Ecosystem ( ancient Greek οἶκος oikós , house 'and σύστημα sýstema "the compiled " "the connected") is a technical term of the ecological sciences . An ecosystem consists of a community of organisms of several species ( biocenosis ) and their inanimate environment, which is known as a habitat , habitat or biotope .
The term ecosystem is used in the natural sciences in a non-judgmental sense. In politics and everyday life, however, it is often spoken as if ecosystems in themselves are worth protecting. When this happens, it does not refer to ecosystems in general, but to specific ecosystems that are considered useful or otherwise valuable.
Delimitation of the term
An ecosystem is a “dynamic complex of communities made up of plants, animals and microorganisms as well as their non-living environment, which interact as a functional unit”. This common definition is used in the Convention on Biological Diversity . The following definitions by ecologists are very similar:
- "Relationship structure of living beings with one another ( biocenosis ) and with their habitat ( biotope )" - Matthias Schaefer
- “Ecological system, made up of all organisms in an area and the physical environment with which they interact” - Terry Chapin
- "Assembling organisms of different categories (species or life forms), together with their abiotic environment, in space and time" - Kurt Jax
The nature and properties of an ecosystem are understood differently by ecologists. Some assume their actual existence, which is only discovered and described by the researchers (so-called ontological approach), but most see them as abstractions created by the observer, which must be appropriate for a certain purpose, but also in another context could be defined and delimited differently (so-called epistemological approach). Using the example of a certain ecosystem, such as a boreal coniferous forest , some ecologists would state that the ecosystem has changed its character when its community has changed significantly due to the exchange of species. For others it would still be the same system if its general shape and primary production remained roughly the same (e.g. the most common conifer species were replaced by other species that are also conifers), for others it would only be a different system if its functional components, i.e. energy and material flows, change while they consider the species composition to be less important.
The basic types of terrestrial and aquatic ecosystems that have a large geographical spread are also known as biomes . A distinction must be made here between the scientific and common usage of the term ecosystem: Much of what is popularly referred to as “ecosystem” would mostly be more technically referred to as “ biome ”. The term biome originally goes back to Frederic Edward Clements , but was shaped today by the geobotanist Heinrich Walter . Biomes (or as a smaller unit: biogeocenoses) are empirically and descriptively derived sections of the earth's surface that can be characterized by a specific community (especially: vegetation). The functional aspect of the eco “system” can take a back seat. Biomes can be viewed as ecosystems, but do not have to be; they are often taken purely biogeographically. However, since the term is completely uncommon outside of the specialist public, it usually stands for “ecosystem” in popular publications. Biomes, using the example of forests would be, for example, tropical rain forest , temperate rain forest , boreal coniferous forest , subtropical forest Hartlaub , laurel forest , moderate (temperate), deciduous forest.
Comparable ecosystems of separate large areas, which are structured similarly in terms of their appearance, but not in terms of their species composition, can be combined into abstract units (e.g. boreal coniferous forest , desert , steppe ). Depending on how you look at it, the specialist literature u. a. spoken of plant or vegetation formations , vegetation zones , zonobiomes or eco-zones .
Properties of ecosystems
Size and limits
The definition of “ecosystem” does not include any restriction to a certain size (scale independence), regardless of whether this size is defined spatially or functionally. Ecosystems can therefore be of different sizes. A decomposing tree stump can be understood as an ecosystem, just like the forest in which the tree stump has its place. However, many ecologists use the term ecosystem in a larger context. The largest ecosystem is the biosphere , which includes the entirety of all terrestrial and aquatic ecosystems.
As open systems, ecosystems have no actual system boundaries compared to the rest of the biosphere. Delimited ecosystems are constructs selected by the investigator. The delimitation is therefore a pragmatic decision (based on the question, the research interest or the available budget) and does not necessarily correspond to an actual delimitation in nature. Ideally, subsystems should be selected whose relationship structure is more important within than that to the outside, i.e. which are linked to their environment through as basic and as few interactions as possible. The term ecotope was coined for the spatial delimitation and location of an ecosystem, but it is not very common outside of landscape ecology.
