. Ecosystems include a network of interactions among
organisms, and between organisms and their environment. Ecosystems
can be of any size but one ecosystem has a specific, limited space.
Some scientists view the entire planet as one ecosystem.
Energy, water, nitrogen and soil minerals are other essential abiotic
components of an ecosystem. The energy that flows through ecosystems
comes primarily from the sun, through photosynthesis. Photosynthesis
also captures carbon dioxide from the atmosphere. Animals also play an
important role in the movement of matter and energy through ecoystems.
They influence the amount of plant and microbial biomass that lives in
the system. As organic matter dies, decomposers release carbon back to
the atmosphere. This process also facilitates nutrient cycling by
converting nutrients stored in dead biomass back to a form that can be
used again by plants and other microbes.
Ecosystems are controlled both by external and internal factors.
External factors such as climate, the parent material that forms the
soil, topography and time have a big impact on ecosystems, but they
are not themselves influenced by the ecosystem. Ecosystems are
dynamic: they are subject to periodic disturbances and are in the
process of recovering from past disturbances. Internal factors are
different: They not only control ecosystem processes but are also
controlled by them. Internal factors are subject to feedback loops.
Humans operate within ecosystems. The effects of human activities can
influence internal and external factors.
Global warming is an
example of a cumulative impact of human activities. Ecosystems provide
benefits, called "ecosystem services", which people depend on for
Ecosystem management is more efficient than trying
to manage individual species.
1.1 Related concepts
2.1 External and internal factors
2.2 Primary production
2.4.3 Chemical alteration
2.5 Nutrient cycling
2.5.2 Other nutrients
2.6 Function and biodiversity
3 Classification methods
Ecosystem goods and services
4.3 Threats caused by humans
6 See also
9 Literature cited
10 External links
There is no single definition of what constitutes an ecosystem.
German ecologist Ernst-Detlef Schulze and coauthors defined an
ecosystem as an area which is "uniform regarding the biological
turnover, and contains all the fluxes above and below the ground area
under consideration." They explicitly reject Gene Likens' use of
entire river catchments as "too wide a demarcation" to be a single
ecosystem, given the level of heterogeneity within such an area.
Other authors have suggested that an ecosystem can encompass a much
larger area, even the whole planet. Schulze and coauthors also
rejected the idea that a single rotting log could be studied as an
ecosystem because the size of the flows between the log and its
surroundings are too large, relative to the proportion cycles within
the log. Philosopher of science Mark Sagoff considers the failure
to define "the kind of object it studies" to be an obstacle to the
development of theory in ecosystem ecology.
Ecosystems can be studied through a variety of
approaches—theoretical studies, studies monitoring specific
ecosystems over long periods of time, those that look at differences
between ecosystems to elucidate how they work and direct manipulative
experimentation. Studies can be carried out at a variety of
scales, from microcosms and mesocosms which serve as simplified
representations of ecosystems, through whole-ecosystem studies.
Stephen R. Carpenter
Stephen R. Carpenter has argued that microcosm
experiments can be "irrelevant and diversionary" if they are not
carried out in conjunction with field studies carried out at the
ecosystem scale, because microcosm experiments often fail to
accurately predict ecosystem-level dynamics.
The Hubbard Brook
Ecosystem Study, established in the White Mountains,
New Hampshire in 1963, was the first successful attempt to study an
entire watershed as an ecosystem. The study used stream chemistry as a
means of monitoring ecosystem properties, and developed a detailed
biogeochemical model of the ecosystem. Long-term research at the
site led to the discovery of acid rain in
North America in 1972, and
was able to document the consequent depletion of soil cations
(especially calcium) over the next several decades.
The term "ecosystem" is often used very imprecisely and linked with a
descriptive term (adjective) even if those systems are rather biomes,
not ecosystems. Examples include: terrestrial
ecosystem or aquatic ecosystems.
Aquatic ecosystems are split into
marine ecosystems (
Large marine ecosystem
Large marine ecosystem is another term used) and
Rainforest ecosystems are rich in biodiversity. This is the Gambia
River in Senegal's Niokolo-Koba National Park.
