Ecological niche

In ecology, a niche (CanE, UK: /ˈniːʃ/ or US: /ˈnɪtʃ/)[1] is the match of a species to a specific environmental condition.[2][3] It describes how an organism or population responds to the distribution of resources and competitors (for example, by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (for example, limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey). "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".[4]

A Grinnellian niche is determined by the habitat in which a species lives and its accompanying behavioral adaptations. An Eltonian niche emphasizes that a species not only grows in and responds to an environment, it may also change the environment and its behavior as it grows. The Hutchinsonian niche uses mathematics and statistics to try to explain how species coexist within a given community.

The concept of ecological niche is central to ecological biogeography, which focuses on spatial patterns of ecological communities.[5] "Species distributions and their dynamics over time result from properties of the species, environmental variation..., and interactions between the two—in particular the abilities of some species, especially our own, to modify their environments and alter the range dynamics of many other species."[6] Alteration of an ecological niche by its inhabitants is the topic of niche construction.[7]

The majority of species exist in a standard ecological niche, sharing behaviors, adaptations, and functional traits similar to the other closely related species within the same broad taxonomic class, but there are exceptions. A premier example of a non-standard niche filling species is the flightless, ground-dwelling kiwi bird of New Zealand, which feeds on worms and other ground creatures, and lives its life in a mammal-like niche. Island biogeography can help explain island species and associated unfilled niches.

Flightless Dung Beetle Circellium Bachuss, Addo Elephant National Park, South Africa
The flightless dung beetle occupies an ecological niche, exploiting animal droppings as a food source.

Grinnellian niche

P1180957 Arles rue du Quatre-Septembre n14 rwk
A niche: the place where a statue may stand

The ecological meaning of niche comes from the meaning of niche as a recess in a wall for a statue,[8] which itself is probably derived from the Middle French word nicher, meaning to nest.[1][8] The term was coined by the naturalist Roswell Hill Johnson[9] but Joseph Grinnell was probably the first to use it in a research program in 1917, in his paper "The niche relationships of the California Thrasher".[10][2]

The Grinnellian niche concept embodies the idea that the niche of a species is determined by the habitat in which it lives and its accompanying behavioral adaptations. In other words, the niche is the sum of the habitat requirements and behaviors that allow a species to persist and produce offspring. For example, the behavior of the California thrasher is consistent with the chaparral habitat it lives in—it breeds and feeds in the underbrush and escapes from its predators by shuffling from underbrush to underbrush. Its 'niche' is defined by the felicitous complementing of the thrasher's behavior and physical traits (camouflaging color, short wings, strong legs) with this habitat.[10]

This perspective of niche allows for the existence of both ecological equivalents and empty niches. An ecological equivalent to an organism is an organism from a different taxonomic group exhibiting similar adaptations in a similar habitat, an example being the different succulents found in American and African deserts, cactus and euphorbia, respectively.[11] As another example, the anole lizards of the Greater Antilles are a rare example of convergent evolution, adaptive radiation, and the existence of ecological equivalents: the anole lizards evolved in similar microhabitats independently of each other and resulted in the same ecomorphs across all four islands.

Eltonian niche

In 1927 Charles Sutherland Elton, a British ecologist, defined a niche as follows: "The 'niche' of an animal means its place in the biotic environment, its relations to food and enemies."[12]

Elton classified niches according to foraging activities ("food habits"):[13]

For instance there is the niche that is filled by birds of prey which eat small animals such as shrews and mice. In an oak wood this niche is filled by tawny owls, while in the open grassland it is occupied by kestrels. The existence of this carnivore niche is dependent on the further fact that mice form a definite herbivore niche in many different associations, although the actual species of mice may be quite different.[12]

Conceptually, the Eltonian niche introduces the idea of a species' response to and effect on the environment. Unlike other niche concepts, it emphasizes that a species not only grows in and responds to an environment based on available resources, predators, and climatic conditions, but also changes the availability and behavior of those factors as it grows. In an extreme example, beavers require certain resources in order to survive and reproduce, but also construct dams that alter water flow in the river where the beaver lives. Thus, the beaver affects the biotic and abiotic conditions of other species that live in and near the watershed.[14] In a more subtle case, competitors that consume resources at different rates can lead to cycles in resource density that differ between species.[15] Not only do species grow differently with respect to resource density, but their own population growth can affect resource density over time.

