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106-796: The region supports one of the largest remaining areas of dry limestone forest in the Caribbean. A 1970 survey of the forest noted 271 species of plants in the forest of which 53 are only found in Jamaica. The forest is home to threatened Jamaican endemic animals, including the Jamaican iguana and the blue-tailed galliwasp . The area has also been designated an Important Bird Area (IBA) by BirdLife International because it supports significant populations of many Jamaican bird species. 17°54′N 76°57′W  /  17.900°N 76.950°W  / 17.900; -76.950 This Jamaican location article

212-399: A cline . Various alternative models have been developed concerning allopatric speciation. Special cases of vicariant speciation have been studied in great detail, one of which is peripatric speciation, whereby a small subset of a species population becomes isolated geographically; and centrifugal speciation, an alternative model of peripatric speciation concerning expansion and contraction of

318-461: A neutral , stochastic model of speciation by genetic drift alone. Both selection and drift can lead to postzygotic isolation, supporting the fact that two geographically separated populations can evolve reproductive isolation —sometimes occurring rapidly. Fisherian sexual selection can also lead to reproductive isolation if there are minor variations in selective pressures (such as predation risks or habitat differences) among each population. (See

424-415: A "mixed-mode" speciation event—exhibiting both allopatric and sympatric speciation processes. Developed in the context of the genetic basis of reproductive isolation, mathematical scenarios model both pre zygotic and postzygotic isolation with respect to the effects of genetic drift, selection, sexual selection , or various combinations of the three. Masatoshi Nei and colleagues were the first to develop

530-546: A bias in reporting of positive allopatric speciation events, and in one study reviewing 73 speciation papers published in 2009, only 30 percent that suggested allopatric speciation as the primary explanation for the patterns observed considered other modes of speciation as possible. Contemporary research relies largely on multiple lines of evidence to determine the mode of a speciation event; that is, determining patterns of geographic distribution in conjunction with phylogenetic relatedness based on molecular techniques. This method

636-442: A byproduct. It can be distinguished from allopatric speciation by three important features: 1) the size of the isolated population, 2) the strong selection imposed by the dispersal and colonization into novel environments, and 3) the potential effects of genetic drift on small populations. However, it can often be difficult for researchers to determine if peripatric speciation occurred as vicariant explanations can be invoked due to

742-556: 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. Isolated islands commonly develop

848-478: A close and important manner to the differences between the productions of various regions [of the world]". F. J. Sulloway contends that Darwin's position on speciation was "misleading" at the least and may have later misinformed Wagner and David Starr Jordan into believing that Darwin viewed sympatric speciation as the most important mode of speciation. Nevertheless, Darwin never fully accepted Wagner's concept of geographical speciation. David Starr Jordan played

954-737: A complex of closely related allopatrically distributed species, also called allospecies ) include: In birds, some areas are prone to high rates of superspecies formation such as the 105 superspecies in Melanesia , comprising 66 percent of all bird species in the region. Patagonia is home to 17 superspecies of forest birds, while North America has 127 superspecies of both land and freshwater birds. Sub-Saharan Africa has 486 passerine birds grouped into 169 superspecies. Australia has numerous bird superspecies as well, with 34 percent of all bird species grouped into superspecies. Experiments on allopatric speciation are often complex and do not simply divide

1060-478: A euendemic the vicariance was geologic in nature, such as the movement of tectonic plates, but in a cryptoendemic the disjunct distribution was due to the extinction of the intervening populations. There is yet another possible situation that can cause a disjunct distribution, where a species is able to colonize new territories by crossing over areas of unsuitable habitat, such as plants colonizing an island – this situation they dismiss as extremely rare and do not devise

1166-404: A global level. As topographical elevation increases, species become isolated from one another; often constricted to graded zones. This isolation on "mountain top islands" creates barriers to gene flow, encouraging allopatric speciation, and generating the formation of endemic species. Mountain building ( orogeny ) is directly correlated with—and directly affects biodiversity. The formation of

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1272-479: A higher resolution ( i.e. on a small, localized scale within the population) it is "microallopatric". Ben Fitzpatrick and colleagues contend that this original definition, "is misleading because it confuses geographical and ecological concepts". Ecological speciation can occur allopatrically, sympatrically, or parapatrically; the only requirement being that it occurs as a result of adaptation to different ecological or micro-ecological conditions. Ecological allopatry

