An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact.
These biotic and
abiotic component
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them un ...
s are linked together through nutrient cycles and energy flows. Energy enters the system through
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
and is incorporated into plant tissue. By feeding on plants and on one another, animals play an important role in the movement of
matter
In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...
and
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
through the system. They also influence the quantity of plant and
microbial
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
present. By breaking down dead
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
,
decomposer
Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that they use o ...
s release
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
back to the atmosphere and facilitate
nutrient cycling
A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cycli ...
by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.
Ecosystems are controlled by external and internal
factors
Factor, a Latin word meaning "who/which acts", may refer to:
Commerce
* Factor (agent), a person who acts for, notably a mercantile and colonial agent
* Factor (Scotland), a person or firm managing a Scottish estate
* Factors of production, su ...
. External factors such as
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
,
parent material
Parent material is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are ...
which forms the soil and
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
, control the overall structure of an ecosystem but are not themselves influenced by the ecosystem. Internal factors are controlled, for example, by
decomposition
Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...
, root competition, shading, disturbance, succession, and the types of species present. While the
resource
Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their ...
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
dynamic
Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' "power") or dynamic may refer to:
Physics and engineering
* Dynamics (mechanics)
** Aerodynamics, the study of the motion of air
** Analytical dyna ...
entities—they are subject to periodic disturbances and are always in the process of recovering from some past disturbance. The tendency of an ecosystem to remain close to its equilibrium state, despite that disturbance, is termed its
resistance. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its
ecological resilience
In ecology, resilience is the capacity of an ecosystem to respond to a perturbation or disturbance by resisting damage and recovering quickly. Such perturbations and disturbances can include stochastic events such as fires, flooding, windstorm ...
. 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.
Biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
s are general classes or categories of ecosystems. However, there is no clear distinction between biomes and ecosystems.
Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of
ecosystems
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
: a biotic component, an
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
complex, the interactions between and within them, and the physical space they occupy.
Ecosystems provide a variety of goods and services upon which people depend. Ecosystem goods include the "tangible, material products" of ecosystem processes such as water, food, fuel, construction material, and
medicinal plant
Medicinal plants, also called medicinal herbs, have been discovered and used in traditional medicine practices since prehistoric times. Plants synthesize hundreds of chemical compounds for various functions, including Plant defense against her ...
s.
Ecosystem services
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. Th ...
, 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
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...
and even things like beauty, inspiration and opportunities for research. Many ecosystems become degraded through human impacts, such as
soil loss,
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
and
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
,
habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
,
water diversion
Interbasin transfer or transbasin diversion are (often hyphenated) terms used to describe man-made conveyance schemes which move water from one river basin where it is available, to another basin where water is less available or could be utilized ...
,
fire suppression
Wildfire suppression is a range of firefighting tactics used to suppress wildfires. Firefighting efforts in wild land areas require different techniques, equipment, and training from the more familiar structure fire fighting found in populated ...
, and
introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
and
invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
. These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
conditions of the ecosystem. Once the original ecosystem has lost its defining features, it is considered
"collapsed".
Ecosystem restoration
Restoration ecology is the scientific study supporting the practice of ecological restoration, which is the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human interrupt ...
can contribute to achieving the
Sustainable Development Goals
The Sustainable Development Goals (SDGs) or Global Goals are a collection of 17 interlinked objectives designed to serve as a "shared blueprint for peace and prosperity for people and the planet, now and into the future".United Nations (2017) R ...
.
Definition
An ecosystem (or ecological system) consists of all the organisms and the abiotic pools (or physical environment) with which they interact.
The biotic and
abiotic component
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them un ...
s are linked together through nutrient cycles and energy flows.
"Ecosystem processes" are the transfers of energy and materials from one pool to another.
Ecosystem processes are known to "take place at a wide range of scales". Therefore, the correct scale of study depends on the question asked.
Origin and development of the term
The term "ecosystem" was first used in 1935 in a publication by British ecologist
Arthur Tansley
Sir Arthur George Tansley FLS, FRS (15 August 1871 – 25 November 1955) was an English botanist and a pioneer in the science of ecology.
