Ecosystem

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For other uses, see Ecosystem (disambiguation). "Biosystem" redirects here. For the journal, see BioSystems.

Coral reefs are a highly productive marine ecosystem.
Left: Coral reef ecosystems are highly productive marine systems.[1] Right: Temperate rainforest, a terrestrial ecosystem.
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An ecosystem (or ecological system) is a system that

environments and their organisms form through their interaction.[2]: 458  The biotic and abiotic components are linked together through nutrient cycles and energy
flows.

Ecosystems are controlled by external and internal factors. External factors such as climate, parent material which forms the soil and topography, control the overall structure of an ecosystem but are not themselves influenced by the ecosystem. Internal factors are controlled, for example, by decomposition, root competition, shading, disturbance, succession, and the types of species present. While the resource inputs are generally controlled by external processes, the availability of these resources within the ecosystem is controlled by internal factors. Therefore, internal factors not only control ecosystem processes but are also controlled by them.

Ecosystems are

abiotic
complex, the interactions between and within them, and the physical space they occupy. Biotic factors of the ecosystem are living things; such as plants, animals, and bacteria, while abiotic are non-living components; such as water, soil and atmosphere.

Plants allow energy to enter the system through

nutrient cycling
by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.

Ecosystems provide a variety of goods and services upon which people depend, and may be part of. Ecosystem goods include the "tangible, material products" of ecosystem processes such as water, food, fuel, construction material, and

Ecosystem restoration can contribute to achieving the Sustainable Development Goals
.

Definition

An ecosystem (or ecological system) consists of all the organisms and the abiotic pools (or physical environment) with which they interact.[3][4]: 5 [2]: 458  The biotic and abiotic components are linked together through nutrient cycles and energy flows.[5]

"Ecosystem processes" are the transfers of energy and materials from one pool to another.[2]: 458  Ecosystem processes are known to "take place at a wide range of scales". Therefore, the correct scale of study depends on the question asked.[4]: 5 

Origin and development of the term

The term "ecosystem" was first used in 1935 in a publication by British ecologist Arthur Tansley. The term was coined by Arthur Roy Clapham, who came up with the word at Tansley's request.[6] Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.[4]: 9  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".[3] Tansley regarded ecosystems not simply as natural units, but as "mental isolates".[3] Tansley later defined the spatial extent of ecosystems using the term "ecotope".[7]

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.[4]
: 9 

Processes

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

External and internal factors

Ecosystems are controlled by both 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. On broad geographic scales, climate is the factor that "most strongly determines ecosystem processes and structure".[4]: 14  Climate determines the biome in which the ecosystem is embedded. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of energy available to the ecosystem.[8]: 145 

Parent material determines the nature of the soil in an ecosystem, 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. For example, ecosystems can be quite different if situated in a small depression on the landscape, versus one present on an adjacent steep hillside.[9]: 39 [10]: 66 

Other external factors that play an important role in ecosystem functioning include time and potential

biota, the organisms that are present in a region and could potentially occupy a particular site. 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.[11]: 321  The introduction of non-native species can cause substantial shifts in ecosystem function.[12]

Unlike external factors, internal factors in ecosystems not only control ecosystem processes but are also controlled by them.[4]: 16  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.[13] Other factors like disturbance, succession or the types of species present are also internal factors.

Primary production

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

net primary production (NPP).[14]: 157  Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), the rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.[8]
: 155 

Energy flow

Main article: Energy flow (ecology)
See also: 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 through respiration.[14]: 157  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, the vast majority of the net primary production ends up being broken down by decomposers. The remainder is consumed by animals while still alive and enters the plant-based trophic system. After plants and animals die, the organic matter contained in them enters the detritus-based trophic system.[15]

Ecosystem respiration is the sum of respiration by all living organisms (plants, animals, and decomposers) in the ecosystem.[16] Net ecosystem production is the difference between gross primary production (GPP) and ecosystem respiration.[17] In the absence of disturbance, net ecosystem production is equivalent to the net carbon accumulation in the ecosystem.

Energy can also be released from an ecosystem through disturbances such as wildfire or transferred to other ecosystems (e.g., from a forest to a stream to a lake) by erosion.

In

microbivores. Animals that feed on primary consumers—carnivores—are secondary consumers. Each of these constitutes a trophic level.[15]

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 that is 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.[15]

Decomposition

See also: Decomposition
Sequence of a decomposing pig carcass over time

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, the dead organic matter would accumulate in an ecosystem, and nutrients and atmospheric carbon dioxide would be depleted.[18]: 183 

Decomposition processes can be separated into three categories—leaching, fragmentation and chemical alteration of dead material. 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).[19]: 271–280  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 less important in dry ones.[10]: 69–77 

Fragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shed

Freeze-thaw cycles and cycles of wetting and drying also fragment dead material.[18]
: 186 