1378-402: A holoendemic is a cosmopolitan species. Stenoendemics, also known as local endemics, have a reduced distribution and are synonymous with the word 'endemics' in the traditional sense, whereas euryendemics have a larger distribution -both these have distributions that are more or less continuous. A rhoendemic has a disjunct distribution . Where this disjunct distribution is caused by vicariance, in

1484-437: A limited range. Paleoendemism is more or less synonymous with the concept of a ' relict species ': a population or taxon of organisms that were more widespread or more diverse in the past. A 'relictual population' is a population that currently occurs in a restricted area, but whose original range was far wider during a previous geologic epoch . Similarly, a 'relictual taxon' is a taxon (e.g. species or other lineage) that

1590-513: 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

1696-522: A name for. Traditionally, none of Myers and de Grave's categories would be considered endemics except stenoendemics. 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. Serpentine soils act as ' edaphic islands' of low fertility and these soils lead to high rates of endemism. These soils are found in

1802-408: A narrow zone of contact. Historically, the language used to refer to modes of speciation directly reflected biogeographical distributions. As such, allopatry is a geographical distribution opposed to sympatry (speciation within the same area). Furthermore, the terms allopatric, vicariant, and geographical speciation are often used interchangeably in the scientific literature. This article will follow

1908-461: 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

2014-418: A physical barrier ) and Robert Greenleaf Leavitt ; however, it is thought that Wagner, Karl Jordan , and David Starr Jordan played a large role in the formation of allopatric speciation as an evolutionary concept; where Mayr and Dobzhansky contributed to the formation of the modern evolutionary synthesis . The late 20th century saw the development of mathematical models of allopatric speciation, leading to

2120-607: A positive value denotes positive assortive mating (i. e. expressing reproductive isolation), and a null value (of zero) means the populations are experiencing random mating . The experimental evidence has solidly established the fact that reproductive isolation evolves as a by-product of selection. Reproductive isolation has been shown to arise from pleiotropy ( i.e. indirect selection acting on genes that code for more than one trait)—what has been referred to as genetic hitchhiking . Limitations and controversies exist relating to whether laboratory experiments can accurately reflect

2226-539: A range). Some studies provide a duration in which the experiment was conducted. The "Selection type" column indicates if the study modeled vicariant or peripatric speciation (this may not be explicitly). Direct selection refers to selection imposed to promote reproductive isolation whereas indirect selection implies isolation occurring as a pleiotropic byproduct of natural selection; whereas divergent selection implies deliberate selection of each allopatric population in opposite directions ( e.g. one line with more bristles and

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2332-428: A result of global climate change or even large scale human activities (for example, agricultural, civil engineering developments, and habitat fragmentation ). Such factors can alter a region's geography in substantial ways, resulting in the separation of a species population into isolated subpopulations. The vicariant populations may then undergo genotypic or phenotypic divergence as: (a) different mutations arise in

2438-399: A role in allopatric speciation, whereby the reproductive barrier is removed, reuniting the two previously isolated populations. Upon secondary contact , individuals reproduce, creating low- fitness hybrids. Traits of the hybrids drive individuals to discriminate in mate choice , by which pre-zygotic isolation increases between the populations. Some arguments have been put forth that suggest

2544-603: A significant role in promoting allopatric speciation in the early 20th century, providing a wealth of evidence from nature to support the theory. Much later, the biologist Ernst Mayr was the first to encapsulate the then contemporary literature in his 1942 publication Systematics and the Origin of Species, from the Viewpoint of a Zoologist and in his subsequent 1963 publication Animal Species and Evolution . Like Jordan's works, they relied on direct observations of nature, documenting

2650-494: A similar theme, with the exception of special cases such as peripatric, centrifugal, among others. Observation of nature creates difficulties in witnessing allopatric speciation from "start-to-finish" as it operates as a dynamic process. From this arises a host of issues in defining species , defining isolating barriers, measuring reproductive isolation , among others. Nevertheless, verbal and mathematical models, laboratory experiments, and empirical evidence overwhelmingly supports

2756-650: A special case of allopatric speciation, peripatric speciation is often invoked for instances of isolation in glaciation refugia as small populations become isolated due to habitat fragmentation such as with North American red ( Picea rubens ) and black ( Picea mariana ) spruce or the prairie dogs Cynomys mexicanus and C. ludovicianus . Numerous species pairs or species groups show abutting distribution patterns, that is, reside in geographically distinct regions next to each other. They often share borders, many of which contain hybrid zones. Some examples of abutting species and superspecies (an informal rank referring to