Educated at Highgate School, University College London and Trinity College, Cambridge, Tansley taught a ...
. The term was coined by
Arthur Roy Clapham
Arthur Roy Clapham (24 May 1904 – 18 December 1990), was a British botanist. Born in Norwich and educated at Downing College, Cambridge, Clapham worked at Rothamsted Experimental Station as a crop physiologist (1928–30), and then took a te ...
, who came up with the word at Tansley's request.
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 "
ecotope
Ecotopes are the smallest ecologically distinct landscape features in a landscape mapping and classification system. As such, they represent relatively homogeneous, spatially explicit landscape functional units that are useful for stratifying la ...
".
G. Evelyn Hutchinson, a
limnologist
Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems.
The study of limnology includes aspects of the biological, chemical, physical, and geological characteristi ...
who was a contemporary of Tansley's, combined
Charles Elton Charles Elton may refer to:
*Charles Elton (Born, 1993) Professional Rugby Player for Otago Rugby
* Charles Isaac Elton (1839–1900), English lawyer, politician, writer and antiquarian
* Charles Sutherland Elton (1900–1991), English biologist
...
's ideas about
trophic
Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to:
* Trophic cascade
* Trophic coherence
* Trophic egg
* Trophic function
* Trophic hormone
* Trophic level index
* Trophic level
* Trop ...
ecology with those of Russian geochemist
Vladimir Vernadsky
Vladimir Ivanovich Vernadsky (russian: link=no, Влади́мир Ива́нович Верна́дский) or Volodymyr Ivanovych Vernadsky ( uk, Володи́мир Іва́нович Верна́дський; – 6 January 1945) was ...
. 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
Raymond Laurel Lindeman (1915 – June 29, 1942) was an ecologist whose graduate research is credited with being a seminal study in the field of ecosystem ecology, specifically on the topic of trophic dynamics.
Graduate research work
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 Thomas Odum (September 1, 1924 – September 11, 2002), usually cited as H. T. Odum, was an American ecologist. He is known for his pioneering work on ecosystem ecology, and for his provocative proposals for additional laws of thermod ...
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.
Processes
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
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
is the factor that "most strongly determines ecosystem processes and structure".
Climate determines the
biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
in which the ecosystem is embedded. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of energy available to the ecosystem.
Parent material
Parent material is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are ...
determines the nature of the soil in an ecosystem, and influences the supply of mineral nutrients.
Topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
also controls ecosystem processes by affecting things like
microclimate
A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squ ...
, 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.
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.
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.
While the
resource
Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their ...
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 internal factors.
Primary production
![Seawifs global biosphere](https://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_global_biosphere.jpg)
Primary production is the production of
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
from inorganic carbon sources. This mainly occurs through
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. 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 fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
s. It also drives the
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
, which influences global
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
via the
greenhouse effect
The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
.
Through the process of photosynthesis, plants capture energy from light and use it to combine
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
and water to produce
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ma ...
s and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
. The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP).
About half of the gross GPP is respired by plants in order to provide the energy that supports their growth and maintenance.
The remainder, that portion of GPP that is not used up by respiration, is known as the
net primary production (NPP).
Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of
leaf
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
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
chloroplast
A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...
s to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.
Energy flow
Energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
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.
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 biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
. In
terrestrial ecosystem
Terrestrial ecosystems are ecosystems which are found on land. Examples include tundra, taiga, temperate deciduous forest, tropical rain forest, grassland, deserts.
Terrestrial ecosystems differ from aquatic ecosystems by the predominant presence ...
s, the vast majority of the net primary production ends up being broken down by
decomposers
Decomposers are Organism, organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that t ...
. 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.
Ecosystem respiration
Ecosystem respiration is the sum of all respiration occurring by the living organisms in a specific ecosystem. The two main processes that contribute to ecosystem respiration are photosynthesis and cellular respiration. Photosynthesis uses carbon- ...
is the sum of
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
by all living organisms (plants, animals, and decomposers) in the ecosystem.