To better understand the interrelationships, scientists occasionally construct highly simplified ecosystems in the laboratory that contain only a few species; for this the technical term "microcosms" has become established.
The concept of system implies a functional consideration of causal relationships that goes beyond a mere morphological / topographical description, especially in the form of material and energy flows. If a section of nature is viewed as an ecosystem, an understanding of the natural regularities and relationships is often sought by creating a model of reality. Such a model can be verbal, graphical or mathematical. In ecosystem research, for example, quantitative models that can be expressed in mathematical language are mostly sought. Some aspects of ecosystems can be expressed by systems of differential equations . Terms from thermodynamics and statistical physics are also used .
There are multiple interrelationships and dependencies between the organism community of an ecosystem. These include, for example, the trophic relationships between different types of the ecosystem, such as the exchange of substances between primary producers and heterotrophic links in the food chain in the form of symbiotic relationships ( mycorrhiza ), parasitism and saprophilia .
Openness, dynamism, complexity
In science, the term ecosystem is used as a somewhat fuzzy level of observation that connects the ecology of communities with approaches from systems theory and cybernetics . However, the term is more of a paradigm that prescribes a certain point of view and cannot be used to predict specific properties of the research object. Some ecologists even avoid the term entirely because, from their point of view, the community and its ecology are sufficient for processing; so it is not used in a very popular ecology textbook.
The following terms are often used to describe the general properties of ecosystems:
- open: Ecosystems are open systems that require an energy flow through the system in order to maintain their system state .
- dynamic: ecosystems usually do not remain at fixed points in their state space, but dynamic developments take place on different spatial and temporal scales. These include succession processes , but also developments with a closed phase space curve and many other forms of dynamics. In addition, there are long - term self - organization and adaptation processes that can continuously change an ecosystem;
- complex: ecosystems have biotic and abiotic elements and structures. These structures are linked to one another through interactions. With the number of interactions realized in the system, its complexity increases. The relationship between the complexity on the one hand and the stability of ecosystems on the other hand is an active research area of ecology.
However, the application of the term ecosystem to a natural section alone cannot be used to predict the specific properties, structures or processes of the natural section. Ecosystems can e.g. B. be comparatively complex or simple in structure, behave more stable or more unstable, remain close to a state of equilibrium or move far away from it. The view as an ecosystem only provides a certain analytical perspective.
Functional principles of ecosystems
When looking at the organisms of an ecosystem, the specific species are often abstracted and their functional role in the system as a whole is emphasized. This means that individual species are often viewed in a certain sense as being interchangeable in terms of their function. The organisms can be divided according to their trophic function in the system as
- Primary producers who build organic substances from inorganic substances and energy (sunlight, chemical energy). These are mainly green plants that photosynthesize and autotrophic bacteria and archaea that can also use chemical energy;
- Consumers who feed on the producers, other consumers or on destructors . In particular, it concerns animals including humans . Consumers give off carbon dioxide and more or less energy-rich organic matter: ( urine , feces , body debris, hair and corpses ). The consumers are further subdivided into consumers of the first order, the herbivores (phytophage or herbivores) and consumers of higher orders, collectively referred to as carnivores (carnivores). The most important carnivores are the robbers ( predators ).
- Destructors , which degrade the dead producers and consumers, their excretions or organs (e.g. plant litter and fallen leaves) and finally mineralize them, i.e. return them to abiotic substances. The functionally decisive destructors are especially bacteria and fungi .
A distinction is often made between two sub- food webs . The basis of both food webs are the green plants (or possibly the other primary producers). The plants are wholly or in parts by special consumers, the phytophages (= herbivores ). consumed. This happens as when a oak Spinner leaves an oak eats a mussel einstrudelt algae or a man a carrot eaten. This is the consumer food web. Often, however, large amounts of dead plant material arise, which are broken down by the destructors without the intervention of consumers. This allows a very large community of destructors to build up. These destructors are in turn z. B. eaten by bacteria and fungus-eating species. This subheading includes many protozoa , nematodes and oligochaetes , but also arthropods such as horn mites and springtails . These organisms then form a destructive food web.