2862-1086: A species population into two. This is due to a host of defining parameters: measuring reproductive isolation, sample sizes (the number of matings conducted in reproductive isolation tests), bottlenecks, length of experiments, number of generations allowed, or insufficient genetic diversity. Various isolation indices have been developed to measure reproductive isolation (and are often employed in laboratory speciation studies) such as here (index Y {\displaystyle Y} and index I {\displaystyle I} ): Y = ( A D / B C ) − 1 ( A D / B C ) + 1 {\displaystyle Y={{\sqrt {(AD/BC)}}-1 \over {\sqrt {(AD/BC)+1}}}} I = A + D − B − C A + D + B + C {\displaystyle I={A+D-B-C \over A+D+B+C}} Here, A {\displaystyle A} and D {\displaystyle D} represent

2968-405: A species that is endemic is "precinctive", which applies to species (and other taxonomic levels) that are restricted to a defined geographical area. 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. The word endemic

3074-417: A species underwent in the past using various approaches or combinations thereof: species-level phylogenies, range overlaps, symmetry in range sizes between sister species pairs, and species movements within geographic ranges. Molecular clock dating methods are also often employed to accurately gauge divergence times that reflect the fossil or geological record (such as with the snapping shrimp separated by

3180-522: A species' proclivity to remain in its ecological niche (see phylogenetic niche conservatism ) through changing environmental conditions may also play a role in isolating populations from one another, driving the evolution of new lineages. Allopatric speciation can be represented as the extreme on a gene flow continuum. As such, the level of gene flow between populations in allopatry would be m = 0 {\displaystyle m=0} , where m {\displaystyle m} equals

3286-471: A species' range. Other minor allopatric models have also been developed are discussed below. Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. If a small population of a species becomes isolated ( e.g. a population of birds on an oceanic island), selection can act on the population independent of the parent population. Given both geographic separation and enough time, speciation can result as

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3392-424: A survey of 25 allopatric speciation experiments (included in the table below) found that reproductive isolation was not as strong as typically maintained and that laboratory environments have not been well-suited for modeling allopatric speciation. Nevertheless, numerous experiments have shown pre-zygotic and post-zygotic isolation in vicariance, some in less than 100 generations. Below is a non-exhaustive table of

3498-500: 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. 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

3604-625: 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. Different categorizations of endemism also capture the uniqueness and irreplaceability of biodiversity hotspots differently and impact how those hotspots are defined, affecting how resources for conservation are allocated. 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

3710-437: A wider distributed taxon that has become reproductively isolated without becoming (potentially) genetically isolated – a schizoendemic has the same chromosome count as the parent taxon it evolved from. An apoendemic is a polyploid of the parent taxon (or taxa in the case of allopolyploids ), whereas a patroendemic has a lower, diploid chromosome count than the related, more widely distributed polyploid taxon. Mikio Ono coined

3816-416: Is Jerry Coyne and H. Allen Orr 's 2004 publication Speciation . They list six mainstream arguments that lend support to the concept of vicariant speciation: Allopatric speciation has resulted in many of the biogeographic and biodiversity patterns found on Earth: on islands, continents, and even among mountains. Islands are often home to species endemics —existing only on an island and nowhere else in

3922-472: Is a stub . You can help Misplaced Pages by expanding it . Endemism Endemism is the state of a species being found only in a single 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 is found exclusively in southwestern South Africa and

4028-567: Is a reverse-ordered form of allopatric speciation in conjunction with reinforcement . First, divergent selection separates a non-allopatric population emerging from pre-zygotic barriers, from which genetic differences evolve due to the obstruction of complete gene flow. The terms allo-parapatric and allo-sympatric have been used to describe speciation scenarios where divergence occurs in allopatry but speciation occurs only upon secondary contact. These are effectively models of reinforcement or "mixed-mode" speciation events. As allopatric speciation

4134-457: 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. A rare alternative term for

4240-487: Is endemic to Earth. However, endemism is normally used only when a species has a relatively small or restricted range. This usage of "endemic" contrasts with "cosmopolitan." Endemics are not necessarily rare; some might be common where they occur. Likewise, not all rare species are endemics; some may have a large range but be rare throughout this range. The evolutionary history of a species can lead to endemism in multiple ways. Allopatric speciation , or geographic speciation,

