Disjunct distribution

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Range of the snail Elona quimperiana, an example of a disjunct distribution. Elona.png
Range of the snail Elona quimperiana , an example of a disjunct distribution.

In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but considerably separated from each other geographically. The causes are varied and might demonstrate either the expansion or contraction of a species range. [1]

Taxon Group of one or more populations of an organism or organisms which have distinguishing characteristics in common

In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Contents

Range fragmentation

Also called range fragmentation, disjunct distributions may be caused by changes in the environment, such as mountain building and continental drift or rising sea levels; it may also be due to an organism expanding its range into new areas, by such means as rafting, or other animals transporting an organism to a new location (plant seeds consumed by birds and animals, can be moved to new locations during bird or animals migrations, and those seeds can be deposited in new locations in fecal matter). Other conditions that can produce disjunct distributions include: flooding, or changes in wind, stream, and current flows, plus others such as anthropogenic introduction of alien introduced species either accidentally or deliberately (agriculture and horticulture).

Orogeny The formation of mountain ranges

An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.

Continental drift The movement of the Earths continents relative to each other

Continental drift is the theory that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed. The speculation that continents might have 'drifted' was first put forward by Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegener in 1912, but his theory was rejected by many for lack of any motive mechanism. Arthur Holmes later proposed mantle convection for that mechanism. The idea of continental drift has since been subsumed by the theory of plate tectonics, which explains that the continents move by riding on plates of the Earth's lithosphere.

Sea level Average level for the surface of the ocean at any given geographical position on the planetary surface

Mean sea level (MSL) is an average level of the surface of one or more of Earth's oceans from which heights such as elevation may be measured. MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location.

Habitat fragmentation

Disjunct distributions can occur when suitable habitat is fragmented, which produces fragmented populations, and when that fragmentation becomes so divergent that species movement between one suitable habitat to the next is disrupted, isolated population can be produced. Extinctions can cause disjunct distribution, especially in areas where only scattered areas are habitable by a species; [2] for instance, island chains or specific elevations along a mountain range or areas along a coast or between bodies of water like streams, lakes and ponds. [3]

Habitat ecological or environmental area inhabited by a particular species; natural environment in which an organism lives, or the physical environment that surrounds a species population

In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both physical and biological features. A species' habitat is those places where it can find food, shelter, protection and mates for reproduction.

Habitat fragmentation

Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes that slowly alter the layout of the physical environment (suspected of being one of the major causes of speciation),and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species.

Examples

There are many patterns of disjunct distributions at many scales: Irano-Turanian disjunction, Europe - East Asia, Europe-South Africa (e.g. genus Erica ), Mediterranean-Hoggart disjunction (genus Olea ), etc.

<i>Erica</i> genus of plants

Erica is a genus of roughly 860 species of flowering plants in the family Ericaceae. The English common names heath and heather are shared by some closely related genera of similar appearance. The genus Calluna was formerly included in Erica – it differs in having even smaller scale-leaves, and the flower corolla consisting of separate petals. Erica is sometimes referred to as "winter heather" to distinguish it from Calluna "summer heather".

<i>Olea</i> genus of plants

Olea is a genus of about 40 species in the family Oleaceae, native to warm temperate and tropical regions of the Middle East, southern Europe, Africa, southern Asia, and Australasia. They are evergreen trees and shrubs, with small, opposite, entire leaves. The fruit is a drupe. Leaves of Olea contain trichosclereids.

Lusitanian distribution

The range map of Geomalacus maculosus shows a 'Lusitanian' distribution. Geomalacus maculosus map.png
The range map of Geomalacus maculosus shows a 'Lusitanian' distribution.

This kind of disjunct distribution of a species, such that it occurs in Iberia and in Ireland, without any intermediate localities, is usually called "Lusitanian" (named after the Roman Province Lusitania, corresponding to modern day Portugal).

Ireland Island in north-west Europe, 20th largest in world, politically divided into the Republic of Ireland and Northern Ireland (a part of the UK)

Ireland is an island in the North Atlantic. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the second-largest island of the British Isles, the third-largest in Europe, and the twentieth-largest on Earth.