Hutchinsonian niche

Purple-throated carib hummingbird feeding
The shape of the bill of this purple-throated carib is complementary to the shape of the flower and coevolved with it, enabling it to exploit the nectar as a resource.

The Hutchinsonian niche is an "n-dimensional hypervolume", where the dimensions are environmental conditions and resources, that define the requirements of an individual or a species to practice "its" way of life, more particularly, for its population to persist.[3] The "hypervolume" defines the multi-dimensional space of resources (e.g., light, nutrients, structure, etc.) available to (and specifically used by) organisms, and "all species other than those under consideration are regarded as part of the coordinate system."[16]

The niche concept was popularized by the zoologist G. Evelyn Hutchinson in 1957.[16] Hutchinson inquired into the question of why there are so many types of organisms in any one habitat. His work inspired many others to develop models to explain how many and how similar coexisting species could be within a given community, and led to the concepts of 'niche breadth' (the variety of resources or habitats used by a given species), 'niche partitioning' (resource differentiation by coexisting species), and 'niche overlap' (overlap of resource use by different species).[17]

Resource allocation
Where three species eat some of the same prey, a statistical picture of each niche shows overlap in resource usage between three species, indicating where competition is strongest.

Statistics were introduced into the Hutchinson niche by Robert MacArthur and Richard Levins using the 'resource-utilization' niche employing histograms to describe the 'frequency of occurrence' as a function of a Hutchinson coordinate.[3][18] So, for instance, a Gaussian might describe the frequency with which a species ate prey of a certain size, giving a more detailed niche description than simply specifying some median or average prey size. For such a bell-shaped distribution, the position, width and form of the niche correspond to the mean, standard deviation and the actual distribution itself.[19] One advantage in using statistics is illustrated in the figure, where it is clear that for the narrower distributions (top) there is no competition for prey between the extreme left and extreme right species, while for the broader distribution (bottom), niche overlap indicates competition can occur between all species. The resource-utilization approach consists in postulating that not only competition can occur, but also that it does occur, and that overlap in resource utilization directly enables the estimation of the competition coefficients.[20] This postulate, however, can be misguided, as it ignores the impacts that the resources of each category have on the organism and the impacts that the organism has on the resources of each category. For instance, the resource in the overlap region can be non-limiting, in which case there is no competition for this resource despite niche overlap.[2][17][20]

An organism free of interference from other species could use the full range of conditions (biotic and abiotic) and resources in which it could survive and reproduce which is called its fundamental niche.[21] However, as a result of pressure from, and interactions with, other organisms (i.e. inter-specific competition) species are usually forced to occupy a niche that is narrower than this, and to which they are mostly highly adapted; this is termed the realized niche.[21] Hutchinson used the idea of competition for resources as the primary mechanism driving ecology, but overemphasis upon this focus has proved to be a handicap for the niche concept.[17] In particular, overemphasis upon a species' dependence upon resources has led to too little emphasis upon the effects of organisms on their environment, for instance, colonization and invasions.[17]

The term "adaptive zone" was coined by the paleontologist George Gaylord Simpson to explain how a population could jump from one niche to another that suited it, jump to an 'adaptive zone', made available by virtue of some modification, or possibly a change in the food chain, that made the adaptive zone available to it without a discontinuity in its way of life because the group was 'pre-adapted' to the new ecological opportunity.[22]

Mistletoe infested tree
As a hemi-parasitic plant, the mistletoe in this tree exploits its host for nutrients and as a place to grow.

Hutchinson's "niche" (a description of the ecological space occupied by a species) is subtly different from the "niche" as defined by Grinnell (an ecological role, that may or may not be actually filled by a species—see vacant niches).