4346-464: Is from Neo-Latin endēmicus , from Greek ἔνδημος, éndēmos , "native". Endēmos is formed of en meaning "in", and dēmos meaning "the people". The word entered the English language as a loan word from French endémique , 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. The word

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4452-467: Is often regarded as the default or "null" model of speciation, but this too is debated. Reproductive isolation acts as the primary mechanism driving genetic divergence in allopatry and can be amplified by divergent selection . Pre-zygotic and post-zygotic isolation are often the most cited mechanisms for allopatric speciation, and as such, it is difficult to determine which form evolved first in an allopatric speciation event. Pre-zygotic simply implies

4558-434: 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 . In response to

4664-618: Is the sole surviving representative of a formerly diverse group. The concept of phylogenetic endemism has also been used to measure the relative uniqueness of the species endemic to an area. In measurements that incorporate phylogenetic endemism, branches of the evolutionary tree are weighted by how narrowly they are distributed. 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. Schizoendemics, apoendemics and patroendemics can all be classified as types of neoendemics. Schizoendemics arise from

4770-493: 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 . Similarly many species found in the Western ghats of India are examples of endemism. Endemism is an important concept in conservation biology for measuring biodiversity in a particular place and evaluating the risk of extinction for species. Endemism

4876-574: Is thought that rivers may play a role as the geographic barriers to Charis , not unlike the river barrier hypothesis used to explain the high rates of diversity in the Amazon basin —though this hypothesis has been disputed. Dispersal-mediated allopatric speciation is also thought to be a significant driver of diversification throughout the Neotropics . Patterns of increased endemism at higher elevations on both islands and continents have been documented on

4982-439: Is typically subdivided into two major models: vicariance and peripatric. These models differ from one another by virtue of their population sizes and geographic isolating mechanisms. The terms allopatry and vicariance are often used in biogeography to describe the relationship between organisms whose ranges do not significantly overlap but are immediately adjacent to each other—they do not occur together or only occur within

5088-710: Is when two populations of a species become geographically separated from each other and as a result develop into different species. In isolated areas where there is little possibility for organisms to disperse to new places, or to receive new gene flow from outside, the rate of endemism is particularly high. For example, many endemic species are found on remote islands , such as Hawaii , the Galápagos Islands and Socotra . 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

5194-543: Is widely accepted as a common mode of speciation, the scientific literature is abundant with studies documenting its existence. The biologist Ernst Mayr was the first to summarize the contemporary literature of the time in 1942 and 1963. Many of the examples he set forth remain conclusive; however, modern research supports geographic speciation with molecular phylogenetics —adding a level of robustness unavailable to early researchers. The most recent thorough treatment of allopatric speciation (and speciation research in general)

5300-497: Is widely regarded as the most common form of speciation; and is the primary model of allopatric speciation. Vicariance is a process by which the geographical range of an individual taxon , or a whole biota , is split into discontinuous populations ( disjunct distributions ) by the formation of an extrinsic barrier to the exchange of genes: that is, a barrier arising externally to a species. These extrinsic barriers often arise from various geologic -caused, topographic changes such as:

5406-689: The Himalayan mountains and the Qinghai–Tibetan Plateau for example have driven the speciation and diversification of numerous plants and animals such as Lepisorus ferns; glyptosternoid fishes ( Sisoridae ); and the Rana chensinensis species complex. Uplift has also driven vicariant speciation in Macowania daisies in South Africa's Drakensberg mountains, along with Dendrocincla woodcreepers in

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5512-417: The dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow . Various geographic changes can arise such as the movement of continents , and the formation of mountains, islands, bodies of water, or glaciers. Human activity such as agriculture or developments can also change

5618-440: The gene pools of the populations, (b) they become subjected to different selective pressures, and/or (c) they independently undergo genetic drift . The extrinsic barriers prevent the exchange of genetic information between the two populations, potentially leading to differentiation due to the ecologically different habitats they experience; selective pressure then invariably leads to complete reproductive isolation . Furthermore,

