Disjunct distribution

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

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).

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; 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.

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.

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).

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