Net ecosystem production
Net ecosystem production (NEP) in ecology, limnology, and oceanography, is the difference between Primary production, gross primary production (GPP) and Ecosystem respiration, net ecosystem respiration. Net ecosystem production represents all the ...
is the difference between
gross primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
(GPP) and ecosystem respiration.
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
A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...
or transferred to other ecosystems (e.g., from a forest to a stream to a lake) by
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
.
In
aquatic systems
Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live.
Aquatic(s) may also refer to:
* Aquatic animal, either vertebrate ...
, the proportion of plant biomass that gets consumed by
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s is much higher than in terrestrial systems.
In trophic systems, photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers or
secondary producers—
herbivores
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
. Organisms which feed on
microbe
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s (
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
) are termed
microbivore Microbivory (adj. microbivorous, microbivore) is a feeding behavior consisting of eating microbes (especially bacteria) practiced by animals of the mesofauna, microfauna and meiofauna.
Microbivorous animals include some soil nematodes, springtai ...
s. Animals that feed on primary consumers—
carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
s—are secondary consumers. Each of these constitutes a trophic level.
The sequence of consumption—from plant to herbivore, to carnivore—forms a
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...
. 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 web
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
s rather than food chains.
Decomposition
![Decomposition stages](https://upload.wikimedia.org/wikipedia/commons/3/3a/Decomposition_stages.jpg)
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.
Decomposition processes can be separated into three categories—
leaching
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to:
* Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
, 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).
Newly shed leaves and newly dead animals have high concentrations of water-soluble components and include
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
s,
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
s and mineral nutrients. Leaching is more important in wet environments and less important in dry ones.
Fragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shed
leaf litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...
may be inaccessible due to an outer layer of
cuticle or
bark, and
cell contents are protected by a
cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...
. Newly dead animals may be covered by an
exoskeleton
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...
. 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 cycle
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
s and cycles of wetting and drying also fragment dead material.
The chemical alteration of the dead organic matter is primarily achieved through bacterial and fungal action. Fungal
hypha
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one or ...
e produce enzymes that can break through the tough outer structures surrounding dead plant material. They also produce enzymes that break down
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
, 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.
Decomposition rates
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 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.
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
wetland
A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
s), 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.
Dynamics and resilience
Ecosystems are dynamic entities. They are subject to periodic disturbances and are always in the process of recovering from past disturbances.
When a
perturbation
Perturbation or perturb may refer to:
* Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly
* Perturbation (geology), changes in the nature of alluvial deposits over time
* Perturbat ...
occurs, an ecosystem 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. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its
ecological resilience
In ecology, resilience is the capacity of an ecosystem to respond to a perturbation or disturbance by resisting damage and recovering quickly. Such perturbations and disturbances can include stochastic events such as fires, flooding, windstorm ...
. Resilience thinking also includes humanity as an integral part of the
biosphere
The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be ...
where we are dependent on
ecosystem services
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. Th ...
for our survival and must build and maintain their natural capacities to withstand shocks and disturbances. 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.
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".
This can range from
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
outbreaks, treefalls, fires, hurricanes, floods,
glacial advances, to
volcanic eruptions
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...
. 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."
The frequency and severity of disturbance determine the way it affects ecosystem function. A major disturbance like a volcanic eruption or
glacial
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
advance and retreat leave behind soils that lack plants, animals or organic matter. Ecosystems that experience such disturbances undergo
primary succession
Primary succession is the beginning step of ecological succession after an extreme disturbance, which usually occurs in an environment devoid of vegetation and other organisms. These environments are typically lacking in soil, as disturbances l ...
. A less severe disturbance like forest fires, hurricanes or cultivation result in
secondary succession
Secondary succession is the secondary ecological succession of a plant's life. As opposed to the first, primary succession, secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane, etc.) that reduces an a ...
and a faster recovery.
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 drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...
, 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.
Another example is the
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
production in eastern
Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
n lakes that is controlled by
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
which accumulated during the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
.
