Ecological niche

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Ecological niche describes the totality of biotic and abiotic environmental factors that influence the survival of a species . Some authors also describe the ecological niche of animals as their “occupation” or “permanent position” within the community of the various organisms in the respective biotope .

Concept history

The term niche in an ecological context was first mentioned in a paper by the naturalist Joseph Grinnell in 1917. (There is scattered earlier evidence without any response). The niche term Grinnells is essentially related to the environment: It describes an area of ​​the earth's surface with its specific ecological site properties that is conducive to the survival of the species under consideration. Independently of this, the English ecologist Charles Elton reintroduced the term niche in a similar sense in 1927 . Elton places greater emphasis on biological interactions; his niche concept corresponds more to the role or function of a species in its community, especially its relationship to enemies and food resources.

The term as used today goes back to an influential article by the zoologist George Evelyn Hutchinson , who built on the work of Grinnell and Elton. Hutchinson's most important innovation was that the niche is not viewed as a property of the environment - into which a species can "fit" or "not fit", which may also remain "empty" - but as a property of the species itself.

The Hutchinson concept

Tolerance ranges and optimum of a living being with regard to an environmental factor

Hutchinson's concept is based on the well-known fact that a species can only live if environmental factors are within a certain range; this includes temperature, humidity, soil conditions, food supply, predation pressure and the like. a. The range of values ​​of a factor, e.g. B. the temperature, is usually entered in graphical representations in a simple coordinate system on a scale on the abscissa ("x-axis"), the degree of suitability for the organism on the ordinate ("y-axis"). If a second factor is to be taken into account in the same graph, e.g. B. the humidity, an area diagram must be created with the second dimension for the second factor, i. H. for the combinations of temperature and humidity in which this species can live. (An application example for the niche of the water flea Daphnia magna is offered by Hooper.) A third factor (e.g. pH value of the soil) defines a volume. Adding further factors results in a structure that is no longer clear, but theoretically mathematically comprehensible: an n- dimensional hyperspace .

This hyperspace is composed of the totality of all environmental factors such as temperature, food, soil moisture, habitat, etc., which apply to the respective ecological niche, and forms (in the mathematical sense) a so-called niche space. The individual factors can be represented graphically as dimensions. Each environmental factor represents one dimension. The ecological niche is defined by the boundaries in which a species can live and reproduce , which can be shown as an area on each graph. There is an optimum within this range for each factor at which the species thrives best. Outside the optimum range there is a tolerance range on both sides in which individuals of the species in question can survive. However, in practice there are very many dimensions due to the complexity of life. A diagram of a realistic multidimensional niche is therefore difficult to imagine and cannot be drawn. The n-dimensional hyperspace of the environmental factors can therefore be broken down into two- to three-dimensional niche diagrams for reasons of clarity.

Different lichens on a fireplace. However, it is not the location that describes the ecological niche, but rather the ability of the respective species of lichen, under the given environmental factors, “lack of soil”, a certain “sun exposure”, extreme, but varying degrees of “moisture fluctuations” on this “rock”, “acidity” and “ specific substrate ”, ie to interact with the environment through absorption and excretion of substances under the respective site conditions and to flourish.

Modern applications of the term have emerged from the derivation and modification of the Hutchinsonian concept. The niche term found its way into synecology in particular . Here the coherent with the concept Termini have niche breadth , phenotypic plasticity , niche overlap and ecological niches proven.

Niche overlap means that two species share the same ecological niche. Niche overlap usually leads to competition e.g. B. by reducing resources such as space or food supply or light and water in plants. This results in a decrease in the survivability, growth and reproduction rate of the affected species. The only exceptions are relationships of species with positive effects, especially mutualism .

The term ecological niche is sometimes misunderstood, since the term “niche” is colloquially associated with a room or a place. However, the ecological niche is not a spatial description, in contrast to the terms habitat (or location ) and biotope , which designate a physical place. In fact, the ecological niche is a functional term that describes the "ecological role" that the species plays in the ecosystem under consideration. It therefore describes which biotic and abiotic conditions, environmental and evolutionary factors are important for the life and survival of this species in the ecosystem. It follows from this that niches defined in this way cannot be “occupied”. Rather, they are “formed” through interaction between the organisms of a species and their environment.