Lusitania Roman province

Lusitania or Hispania Lusitana was an ancient Iberian Roman province located where modern Portugal and part of western Spain lie. It was named after the Lusitani or Lusitanian people.

Portugal Republic in Southwestern Europe

Portugal, officially the Portuguese Republic, is a country located mostly on the Iberian Peninsula in southwestern Europe. It is the westernmost sovereign state of mainland Europe, being bordered to the west and south by the Atlantic Ocean and to the north and east by Spain. Its territory also includes the Atlantic archipelagos of the Azores and Madeira, both autonomous regions with their own regional governments.

Examples of animal species with a Lusitanian distribution are: the Kerry slug Geomalacus maculosus and the Pyrenean glass snail Semilimax pyrenaicus . Plant species with this kind of distribution include several heather species (Calluna spp.) and the strawberry tree (Arbutus unedo).

Pyrenees Range of mountains in southwest Europe

The Pyrenees is a range of mountains in southwest Europe that forms a natural border between Spain and France. Reaching a height of 3,404 metres (11,168 ft) altitude at the peak of Aneto, the range separates the Iberian Peninsula from the rest of continental Europe, and extends for about 491 km (305 mi) from the Bay of Biscay to the Mediterranean Sea.

<i>Semilimax pyrenaicus</i> species of mollusc

Semilimax pyrenaicus is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Vitrinidae.

<i>Calluna</i> species of plant

Calluna vulgaris is the sole species in the genus Calluna in the flowering plant family Ericaceae. It is a low-growing perennial shrub growing to 20 to 50 centimetres tall, or rarely to 1 metre (39 in) and taller, and is found widely in Europe and Asia Minor on acidic soils in open sunny situations and in moderate shade. It is the dominant plant in most heathland and moorland in Europe, and in some bog vegetation and acidic pine and oak woodland. It is tolerant of grazing and regenerates following occasional burning, and is often managed in nature reserves and grouse moors by sheep or cattle grazing, and also by light burning.

The theory behind the name "Lusitanian" is now discredited; it posited that there was an ice-free land mass that served as a refugium off of the south-west of Ireland during the Quaternary (last) glaciation. In this refugium, relic fauna and flora from a previous ice-free period survived until the present warmer interstadial period. Although the theory is no longer accepted, the term Lusitanian is still used as a descriptive term for faunal elements such as the Kerry slug.

Recently a better explanation of the occurrence of the Kerry slug and similar faunal elements in southwestern Ireland has been developed. This new theory is supported by two recent discoveries: the genetic similarity of much of Ireland’s fauna to that of northern Spain, and the genetic similarity of much of Ireland’s human population to that of northern Spain.

Mascheretti et al. (2003) [4] examined the genotypes of Eurasian pygmy shrew, a small mammal, across its range in Europe. The Irish population showed close genetic affinity to a population from Andorra but not to that of Britain or other places in Europe. The genetic structure of the population further showed that the entire Irish population of the Eurasian pygmy shrew had originated from a single founder event. The authors concluded that it had been introduced in the early (Palaeolithic) or middle (Mesolithic) Stone Age, by boat, probably from south-west Europe. This coincides with work on human populations, which found [5] [6] a strong genetic similarity in make-up between populations in western Ireland and in northern Spain. This would be explained by a human migration from Spain to Ireland in the late Paleolithic or early Mesolithic.

It seems increasingly likely that much of Ireland’s Lusitanian fauna is in reality an artefact of this era of human expansion in the early part of the Postglacial era. In other words, it seems likely that these species were introduced accidentally with trade items or goods brought by boat from Iberia.