A niche is a very specific segment of ecospace occupied by a single species. On the presumption that no two species are identical in all respects (called Hardin's 'axiom of inequality'[23]) and the competitive exclusion principle, some resource or adaptive dimension will provide a niche specific to each species.[21] Species can however share a 'mode of life' or 'autecological strategy' which are broader definitions of ecospace.[24] For example, Australian grasslands species, though different from those of the Great Plains grasslands, exhibit similar modes of life.[25]

Once a niche is left vacant, other organisms can fill that position. For example, the niche that was left vacant by the extinction of the tarpan has been filled by other animals (in particular a small horse breed, the konik). Also, when plants and animals are introduced into a new environment, they have the potential to occupy or invade the niche or niches of native organisms, often outcompeting the indigenous species. Introduction of non-indigenous species to non-native habitats by humans often results in biological pollution by the exotic or invasive species.

The mathematical representation of a species' fundamental niche in ecological space, and its subsequent projection back into geographic space, is the domain of niche modelling.[26]

Parameters

The different dimensions, or plot axes, of a niche represent different biotic and abiotic variables. These factors may include descriptions of the organism's life history, habitat, trophic position (place in the food chain), and geographic range. According to the competitive exclusion principle, no two species can occupy the same niche in the same environment for a long time. The parameters of a realized niche are described by the realized niche width of that species.[27] Some plants and animals, called specialists, need specific habitats and surroundings to survive, such as the spotted owl, which lives specifically in old growth forests. Other plants and animals, called generalists, are not as particular and can survive in a range of conditions, for example the dandelion.[28]