The hedgehog, an insect eater

For example, the hedgehog's ecological niche, under the fluctuation of temperatures in the temperate zone, is to be active in its "job" as a devourer of snails and insects running on the ground , which the dog cannot prey because its spines protect it while between the spines multiply the fleas, which jump over to the dog as a new host . The mole in the same garden, which is also an insect eater , cannot perform the same ecological functions due to different physical characteristics.

Niche theory and competition between species

The species-related definition of the ecological niche can naturally be made independently for each species. Other species are included in the niche definition indirectly (as environmental factors, e.g. as predators or as food), but do not play a direct role. If one compares the ecological niches of different species found in this way, they can be completely separate from one another if the species do not share any area of ​​a habitat. More often, however, the niches formed in this way will overlap to a greater or lesser extent. This means that parts of the niche space can be used by both types. The niche space of one species in the presence of other species will thus be different from the one without them. It can be larger (in symbiotic or mutualistic relationships), but more often it will be smaller due to competition or other antagonisms.

Fundamental and realized niche

Type 1 could live in the more extensive fundamental niche A (outside not), type 2 in niche B. However, type 1 only realizes the smaller area y, while type 2 lives adapted to the real niche z . At the intersection x of the two circles, the two species compete with each other.

A distinction is therefore made between two basic concepts of an ecological niche:

  1. As a fundamental niche or fundamental niche of a kind is that portion of a niche space in which this type alone because of their physiological potency , so their genetic variability and response standards could live and related adaptability. In practice, this can only be determined under laboratory conditions . In a sense, this is the overall ecological description of the species in question.
  2. As realized niche or Real niche is the portion that is actually used in consideration of the actual current location factors in a specific ecosystem of the species concerned. Here, every individual enters into an interrelationship with strangers or conspecifics and competes with them for resources or is limited in his possibilities in some other way. The realized niche is part of the fundamental niche. This means that the niche that is realized is not only dependent on the biotic factors but also on the abiotic factors.

Importance of the competitive factor

Since, in the opinion of many ecologists, competition between species is one of the essential factors that determine natural communities, an essential area of ​​application of niche theory lies in the consideration of this competition. The starting point is the principle of exclusion of competition : According to this, two species with the same living requirements cannot coexist in one habitat. The competitive superior type will displace the inferior. If the principle applies in natural communities, it needs to be explained why so many species can obviously get along with each other there without most of them being displaced by superior competitors. Hutchinson himself spoke z. B. for the phytoplankton of lakes, which in a seemingly homogeneous habitat competes for a handful of essential resources (essentially: light, phosphorus, nitrogen) and yet is very species-rich, from the "paradox of plankton."

Translated into the language of niche theory, exclusion of competition means that the niches of two species completely overlap for at least one of these species (they do not need to be identical: one niche can be completely enclosed by another). If one of the species has a portion of the niche space that the superior competitor cannot colonize, it has a refuge there. This ensures the survival of the species, but a common occurrence would still be impossible.

There are various possible solutions to this problem within niche theory.

  • Spatial variability: The habitat consists of sub-habitats that differ in one or more environmental factors. In each sub-habitat a different species is superior.
  • Temporal variability: The living conditions change within the season, from year to year or over the long term, favoring different species. The superior species do not have enough time to oust their competitors because the conditions have changed again by then. The species thus have a “temporal niche”.
  • Trade-offs: There are no “super species” that are superior to other species in all respects. Advantages in one area are “bought” by disadvantages in others ( trade-off ). A species cannot have particularly large and particularly many seeds at the same time. A plant can be competitive at high soil nitrogen levels, but defeat at lower levels.
  • Modification through biological interactions: The competitiveness of a species can be influenced by other species, especially by predators. In the presence of a certain predator, an otherwise inferior species can e.g. B. be promoted indirectly, even if the species itself belongs to the prey spectrum, if the competitor suffers even more from it. The grazing by the predator can extent reduce the population density of the competitors that the factor that usually compete for the one available for all competitors sufficiently available.
  • Narrowing down: species can evade interspecific competition. For example, it has been observed that species differ more in their body structure when they occur together than when they occur alone (“character displacement”). A famous example, various finches species on the Galapagos Islands . A “diffuse” competition from related species has been suggested to explain the nestling of different species.