See also

Related Research Articles

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The mountain pygmy possum is a small, mouse-sized nocturnal marsupial of Australia found in dense alpine rock screes and boulder fields, mainly southern Victoria and around Mount Kosciuszko in Kosciuszko National Park in New South Wales at elevations from 1,300 to 2,230 metres. At almost 14 cm (5.5 in), its prehensile tail is longer than its 11 cm (4.3 in) combined head and body length. Its diet consists of insects, fleshy fruits, nuts, nectar and seeds. Its body is covered in a thick coat of fine grey fur except for its stomach, which is cream coloured; its tail is hairless. On the underside of the female's body is a pouch containing four teats. This possum is the only extant species in the genus Burramys. It is also the only Australian mammal restricted to alpine habitat.

Pygmy cormorant species of bird

The pygmy cormorant is a member of the Phalacrocoracidae (cormorant) family of seabirds. It breeds in south-eastern Europe and south-western Asia. It is partially migratory, with northern populations wintering further south, mostly within its breeding range. It is a rare migrant to western Europe.

American pygmy shrew species of mammal

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Lusitanian language language

Lusitanian was an Indo-European Paleohispanic language. There has been support for either a connection with the ancient Italic languages or Celtic languages. It is known from only five sizeable inscriptions, dated from circa 1 CE, and numerous names of places (toponyms) and of gods (theonyms). The language was spoken in the territory inhabited by Lusitanian tribes, from the Douro to the Tagus rivers, territory that nowadays falls in central Portugal and western Spain.

Holarctic

The Holarctic is the name for the biogeographic realm that encompasses the majority of habitats found throughout the northern continents of the world, combining Wallace's Palearctic zoogeographical region, consisting of North Africa and all of Eurasia, and the Nearctic zoogeographical region, consisting of North America, north of Mexico. These regions are further subdivided into a variety of ecoregions. Many ecosystems, and the animal and plant communities that depend on them, are found across multiple continents in large portions of this realm. The continuity of these ecosystems results from the shared glacial history of the realm. The floristic Boreal Kingdom corresponds to the Holarctic realm.

Chalkhill blue species of insect

The chalkhill blue is a butterfly in the family Lycaenidae.

Greater white-toothed shrew species of mammal

The greater white-toothed shrew is a small insectivorous mammal found in Europe and North Africa. It is the most common of the white-toothed shrews. This species is found along the Mediterranean, Netherlands, Belgium, Germany and Portugal; in addition, the Osorio shrew of the Canary island of Gran Canaria, originally described as a separate species, was later discovered to be a population of introduced greater white-toothed shrew. In April 2008, the greater white-toothed shrew was discovered in Ireland. Its preferred habitats are grassland and woodland. It is slightly larger than the lesser white-toothed shrew but otherwise very similar, and can often be distinguished only by close inspection of its teeth which are unpigmented.

Volcano rabbit species of mammal

The volcano rabbit, also known as teporingo or zacatuche, is a small rabbit that resides in the mountains of Mexico. It is the world's second-smallest rabbit, second only to the pygmy rabbit. It has small rounded ears, short legs, and short, thick fur and weighs approximately 390–600 g (0.86–1.3 lb). It has a life span of 7 to 9 years. The volcano rabbit lives in groups of 2 to 5 animals in burrows and runways among grass tussocks. The burrows can be as long as 5 m and as deep as 40 cm. There are usually 2 to 3 young per litter, born in the burrows. In semi-captivity, however, they don't make burrows and the young are born in nests made in the grass tussocks.

Fauna of Great Britain

The island of Great Britain, along with the rest of the archipelago known as the British Isles, has a largely temperate climate. It contains a relatively small fraction of the world's wildlife. The biota was severely diminished in the last Ice Age, and shortly thereafter was separated from the continent by the English Channel's formation. Since then, man has hunted the most dangerous forms to extinction, though domesticated forms such as the dog and the pig remain. The wild boar has subsequently been reintroduced as a meat animal.

Kerry slug species of mollusc

The Kerry slug or Kerry spotted slug is a species of medium-sized to large air-breathing land slug. It is a terrestrial pulmonate gastropod mollusc in the family Arionidae, the roundback slugs.

Fauna of Ireland Animal species of the island of Ireland and surrounding waters

The fauna of Ireland comprises all the animal species inhabiting the island of Ireland and its surrounding waters.