Nutrient cycling
![Nitrogen Cycle](https://upload.wikimedia.org/wikipedia/commons/d/de/Nitrogen_Cycle.jpg)
Ecosystems continually exchange energy and carbon with the wider
environment
Environment most often refers to:
__NOTOC__
* Natural environment, all living and non-living things occurring naturally
* Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...
. 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
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
, is deposited through precipitation, dust, gases or is applied as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
.
Most
terrestrial ecosystems
Terrestrial ecosystems are ecosystems which are found on land. Examples include tundra, taiga, temperate deciduous forest, tropical rain forest, grassland, deserts.
Terrestrial ecosystems differ from aquatic ecosystems by the predominant presence ...
are nitrogen-limited in the short term making
nitrogen cycling
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biolog ...
an important control on ecosystem production.
Over the long term, phosphorus availability can also be critical.
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.
Secondary major nutrients (less often limiting) include: Calcium, magnesium, sulfur.
Micronutrient
Micronutrients are nutrient, essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain health. Micronutrient requirements differ between organisms; for exam ...
s 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.
Until modern times, nitrogen fixation was the major source of nitrogen for ecosystems. Nitrogen-fixing bacteria either live
symbiotically
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
with plants or live freely in the soil. The energetic cost is high for plants that support nitrogen-fixing symbionts—as much as 25% of gross primary production when measured in controlled conditions. Many members of the
legume
A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...
plant family support nitrogen-fixing symbionts. Some
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
are also capable of nitrogen fixation. These are
phototroph
Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconcep ...
s, 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
Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but acid ...
produced through the combustion of fossil fuels,
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
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 ecosystems.
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
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
ions into the soil. This process is known as
nitrogen mineralization. Others convert ammonium to
nitrite and
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
ions, a process known as
nitrification
''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of amm ...
.
Nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
and
nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...
are also produced during nitrification.
Under nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are converted to
nitrogen gas
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...
, a process known as
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
.
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.
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.
Phosphorus enters ecosystems through
weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics).
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.
Function and biodiversity
Biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
plays an important role in ecosystem functioning.
Ecosystem processes are driven by the species in an ecosystem, the nature of the individual species, and the relative abundance of organisms among these species. Ecosystem processes are the net effect of the actions of individual organisms as they interact with their environment.
Ecological theory
Theoretical ecology is the scientific discipline devoted to the study of ecological systems using theoretical methods such as simple conceptual models, mathematical models, computational simulations, and advanced data analysis. Effective models im ...
suggests that in order to coexist, species must have some level of
limiting similarity
Limiting similarity (informally "limsim") is a concept in theoretical ecology and community ecology that proposes the existence of a maximum level of niche overlap between two given species that will allow continued coexistence.
This concept is ...
—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. However, beyond some level of species richness,
additional species may have little additive effect unless they differ substantially from species already present.
This is the case for example for
exotic species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
.
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
A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
tend to have an effect on ecosystem function that is disproportionate to their abundance in an ecosystem.
An
ecosystem engineer is any
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
that creates, significantly modifies, maintains or destroys a
habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
.
Study approaches
Ecosystem ecology
Ecosystem ecology
Ecosystem ecology is the integrated study of living ( biotic) and non-living (abiotic) components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components s ...
is the "study of the interactions between organisms and their environment as an integrated system".
The size of ecosystems can range up to ten
orders of magnitude
An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...
, from the surface layers of rocks to the surface of the planet.
The
Hubbard Brook Ecosystem Study
Hubbard Brook Experimental Forest is an area of land in the towns of Woodstock, Ellsworth and Thornton in the White Mountains of New Hampshire that functions as an outdoor laboratory for ecological studies. It was initially established in 1955 ...
started in 1963 to study the
White Mountains in New Hampshire. It was the first successful attempt to study an entire
watershed as an ecosystem. The study used stream
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
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
Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but acid ...
in North America in 1972. Researchers documented the depletion of soil
cations
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...
(especially calcium) over the next several decades.
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, ranging from whole-ecosystem studies to studying
microcosms or
mesocosm thumb , Diagram of a small form closed system mesocosm.