Flora of Baja California Desert,
Cataviña region, Mexico
Biomes of the world
External and internal factors
Ecosystems are controlled both by external and internal factors.
External factors, also called state factors, control the overall
structure of an ecosystem and the way things work within it, but are
not themselves influenced by the ecosystem. The most important of
these is climate.
Climate determines the biome in which the
ecosystem is embedded. Rainfall patterns and temperature seasonality
determine the amount of water available to the ecosystem and the
supply of energy available (by influencing photosynthesis).
Parent material, the underlying geological material that gives rise to
soils, determines the nature of the soils present, and influences the
supply of mineral nutrients.
Topography also controls ecosystem
processes by affecting things like microclimate, soil development and
the movement of water through a system. This may be the difference
between the ecosystem present in wetland situated in a small
depression on the landscape, and one present on an adjacent steep
Other external factors that play an important role in ecosystem
functioning include time and potential biota. Similarly, the set of
organisms that can potentially be present in an area can also have a
major impact on ecosystems. Ecosystems in similar environments that
are located in different parts of the world can end up doing things
very differently simply because they have different pools of species
present. The introduction of non-native species can cause
substantial shifts in ecosystem function.
Unlike external factors, internal factors in ecosystems not only
control ecosystem processes, but are also controlled by them.
Consequently, they are often subject to feedback loops. While the
resource inputs are generally controlled by external processes like
climate and parent material, the availability of these resources
within the ecosystem is controlled by internal factors like
decomposition, root competition or shading. Other factors like
disturbance, succession or the types of species present are also
Global oceanic and terrestrial phototroph abundance, from September
1997 to August 2000. As an estimate of autotroph biomass, it is only a
rough indicator of primary production potential, and not an actual
estimate of it.
Main article: Primary production
Primary production is the production of organic matter from inorganic
carbon sources. This mainly occurs through photosynthesis. The energy
incorporated through this process supports life on earth, while the
carbon makes up much of the organic matter in living and dead biomass,
soil carbon and fossil fuels. It also drives the carbon cycle, which
influences global climate via the greenhouse effect.
Through the process of photosynthesis, plants capture energy from
light and use it to combine carbon dioxide and water to produce
carbohydrates and oxygen. The photosynthesis carried out by all the
plants in an ecosystem is called the gross primary production
(GPP). About 48–60% of the GPP is consumed in plant respiration.
The remainder, that portion of GPP that is not used up by respiration,
is known as the net primary production (NPP).
Energy flow (ecology)
Food web and Trophic level
Energy and carbon enter ecosystems through photosynthesis, are
incorporated into living tissue, transferred to other organisms that
feed on the living and dead plant matter, and eventually released
The carbon and energy incorporated into plant tissues (net primary
production) is either consumed by animals while the plant is alive, or
it remains uneaten when the plant tissue dies and becomes detritus. In
terrestrial ecosystems, roughly 90% of the net primary production ends
up being broken down by decomposers. The remainder is either consumed
by animals while still alive and enters the plant-based trophic
system, or it is consumed after it has died, and enters the
detritus-based trophic system.
In aquatic systems, the proportion of plant biomass that gets consumed
by herbivores is much higher. In trophic systems photosynthetic
organisms are the primary producers. The organisms that consume their
tissues are called primary consumers or secondary
producers—herbivores. Organisms which feed on microbes (bacteria and
fungi) are termed microbivores. Animals that feed on primary
consumers—carnivores—are secondary consumers. Each of these
constitutes a trophic level.
The sequence of consumption—from plant to herbivore, to
carnivore—forms a food chain. Real systems are much more complex
than this—organisms will generally feed on more than one form of
food, and may feed at more than one trophic level. Carnivores may
capture some prey which are part of a plant-based trophic system and
others that are part of a detritus-based trophic system (a bird that
feeds both on herbivorous grasshoppers and earthworms, which consume
detritus). Real systems, with all these complexities, form food webs
rather than food chains.