Pygmy shrew tenrec species of mammal

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North African hedgehog species of mammal

The North African hedgehog or Algerian hedgehog, is a species of mammal in the family Erinaceidae. It is found in Algeria, Libya, Malta, Morocco, Spain, and Tunisia. Little is known about this species of hedgehog, even though the most common breed of domesticated hedgehogs is a result of crossing a four-toed hedgehog with a North African hedgehog. Because this species of hedgehog is native to Africa, it has been suggested that it was introduced by humans to the other countries where it is now found, including France and Spain. Of the four African species of hedgehogs, the North African hedgehog is the only one of these hedgehogs that can be found outside the continent of Africa. Because the North African hedgehog has such a wide habitat range and has a seemingly stable population, both in the wild and in the domesticated capacity, it does not appear to be at risk at this time.

<i>Myosorex varius</i> species of mammal

The forest shrew is a species of shrew in the mouse shrew family, Soricidae. It is found in Lesotho, South Africa, and Swaziland. Its natural habitats include temperate forests, dry savanna, Mediterranean-type shrubby vegetation, and temperate grassland. The term "forest shrews" in the plural is sometimes confusingly used to collectively refer to a different genus, Sylvisorex.

Alpine shrew species of mammal

The alpine shrew is a species of mammal in the family Soricidae. It is found in the alpine meadows and coniferous forests of Southern European mountain ranges: the Alps, the Pyrenees, the Carpathian Mountains and the Balkans.

Defaunation is the global, local or functional extinction of animal populations or species from ecological communities. The growth of the human population, combined with advances in harvesting technologies, has led to more intense and efficient exploitation of the environment. This has resulted in the depletion of large vertebrates from ecological communities, creating what has been termed "empty forest". Defaunation differs from extinction; it includes both the disappearance of species and declines in abundance. Defaunation effects were first implied at the Symposium of Plant-Animal Interactions at the University of Campinas, Brazil in 1988 in the context of neotropical forests. Since then, the term has gained broader usage in conservation biology as a global phenomenon.

The fauna of England is similar to that of other areas British Isles and lies within the Palearctic realm. England's fauna is mainly made up of small animals and is notable for having few large mammals, but in similarity with other island nations; many bird species.

The Cantabrian capercaillie is a subspecies of the western capercaillie in the grouse family Tetraonidae. It is one of two subspecies found in Spain.

In biogeography and paleontology a relict is a population or taxon of organisms that was more widespread or more diverse in the past. A relictual population is a population that presently occurs in a restricted area, but whose original range was far wider during a previous geologic epoch. Similarly, a relictual taxon is a taxon that is the sole surviving representative of a formerly diverse group.

References

  1. Tallis, J. H. (1991), Plant community history, 2, London u.a.: Chapman and Hall, pp. 140–43, ISBN   0-412-30320-5
  2. Ernst Mayr, Jared Diamond; Douglas Pratt, Color Plates by H. (2001), The birds of northern Melanesia : speciation, ecology & biogeography, 2, Oxford: Oxford University Press, p. 257, ISBN   0-19-514170-9
  3. Tomascik, Tomas (1997), The ecology of the Indonesian seas, 2, Oxford: Oxford University Press, p. 842, ISBN   962-593-163-5
  4. Masheretti S., Rogatcheva M. B., Gündüz I., Fredga K. & Searle J. B. 2003. How did pygmy shrews colonize Ireland? Clues from a phylogenetic analysis of mitochondrial cytochrome b sequences. Proc. Roy. Soc. B 270: 1593-1599.
  5. Hill E. W., Jobling M. A. & Bradley D. G. 2000. Y chromosome variation and Irish origins. Nature 404: 351.
  6. McEvoy B., Richards M., Forster P. & Bradley D. G. 2004. The longue durée of genetic ancestry: multiple genetic marker systems and Celtic origins on the Atlantic facade of Europe. Am. J. Hum. Genet. 75: 693-702.