5724-410: The honeycreepers of Hawaii represent cases of limited geographic separation and were likely driven by ecological speciation . Geological evidence supports the final closure of the isthmus of Panama approximately 2.7 to 3.5 mya, with some evidence suggesting an earlier transient bridge existing between 13 and 15 mya. Recent evidence increasingly points towards an older and more complex emergence of

5830-935: The Balkan Peninsula, Turkey, 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 which recently evolved from subsp. glandulosus . Obligate cave-dwelling species, known as troglobites, are often endemic to small areas, even to single individual caves, because cave habitats are by nature restricted, isolated, and fragmented. A high level of adaptation to

5936-561: 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. Plants that become endemic on isolated islands are often those which have a high rate of dispersal and are able to reach such islands by being dispersed by birds. 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 which are considered endemic, meaning that

6042-575: The Further reading section below). Mathematical models concerning reproductive isolation-by distance have shown that populations can experience increasing reproductive isolation that correlates directly with physical, geographical distance. This has been exemplified in models of ring species ; however, it has been argued that ring species are a special case, representing reproductive isolation-by distance, and demonstrate parapatric speciation instead —as parapatric speciation represents speciation occurring along

6148-742: 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 which 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

6254-506: The Isthmus, with fossil and extant species dispersal (part of the American biotic interchange ) occurring in three major pulses, to and from North and South America. Further, the changes in terrestrial biotic distributions of both continents such as with Eciton army ants supports an earlier bridge or a series of bridges. Regardless of the exact timing of the isthmus closer, biologists can study

6360-689: The South American Andes . The Laramide orogeny during the Late Cretaceous even caused vicariant speciation and radiations of dinosaurs in North America. Adaptive radiation , like the Galapagos finches observed by Charles Darwin , is often a consequence of rapid allopatric speciation among populations. However, in the case of the finches of the Galapagos, among other island radiations such as

6466-537: The above, the World Wildlife Fund has split the world into a few hundred geographical ' ecoregions '. These have been designed to include as many species as possible that only occur in a single ecoregion, and these species are thus 'endemics' to these ecoregions. Since plenty of these ecoregions have a high prevalence of endemics existing within them, many National Parks have been formed around or within them to further promote conservation. The Caparaó National Park

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6572-477: The clear theoretical plausibility that geographic isolation can result in the reproductive isolation of two populations. Since the 1940s, allopatric speciation has been accepted. Today, it is widely regarded as the most common form of speciation taking place in nature. However, this is not without controversy, as both parapatric and sympatric speciation are both considered tenable modes of speciation that occur in nature. Some researchers even consider there to be

6678-622: The closure of the Isthmus of Panama or speciation events within the genus Cyclamen ). Other techniques used today have employed measures of gene flow between populations, ecological niche modelling (such as in the case of the Myrtle and Audubon's warblers or the environmentally-mediated speciation taking place among dendrobatid frogs in Ecuador ), and statistical testing of monophyletic groups. Biotechnological advances have allowed for large scale, multi- locus genome comparisons (such as with

6784-853: The concept by using WWF ecoregions and reptiles, finding that most reptile endemics occur in WWF ecoregions with high biodiversity. Other conservation efforts for endemics include keeping captive and semi-captive populations in zoological parks and botanical gardens. These methods are ex situ ("off-site") conservation methods. The use of such methods may not only offer refuge and protection for individuals of declining or vulnerable populations, but it may also allow biologists valuable opportunities to research them as well. Allopatric speciation Allopatric speciation (from Ancient Greek ἄλλος (állos)  'other' and πατρίς (patrís)  'fatherland') – also referred to as geographic speciation , vicariant speciation , or its earlier name

6890-583: The concept. In their view, everything is endemic, even cosmopolitan species are endemic to Earth, and earlier definitions restricting endemics to specific locations are wrong. Thus the subdivisions neoendemics and paleoendemics are without merit regarding the study of distributions, because these concepts consider that an endemic has a distribution limited to one place. Instead, they propose four different categories: holoendemics, euryendemics, stenoendemics and rhoendemics. In their scheme cryptoendemics and euendemics are further subdivisions of rhoendemics. In their view,

6996-518: 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. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants, and have not dispersed beyond

7102-587: 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

7208-430: The distribution of species populations. These factors can substantially alter a region's geography, resulting in the separation of a species population into isolated subpopulations. The vicariant populations then undergo genetic changes as they become subjected to different selective pressures , experience genetic drift , and accumulate different mutations in the separated populations' gene pools . The barriers prevent