The chemical alteration of the dead organic matter is primarily achieved through bacterial and fungal action. Fungal hyphae produce enzymes that can break through the tough outer structures surrounding dead plant material. They also produce enzymes that break down lignin, which allows them access to both cell contents and the nitrogen in the lignin. Fungi can transfer carbon and nitrogen through their hyphal networks and thus, unlike bacteria, are not dependent solely on locally available resources.[18]: 186 

Decomposition rates

Decomposition rates vary among ecosystems.[20] 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.[18]: 194  Temperature controls the rate of microbial respiration; the higher the temperature, the faster the microbial decomposition occurs. Temperature also affects soil moisture, which affects decomposition. 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 that become available.[19]: 280 

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 plant growth.[18]: 200 

Dynamics and resilience

Further information: Resistance (ecology) and Ecological resilience

Ecosystems are dynamic entities. They are subject to periodic disturbances and are always in the process of recovering from past disturbances.

ecosystem services for our survival and must build and maintain their natural capacities to withstand shocks and disturbances.[24] Time plays a central role over a wide range, for example, in the slow development of soil from bare rock and the faster recovery of a community from disturbance.[14]
: 67 

Disturbance also plays an important role in ecological processes. F. Stuart Chapin and coauthors define disturbance as "a relatively discrete event in time that removes plant biomass".[21]: 346  This can range from herbivore outbreaks, treefalls, fires, hurricanes, floods, glacial advances, to volcanic eruptions. Such disturbances can cause large changes in plant, animal and microbe populations, as well as soil organic matter content. Disturbance is followed by succession, a "directional change in ecosystem structure and functioning resulting from biotically driven changes in resource supply."[2]: 470 

The frequency and severity of disturbance determine the way it affects ecosystem function. A 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. A less severe disturbance like forest fires, hurricanes or cultivation result in secondary succession and a faster recovery.[21]: 348  More severe and more frequent disturbance result in longer recovery times.

From one year to another, ecosystems experience variation in their biotic and abiotic environments. A drought, a colder than usual winter, and a pest outbreak all are short-term variability in environmental conditions. Animal populations vary from year to year, building up during resource-rich periods and crashing as they overshoot their food supply. Longer-term changes also shape ecosystem processes. For example, the forests of eastern North America still show legacies of cultivation which ceased in 1850 when large areas were reverted to forests.[21]: 340  Another example is the methane production in eastern Siberian lakes that is controlled by organic matter which accumulated during the Pleistocene.[25]

freshwater lake in Gran Canaria, an island of the Canary Islands. Clear boundaries make lakes convenient to study using an ecosystem approach
.

Nutrient cycling

See also: Nutrient cycle, Biogeochemical cycle, and Nitrogen cycle
Biological nitrogen cycling

Ecosystems continually exchange energy and carbon with the wider

terrestrial ecosystems are nitrogen-limited in the short term making nitrogen cycling an important control on ecosystem production.[19]: 289  Over the long term, phosphorus availability can also be critical.[26]

Macronutrients which are required by all plants in large quantities include the primary nutrients (which are most limiting as they are used in largest amounts): Nitrogen, phosphorus, potassium.[27]: 231  Secondary major nutrients (less often limiting) include: Calcium, magnesium, sulfur. Micronutrients required by all plants in small quantities include boron, chloride, copper, iron, manganese, molybdenum, zinc. Finally, there are also beneficial nutrients which may be required by certain plants or by plants under specific environmental conditions: aluminum, cobalt, iodine, nickel, selenium, silicon, sodium, vanadium.[27]: 231 

Until modern times, nitrogen fixation was the major source of nitrogen for ecosystems. Nitrogen-fixing bacteria either live

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.[19]: 270  Anthropogenic nitrogen inputs account for about 80% of all nitrogen fluxes in ecosystems.[19]
: 270 

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

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.[19]: 277  Under nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are converted to nitrogen gas, a process known as denitrification.[19]
: 281 

Mycorrhizal fungi which are symbiotic with plant roots, use carbohydrates supplied by the plants and in return transfer phosphorus and nitrogen compounds back to the plant roots.[28][29] This is an important pathway of organic nitrogen transfer from dead organic matter to plants. This mechanism may contribute to more than 70 Tg of annually assimilated plant nitrogen, thereby playing a critical role in global nutrient cycling and ecosystem function.[29]

Phosphorus enters ecosystems through weathering. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics).[19]: 287–290  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. Potassium is primarily cycled between living cells and soil organic matter.[19]: 291 

Function and biodiversity

Main article: Biodiversity
See also: Ecosystem diversity
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 web.[30]
Spiny forest at Ifaty, Madagascar, featuring various Adansonia (baobab) species, Alluaudia procera (Madagascar ocotillo) and other vegetation

competitively exclude the other.[32] Despite this, the cumulative effect of additional species in an ecosystem is not linear: additional species may enhance nitrogen retention, for example. However, beyond some level of species richness,[11]: 331  additional species may have little additive effect unless they differ substantially from species already present.[11]: 324  This is the case for example for exotic species.[11]
: 321 

The addition (or loss) of species that 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 effect 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.[11]: 324 

An

habitat.[33]

Study approaches

Ecosystem ecology

Main article: Ecosystem ecology
See also: Ecosystem model
A hydrothermal vent is an ecosystem on the ocean floor. (The scale bar is 1 m.)