A hydrothermal vent is an ecosystem on the ocean floor. (The scale bar
is 1 m.)
Ecosystem ecology studies "the flow of energy and materials through
organisms and the physical environment". It seeks to understand the
processes which govern the stocks of material and energy in
ecosystems, and the flow of matter and energy through them. The study
of ecosystems can cover 10 orders of magnitude, from the surface
layers of rocks to the surface of the planet.
See also: Decomposition
The carbon and nutrients in dead organic matter are broken down by a
group of processes known as decomposition. This releases nutrients
that can then be re-used for plant and microbial production, and
returns carbon dioxide to the atmosphere (or water) where it can be
used for photosynthesis. In the absence of decomposition, dead organic
matter would accumulate in an ecosystem, and nutrients and atmospheric
carbon dioxide would be depleted. Approximately 90% of terrestrial
net primary production goes directly from plant to decomposer.
Decomposition processes can be separated into three
categories—leaching, fragmentation and chemical alteration of dead
As water moves through dead organic matter, it dissolves and carries
with it the water-soluble components. These are then taken up by
organisms in the soil, react with mineral soil, or are transported
beyond the confines of the ecosystem (and are considered lost to
it). Newly shed leaves and newly dead animals have high
concentrations of water-soluble components, and include sugars, amino
acids and mineral nutrients. Leaching is more important in wet
environments, and much less important in dry ones.
Fragmentation processes break organic material into smaller pieces,
exposing new surfaces for colonization by microbes. Freshly shed leaf
litter may be inaccessible due to an outer layer of cuticle or bark,
and cell contents are protected by a cell wall. Newly dead animals may
be covered by an exoskeleton. Fragmentation processes, which break
through these protective layers, accelerate the rate of microbial
decomposition. Animals fragment detritus as they hunt for food, as
does passage through the gut. Freeze-thaw cycles and cycles of wetting
and drying also fragment dead material.
The chemical alteration of dead organic matter is primarily achieved
through bacterial and fungal action. Fungal hyphae produce enzymes
which can break through the tough outer structures surrounding dead
plant material. They also produce enzymes which break down lignin,
which allows them access to both cell contents and to the nitrogen in
Fungi can transfer carbon and nitrogen through their
hyphal networks and thus, unlike bacteria, are not dependent solely on
locally available resources.
Decomposition § Rate of decomposition
Decomposition rates vary among ecosystems. The rate of decomposition
is governed by three sets of factors—the physical environment
(temperature, moisture and soil properties), the quantity and quality
of the dead material available to decomposers, and the nature of the
microbial community itself. Temperature controls the rate of
microbial respiration; the higher the temperature, the faster
microbial decomposition occurs. It also affects soil moisture, which
slows microbial growth and reduces leaching. Freeze-thaw cycles also
affect decomposition—freezing temperatures kill soil microorganisms,
which allows leaching to play a more important role in moving
nutrients around. This can be especially important as the soil thaws
in the spring, creating a pulse of nutrients which become
Decomposition rates are low under very wet or very dry conditions.
Decomposition rates are highest in wet, moist conditions with adequate
levels of oxygen. Wet soils tend to become deficient in oxygen (this
is especially true in wetlands), which slows microbial growth. In dry
soils, decomposition slows as well, but bacteria continue to grow
(albeit at a slower rate) even after soils become too dry to support
Nutrient cycle and Biogeochemical cycle
Biological nitrogen cycling
Ecosystems continually exchange energy and carbon with the wider
environment. Mineral nutrients, on the other hand, are mostly cycled
back and forth between plants, animals, microbes and the soil. Most
nitrogen enters ecosystems through biological nitrogen fixation, is
deposited through precipitation, dust, gases or is applied as
Since most terrestrial ecosystems are nitrogen-limited, nitrogen
cycling is an important control on ecosystem production.