Various substances can be tracked on their way through the ecosystem. This applies, for example, to water and also to individual chemical elements (C, N, P etc.). The ecosystem research examining the resulting material cycles and maps them in material flow charts and complex models. The same applies to the flow of energy . The term “material cycle” indicates that many substances are implemented several times in the ecosystem. However, this depends on the type of ecosystem. The cycle percentage in a forest is rather high for many elements. This is especially true for elements that are not regularly released into the atmosphere as a gas . In contrast, the ecosystem of a river is characterized by the constant, non-recurring throughput of substances. If geological time periods are considered, it is noticeable that considerable amounts of substances and elements are eliminated from the cycle for (possibly hundreds) millions of years (see e.g. limestone , coal seam ).
Ecosystems influence each other through the flow of information , substance and energy. The construction and change of ecosystems can have strong repercussions on the abiotic factors. The individual mechanisms of action and their relative importance are an active field of research. For example, marine ecosystems influence the atmosphere and thus also terrestrial ecosystems through their material and energy balance . An example of global interrelationships is the increase in the greenhouse effect and the climate change it causes . In order to derive practical benefit from this knowledge, the relative strength of the interactions must be known.
For a long time, physical terms from thermodynamics have been applied to ecosystems (especially entropy , dissipation ), mostly in qualitative form as analogies. In the last 20 years or so, a branch of research has started to establish itself that aims to make thermodynamic terms usable in more depth for modeling and predicting ecosystems.
The key term for the thermodynamic interpretation is entropy, especially the second law of thermodynamics. Above all, it needs to be explained why life and ecosystems could become so complex if the entropy is not allowed to decrease globally. The only physically possible explanation for this is that the apparently low entropy in the biosphere is more than compensated for by increasing the entropy in its (physical) environment. The development and maintenance of life obviously takes place far from thermodynamic equilibrium. This is only possible in an environment that is also far from equilibrium. An ecosystem therefore needs a thermodynamic gradient as a drive, on the one hand it has to receive (energetic or material) resources from the outside, and on the other hand it has to give off “waste” with a higher entropy than that of the resources. For the earth as a whole, this gradient is the difference between the energy-rich solar radiation and the cold universe (into which heat can be radiated). An ecosystem can only exist thermodynamically if it converts “resources” into “waste” faster than a comparable inanimate system would.
The entropy production of an ecosystem cannot be measured directly, since important partial quantities (above all the chemical energy of living biomass) cannot be measured (or: cannot even be defined satisfactorily). Ecologists try to define different sizes to circumvent this problem. With these variables, general statements about ecosystems should be possible, which allow predictions about the structure and development of ecosystems. Important approaches are: Ascendancy (roughly: “Ascent”), Emergie (with an “m” in the middle), Exergy and Eco-Exergy.
In ecology, it is still controversial today what ultimately controls the dynamics and structure of ecosystems. Traditionally there are two basic assumptions:
- From the bottom up: According to this approach, primary producers produce about as much biomass as their resources allow. Some of this is available to primary consumers (herbivores). Due to the energetic losses, they cannot use more than 10% of the food energy used to build up their own biomass. This continues in the further trophic levels (consumers of the second, third ... order). The length of the food chain is limited by productivity because at some point the remaining energy will no longer be sufficient for another trophic level. Limnologist Raymond L. Lindeman is considered the founder of this theory
- From top to bottom: According to this model, the biomass and production of green plants is controlled and controlled by the herbivores. The herbivores would be able to use more or less the entire biomass for themselves. The only reason the world stays so green is because the production of herbivores is also kept in check by predators.
Alternatives or variants to these basic models exist in large numbers.