A mesocosm (''meso-'' or 'medium' and ''-cosm'' 'world') is any outdoor experimental system that examines the natural environment under controlled conditions. In this way mesocosm studie ...
s (simplified representations of ecosystems).
American ecologist
Stephen R. Carpenter
Stephen Russell Carpenter (born July 5, 1952) is an American lake ecologist who focuses on lake eutrophication which is the over-enrichment of lake ecosystems leading to toxic blooms of micro-organisms and fish kills.
Early life
Born in Kansas ...
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.
Classifications
Biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
s are general classes or categories of ecosystems.
However, there is no clear distinction between biomes and ecosystems. 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
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
. Biomes are often defined by their structure: at a general level, for example,
tropical forest
Tropical forests (a.k.a. jungle) are forested landscapes in tropical regions: ''i.e.'' land areas approximately bounded by the tropic of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds.
Some tropical fores ...
s,
temperate grasslands
Temperate grasslands, savannas, and shrublands is a terrestrial biome defined by the World Wide Fund for Nature. The predominant vegetation in this biome consists of grass and/or shrubs. The climate is temperate and ranges from semi-arid to sem ...
, and arctic
tundra
In physical geography, tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term ''tundra'' comes through Russian (') from the Kildin Sámi word (') meaning "uplands", "treeless moun ...
.
There can be any degree of subcategories among ecosystem types that comprise a biome, e.g., needle-leafed
boreal forests
Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, ...
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
Anthropogenic biomes, also known as anthromes, human biomes or intensive land-use biome, describe the terrestrial biosphere (biomes) in its contemporary, human-altered form using global ecosystem units defined by global patterns of sustained direct ...
), or by their integration with social processes or technological processes or their novelty (e.g.
novel ecosystem Novel ecosystems are human-built, modified, or engineered niches of the Anthropocene. They exist in places that have been altered in structure and function by human agency. Novel ecosystems are part of the human environment and niche (including u ...
). Each of these
taxonomies of ecosystems tends to emphasize different structural or functional properties.
None of these is the “best” classification.
Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of
ecosystems
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
: a biotic component, an
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
complex, the interactions between and within them, and the physical space they occupy.
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.
Examples
The following articles are examples of ecosystems for particular regions, zones or conditions:
*
Aquatic ecosystem
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
*
Boreal ecosystem
A boreal ecosystem is an ecosystem with a subarctic climate located in the Northern Hemisphere, approximately between 50° to 70°N latitude. These ecosystems are commonly known as taiga and are located in parts of North America, Europe, and Asia. ...
*
Freshwater ecosystem
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats ...
*
Groundwater-dependent ecosystems
*
Lake ecosystem
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems (''lentic'' ref ...
(lentic ecosystem)
*
Large marine ecosystem
Large marine ecosystems (LMEs) are regions of the world's oceans, encompassing coastal areas from river basins and estuaries to the seaward boundaries of continental shelves and the outer margins of the major ocean current systems. They are rela ...
*
Marine ecosystem
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surf ...
*
Montane ecosystem
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...
*
River ecosystem
River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...
(lotic ecosystem)
*
Terrestrial ecosystem
Terrestrial ecosystems are ecosystems which are found on land. Examples include tundra, taiga, temperate deciduous forest, tropical rain forest, grassland, deserts.
Terrestrial ecosystems differ from aquatic ecosystems by the predominant presence ...
*
Urban ecosystem
In ecology, urban ecosystems are considered a ecosystem functional group within the intensive land-use biome. They are structurally complex ecosystems with highly heterogeneous and dynamic spatial structure that is created and maintained by huma ...
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.
Ecosystem goods and services
![Avalanche Lake, looking south](https://upload.wikimedia.org/wikipedia/commons/7/78/Avalanche_Lake%2C_looking_south.jpg)
Ecosystems provide a variety of goods and services upon which people depend.
Ecosystem goods include the "tangible, material products" of ecosystem processes such as water, food, fuel, construction material, and
medicinal plant
Medicinal plants, also called medicinal herbs, have been discovered and used in traditional medicine practices since prehistoric times. Plants synthesize hundreds of chemical compounds for various functions, including Plant defense against her ...
s.