Until modern times, nitrogen fixation was the major source of nitrogen
Nitrogen fixing bacteria either live symbiotically
with plants, or live freely in the soil. The energetic cost is high
for plants which support nitrogen-fixing symbionts—as much as 25% of
gross primary production when measured in controlled conditions. Many
members of the legume plant family support nitrogen-fixing symbionts.
Some cyanobacteria are also capable of nitrogen fixation. These are
phototrophs, which carry out photosynthesis. Like other
nitrogen-fixing bacteria, they can either be free-living or have
symbiotic relationships with plants. Other sources of nitrogen
include acid deposition produced through the combustion of fossil
fuels, ammonia gas which evaporates from agricultural fields which
have had fertilizers applied to them, and dust. Anthropogenic
nitrogen inputs account for about 80% of all nitrogen fluxes in
When plant tissues are shed or are eaten, the nitrogen in those
tissues becomes available to animals and microbes. Microbial
decomposition releases nitrogen compounds from dead organic matter in
the soil, where plants, fungi and bacteria compete for it. Some soil
bacteria use organic nitrogen-containing compounds as a source of
carbon, and release ammonium ions into the soil. This process is known
as nitrogen mineralization. Others convert ammonium to nitrite and
nitrate ions, a process known as nitrification.
Nitric oxide and
nitrous oxide are also produced during nitrification. Under
nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are
converted to nitrogen gas, a process known as denitrification.
Other important nutrients include phosphorus, sulfur, calcium,
potassium, magnesium and manganese.
Phosphorus enters ecosystems
through weathering. As ecosystems age this supply diminishes, making
phosphorus-limitation more common in older landscapes (especially in
Calcium and sulfur are also produced by weathering,
but acid deposition is an important source of sulfur in many
ecosystems. Although magnesium and manganese are produced by
weathering, exchanges between soil organic matter and living cells
account for a significant portion of ecosystem fluxes.
primarily cycled between living cells and soil organic matter.
Function and biodiversity
Main article: Biodiversity
Loch Lomond in
Scotland forms a relatively isolated ecosystem. The
fish community of this lake has remained stable over a long period
until a number of introductions in the 1970s restructured its food
Spiny forest at Ifaty, Madagascar, featuring various Adansonia
Alluaudia procera (
Madagascar ocotillo) and other
Biodiversity plays an important role in ecosystem functioning. The
reason for this is that ecosystem processes are driven by the number
of species in an ecosystem, the exact nature of each individual
species, and the relative abundance organisms within these
Ecosystem processes are broad generalizations that
actually take place through the actions of individual organisms. The
nature of the organisms—the species, functional groups and trophic
levels to which they belong—dictates the sorts of actions these
individuals are capable of carrying out, and the relative efficiency
with which they do so.
Ecological theory suggests that in order to coexist, species must have
some level of limiting similarity—they must be different from one
another in some fundamental way, otherwise one species would
competitively exclude the other. Despite this, the cumulative
effect of additional species in an ecosystem is not
linear—additional species may enhance nitrogen retention, for
example, but beyond some level of species richness, additional species
may have little additive effect.
The addition (or loss) of species which are ecologically similar to
those already present in an ecosystem tends to only have a small
effect on ecosystem function. Ecologically distinct species, on the
other hand, have a much larger effect. Similarly, dominant species
have a large impact on ecosystem function, while rare species tend to
have a small effect.
Keystone species tend to have an effect on
ecosystem function that is disproportionate to their abundance in an
ecosystem. Similarly, an ecosystem engineer is any organism that
creates, significantly modifies, maintains or destroys a habitat.
Temperate rainforest on the
Olympic Peninsula in Washington state
Ecosystems are dynamic entities. They are subject to periodic
disturbances and are in the process of recovering from some past
disturbance. When a perturbation occurs, an ecoystem responds by
moving away from its initial state. The tendency of an ecosystem to
remain close to its equilibrium state, despite that disturbance, is
termed its resistance. On the other hand, the speed with which it
returns to its initial state after disturbance is called its
Time plays a role in the development of soil from bare
rock and the recovery of a community from disturbance.
