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]
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 animal 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).
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]
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.
Lusitanian distribution
This kind of disjunct distribution of a species, such that it occurs in
Examples of animal species with a Lusitanian distribution are: the Kerry slug
The theory behind the name "Lusitanian" is now discredited; it posited that there was an ice-free land mass that served as a
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)
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
- Geographical isolation
- Habitat
- Habitat fragmentation
References
- ISBN 0-412-30320-5
- ISBN 0-19-514170-9
- ISBN 962-593-163-5
- ^ 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.
- ^ Hill E. W., Jobling M. A. & Bradley D. G. 2000. Y chromosome variation and Irish origins. Nature 404: 351.
- ^ 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.