They also include less tangible items like
tourism
Tourism is travel for pleasure or business; also the theory and practice of touring (disambiguation), touring, the business of attracting, accommodating, and entertaining tourists, and the business of operating tour (disambiguation), tours. Th ...
and recreation, and genes from wild plants and animals that can be used to improve domestic species.
Ecosystem services
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. Th ...
, 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
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...
and even things like beauty, inspiration and opportunities for research.
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.
The ''
Millennium Ecosystem Assessment
The Millennium Ecosystem Assessment (MA) is a major assessment of the human impact on the environment, called for by the United Nations Secretary-General Kofi Annan in 2000, launched in 2001 and published in 2005 with more than $14 million of g ...
'' is an international synthesis by over 1000 of the world's leading biological scientists that analyzes the state of the Earth's ecosystems and provides summaries and guidelines for decision-makers. The report identified four major categories of ecosystem services: provisioning, regulating, cultural and supporting services.
It concludes that human activity is having a significant and escalating impact on the biodiversity of the world ecosystems, reducing both their
resilience and
biocapacity
The biocapacity or biological capacity of an ecosystem is an estimate of its production of certain biological materials such as natural resources, and its absorption and filtering of other materials such as carbon dioxide from the atmosphere.
Bio ...
. 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.
The
(IPBES) is an intergovernmental organization established to improve the interface between science and policy on issues of
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
and ecosystem services. It is intended to serve a similar role to the
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) a ...
. The conceptual framework of the IPBES includes six primary interlinked elements: nature, nature’s benefits to people, anthropogenic assets, institutions and governance systems and other indirect drivers of change, direct drivers of change, and good quality of life.
Ecosystem services are limited and also threatened by human activities.
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 Biodiversity banking, also known as biodiversity trading or conservation banking, biodiversity mitigation banks, compensatory habitat, set-asides, biodiversity offsets, are conservation activities that compensate for the loss of biodiversity with ...
, is prompting transdisciplinary shifts in how we recognize and manage the environment,
social responsibility
Social responsibility is an ethical framework in which an individual is obligated to work and cooperate with other individuals and organizations for the benefit of the community that will inherit the world that individual leaves behind.
Social ...
, business opportunities, and our future as a species.
Degradation and decline
![Flii globe](https://upload.wikimedia.org/wikipedia/commons/1/19/Flii_globe.png)
As human population and per capita consumption grow, so do the resource demands imposed on ecosystems and the effects 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
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...
,
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
and
biodiversity loss
Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
. For terrestrial ecosystems further threats include
air pollution
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...
,
soil degradation
Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land t ...
, and
deforestation
Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated d ...
. For
aquatic ecosystems
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
threats also include unsustainable exploitation of marine resources (for example
overfishing
Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in th ...
),
marine pollution
Marine pollution occurs when substances used or spread by humans, such as industrial waste, industrial, agricultural pollution, agricultural and municipal solid waste, residential waste, particle (ecology), particles, noise, excess carbon dioxid ...
,
microplastics
Microplastics are fragments of any type of plastic less than in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They cause pollution by entering natural ecosystems from a v ...
pollution, the
effects of climate change on oceans
Among the effects of climate change on oceans are: an increase in sea surface temperature as well as ocean temperatures at greater depths, more frequent marine heatwaves, a reduction in pH value, a rise in sea level from ocean warming and ice ...
(e.g. warming and
acidification
Acidification may refer to:
* Ocean acidification, decrease in the pH of the Earth's oceans
* Freshwater acidification, atmospheric depositions and soil leaching of SOx and NOx
* Soil acidification, buildup of hydrogen cations, which reduces the ...
), and building on coastal areas.
Many ecosystems become degraded through human impacts, such as
soil loss,
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
and
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
,
habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
,
water diversion
Interbasin transfer or transbasin diversion are (often hyphenated) terms used to describe man-made conveyance schemes which move water from one river basin where it is available, to another basin where water is less available or could be utilized ...