7314-822: The evolution of reproductive isolation. Centrifugal speciation has been largely ignored in the scientific literature. Nevertheless, a wealth of evidence has been put forth by researchers in support of the model, much of which has not yet been refuted. One example is the possible center of origin in the Indo-West Pacific . Microallopatry refers to allopatric speciation occurring on a small geographic scale. Examples of microallopatric speciation in nature have been described. Rico and Turner found intralacustrine allopatric divergence of Pseudotropheus callainos ( Maylandia callainos ) within Lake Malawi separated only by 35 meters. Gustave Paulay found evidence that species in

7420-488: The exchange of genetic information between the two populations leading to reproductive isolation . If the two populations come into contact they will be unable to reproduce—effectively speciating. Other isolating factors such as population dispersal leading to emigration can cause speciation (for instance, the dispersal and isolation of a species on an oceanic island) and is considered a special case of allopatric speciation called peripatric speciation . Allopatric speciation

7526-636: The fact that interspecific mate discrimination occurs to a greater extent between sympatric populations than it does in purely allopatric populations; however, other factors have been proposed to account for the observed patterns. Reinforcement in allopatry has been shown to occur in nature ( evidence for speciation by reinforcement ), albeit with less frequency than a classic allopatric speciation event. A major difficulty arises when interpreting reinforcement's role in allopatric speciation, as current phylogenetic patterns may suggest past gene flow. This masks possible initial divergence in allopatry and can indicate

7632-424: The fact that both models posit the absence of gene flow between the populations. The size of the isolated population is important because individuals colonizing a new habitat likely contain only a small sample of the genetic variation of the original population. This promotes divergence due to strong selective pressures, leading to the rapid fixation of an allele within the descendant population. This gives rise to

7738-418: The formation of mountains ( orogeny ); the formation of rivers or bodies of water; glaciation ; the formation or elimination of land bridges ; the movement of continents over time (by tectonic plates ); or island formation, including sky islands . Vicariant barriers can change the distribution of species populations. Suitable or unsuitable habitat may be come into existence, expand, contract, or disappear as

7844-449: The hybrids themselves can possibly become their own species: known as hybrid speciation . Reinforcement can play a role in all geographic modes (and other non-geographic modes) of speciation as long as gene flow is present and viable hybrids can be formed. The production of inviable hybrids is a form of reproductive character displacement , under which most definitions is the completion of a speciation event. Research has well established

7950-425: The laboratory experiments conducted on allopatric speciation. The first column indicates the species used in the referenced study, where the "Trait" column refers to the specific characteristic selected for or against in that species. The "Generations" column refers to the number of generations in each experiment performed. If more than one experiment was formed generations are separated by semicolons or dashes (given as

8056-430: The life cycle of the species can indicate whether or not divergence occurred due to a pre-zygotic or post-zygotic factor. However, establishing the specific mechanism may not be accurate, as a species pair continually diverges over time. For example, if a plant experiences a chromosome duplication event , reproduction will occur, but sterile hybrids will result—functioning as a form of post-zygotic isolation. Subsequently,

8162-472: The long-scale process of allopatric speciation that occurs in nature. Experiments often fall beneath 100 generations, far less than expected, as rates of speciation in nature are thought to be much larger. Furthermore, rates specifically concerning the evolution of reproductive isolation in Drosophila are significantly higher than what is practiced in laboratory settings. Using index Y presented previously,

8268-496: The mid-twentieth century. The vicariance theory, which showed coherence along with the acceptance of plate tectonics in the 1960s, was developed in the early 1950s by this Venezuelan botanist, who had found an explanation for the similarity of plants and animals found in South America and Africa by deducing that they had originally been a single population before the two continents drifted apart. Currently, speciation by vicariance

8374-523: The newly formed species pair may experience pre-zygotic barriers to reproduction as selection, acting on each species independently, will ultimately lead to genetic changes making hybrids impossible. From the researcher's perspective, the current isolating mechanism may not reflect the past isolating mechanism. Reinforcement has been a contentious factor in speciation. It is more often invoked in sympatric speciation studies, as it requires gene flow between two populations. However, reinforcement may also play

8480-519: The number of matings in heterogameticity where B {\displaystyle B} and C {\displaystyle C} represent homogametic matings . A {\displaystyle A} and B {\displaystyle B} is one population and D {\displaystyle D} and C {\displaystyle C} is the second population. A negative value of Y {\displaystyle Y} denotes negative assortive mating,