See also

References

  1. ^ a b "Niche". Merriam-Webster Dictionary. Merriam-Webster. Retrieved 30 October 2014.
  2. ^ a b c a Pocheville, Arnaud (2015). "The Ecological Niche: History and Recent Controversies". In Heams, Thomas; Huneman, Philippe; Lecointre, Guillaume; et al. (eds.). Handbook of Evolutionary Thinking in the Sciences. Dordrecht: Springer. pp. 547–586. ISBN 978-94-017-9014-7.
  3. ^ a b c Three variants of ecological niche are described by Thomas W Schoener (2009). "§I.1 Ecological niche". In Simon A. Levin; Stephen R. Carpenter; H. Charles J. Godfray; Ann P. Kinzig; Michel Loreau; Jonathan B. Losos; Brian Walker; David S. Wilcove (eds.). The Princeton Guide to Ecology. Princeton University Press. pp. 3 ff. ISBN 9781400833023.
  4. ^ A Townsend Peterson; Jorge Soberôn; RG Pearson; Roger P Anderson; Enrique Martínez-Meyer; Miguel Nakamura; Miguel Bastos Araújo (2011). "Species-environment relationships". Ecological Niches and Geographic Distributions (MPB-49). Princeton University Press. p. 82. ISBN 9780691136882. See also Chapter 2: Concepts of niches, pp. 7 ff
  5. ^ Mark V Lomolino; Brett R Riddle; James H Brown (2009). "The geographic range as a reflection of the niche". Biogeography (3rd ed.). Sunderland, Mass: Sinauer Associates. p. 73. ISBN 978-0878934867. The geographic range of a species can be viewed as a spatial reflection of its niche Viewable on line via Amazon's 'look-inside' feature.
  6. ^ Mark V Lomolino; Brett R Riddle; James H Brown (2009). "Areography: Sizes, shapes and overlap of ranges". Biogeography (3rd ed.). Sunderland, Mass: Sinauer Associates. p. 579. ISBN 978-0878934867. Viewable on line via Amazon's 'look-inside' feature.
  7. ^ A Townsend Peterson; Jorge Soberôn; RG Pearson; Roger P Anderson; Enrique Martínez-Meyer; Miguel Nakamura; Miguel Bastos Araújo (2011). "Major themes in niche concepts". Ecological Niches and Geographic Distributions (MPB-49). Princeton University Press. p. 11. ISBN 9780691136882. We will make the crucial distinction between variables that are dynamically modified (linked) by the presence of the species versus those that are not. ... [Our construction] is based upon variables not dynamically affected by the species...in contrast to...those that are subject to modification by niche construction.
  8. ^ a b "Niche". Oxford English Dictionary (subscription required). Retrieved 8 June 2013.
  9. ^ Johnson, Roswell (1910). Determinate evolution in the color-pattern of the lady-beetles. Washington: Carnegie Institution of Washington.
  10. ^ a b Joseph Grinnell (1917). "The niche-relationships of the California Thrasher" (PDF). The Auk. 34 (4): 427–433. doi:10.2307/4072271. JSTOR 4072271. Archived from the original (PDF) on 2016-03-10.
  11. ^ Richard J. Huggett (2004). Fundamentals of Biogeography. Psychology Press. p. 76. ISBN 9780415323475.
  12. ^ a b Elton, Charles Sutherland (2001). Animal Ecology. University of Chicago Press. p. 64. ISBN 978-0226206394. Retrieved May 14, 2014.
  13. ^ "Elton focused on the niche of a species as its functional role within the food chain and its impact upon the environment" Jonathan M. Chase; Mathew A. Leibold (2003). Ecological Niches: Linking Classical and Contemporary Approaches. University of Chicago Press. p. 7. ISBN 9780226101804.
  14. ^ Pollock, Michael M.; Naiman, Robert J.; Erickson, Heather E.; Johnston, Carol A.; Pastor, John; Pinay, Gilles (1995). Jones, Clive G.; Lawton, John H. (eds.). Beaver as Engineers: Influences on Biotic and Abiotic Characteristics of Drainage Basins. Springer. pp. 117–126. doi:10.1007/978-1-4615-1773-3_12. ISBN 978-1-4613-5714-8.
  15. ^ Armstrong, Robert A.; McGehee, Richard (February 1980). "Competitive Exclusion". The American Naturalist. 115 (2): 151–170. doi:10.1086/283553. JSTOR 2460592.
  16. ^ a b Hutchinson, G.E. (1957). "Concluding remarks" (PDF). Cold Spring Harbor Symposia on Quantitative Biology. 22 (2): 415–427. doi:10.1101/sqb.1957.022.01.039. Retrieved 2007-07-24.
  17. ^ a b c d Jonathan M. Chase; Mathew A. Leibold (2003). Ecological Niches: Linking Classical and Contemporary Approaches. University of Chicago Press. p. 11. ISBN 9780226101804.
  18. ^ Robert H. MacArthur (1958). "Population ecology of some warblers of northeastern coniferous forests" (PDF). Ecology. 39 (4): 599–619. doi:10.2307/1931600. JSTOR 1931600.
  19. ^ Rory Putman; Stephen D. Wratten (1984). "§5.2 Parameters of the niche". Principles of ecology. University of California Press. p. 107. ISBN 9780520052543.
  20. ^ a b Schoener, Thomas W. (1986). "The Ecological Niche". In Cherret, J. M. (ed.). Ecological concepts: the contribution of ecology to an understanding of the natural world. Cambridge: Blackwell Scientific Publications.
  21. ^ a b c James R. Griesemer (1994). "Niche: Historical perspectives". In Evelyn Fox Keller, Elisabeth A. Lloyd (eds.). Keywords in Evolutionary Biology. Harvard University Press. p. 239. ISBN 9780674503137.CS1 maint: Uses editors parameter (link)
  22. ^ Dolph Schluter (2000). "§4.2: The ecological theory". The Ecology of Adaptive Radiation. Oxford University Press. p. 69. ISBN 9780191588327.
  23. ^ Garrett Hardin (1960). "The competitive exclusion principle" (PDF). Science. 131 (3409): 1292–1297. doi:10.1126/science.131.3409.1292. PMID 14399717.
  24. ^ Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land". Biology Letters. 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856.CS1 maint: Multiple names: authors list (link)
  25. ^ Glossary for the Nature of Alberta
  26. ^ On the logic of the relation between the niche and the corresponding geographic environment see Barry Smith and Achille Varzi, "The Niche", Nous, 33:2 (1999), 198–222.
  27. ^ Hardin G. (1960). "The Competitive Exclusion Principle". Science. 131 (3409): 1292–1297. doi:10.1126/science.131.3409.1292. PMID 14399717.
  28. ^ Moseley, William; Perramond, Eric; Hapke, Holly; Laris, Paul (2014). An Introduction to Human-Environment Geography. West Sussex, UK: Wiley Blackwell. p. 81. ISBN 978-1-4051-8932-3.

