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.


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.


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

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Lusitanian language language

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  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.