Insular dwarfism
5485600
225173831
2008-07-12T07:58:05Z
Jonathan Cardy
4071608
disambig Buffalo
[[Image:Cretanelephant-petermaas.jpg|thumb|right|250px|The skeleton of a [[dwarf elephant]] from the island of [[Crete]].]]'''Insular dwarfism''' is the process and condition of the reduction in size of large animals – almost always [[mammal]]s – when their gene pool is limited to a very small environment, primarily islands.
This effect has manifested itself many times throughout natural history, including with [[dinosaur]]s and modern animals such as [[elephants]] and [[human being]]s.
There are several proposed explanations for the mechanism which produces such dwarfism, which are often considered likely to be co-contributing factors, including an evolved gene-encoded response to environmental stress, as well as a selective process where only the smaller of the animals trapped on the island survive, as food declines to a borderline level. The smaller animals need fewer resources, and so are more likely to get past the break-point where population decline allows food sources to replenish enough for the survivors to flourish.
==Examples==
Among the most famous examples of insular dwarfism are:
* The [[Channel Islands Mammoth]] which lived on the prehistoric island of [[Santa Rosae]] in the [[California Channel Islands]], and the small [[woolly mammoth]]s of [[Saint Paul Island (Alaska)|Saint Paul Island]] off [[Alaska]], and [[Wrangel Island]] north of [[Siberia]].
* [[Dwarf elephant]]s in the recent natural history of [[Malta]], [[Crete]], [[Cyprus]], and [[Sicily]].
* Dwarf [[stegodon]]s (elephant relatives) from the recent natural history of [[Flores]], [[Sulawesi]], [[Sumba]] and [[Timor]].
* A (disputed) species of [[hominin]] called ''[[Homo floresiensis]]'', from fossils found on [[Flores Island]], [[Indonesia]].
* Small-Bodied [[Human]]s from [[Palau]], [[Micronesia]], similar in size to the Flores hominins.<ref>[http://www.independent.co.uk/news/science/skull-may-identify-tiny-islanders-who-shrank-to-survive-794487.html Skull may identify tiny islanders who shrank to survive], The Independent</ref>
* [[Dinosaur]]s, including the recently validated ''[[Europasaurus]]'', on [[Mesozoic]] islands such as [[Haţeg Island]].
There are also proposed instances of this process occurring among plant life, the appearance of dwarf [[sequoia]] / redwood trees being one such proposal.{{Fact|date=June 2007}}
This process, and other "[[island genetics]]" artifacts, can occur not only on islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include [[caves]], desert [[oases]], and isolated valleys. An example of this is the "[[pygmy]]" people of Africa, such as the [[Mbuti]], who evolved a small size while in genetic and ecological isolation in a dense jungle region.{{Fact|date=May 2008}}
There is an inverse form of this process, [[island gigantism]], wherein small animals, lacking the predators of their normal homes, may become "gigantic" when breeding in isolation. An excellent example is the [[dodo]], the ancestors of which were normal-sized [[pigeon]]s.
== Additional examples==
[[Carnivora]]
*[[Channel Island fox]] in [[California]], [[United States]], and the enigmatic, nearly extinct [[Cozumel fox]]
*[[Honshū Wolf]] in [[Japan]]
*[[Bali Tiger]]
*[[Cozumel Island Raccoon]]
*[[Sardinian Dhole]]
*[[Sardinian Lynx]]
[[Ungulate]]s
*The strange, tiny [[Balearic Islands]] Cave Goat (''[[Myotragus balearicus]]'') in [[Majorca]] and [[Minorca]] and its close relative ''[[Nesogoral]]'', from [[Sardinia]] which became extinct after human settlement
*Philippine [[Bubalus|water buffalo]], [[Tamaraw]], [[Anoa]], the extinct [[Bubalus cebuensis]] and other dwarf [[bovid]]s from South East Asia
*Several prehistoric species of [[hippopotamus]] from the Pleistocene of [[Mediterranean]] islands (such as ''[[Phanourios minutis]]'') and [[Madagascar]]
*Dwarf [[deer]] species on the Philippines ([[Philippine Sambar]], extant), and Crete (''[[Candiacervus]] ropalophorus''), and Ryukyu Islands of Japan (''Cervus astylodon'') (all extinct)
*[[Key Deer]]
Other
* The tiny flightless [[Inaccessible Island Rail|Inaccessible Island]] and [[Laysan Rail]]s
*The dwarf [[nodosaurus|nodosaurid]] ''[[Struthiosaurus]]'' from [[Europe]], and the dwarf [[allosaur]] from South [[Australia]]
==See also==
{{wikinews|Bones of "small-bodied humans" found in cave}}
*[[Island gigantism]]
*[[Foster's rule]]
*[[Deep-sea gigantism]]
*Baron [[Franz Nopcsa]]
==References==
{{reflist}}
==External links==
*[http://www.guardian.co.uk/life/science/story/0,12996,1340300,00.html Strange world of island species October 31, 2004 The Observer ]
[[Category:Zoology]]
[[Category:Paleontology]]
[[Category:Ecology]]
[[Category:Evolutionary biology]]
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