External links

Asylosaurus

Asylosaurus (meaning "unharmed or sanctuary lizard") is a genus of basal sauropodomorph dinosaur from the Late Triassic of England. It is based on partial remains, described in 1836 by Henry Riley and Samuel Stutchbury as pertaining to Thecodontosaurus, that Othniel Charles Marsh brought to Yale University between 1888 and 1890. These remains thus escaped destruction by a bombardment in 1940 during World War II, unlike the original holotype of Thecodontosaurus. Asylosaurus was described in 2007 by Peter Galton. The type species is A. yalensis, referring to Yale. The bones originally came from a Rhaetian-age cave fill at Durdham Down, Clifton, Bristol.Asylosaurus is based on YPM 2195, a partial skeleton of the torso region, including back vertebrae, ribs, gastralia, a shoulder girdle, humeri, a partial forearm, and a hand; additional bones from the neck, tail, pelvis, arm and leg that may represent the same individual were also referred to Asylosaurus. It differs from Thecodontosaurus and Pantydraco, contemporaneous basal sauropodomorphs of similar builds, in the structure of its humerus (upper arm). It may have had a separate ecological niche from these other related animals based on how omnivorous or herbivorous it was. According to Gregory S. Paul, it was 2 metres (6 ft 7 in) long and its weight was about 25 kilograms (55 lb).

Breeding back

Breeding back is a form of artificial selection by the deliberate selective breeding of domestic animals, in an attempt to achieve an animal breed with a phenotype that resembles a wild type ancestor, usually one that has gone extinct. Breeding back is not to be confused with dedomestication.

It must be kept in mind that a breeding-back breed may be very similar to the extinct wild type in phenotype, ecological niche, and to some extent genetics, but the original gene pool of that wild type was eliminated with its extinction. A breeding-back attempt cannot actually recreate the extinct wild type of the breeding target, as an extinct wild type cannot be resurrected via selective breeding alone. Furthermore, even the superficial authenticity of a bred-back animal depends on the quality of the stock used to breed the new lineage. As a result of this, some breeds, like Heck cattle, are at best a vague look-alike of the extinct wild type aurochs, according to the literature.

Bryology

Bryology (from Greek bryon, a moss, a liverwort) is the branch of botany concerned with the scientific study of bryophytes (mosses, liverworts, and hornworts). Bryologists are people who have an active interest in observing, recording, classifying or researching bryophytes. The field is often studied along with lichenology due to the similar appearance and ecological niche of the two organisms, even though bryophytes and lichens are not classified in the same kingdom.

Character displacement

Character displacement is the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species’ distributions do not overlap. This pattern results from evolutionary change driven by biological competition among species for a limited resource (e.g. food). The rationale for character displacement stems from the competitive exclusion principle, also called Gause's Law, which contends that to coexist in a stable environment two competing species must differ in their respective ecological niche; without differentiation, one species will eliminate or exclude the other through competition.

Character displacement was first explicitly explained by William L. Brown Jr. and E. O. Wilson in 1956: "Two closely related species have overlapping ranges. In the parts of the ranges where one species occurs alone, the populations of that species are similar to the other species and may even be very difficult to distinguish from it. In the area of overlap, where the two species occur together, the populations are more divergent and easily distinguished, i.e., they 'displace' one another in one or more characters. The characters involved can be morphological, ecological, behavioral, or physiological; they are assumed to be genetically based."

