Insular dwarfism
Insular dwarfism, a form of phyletic dwarfism,[1] is the process and condition of large animals evolving or having a reduced body size[lower-alpha 1] when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called dwarfing. This process has occurred many times throughout evolutionary history, with examples including dinosaurs, like Europasaurus, and modern animals such as elephants and their relatives. This process, and other "island genetics" artifacts, can occur not only on traditional islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include caves, desert oases, isolated valleys and isolated mountains ("sky islands"). Insular dwarfism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies.
Possible causes
There are several proposed explanations for the mechanism which produces such dwarfism.[3][4]
One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, 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. Smaller size is also advantageous from a reproductive standpoint, as it entails shorter gestation periods and generation times.[3]
In the tropics, small size should make thermoregulation easier.[3]
Among herbivores, large size confers advantages in coping with both competitors and predators, so a reduction or absence of either would facilitate dwarfing; competition appears to be the more important factor.[4]
Among carnivores, the main factor is thought to be the size and availability of prey resources, and competition is believed to be less important.[4] In tiger snakes, insular dwarfism occurs on islands where available prey is restricted to smaller sizes than are normally taken by mainland snakes. Since prey size preference in snakes is generally proportional to body size, small snakes may be better adapted to take small prey.[5]
Dwarfism versus gigantism
The inverse process, wherein small animals breeding on isolated islands lacking the predators of large land masses may become much larger than normal, is called island gigantism. An excellent example is the dodo, the ancestors of which were normal-sized pigeons. There are also several species of giant rats, one still extant, that coexisted with both Homo floresiensis and the dwarf stegodons on Flores.
The process of insular dwarfing can occur relatively rapidly by evolutionary standards. This is in contrast to increases in maximum body size, which are much more gradual. When normalized to generation length, the maximum rate of body mass decrease during insular dwarfing was found to be over 30 times greater than the maximum rate of body mass increase for a ten-fold change in mammals.[6] The disparity is thought to reflect the fact that pedomorphism offers a relatively easy route to evolve smaller adult body size; on the other hand, the evolution of larger maximum body size is likely to be interrupted by the emergence of a series of constraints that must be overcome by evolutionary innovations before the process can continue.[6]
Factors influencing the extent of dwarfing
For both herbivores and carnivores, island size, the degree of island isolation and the size of the ancestral continental species appear not to be of major direct importance to the degree of dwarfing.[4] However, when considering only the body masses of recent top herbivores and carnivores, and including data from both continental and island land masses, the body masses of the largest species in a land mass were found to scale to the size of the land mass, with slopes of about 0.5 log(body mass/kg) per log(land area/km2).[7] There were separate regression lines for endothermic top predators, ectothermic top predators, endothermic top herbivores and (on the basis of limited data) ectothermic top herbivores, such that food intake was 7 to 24-fold higher for top herbivores than for top predators, and about the same for endotherms and ectotherms of the same trophic level (this leads to ectotherms being 5 to 16 times heavier than corresponding endotherms).[7]
Examples
Non-avian dinosaurs
Recognition that insular dwarfism could apply to dinosaurs arose through the work of Ferenc Nopcsa, a Hungarian-born aristocrat, adventurer, scholar, and paleontologist. Nopcsa studied Transylvanian dinosaurs intensively, noticing that they were smaller than their cousins elsewhere in the world. For example, he unearthed six-meter-long sauropods, a group of dinosaurs which elsewhere commonly grew to 30 meters or more. Nopcsa deduced that the area where the remains were found was an island, Hațeg Island (now the Haţeg or Hatzeg basin in Romania) during the Mesozoic era.[8][9] Nopcsa's proposal of dinosaur dwarfism on Hațeg Island is today widely accepted after further research confirmed that the remains found are not from juveniles.[10]
Example | Species | Range | Timeframe | Continental relatives |
---|---|---|---|---|
Europasaurus | E. holgeri | Lower Saxony | Late Jurassic / Middle Kimmeridgian | Brachiosaurs |
Magyarosaurus | M. dacus | Hateg Island | Late Cretaceous / Maastrichtian | Rapetosaurus |
Paludititan | P. nalatzensis | Hateg Island | Late Cretaceous / Maastrichtian | Epachthosaurus |
Telmatosaurus | T. transsylvanicus | Hateg Island | Late Cretaceous | Hadrosaurids |
Tethyshadros | T. insularis | Trieste province | Late Cretaceous | Jintasaurus |
Thecodontosaurus[9] | T. antiquus | Southern England | Late Triassic / Rhaetian | Plateosaurus Lufengosaurus |
Zalmoxes[9] | Z. robustus Z. shqiperorum | Hateg Island | Late Cretaceous | Camptosaurus Rhabdodon Tenontosaurus |
In addition, the genus Balaur was initially described as a Velociraptor-sized dromaeosaurid (and in consequence a dubious example of insular dwarfism), but has been since reclassified as a secondarily flightless stem bird, closer to modern birds than Jeholornis (thus actually an example of insular gigantism).