8586-598: The number of endemics on an island is directly correlated with the relative isolation of the island and its area. In some cases, speciation on islands has occurred rapidly. Dispersal and in situ speciation are the agents that explain the origins of the organisms in Hawaii. Various geographic modes of speciation have been studied extensively in Hawaiian biota, and in particular, angiosperms appear to have speciated predominately in allopatric and parapatric modes. Islands are not

8692-427: The occurrence of allopatric speciation in nature. Mathematical modeling of the genetic basis of reproductive isolation supports the plausibility of allopatric speciation; whereas laboratory experiments of Drosophila and other animal and plant species have confirmed that reproductive isolation evolves as a byproduct of natural selection . The notion of vicariant evolution was first developed by Léon Croizat in

8798-502: The occurrence of allopatric speciation, of which is widely accepted today. Prior to this research, Theodosius Dobzhansky published Genetics and the Origin of Species in 1937 where he formulated the genetic framework for how speciation could occur. Other scientists noted the existence of allopatrically distributed pairs of species in nature such as Joel Asaph Allen (who coined the term "Jordan's Law", whereby closely related, geographically isolated species are often found divided by

8904-494: The only geographic locations that have endemic species. South America has been studied extensively with its areas of endemism representing assemblages of allopatrically distributed species groups. Charis butterflies are a primary example, confined to specific regions corresponding to phylogenies of other species of butterflies, amphibians , birds, marsupials , primates , reptiles , and rodents . The pattern indicates repeated vicariant speciation events among these groups. It

9010-436: The origin of the genetic novelty that leads to reproductive isolation. When a population of a species experiences a period of geographic range expansion and contraction, it may leave small, fragmented, peripherally isolated populations behind. These isolated populations will contain samples of the genetic variation from the larger parent population. This variation leads to a higher likelihood of ecological niche specialization and

9116-742: The other line with less). Some studies performed experiments modeling or controlling for genetic drift. Reproductive isolation occurred pre-zygotically, post-zygotically, both, or not at all. It is important to note that many of the studies conducted contain multiple experiments within—a resolution of which this table does not reflect. number desiccation resistance , fecundity , ethanol resistance; courtship display , re-mating speed, lek behavior ; pupation height, clumped egg laying, general activity D. persimilis Early speciation research typically reflected geographic distributions and were thus termed geographic, semi-geographic, and non-geographic. Geographic speciation corresponds to today's usage of

9222-656: 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 can be seen as ' sky islands ': refugia of endemics because species that live in

9328-494: The potential for genetic incompatibilities to evolve. These incompatibilities cause reproductive isolation, giving rise to rapid speciation events. Models of peripatry are supported mostly by species distribution patterns in nature. Oceanic islands and archipelagos provide the strongest empirical evidence that peripatric speciation occurs. Centrifugal speciation is a variant, alternative model of peripatric speciation. This model contrasts with peripatric speciation by virtue of

9434-417: The presence of a barrier prior to any act of fertilization (such as an environmental barrier dividing two populations), while post-zygotic implies the prevention of successful inter-population crossing after fertilization (such as the production of an infertile hybrid ). Since species pairs who diverged in allopatry often exhibit pre- and post-zygotic isolation mechanisms, investigation of the earliest stages in

9540-404: 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

9646-430: The rate of gene exchange. In sympatry m = 0.5 {\displaystyle m=0.5} (panmixis), while in parapatric speciation , 0 < m < 0.5 {\displaystyle 0<m<0.5} represents the entire continuum, although some scientists argue that a classification scheme based solely on geographic mode does not necessarily reflect the complexity of speciation. Allopatry

9752-435: The relationships of 15 pairs of sister species of Alpheus , each pair divided across the isthmus and molecular clock dating supports their separation between 3 and 15 million years ago. Recently diverged species live in shallow mangrove waters while older diverged species live in deeper water, correlating with a gradual closure of the isthmus. Support for an allopatric divergence also comes from laboratory experiments on

9858-519: The role of geographic isolation in promoting speciation, in the process coining the term "sympatric speciation" in 1903. Controversy exists as to whether Charles Darwin recognized a true geographical-based model of speciation in his publication of the Origin of Species . In chapter 11, "Geographical Distribution", Darwin discusses geographic barriers to migration, stating for example that "barriers of any kind, or obstacles to free migration, are related in