Ecosystem ecology is the "study of the interactions between organisms and their environment as an integrated system".[2]: 458  The size of ecosystems can range up to ten orders of magnitude, from the surface layers of rocks to the surface of the planet.[4]: 6 

The

cations (especially calcium) over the next several decades.[35]

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.

microcosms or mesocosms (simplified representations of ecosystems).[37] American ecologist Stephen R. Carpenter has argued that microcosm experiments can be "irrelevant and diversionary" if they are not carried out in conjunction with field studies done at the ecosystem scale. In such cases, microcosm experiments may fail to accurately predict ecosystem-level dynamics.[38]

Classifications

Further information:
Ecosystem classification and Biogeoclimatic ecosystem classification

Biomes are general classes or categories of ecosystems.[4]: 14  However, there is no clear distinction between biomes and ecosystems.[39] Biomes are always defined at a very general level. Ecosystems can be described at levels that range from very general (in which case the names are sometimes the same as those of biomes) to very specific, such as "wet coastal needle-leafed forests".

Biomes vary due to global variations in climate. Biomes are often defined by their structure: at a general level, for example, tropical forests, temperate grasslands, and arctic tundra.[4]: 14  There can be any degree of subcategories among ecosystem types that comprise a biome, e.g., needle-leafed boreal forests or wet tropical forests. Although ecosystems are most commonly categorized by their structure and geography, there are also other ways to categorize and classify ecosystems such as by their level of human impact (see anthropogenic biome), or by their integration with social processes or technological processes or their novelty (e.g. novel ecosystem). Each of these taxonomies of ecosystems tends to emphasize different structural or functional properties.[40] None of these is the "best" classification.

abiotic complex, the interactions between and within them, and the physical space they occupy.[40] Different approaches to ecological classifications have been developed in terrestrial, freshwater and marine disciplines, and a function-based typology has been proposed to leverage the strengths of these different approaches into a unified system.[41]

Human interactions with ecosystems

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.[4]: 14 

Ecosystem goods and services

The High Peaks Wilderness Area in the 6,000,000-acre (2,400,000 ha) Adirondack Park is an example of a diverse ecosystem.
Main articles:
Ecosystem services and Ecological goods and services
See also: Ecosystem valuation and Ecological yield

Ecosystems provide a variety of goods and services upon which people depend.

medicinal plants.[43][44] 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.[42]

Ecosystem services, on the other hand, are generally "improvements in the condition or location of things of value".[44] 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.[42] While material from the ecosystem had traditionally been recognized as being the basis for things of economic value, ecosystem services tend to be taken for granted.[44]

The

resilience and biocapacity. The report refers to natural systems as humanity's "life-support system", providing essential ecosystem services. The assessment measures 24 ecosystem services and concludes that only four have shown improvement over the last 50 years, 15 are in serious decline, and five are in a precarious condition.[45]
: 6–19 

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is an intergovernmental organization established to improve the interface between science and policy on issues of biodiversity and ecosystem services.[46][47] It is intended to serve a similar role to the Intergovernmental Panel on Climate Change.[48]

Ecosystem services are limited and also threatened by human activities.[49] 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.[49]

Degradation and decline

See also: Ecosystem collapse, Biodiversity loss, and Effects of climate change on biomes

As human population and per capita consumption grow, so do the resource demands imposed on ecosystems and the effects of the human

aquatic ecosystems threats also include unsustainable exploitation of marine resources (for example overfishing), marine pollution, microplastics pollution, the effects of climate change on oceans (e.g. warming and acidification), and building on coastal areas.[50]

Many ecosystems become degraded through human impacts, such as soil loss, air and water pollution, habitat fragmentation, water diversion, fire suppression, and introduced species and invasive species.[51]: 437 

These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of

species extinction.[53] Quantitative assessments of the risk of collapse
are used as measures of conservation status and trends.

Management

Main articles: Ecosystem management, Ecosystem-based management, and Ecosystem approach

When natural resource management is applied to whole ecosystems, rather than single species, it is termed ecosystem management.[54] 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;[51] "intergenerational sustainability [is] a precondition for management, not an afterthought".[42] While ecosystem management can be used as part of a plan for wilderness conservation, it can also be used in intensively managed ecosystems[42] (see, for example, agroecosystem and close to nature forestry).

Restoration and sustainable development

See also:
Restoration ecology

Integrated conservation and development projects (ICDPs) aim to address conservation and human livelihood (sustainable development) concerns in developing countries together, rather than separately as was often done in the past.[51]: 445 

See also

Types

The following articles are types of ecosystems for particular types of regions or zones:

Ecosystems grouped by condition

Instances

Main category: Ecosystems by region

Ecosystem instances in specific regions of the world:

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External links
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