From one year to another, ecosystems experience variation in their
biotic and abiotic environments. A drought, an especially cold winter
and a pest outbreak all constitute short-term variability in
Animal populations vary from year to year,
building up during resource-rich periods and crashing as they
overshoot their food supply. These changes play out in changes in net
primary production decomposition rates, and other ecosystem
processes. Longer-term changes also shape ecosystem
processes—the forests of eastern
North America still show legacies
of cultivation which ceased 200 years ago, while methane production in
eastern Siberian lakes is controlled by organic matter which
accumulated during the Pleistocene.
Disturbance also plays an important role in ecological processes. F.
Stuart Chapin and coauthors define disturbance as "a relatively
discrete event in time and space that alters the structure of
populations, communities and ecosystems and causes changes in
resources availability or the physical environment". This can
range from tree falls and insect outbreaks to hurricanes and wildfires
to volcanic eruptions. Such disturbances can cause large changes in
plant, animal and microbe populations, as well soil organic matter
content. Disturbance is followed by succession, a "directional
change in ecosystem structure and functioning resulting from
biotically driven changes in resources supply."
The frequency and severity of disturbance determines the way it
impacts ecosystem function. Major disturbance like a volcanic eruption
or glacial advance and retreat leave behind soils that lack plants,
animals or organic matter. Ecosystems that experience such
disturbances undergo primary succession. Less severe disturbance like
forest fires, hurricanes or cultivation result in secondary succession
and a faster recovery. More severe disturbance and more frequent
disturbance result in longer recovery times.
A freshwater ecosystem in Gran Canaria, an island of the Canary
Ecosystem diversity, Ecoregion, Ecological land
classification, and Ecotope
Classifying ecosystems into ecologically homogeneous units is an
important step towards effective ecosystem management. There is no
single, agreed-upon way to do this. A variety of systems exist, based
on vegetation cover, remote sensing, and bioclimatic classification
Ecological land classification is a cartographical delineation or
regionalisation of distinct ecological areas, identified by their
geology, topography, soils, vegetation, climate conditions, living
species, habitats, water resources, and sometimes also anthropic
Human activities are important in almost all ecosystems. Although
humans exist and operate within ecosystems, their cumulative effects
are large enough to influence external factors like climate.
Ecosystem goods and services
High Peaks Wilderness Area
High Peaks Wilderness Area in the 6,000,000-acre
Adirondack Park is an example of a diverse
Ecosystem services and Ecological goods and services
Ecosystem valuation and Ecological yield
Ecosystems provide a variety of goods and services upon which people
Ecosystem goods include the "tangible, material products"
of ecosystem processes such as food, construction material, medicinal
plants. They also include less tangible items like tourism and
recreation, and genes from wild plants and animals that can be used to
improve domestic species.
Ecosystem services, on the other hand, are generally "improvements in
the condition or location of things of value". These include
things like the maintenance of hydrological cycles, cleaning air and
water, the maintenance of oxygen in the atmosphere, crop pollination
and even things like beauty, inspiration and opportunities for
research. While ecosystem goods have traditionally been recognized
as being the basis for things of economic value, ecosystem services
tend to be taken for granted.
See also: Ecological economics, Sustainability, and Sustainable
When natural resource management is applied to whole ecosystems,
rather than single species, it is termed ecosystem management.
Although definitions of ecosystem management abound, there is a common
set of principles which underlie these definitions. A fundamental
principle is the long-term sustainability of the production of goods
and services by the ecosystem; "intergenerational sustainability
[is] a precondition for management, not an afterthought".
While ecosystem management can be used as part of a plan for
wilderness conservation, it can also be used in intensively managed
ecosystems (see, for example, agroecosystem and close to nature
Threats caused by humans
See also: Planetary boundaries
As human populations and per capita consumption grow, so do the
resource demands imposed on ecosystems and the impacts of the human
ecological footprint. Natural resources are vulnerable and limited.