9964-480: The species is restricted to an area less than five million hectares (twelve million acres). 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. Endemism can reflect

10070-517: The species on the Pacific and Caribbean sides in what has been called, "one of the greatest natural experiments in evolution". Additionally, as with most geologic events, the closure was unlikely to have occurred rapidly, but instead dynamically—a gradual shallowing of sea water over millions of years. Studies of snapping shrimp in the genus Alpheus have provided direct evidence of an allopatric speciation event, as phylogenetic reconstructions support

10176-592: The species pairs showing nearly complete reproductive isolation. Similar patterns of relatedness and distribution across the Pacific and Atlantic sides have been found in other species pairs such as: Ice ages have played important roles in facilitating speciation among vertebrate species. This concept of refugia has been applied to numerous groups of species and their biogeographic distributions. Glaciation and subsequent retreat caused speciation in many boreal forest birds, such as with North American sapsuckers ( Yellow-bellied , Red-naped , and Red-breasted );

10282-482: The subfamily Cryptorhynchinae have microallopatrically speciated on Rapa and its surrounding islets . A sympatrically distributed triplet of diving beetle ( Paroster ) species living in aquifers of Australia's Yilgarn region have likely speciated microallopatrically within a 3.5 km area. The term was originally proposed by Hobart M. Smith to describe a level of geographic resolution. A sympatric population may exist in low resolution, whereas viewed with

10388-424: The term 'aneuendemics' in 1991 for species that have more or fewer chromosomes than their relatives due to aneuploidy . Pseudoendemics are taxa that have possibly recently evolved from a mutation. Holoendemics is a concept introduced by Richardson in 1978 to describe taxa that have remained endemic to a restricted distribution for a very long time. In a 2000 paper, Myers and de Grave further attempted to redefine

10494-435: The term allopatric speciation, and in 1868, Moritz Wagner was the first to propose the concept of which he used the term Separationstheorie . His idea was later interpreted by Ernst Mayr as a form of founder effect speciation as it focused primarily on small geographically isolated populations. Edward Bagnall Poulton , an evolutionary biologist and a strong proponent of the importance of natural selection, highlighted

10600-565: 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

10706-647: The warblers in the genus Setophaga ( S. townsendii , S. occidentalis , and S. virens ), Oreothlypis ( O. virginiae , O. ridgwayi , and O. ruficapilla ), and Oporornis ( O. tolmiei and O. philadelphia now classified in the genus Geothlypis ); Fox sparrows (sub species P. (i.) unalaschensis , P. (i.) megarhyncha , and P. (i.) schistacea ); Vireo ( V. plumbeus , V. cassinii , and V. solitarius ); tyrant flycatchers ( E. occidentalis and E. difficilis ); chickadees ( P. rufescens and P. hudsonicus ); and thrushes ( C. bicknelli and C. minimus ). As

10812-402: The world—with nearly all taxa residing on isolated islands sharing common ancestry with a species on the nearest continent. Not without challenge, there is typically a correlation between island endemics and diversity ; that is, that the greater the diversity (species richness) of an island, the greater the increase in endemism. Increased diversity effectively drives speciation. Furthermore,

10918-518: Was effectively introduced by John D. Lynch in 1986 and numerous researchers have employed it and similar methods, yielding enlightening results. Correlation of geographic distribution with phylogenetic data also spawned a sub-field of biogeography called vicariance biogeography developed by Joel Cracraft , James Brown , Mark V. Lomolino , among other biologists specializing in ecology and biogeography. Similarly, full analytical approaches have been proposed and applied to determine which speciation mode

11024-460: Was first used in botany by Vaughan MacCaughey in Hawaii in 1917. 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, and all known life

11130-555: Was formed in the Atlantic Forest , a biodiversity hotspot located in Brazil, in order to help protect valuable and vulnerable species. 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

11236-413: Was used in biology in 1872 to mean a species restricted to a specific location by Charles Darwin . The less common term 'precinctive' has been used by some entomologists as the equivalent of 'endemic'. Precinctive was coined in 1900 by David Sharp when describing the Hawaiian insects, as he was uncomfortable with the fact that the word ' endemic ' is often associated with diseases. 'Precinctive'

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