- A more recent model emphasizes the special role of environmental stress factors on the species structure. Accordingly, unfavorable environmental factors have a greater impact on consumers than on producers (e.g. because the environment becomes less predictable and strong fluctuations have stronger effects for species higher up in the food chain). Accordingly, in ecosystems that are favorable to organisms, consumers would be decisive. Under unfavorable environmental conditions (and thus low productivity), the competition between plants would be decisive. Each of these models has its supporters in ecological science. A large number of combinations of the basic models have also been proposed. (e.g.).
Temporal dimension of ecosystems
As natural systems, ecosystems have a spatial and a temporal dimension. On the temporal level, one tries to understand the changes that are taking place, that is, the dynamics of the system. Systems can remain more or less unchanged, or they are subject to (directed or random) changes. Since living organisms can react to changes, self-regulating processes can take place in ecosystems, unlike in inanimate systems, which can make the system's reaction to changes difficult to predict. For the holistic-organismic school of thought in research, these self-regulating processes are of all decisive importance, for them an ecosystem is therefore analogous to a living organism. The more reductionist mainstream of science recognizes the patterns and regularities that result in the development of systems, but does not consider the strong emphasis on constancy resulting from the organism metaphor to be appropriate. Researching completely chaotic and unregulated changes is possible, but scientifically not very productive, since one could hardly generalize the knowledge gained in this way to anything outside of the examined system itself. Ecosystem research therefore mostly focuses on more or less constant systems or at least on those whose change can be traced back to explanatory factors. The starting point of research is therefore (as in general in science) patterns and regularities in nature itself.
Dynamism and constancy, stability
In numerous examined ecosystems, no significant changes are observed over a longer period of time; they are stable over time. Stability is trivial if the environmental factors and the abiotic components of the system have not changed. It is more interesting if a system can maintain its stability even when external factors change. Research into these relationships has long been hampered by the ambiguity of the concept of stability. Grimm and Wissel found z. E.g. in a literature study 163 different definitions of stability related to 70 concepts. Today (according to Pimm 1984), a distinction is usually made between: persistence (few changes are observed in long-term observations), resilience (the system returns to its original state after disruptions), and resistance (the system remains unchanged for a long time in the event of disruptions).
Stability and constancy in ecosystems are dependent on the spatial and temporal scale considered. The population size of a species may e.g. B. fluctuate year after year, but stay the same in the longer term. The stability and stability conditions of ecosystems, especially the connection between stability and complexity, are active research fields in ecological sciences. The traditional views that ecosystems are usually in ecological equilibrium and that their stability increases with an increase in the number of species or biodiversity have been increasingly questioned for about 30 years.
The term "disturbance"
In the development of an ecosystem over time, the concept of disturbance is a key concept. Without disturbances, a system is exclusively subject to endogenous dynamics. B. occur through interactions between the species involved. In this context, it is important that the term disruption is used in ecology without any value judgment. A disorder is not a bad thing per se ; often certain ecosystems can only be maintained through regular disturbances (see below).
The size of a population can be regulated by the structure of relationships at a certain level, or, e.g. Cyclical fluctuations can occur, for example due to delayed reactions (for mammalian populations, for example). Directed, permanent changes in the system are called succession . A disorder is a factor that changes the system and has an impact from outside this internal relationship. A distinction is often made between rare and major faults (catastrophes) and smaller and recurring faults. The term disorder is also dependent on the scale, e.g. For example, eating away by a grazing animal can be seen as a disturbance for a single plant, but as a constituent and systemic factor for the meadow ecosystem. White and Pickett have attempted to define faults in absolute terms, and Smith provides a definition of extreme climatic events as faults. The temporal pattern of disturbances or disturbance regimes is a defining factor for many ecosystems, recurring disturbances such as mowing or grazing in grassland, flooding in alluvial forests, but also catastrophic disturbances such as forest fires or storms in forest ecosystems can have a decisive impact on the structure and composition of an ecosystem.