Brown and Wilson used the term character displacement to refer to instances of both reproductive character displacement, or reinforcement of reproductive barriers, and ecological character displacement driven by competition. As the term character displacement is commonly used, it generally refers to morphological differences due to competition. Brown and Wilson viewed character displacement as a phenomenon involved in speciation, stating, "we believe that it is a common aspect of geographical speciation, arising most often as a product of the genetic and ecological interaction of two (or more) newly evolved, cognate species [derived from the same immediate parental species] during their period of first contact." While character displacement is important in various scenarios of speciation, including adaptive radiations like the cichlid fish faunas in the rift lakes of East Africa, it also plays an important role in structuring communities. It also plays a role in speciation by reinforcement in such that allopatric populations overlapping in sympatry exhibit greater trait divergence. The results of numerous studies contribute evidence that character displacement often influences the evolution of resource acquisition among members of an ecological guild.Competitive release, defined as the expansion of an ecological niche in the absence of a competitor, is essentially the mirror image of character displacement. It too was described by Brown and Wilson: “Two closely related species are distinct where they occur together, but where one member of the pair occurs alone it converges toward the second, even to the extent of being nearly identical with it in some characters.”

Chiniquodon

Chiniquodon is an extinct genus of carnivorous cynodonts, which lived during the Late Triassic (Carnian) in South America (Argentina and Brazil) and Africa (Namibia and Madagascar). Chiniquodon is closely related to a contemporary genus, Probelesodon, and close to the ancestry of mammals.

Other contemporaries included early dinosaurs. As both groups filled a similar ecological niche, fairly large therapsid hunters such as Chiniquodon may have been outcompeted by dinosaurs.

Chrotomys

The genus Chrotomys contain a unique group of rodents found only in the Philippines, specifically the islands of Luzon, Mindoro, and Sibuyan. Instead of being predominantly herbivorous or omnivorous like other murines, these rats feed predominantly on invertebrates although they do eat some vegetable matter. This vermivory is probably the result of a rat-like animal moving into an ecological niche usually filled by shrews. Shrews and other insectivores are absent on these Philippine islands.

Competitive exclusion principle

In ecology, the competitive exclusion principle, sometimes referred to as Gause's law, is a proposition named for Georgy Gause that two species competing for the same limiting resource cannot coexist at constant population values. When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term. This leads either to the extinction of the weaker competitor or to an evolutionary or behavioral shift toward a different ecological niche. The principle has been paraphrased in the maxim "complete competitors can not coexist".

Ctenosaura hemilopha

Ctenosaura hemilopha, also known as the cape spinytail iguana , is a species of spinytail iguana endemic to Baja California. It is arboreal and primarily herbivorous, although it can be an opportunistic carnivore. Males may grow up to 100 centimeters (39 in) in length, while females are smaller, with a length of up to 70 centimeters (28 in). Five subspecies are currently recognized.

The existence of mainland and insular populations of this species has been valuable in providing biologists with study and control groups comparing the evolution of island populations and their mainland counterparts. The San Esteban Island subspecies (C.h. conspicuosa) coexists with the giant San Esteban chuckwalla, contrary to predictions of ecological niche theory.

Ecological trap

Ecological traps are scenarios in which rapid environmental change leads organisms to prefer to settle in poor-quality habitats.

The concept stems from the idea that organisms that are actively selecting habitat must rely on environmental cues to help them identify high-quality habitat. If either the habitat quality or the cue changes so that one does not reliably indicate the other, organisms may be lured into poor-quality habitat.

Ecosystem engineer

An ecosystem engineer is any organism that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on the species richness and landscape-level heterogeneity of an area. As a result, ecosystem engineers are important for maintaining the health and stability of the environment they are living in. Since all organisms impact the environment they live in in one way or another, it has been proposed that the term "ecosystem engineers" be used only for keystone species whose behavior very strongly affects other organisms.

Guild (ecology)

A guild (or ecological guild) is any group of species that exploit the same resources, or that exploit different resources in related ways. It is not necessary that the species within a guild occupy the same, or even similar, ecological niches. An ecological niche is defined as the role an organism plays in its community, i.e. decomposer, primary producer, etc. Guilds are defined according to the locations, attributes, or activities of their component species. For example, the mode of acquiring nutrients, the mobility, and the habitat zones that the species occupy or exploit can be used to define a guild. The number of guilds occupying an ecosystem is termed its disparity. Members of a guild within a given ecosystem could be competing for resources, such as space or light, while cooperating in resisting wind stresses, attracting pollinators, or detecting predators, such as happens among savannah-dwelling antelope and zebra.