The environmental impacts of anthropogenic actions are becoming more
apparent. Problems for all ecosystems include: environmental
pollution, climate change and biodiversity loss. For terrestrial
ecosystems further threats include air pollution, soil degradation,
and deforestation. For aquatic ecosystems threats include also
unsustainable exploitation of marine resources (for example
overfishing of certain species), marine pollution, microplastics
pollution, water pollution, and building on coastal areas.
Society is increasingly becoming aware that ecosystem services are not
only limited, but also that they are threatened by human activities.
The need to better consider long-term ecosystem health and its role in
enabling human habitation and economic activity is urgent. To help
inform decision-makers, many ecosystem services are being assigned
economic values, often based on the cost of replacement with
anthropogenic alternatives. The ongoing challenge of prescribing
economic value to nature, for example through biodiversity banking, is
prompting transdisciplinary shifts in how we recognize and manage the
environment, social responsibility, business opportunities, and our
future as a species.
The term "ecosystem" was first used in 1935 in a publication by
British ecologist Arthur Tansley.[fn 1] Tansley devised the
concept to draw attention to the importance of transfers of materials
between organisms and their environment. He 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
G. Evelyn Hutchinson, a limnologist who was a contemporary of
Tansley's, combined Charles Elton's ideas about trophic ecology with
those of Russian geochemist Vladimir Vernadsky. As a result he
suggested that mineral nutrient availability in a lake limited algal
production. This would, in turn, limit the abundance of animals that
feed on algae.
Raymond Lindeman took these ideas further to suggest
that the flow of energy through a lake was the primary driver of the
ecosystem. Hutchinson's students, brothers
Howard T. Odum
Howard T. Odum and Eugene
P. Odum, further developed a "systems approach" to the study of
ecosystems. This allowed them to study the flow of energy and material
through ecological systems.
Earth sciences portal
Sustainable development portal
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Ecosystem Assessment (2005)
The State of the Nation's Ecosystems (U.S.)
Ecology: Modelling ecosystems: Trophic components
List of feeding behaviours
Metabolic theory of ecology
Primary nutritional groups
Generalist and specialist species
Mesopredator release hypothesis
Optimal foraging theory
Microbial food web
North Pacific Subtropical Gyre
San Francisco Estuary
Competitive exclusion principle
Energy Systems Language
Feed conversion ratio
Paradox of the plankton
Trophic state index
Herbivore adaptations to plant defense
Plant defense against herbivory
Predator avoidance in schooling fish
Ecology: Modelling ecosystems: Other components
Effective population size
Malthusian growth model
Maximum sustainable yield
Overpopulation in wild animals
Predator–prey (Lotka–Volterra) equations
Small population size
Ecological effects of biodiversity
Latitudinal gradients in species diversity
Minimum viable population
Population viability analysis
Relative abundance distribution
Relative species abundance
Ideal free distribution
Intermediate Disturbance Hypothesis
r/K selection theory
Resource selection function
Environmental niche modelling
Niche apportionment models
Liebig's law of the minimum
Marginal value theorem
Alternative stable state
Balance of nature
Biological data visualization
Ecosystem based fisheries
List of ecology topics
Hierarchy of life
Biosphere > Ecosystem > Biocoenosis >
Population > Organism > Organ system >
Organ > Tissue > Cell > Organelle >
Biomolecular complex > Macromolecule > Biomolecule
Future of Earth
Geological history of Earth
History of Earth
Structure of the Earth
Geology of solar terrestrial planets
Location in Universe
Elements of nature
Earth system science
Russell L. Ackoff
William Ross Ashby
Béla H. Bánáthy
Anthony Stafford Beer
Richard E. Bellman
Ludwig von Bertalanffy
Kenneth E. Boulding
C. West Churchman
Edsger W. Dijkstra
Heinz von Foerster
Jay Wright Forrester
Charles A S Hall
James J. Kay
Faina M. Kirillova
Edward Norton Lorenz
Mihajlo D. Mesarovic
James Grier Miller
Howard T. Odum
Manuela M. Veloso
Systems theory in anthropology
Systems theory in archaeology
Systems theory in political science