Endemism - WikiHQ

thumb|Both the [[orange-breasted sunbird (Anthobaphes violacea) and the Kniphofia uvaria plant it feeds on are found exclusively in South Africa.]]

thumb|[[Bicolored frog (Clinotarsus curtipes) is endemic to the Western Ghats of India.]]

thumb|[[Montezuma Well in the Verde Valley of Arizona contains at least five endemic species found exclusively in the sinkhole.]]

Endemism is the state of a species being found only in a singular defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, the Cape sugarbird (Promerops cafer) is found exclusively in southwestern South Africa and is therefore said to be endemic to that particular part of the world. An endemic species can also be referred to as an endemism or, in scientific literature, as an endemite.

Endemism is an important concept in conservation biology for measuring biodiversity in a particular place and evaluating the risk of extinction for species. Endemism is also of interest in evolutionary biology, because it provides clues about how changes in the environment cause species to undergo range shifts (potentially expanding their range into a larger area or becoming extirpated from an area they once lived), go extinct, or diversify into more species.

The extreme opposite of an endemic species is one with a cosmopolitan distribution, having a global or widespread range. Other terms that sometimes are used interchangeably, but less often, include autochthonal, autochthonic, and indigenous; however, these terms do not reflect the status of a species that specifically belongs only to a determined place.

Etymology

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The word endemic is from Neo-Latin , from Greek , , "native". Éndēmos is formed of , , meaning "in, within", and , , "the people". The word entered the English language as a loan word from the French , and originally seems to have been used in the sense of diseases that occur at a constant amount in a country, as opposed to epidemic diseases, which are exploding in cases.<section end=original_etymology /> In 1872, it was Charles Darwin who first used endemic to mean a species restricted to a specific location, although, as already mentioned, it now can apply to a genus, family, or even a higher taxonomic rank.

The less common term precinctive has been used by some biologists as the equivalent of endemic. Precinctive was coined in 1900 by entomologist David Sharp when describing Hawaiian insects, for he was uncomfortable with the public health associations of endemic. In 1917, botanist Vaughan MacCaughey, also working in Hawaii, was the first to use precinctive in his speciality.

Overview

thumb|Chorus cicada ([[Amphipsalta zelandica), a species endemic to New Zealand]]

A species is considered to be endemic to the area where it is found naturally, to the exclusion of other areas; presence in captivity or botanical gardens does not disqualify a species from being endemic. In theory, the term "endemic" could be applied on any scale; for example, the cougar is endemic to the Americas,

Origins

The evolutionary history of a species can lead to endemism in multiple ways. Allopatric speciation, or geographic speciation, is when two populations of a species become geographically separated from each other and, as a result, develop into different species. Populations on an island are isolated, with little opportunity to interbreed with outside populations, which eventually causes reproductive isolation and separation into different species. Darwin's finches in the Galápagos archipelago are examples of species endemic to islands. Similarly, isolated mountainous regions like the Ethiopian Highlands, or large bodies of water far from other lakes, like Lake Baikal, can also have high rates of endemism.

Endemism can also be created in areas that act as refuges for species during times of climate change like ice ages. These changes may have caused species to become repeatedly restricted to regions with unusually stable climate conditions, leading to high concentrations of endemic species in areas resistant to climate fluctuations. Endemic species that used to exist in a much larger area but died out in most of their range are called paleoendemic, in contrast to neoendemic species, which are new species that have not dispersed beyond their range. The ginkgo tree, Ginkgo biloba, is one example of a paleoendemic species.

In many cases, biological factors, such as low rates of dispersal or returning to the spawning area (philopatry), can cause a particular group of organisms to have high speciation rates and thus many endemic species. For example, cichlids in the East African Rift Lakes have diversified into many more endemic species than the other fish families in the same lakes, possibly due to such factors. While birds are less likely to be endemic to a region based on their ability to disperse via flight, there are over 2,500 species that are considered endemic, meaning that the species is restricted to an area less than .

Microorganisms were traditionally not believed to form endemics. The hypothesis 'everything is everywhere,' first stated in Dutch by Lourens G.M. Baas Becking in 1934, describes the theory that the distribution of organisms smaller than 2 mm is cosmopolitan where habitats occur that support their growth.

Subtypes and definitions

Endemism can reflect a wide variety of evolutionary histories, so researchers often use more specialized terms that categorize endemic species based upon how they came to be endemic to an area.

The first subcategories were first introduced by Claude P. E. Favager and Juliette Contandriopoulis in 1961: schizoendemics, apoendemics and patroendemics. Using this work, Ledyard Stebbins and Jack Major then introduced the concepts of neoendemics and paleoendemics in 1965 to describe the endemics of California. Endemic taxa can also be classified into autochthonous, allochthonous, taxonomic relicts and biogeographic relicts. and have not dispersed beyond a limited range.