Neutral theories

As an alternative to the options mentioned, a group of ecologists denies the paramount importance of competition. In this case, overlapping niches are no longer a problem that needs to be solved. In these theories, niches and niches lose their central role in the structuring of communities. The local composition is shaped by random (“stochastic”) factors: v. a. Immigration and extinction rates, colonization speed, random changes in the order of the incoming species (and in evolutionary periods: new emergence of species). This "neutral theory" has been worked out especially by the ecologist Stephen P. Hubbell . Beeravolu et al. Give a modern overview of this. Even in the neutral theory, the competition factor is implicitly taken into account, because the space available for each individual is limited. Establishing a new individual is only possible in a gap that becomes free when an older one dies. Such a “gap lottery” for establishment niches had already been proposed to explain the biodiversity of limestone grasslands . The ecologist PJ Grubb coined the term regeneration niche for this .

Modern syntheses

The new version of the neutral theory has sparked heated controversy in ecology. Although the theory in its pure form is rejected by most ecologists, it has contributed to a modification of the niche theory. In most of the modern versions, stochastic elements are introduced into the (essentially completely deterministic) niche theory. Possible explanations for species richness are given by a combination of both factors. Other possibilities offer e.g. B. multiple equilibria. A modern overview of niche theory is offered by B. Holt.

Adaptation of niches

According to recent findings, the ecological niche of animal species is more flexible than assumed in previous theories. A 2011 study showed that the hunting habits of diving seabirds differ greatly both between species and within a species. The ecological niches are not rigidly fixed: Different habitats, avoiding competition with neighbors or avoiding predators lead to different behavior even within a species. The scientists from the Max Planck Institute for Ornithology in Radolfzell chose seabirds as an object of study, as they are bound to the land to breed and, especially at this time, many animals have to share space and food. Since several species with similar demands breed together on one island, the question was how they differ in ecological niches. The data showed that the spatial and temporal distribution of birds can also differ greatly within a species. Narrowing down within a species through specializations alleviates competition. The animals dive for food at different depths and temperatures in geographically far apart marine areas.

Application of niche theory to predict species areas

The niche theory is being used increasingly in biogeographical research. Here, known occurrences of a species are correlated with measured environmental factors (especially climate) in order to be able to predict its potential area from the ecological niche of the species by transferring the results to areas with similar environmental factors in which the species has not yet been detected . These models are known as habitat modeling . This approach is particularly widespread for predicting the effects of climate change. For this purpose, a model of the area under the changed climatic conditions is constructed based on the available climate models. The basis of the processing is the observation that the ecological niche of a species hardly changes in a short period of time. It is therefore more likely that the species will shift its area through migratory movements than it will adaptively adapt to the new conditions on the spot . One speaks clearly of the "climatic envelope" of the species. Some American ecologists draw attention to possible dangers and false conclusions with this method, who can use it to construct an area for the Yeti.

Different use of the term niche outside of ecology

The term ecological niche has found wide use outside of ecology. The popular concepts that it circumscribes, however, differ greatly from the scientific use of the term. An ecological niche in common parlance means a sheltered place outside of the harsh winds of competition, in which one can lead a limited but reasonably secure existence. The politician Günter Gaus characterized the society of the former GDR as a "niche society ".

The term has had a special career in economics , in particular in market psychology , into which it was deliberately introduced as an "economic niche" by the psychologist Bernt Spiegel . The common terms such as “market niche” or “ niche product ” go back to the transfer of an ecological concept to the economy. This ambivalence is kept alive by business journalists especially in connection with so-called “eco products” , who like to introduce headlines with puns like “ biodiesel - get out of the niche” .

See also

  • Phytotelma for a tiny body of water as a microbiotope within a living plant.

literature

  • Andrew Cockburn: Evolutionary Ecology. Gustav Fischer, Stuttgart 1995, ISBN 3-437-30775-4 .
  • BD Collier, GW Cox, AW Johnson, PC Miller: Dynamic Ecology. London 1974, ISBN 0-13-221309-5 .
  • Townsend, Harper, Begon: Ecology. 1st edition, Springer-Verlag, Berlin / Heidelberg 2003, ISBN 3-540-00674-5 .
  • Katharina Munk (ed.): Basic studies in biology. Spectrum Akad. Verl., Heidelberg 2000, ISBN 3-8274-0910-1 .