Endangerment and assessment of ecosystems
“Ecosystem” in the biological-scientific sense is a neutral term. Talking about the existence of a certain ecosystem or the stability of one of its states does not, therefore, imply a positive appreciation on this conceptual level; Efforts to protect ecosystems must be justified separately. Natural science cannot provide such justifications, since it is required to always provide value-free descriptions and explanations. The conditions that arise after the destruction of a highly developed ecosystem are to be addressed as an ecosystem in the same way as the initial condition, as long as some form of life still occurs in them. An ecosystem only has a value if it has been assigned to it through a value decision by people. The value decision stands outside of natural science. It can be supported by scientific arguments, but not derived from science or from the scientifically described nature (cf. on this: Naturalistic fallacy , Hume's law ).
Values that are attributed to an ecosystem can be related to its functional level, is then often speaks of ecosystem functioning and ecosystem services (engl. Ecosystem services ). For example, the maintenance could a forest with his role as carbon -Speicher for the prevention of global warming , with its erosion contraceptive role on steep slopes or with his positive role in the formation of usable groundwater justified, and not least by the harvested here wood or killed wild game become.
Ecosystem services are often replaceable. It is conceivable that with a corresponding technical and financial effort, CO 2 will be injected into deep rock layers and thus withdrawn from the atmosphere . Erosion protection could also be substituted by grassland , groundwater protection through the use of technical filters or treated surface water. Environmental economic studies show that the costs of technical substitution are often so high that natural or near-natural ecosystems should not be carelessly degraded for economic reasons. It should also be borne in mind that the usability of an ecosystem can also gradually be reduced more and more by constant influences, which is not recognizable on a short-term view. Within environmental economics, a special field has emerged for the study of ecosystem services (see TEEB study ).
The protection of natural ecosystems is largely not based on this purely functional level. If people want to preserve the biodiversity of certain ecosystems, they usually do not do so for functional reasons (although there are people who want to justify this, for example, with the preservation of unusual natural substances as the basis for new drugs). Rather, the diversity and complexity of nature are given their own value. Environmental economists find it somewhat difficult to justify this because they do not enter into the universal value medium of economics, i.e. H. Money, converts. Alternatively, an attempt is made to grasp the value by asking in surveys how much money the respondents would be willing to give to save natural ecosystems.
Human efforts to create ecosystems for the preservation of nature itself, e.g. B. to protect biodiversity are summarized as nature conservation . Most of the efforts made at the functional level, i.e. H. Direct usability and ecosystem services are the domain of environmental protection .
The various justifications and values that are used to preserve ecosystems can conflict with one another. Used ecosystems are changed by their use and are therefore no longer completely autonomous and natural. Today, due to global emissions from technical processes, it can be assumed that there are practically no more completely unaffected natural landscapes . In this context, ecology divides ecosystems into so-called degrees of hemerobia according to the degree of human (anthropogenic) influence . The lower the degree, the lower the anthropogenic influence. A distinction is often made between the total destruction and the degradation of ecosystems due to strong human influences. The most intact ecosystem complexes are found in the oligohemerobic (near-natural, slightly influenced) wilderness areas of the world. The biodiversity of used ecosystems often decreases with increasing hemerobia, but it can also increase. For terrestrial ecosystems and their biodiversity , in Central Europe the intensification of the agricultural use of favored areas with simultaneous abandonment of marginal areas is a major problem. Cultural landscapes based on traditional forms of use such as heaths and grasslands are trying to preserve nature conservation due to their biodiversity. It thus limits their usability for humans. These conflicts are exacerbated in poorer countries with extensive and species-rich ecosystems that are, however, hardly usable. The final argument for their preservation is often their importance for tourism from rich countries. There is also increasing talk of direct transfer payments from the rich to the poor nations.
In 2017, more than 15,000 scientists published an urgent warning to humanity , which proves that many ecosystem services are seriously endangered and that the chances of their maintenance are currently assessed negatively.
The view that living beings and habitats must be viewed together can be traced back in science to the 19th century, when John Scott Haldane wrote that "the parts of an organism and its surroundings form a system". In 1928, the Leipzig biologist and limnologist Richard Woltereck spoke of "ecological shape systems".