,
fire suppression
Wildfire suppression is a range of firefighting tactics used to suppress wildfires. Firefighting efforts in wild land areas require different techniques, equipment, and training from the more familiar structure fire fighting found in populated ...
, and
introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
and
invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
.
These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
conditions of the ecosystem. Once the original ecosystem has lost its defining features, it is considered ''
collapsed'' (see also
IUCN Red List of Ecosystems
The IUCN Red List of Ecosystems (RLE) is a global framework for monitoring and documenting the status of ecosystems. It was developed by the International Union for Conservation of Nature for biodiversity risk assessment. Its main objectives are ...
).
Ecosystem collapse could be reversible and in this way differs from
species extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
.
Quantitative assessments of the
risk of collapse are used as measures of conservation status and trends.
Management
When
natural resource management
Natural resource management (NRM) is the management of natural resources such as land, water, soil, plants and animals, with a particular focus on how management affects the quality of life for both present and future generations ( stewardship) ...
is applied to whole ecosystems, rather than single species, it is termed
ecosystem management
Ecosystem management is an approach to natural resource management that aims to ensure the long-term sustainability and persistence of an ecosystems function and ecosystem service, services while meeting socioeconomic, political, and cultural need ...
.
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
Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...
of the production of goods and services by the ecosystem;
"intergenerational sustainability
sa precondition for management, not an afterthought".
While ecosystem management can be used as part of a plan for
wilderness
Wilderness or wildlands (usually in the plural), are natural environments on Earth that have not been significantly modified by human activity or any nonurbanized land not under extensive agricultural cultivation. The term has traditionally re ...
conservation, it can also be used in intensively managed ecosystems
(see, for example,
agroecosystem
Agroecosystems are the ecosystems supporting the food production systems in our farms and gardens. As the name implies, at the core of an agroecosystem lies the human activity of agriculture. As such they are the basic unit of study in Agroecology ...
and
close to nature forestry
Close to nature forestry is a management approach treating forest as an ecological system performing multiple functions. Close to nature silviculture tries to achieve the management objectives with minimum necessary human intervention aimed at ac ...
).
Restoration and sustainable development
Ecosystem restoration
Restoration ecology is the scientific study supporting the practice of ecological restoration, which is the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human interrupt ...
will contribute to all 17
Sustainable Development Goals
The Sustainable Development Goals (SDGs) or Global Goals are a collection of 17 interlinked objectives designed to serve as a "shared blueprint for peace and prosperity for people and the planet, now and into the future".United Nations (2017) R ...
, in particular to
SDG 2 (Zero Hunger),
SDG 6 (Clean Water and Sanitation),
SDG 14 (Life below water) and
SDG 15 (Life on Land).
Paragraph 27 of the Ministerial Declaration of the High-Level Political Forum on the SDGs held in July 2018 sets out commitments made to achieve sustainable management of all types of forests, halt deforestation, restore degraded forests, and substantially increase afforestation and
reforestation
Reforestation (occasionally, reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation, but also after clearcutting.
Management
A debate ...
globally by 2020.
Integrated conservation and development projects (ICDPs) aim to address
conservation
Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws.
Conservation may also refer to:
Environment and natural resources
* Nature conservation, the protection and managem ...
and human livelihood (
sustainable development
Sustainable development is an organizing principle for meeting human development goals while also sustaining the ability of natural systems to provide the natural resources and ecosystem services on which the economy and society depend. The des ...
) concerns in Developing country, developing countries together, rather than separately as was often done in the past.
See also
* Complex system
* Earth science
*Ecosystem-based adaptation
Ecosystems in specific regions of the world:
* Leuser Ecosystem
* Longleaf pine ecosystem
* Tarangire Ecosystem
* Tropical salt pond ecosystem
Ecosystems grouped by condition:
* Agroecosystem
* Closed ecosystem
* Depauperate ecosystem
* Novel ecosystem
* Reference ecosystem
References
Notes
{{Authority control
Ecosystems,
Ecology
Biological systems
Superorganisms
Symbiosis
Systems ecology