Individual evidence

  1. ↑ a b c d A. Pocheville: The Ecological Niche: History and Recent Controversies . In: Thomas Heams et al. (Ed.): Handbook of Evolutionary Thinking in the Sciences . Springer, Dordrecht 2015, ISBN 978-94-017-9014-7 , pp. 547-586 ( full text ).
  2. ↑ Werner J. Kloft: Ecology of the animals. Ulmer, UTB 729, Stuttgart 1978, p. 161 ff.
  3. ^ J. Grinnell: The niche relationships of the California thrasher. In: The Auk . 1017, 34, pp. 427-433.
  4. ^ CS Elton: Animal Ecology. Sidgwick and Jackson, London 1927.
  5. ↑ GE Hutchinson (1957): Concluding remarks. In: Cold Spring Harbor Symposium on Quantitative Biology. 22, 415-427.
  6. ↑ In the German-speaking area, the niche concept by Klaus Günther or the concept of the ecological license by Günther Osche is sometimes used, which differ in details. See: Michael Schmitt: Ecological niche sensu Günther and ecological license sensu Osche - two valuable but poorly appreciated explanatory concepts. In: Zoological contributions NF 31, 1987, 49-60.
  7. ↑ Helen L. Hooper et al. a: The ecological niche of Daphnia magna characterized using population growth rate. In: Ecology. 89 (4), 2008, 1015-1022.
  8. ↑ Munk 2000, pp. 14-24.
  9. ^ GE Hutchinson: The paradox of the plankton. In: The American Naturalist. Volume 95, No. 882, 1961, pp. 137-145.
  10. ↑ Andrew Cockburn: Evolutionary Ecology. Gustav Fischer, Stuttgart 1995, ISBN 3-437-30775-4 , p. 12.
  11. ^ Peter R. Grant, B. Rosemary Grant: Evolution of character displacement in Darwin's finches. In: Science . 313, 224, 2006, 224-226.
  12. ↑ Eric R. Pianka: Niche Overlap and Diffuse Competition. Proceedings of the National Academy of Science 71 (5), 1974, 2141-2145.
  13. ↑ SP Hubbell: A unified theory of biogeography and relative species abundance and its application to tropical rain forests and coral reefs. In: Coral Reefs. 1007, 16, pp. 9-21.
  14. ^ SP Hubbell: The Unified Neutral Theory of Biodiversity and Biogeography. Princeton University Press, Princeton, NJ 2001, p. 375 ff.
  15. ↑ Champak R. Beeravolu, Pierre Couteron, Raphaël Pélissier, Francois Munoz: Studying ecological communities from a neutral standpoint: A review of models' structure and parameter estimation. In: Ecological Modeling. 220, 2009, 2603-2610.
  16. ^ PJ Grubb: The maintenance of species-richness in plant communities: the importance of the regeneration niche. In: Biological reviews. 1977, 52, 107-145.
  17. ^ For example, David Tilman: Niche tradeoffs, neutrality, and community structure: A stochastic theory of resource competition, invasion, and community assembly. In: PNAS. 101 (30), 2004, 10854-10861.
  18. ^ For example, Jonathan M. Chase: Stochastic community assembly causes higher biodiversity in more productive environments. Science 328, 2010, 1388-1391.
  19. ^ Robert D. Holt: Bringing the Hutchinsonian niche into the 21st century: Ecological and evolutionary perspectives. In: PNAS . 106 (17) Suppl. 2, 2009, 19659-19665.
  20. ↑ JF Masello, R. Mundry, M. Poisbleau, L. Demongin, C. Voigt, M. Wikelski, P. Quillfeldt: Diving seabirds share foraging space and time within and among species. In: Ecosphere. 1: art19. doi: 10.1890 / ES10-00103.1 .
  21. ^ RJ Hijmans, CH Graham: The ability of climate envelope models to predict the effect of climate change on species distributions. In: Global Change Biology. 12, 2006, 1-10.
  22. ↑ JD Lozier, P. Aniello, MJ Hickerson: Predicting the distribution of Sasquatch in western North America: anything goes with ecological niche modeling. In: Journal of Biogeography. 2009, 1-5.