The concept of phylogenetic endemism has also been used to measure the relative uniqueness of the species endemic to an area. Measurements that incorporate phylogenetic endemism weight the branches of the evolutionary tree according to their narrow distribution. This captures not only the total number of taxa endemic to the area (taxonomic endemism) but also how distant those species are from their living relatives.

Environments

Some environments are particularly conducive to the development of endemic species, either because they allow the persistence of relict taxa that were extirpated elsewhere or because they provide mechanisms for isolation and opportunities to fill new niches. These soils are found in the Balkan Peninsula, Turkey, the Alps, Cuba, New Caledonia, South Africa, Zimbabwe, the North American Appalachians, and scattered distribution in California, Oregon, and Washington and elsewhere. For example, Mayer and Soltis considered the widespread subspecies Streptanthus glandulosus subsp. glandulosus which grows on normal soils, to be a paleoendemic, whereas closely related endemic forms of S. glandulosus occurring on serpentine soil patches are neoendemics that recently evolved from subsp. glandulosus. A high level of adaptation to a cave environment limits an organism's ability to disperse, since caves are often not connected to each other. One hypothesis for how closely related troglobite species could become isolated from one another in different caves is that their common ancestor may have been less restricted to cave habitats. When climate conditions became unfavorable, the ancestral species was extirpated from the surface, but some populations survived in caves, and diverged into different species due to lack of gene flow between them.

Islands

Isolated islands commonly develop a number of endemics. Many species and other higher taxonomic groups exist in very small terrestrial or aquatic islands, which restrict their distribution. The Devil's Hole pupfish, Cyprinodon diabolis, has its whole native population restricted to a spring that is 20 x 3 meters in Nevada's Mojave Desert. This 'aquatic island' is connected to an underground basin; however, the population present in the pool remains isolated.

Other areas very similar to the Galapagos Islands of the Pacific Ocean exist and foster high rates of endemism. The Socotra Archipelago of Yemen, located in the Indian Ocean, has seen a new endemic species of parasitic leech, Myxobdella socotrensis, appear. This species is restricted to freshwater springs, where it may attach to and feed upon native crabs.

Mountains

thumb|Cinder cones and vegetation of Kula [[Volcano in Turkey]]

Mountains can be seen as 'sky islands': refugia of endemics because species that live in the cool climates of mountain peaks are geographically isolated. For example, in the Alpes-Maritimes department of France, Saxifraga florulenta is an endemic plant that may have evolved in the Late Miocene and could have once been widespread across the Mediterranean Basin.

Volcanoes also tend to harbor a number of endemic species. Plants on volcanoes tend to fill a specialized ecological niche, with a very restrictive range due to the unique environmental characteristics. The Kula Volcano, one of the fourteen volcanoes in Turkey, is home to 13 endemic species of plants.

Conservation

thumb|[[Aplastodiscus arildae, a species of frog that is endemic to Brazil]]

thumb|The [[Nene (bird)|nene (Branta sandvicensis) is endemic to the Hawaiian islands, but was introduced to WWT Slimbridge in the UK to increase its numbers for reintroduction to its native range.]]

Endemics might more easily become endangered or extinct because they are already restricted in distribution. This puts endemic plants and animals at greater risk than widespread species during the rapid climate change of this century. Some scientists claim that the presence of endemic species in an area is a good method to find geographical regions that can be considered priorities for conservation. Endemism can thus be studied as a proxy for measuring biodiversity of a region.

The concept of finding endemic species that occur in the same region to designate 'endemism hotspots' was first proposed by Paul Müller in a 1973 book. According to him, this is only possible where 1.) the taxonomy of the species in question is not in dispute; 2.) the species distribution is accurately known; and 3.) the species have relatively small distributional ranges.

In a 2000 article, Myers et al. used the standard of having more than 0.5% of the world's plant species being endemic to the region to designate 25 geographical areas of the world as biodiversity hotspots.

Other scientists have argued that endemism is not an appropriate measure of biodiversity because the levels of threat or biodiversity are not actually correlated to areas of high endemism. When using bird species as an example, it was found that only 2.5% of biodiversity hotspots correlate with endemism and the threatened nature of a geographic region. A similar pattern had been found regarding mammals, Lasioglossum bees, Plusiinae moths, and swallowtail butterflies in North America: these different groups of taxa did not correlate geographically with each other regarding endemism and species richness. Especially using mammals as flagship species proved to be a poor system of identifying and protecting areas of high invertebrate biodiversity. In response to this, other scientists again defended the concept by using WWF ecoregions and reptiles, finding that most reptile endemics occur in WWF ecoregions with high biodiversity.