In 1935, the British biologist and geobotanist Arthur George Tansley created the current term "ecosystem" (ecosystem). His definition of “ecosystem”: “the entire system (in the physical sense) including not only the complex of organisms, but also the entire complex of physical factors that form what we call the environment - the habitat factors in the broadest sense. "" (In the systems) ... there is constant exchange in the most varied of forms within the system, not only between the organisms, but between organic and inorganic areas. "Is still valid in this form to this day. His system concept is that of a partially observer-constructed, mental isolate .
The immediate reason for Tansleys formulation was a series of articles of the South African ecologist John Phillips about the nature of the biotic community ( biotic community ). Phillips was inspired by Jan Christiaan Smuts ' holism . In these articles Phillips advocated a “strong” interpretation of the biotic community in the sense of the concept of a complex organism coined by Frederic Edward Clements . With his rather mechanistic proposal, Tansley sharply opposes the use of an idealistic , empirically inaccessible organism metaphor in the epistemological sense , to which his term should expressly serve as an alternative.
The development of a physically shaped ecosystem concept has important foundations in European and North American aquatic ecology, especially limnology . In 1877, Karl August Möbius, professor of zoology from Kiel , coined the term biocenosis for organismic socialization in oyster banks. Stephen Alfred Forbes , a limnologist from Illinois, referred to lakes as "organic systems" with cyclical metabolism ( matter cycling ) in 1887 , in which superordinate control mechanisms maintained a balance. While Forbes' work was little received outside of the American Midwest, August Thienemann built up the hydrobiological department of the Kaiser Wilhelm Society in Plön from 1891 . From there, Thienemann spread his view of lakes as biotic systems that result from the interaction of living beings and the environment ("habitat ( milieu ) and community ( biocoenosis ) as a solid, organic unit", 1916). Thienemann uses the concept of the holocoen, which the entomologist Karl Friedrichs introduced in 1927, which is largely identical to "ecosystem" (but closer to the holistic, organismic view of Clements and Phillips).
From the 1920s onwards, increasingly more precise analyzes of food chains and the material and energy turnover occurring in them began to appear (e.g. Charles Sutherland Elton , EV Borutsky, Chancey Juday). In 1939 these studies led to Thiemann's distinction between producers , consumers ( herbivores and carnivores ) and reducers . Tansley's ecosystem concept was first systematically applied empirically at the end of the 1930s by Limnologist Raymond Laurel Lindeman , who worked in Minnesota and who presented the first complete description of the energy turnover in a (lake) ecosystem. Another influential research direction was the biogeochemistry founded by the Russian Vladimir Verdadsky , which imagined the exchange of substances between living beings and the environment as an exchange within a chemical system. In 1944, the Soviet biologist Sukachev created his term "biogeocenosis" from this, which was used in Eastern Europe instead of an ecosystem for a long time (by geographically shaped landscape ecologists in some cases until today). In collaboration with Lindemann, George Evelyn Hutchinson spread the Russian approach.
The American ecologist Eugene P. Odum helped the ecosystem concept to make its international breakthrough . In 1953 Odum published his short textbook "Principles of Ecology". Its first pages implicitly unfold the research program that ecosystem research largely followed until the end of the 1960s.
Use of the term outside of ecology
Originally borrowed from English, the term ecosystem is also transferred to the field of economy and then stands for the entirety of the actors within an industry ( business ecosystem ), in German one also speaks of economic ecosystems or corporate ecosystems . In particular, the will in view of the start-up scene and encouraging entrepreneurship also founder ecosystems and start-up -Ökosystemen spoken. The RKW tries to establish this term . The best-known example of a holistic startup ecosystem is Silicon Valley , and in Europe also the urban quarters of Berlin .
- Information technology
With the term digital ecosystem is figuratively in information technology , a software and hardware - architecture called, which is based on each own devices, systems and entry requirements and therefore requires appropriate accessories and produces. An example of a closed digital ecosystem are the products of the Apple company .
- Biological cybernetics
- Bronfenbrenner's ecosystem approach
- Resilience (ecosystem)
- Systems theory
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