A guild does not typically have strict, or even clearly defined boundaries, nor does it need to be taxonomically cohesive. A broadly defined guild will almost always have constituent guilds; for example, grazing guilds will have some species that concentrate on coarse, plentiful forage, while others concentrate on low-growing, finer plants. Each of those two sub-guilds may be regarded as guilds in appropriate contexts, and they might, in turn, have sub-guilds in more closely selective contexts. Some authorities even speak of guilds in terms of a fractal resource model. This concept arises in several related contexts, such as the metabolic theory of ecology, the scaling pattern of occupancy, and spatial analysis in ecology, all of which are fundamental concepts in defining guilds.

An ecological guild is not to be confused with a taxocene, a group of phylogenetically related organisms in a community that do not necessarily share the same or similar niches (for example, "the insect community"). Nor is a guild the same as a trophic species, organisms of the same species that have mutual predators and prey.

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 a corollary of the competitive exclusion principle, which states that, controlling for all else, two species competing for exactly the same resources cannot stably coexist. It assumes normally-distributed resource utilization curves ordered linearly along a resource axis, and as such, it is often considered to be an oversimplified model of species interactions. Moreover, it has theoretical weakness, and it is poor at generating real-world predictions or falsifiable hypotheses. Thus, the concept has fallen somewhat out of favor except in didactic settings (where it is commonly referenced), and has largely been replaced by more complex and inclusive theories.

Niche (architecture)

A niche (CanE, UK: or US: ) in classical architecture is an exedra or an apse that has been reduced in size, retaining the half-dome heading usual for an apse. Nero's Domus Aurea (AD 64–69) was the first semi-private dwelling that possessed rooms that were given richly varied floor plans, shaped with niches and exedras; sheathed in dazzling polished white marble, such curved surfaces concentrated or dispersed the daylight.

The word derives from the Latin nidus or nest, via the French niche. The Italian nicchio for a sea-shell may also be involved, as the traditional decoration for the top of a niche is a scallop shell, as in the illustration, hence also the alternative term of "conch" for a semi-dome, usually reserved for larger exedra.

In Gothic architecture, a niche may be set within a tabernacle framing, like a richly decorated miniature house ("aedicule"), such as might serve for a reliquary. The backings for the altars in churches ("reredos") can be embedded with niches for statues. Though a niche in either Classical or Gothic contexts may be empty and merely provide some articulation and variety to a section of wall, the cult origins of the niche suggested that it be filled with a statue. One of the earliest buildings which uses external niches containing statues is the Church of Orsanmichele in Florence, built between 1380 and 1404. The Uffizi Palace in Florence (1560–81) modified the concept by setting the niche within the wall so it did not protrude. The Uffizi has two dozen or so such niches containing statues of great historical figures. In England the Uffizi style niches were adopted at Montacute House (c. 1598), where there are 9 exterior niches containing statues of the Nine Worthies. In Fra Filippo Lippi's Madonna, the trompe-l'oeil niche frames her as with the canopy of estate that was positioned over a personage of importance in the late Middle Ages and Early Modern Europe. At the same time, the Madonna is represented as an iconic sculpture who has "come alive" with miraculous immediacy.

Expanding from its primary sense as an architectural recess, a niche can be applied to a rocky hollow, crack, crevice, or foothold. The sense of a niche as a clearly defined narrow space led to its use describing the relational position of an organism's species, its ecological niche.

Niche apportionment models

Mechanistic models for niche apportionment are biological models used to explain relative species abundance distributions. These niche apportionment models describe how species break up resource pool in multi-dimensional space, determining the distribution of abundances of individuals among species. The relative abundances of species are usually expressed as a Whittaker plot, or rank abundance plot, where species are ranked by number of individuals on the x-axis, plotted against the log relative abundance of each species on the y-axis. The relative abundance can be measured as the relative number of individuals within species or the relative biomass of individuals within species.

Niche construction

Niche construction is the process by which an organism alters its own (or another species') local environment. These alterations can be a physical change to the organism’s environment or encompass when an organism actively moves from one habitat to another to experience a different environment. Examples of niche construction include the building of nests and burrows by animals, and the creation of shade, influencing of wind speed, and alternation of nutrient cycling by plants. Although these alterations are often beneficial to the constructor they are not always (for example, when organisms dump detritus they can degrade their own environments).

Niche differentiation

The term niche differentiation (synonymous with niche segregation, niche separation and niche partitioning), as it applies to the field of ecology, refers to the process by which competing species use the environment differently in a way that helps them to coexist. Niche differentiation is also defined as the role in which a species plays in the ecosystem, otherwise known as how an organism or species "makes a living." The competitive exclusion principle states that if two species with identical niches (i.e., ecological roles) compete, then one will inevitably drive the other to extinction. This rule also tells us that two species can't have the same exact niche in a habitat and coexist together, at least in a stable manner. When two species differentiate their niches, they tend to compete less strongly, and are thus more likely to coexist. Species can differentiate their niches in many ways, such as by consuming different foods, or using different parts of the environment.

As an example of niche partitioning, several anole lizards in the Caribbean islands share common food needs—mainly insects. They avoid competition by occupying different physical locations. Although these reptiles might occupy different locations, you may also find groups living around the same area, in which can contain up to as many as fifteen different lizards! For example, some live on the leaf litter floor while others live on branches. Species who live in different areas compete less for food and other resources, which minimizes competition between species. However, species who live in similar areas compete strongly.

Overpopulation

Overpopulation occurs when a species' population exceeds the carrying capacity of its ecological niche. It can result from an increase in births (fertility rate), a decline in the mortality rate, an increase in immigration, or an unsustainable biome and depletion of resources. When overpopulation occurs, individuals limit available resources to survive.

The change in number of individuals per unit area in a given locality is an important variable that has a significant impact on the entire ecosystem.

Poribacteria

Poribacteria are a candidate phylum of bacteria originally identified in the microbiome of sea sponges (Porifera). Poribacteria were distinguished from other microorganisms associated with sea sponges by their distinctive morphology featuring a large membrane-bound cellular compartment that frequently contains DNA, a highly unusual feature for a prokaryote. Poribacteria are Gram-negative mixotrophs.

Species distribution modelling

Species distribution modelling (SDM), also known as environmental (or ecological) niche modelling (ENM), habitat modelling, predictive habitat distribution modelling, and range mapping uses computer algorithms to predict the distribution of a species across geographic space and time using environmental data. The environmental data are most often climate data (e.g. temperature, precipitation), but can include other variables such as soil type, water depth, and land cover. SDMs are used in several research areas in conservation biology, ecology and evolution. These models can be used to understand how environmental conditions influence the occurrence or abundance of a species, and for predictive purposes (ecological forecasting). Predictions from an SDM may be of a species’ future distribution under climate change, a species’ past distribution in order to assess evolutionary relationships, or the potential future distribution of an invasive species. Predictions of current and/or future habitat suitability can be useful for management applications (e.g. reintroduction or translocation of vulnerable species, reserve placement in anticipation of climate change).

There are two main types of SDMs. Correlative SDMs, also known as climate envelope models, bioclimatic models, or resource selection function models, model the observed distribution of a species as a function of environmental conditions. Mechanistic SDMs, also known as process-based models or biophysical models, use independently-derived information about a species' physiology to develop a model of the environmental conditions under which the species can exist.The extent to which such modelled data reflect real-world species distributions will depend on a number of factors, including the nature, complexity, and accuracy of the models used and the quality of the available environmental data layers; the availability of sufficient and reliable species distribution data as model input; and the influence of various factors such as barriers to dispersal, geologic history, or biotic interactions, that increase the difference between the realized niche and the fundamental niche. Environmental niche modelling may be considered a part of the discipline of biodiversity informatics.

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