Birds
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Cozumel curassow[11] | Crax rubra grisconi | Cozumel | Unknown | Great curassow |
Kangaroo Island emu[12] | Dromaius novaehollandiae baudinianus | Kangaroo Island, South Australia | Extinct (c. AD 1827) | Emu |
King Island emu[13] | Dromaius novaehollandiae minor | King Island, Tasmania | Extinct (AD 1822) | |
Cozumel thrasher[11] | Toxostoma gluttatum | Cozumel | Critically endangered | Typical thrashers |
Squamates
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Madagascar dwarf chameleon | Brookesia minima | Nosy Be Island, Madagascar | Endangered | Madagascar leaf chameleons |
Nosy Hara chameleon[14] | Brookesia micra | Nosy Hara Island, Madagascar | Vulnerable | |
Roxby Island tiger snake[5] | Notechis scutatus | Roxby Island, South Australia | Unknown | Tiger snake |
Tanahjampea python[15] | Python reticulatus jampeanus | Tanahjampea Island, between Sulawesi and Flores | Unknown | Reticulated python |
Mammals
Pilosans
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Pygmy three-toed sloth | Bradypus pygmaeus | Isla Escudo de Veraguas, Panama | Critically endangered | Brown-throated sloth |
Acratocnus | A. antillensis A. odontrigonus A. ye | Cuba, Hispaniola and Puerto Rico | Extinct (c. 3000 BC) | Megalonyx |
Imagocnus | I. zazae | Cuba | Extinct (Early Miocene) | |
Megalocnus | M. rodens M. zile | Cuba and Hispaniola | Extinct (c. 2700 BC) | |
Neocnus | Neocnus spp. | Cuba and Hispaniola | Extinct (c. 3000 BC) |
Proboscideans
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Cretan mammoth | Mammuthus creticus | Crete | Extinct | Mammuthus |
Channel Islands mammoth | Mammuthus exilis | Santa Rosae island | Extinct (Late Pleistocene) | Columbian mammoth |
Sardinian mammoth | Mammuthus lamarmorai | Sardinia | Extinct (Late Pleistocene) | Steppe mammoth |
Saint Paul Island woolly mammoth[16][17] | Mammuthus primigenius | Saint Paul Island, Alaska | Extinct (c. 3750 BC) | Woolly mammoth |
Siculo-Maltese elephants | Palaeoloxodon antiquus leonardi P. mnaidriensis P. melitensis P. falconeri | Sicily and Malta | Extinct | Straight-tusked elephant |
Cretan elephants | Palaeoloxodon chaniensis P. creutzburgi | Crete | Extinct | |
Cyprus dwarf elephant | Palaeoloxodon cypriotes | Cyprus | Extinct (c. 9000 BC) | |
Naxos dwarf elephant | Palaeoloxodon sp. | Naxos | Extinct | |
Rhodes and Tilos dwarf elephant | Palaeoloxodon tiliensis | Rhodes and Tilos | Extinct | |
Japanese stegodon[18] | Stegodon aurorae | Japan and Taiwan[19] | Extinct (Early Pleistocene) | Chinese Stegodon |
Larger Flores dwarf stegodon[3] | Stegodon florensis | Flores | Extinct (Late Pleistocene) | Sundaland Stegodon |
Javan dwarf stegodon[20] | Stegodon hypsilophus | Java | Extinct | |
Mindanao pygmy stegodon[21] | Stegodon mindanensis | Mindanao and Sulawesi | Extinct (Middle Pleistocene) | |
Sulawesi dwarf stegodon[20] | Stegodon sompoensis | Sulawesi | Extinct | |
Lesser Flores dwarf stegodon[3] | Stegodon sondaari | Flores | Extinct (Middle Pleistocene) | |
Sumba stegodon[22] | Stegodon sumbaensis | Sumba, Indonesia | Extinct (Middle Pleistocene) | |
Timor dwarf stegodon[20] | Stegodon timorensis | Timor | Extinct | |
Sambungmacan dwarf stegodon[20] | Stegodon sp. | Kalibeng Island (now part of Java) | Extinct (Early Pleistocene) | |
Bumiayu tetralophodon[20] | Tetralophodon bumiajuensis | Bumiayu Island (now part of Java) | Extinct (Early Pleistocene) | Tetralophodon |
Primates
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Nosy Hara dwarf lemur[23] | Cheirogaleus sp. | Nosy Hara island off Madagascar | Unknown | Dwarf lemurs |
Homo floresiensis | Flores | Extinct (Late Pleistocene) | Homo erectus | |
Modern pygmies of Flores[25] | Homo sapiens | Flores | Extant | Humans |
Early Palau modern humans (disputed)[26] | Homo sapiens | Palau | Extinct (?) | Humans |
Andamanese[27][28] | Homo sapiens | Andaman Islands | Endangered | Humans |
Carnivorans
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Honshū wolf | Canis lupus hodophilax | Japan (excluding Hokkaido) | Extinct (AD 1905) | Gray wolf |
Sardinian dhole | Cynotherium sardous | Corsica and Sardinia | Extinct | Xenocyon (?) |
Cozumel Island coati[11] | Nasua narica nelsoni | Cozumel | Critically endangered | Yucatan white-nosed coati |
Zanzibar leopard | Panthera pardus adersi | Unguja Island, Zanzibar | Critically endangered or Extinct | African leopard |
Bali tiger | Panthera tigris balica | Bali | Extinct (c. AD 1940) | Tiger |
Javan tiger | Panthera tigris sondaica | Java | Extinct (c. AD 1975) | |
Cozumel raccoon | Procyon pygmaeus | Cozumel | Critically endangered | Common raccoon |
Channel Island fox | Urocyon littoralis | Channel Islands of California | Near Threatened | Gray fox |
Cozumel fox | Urocyon sp. | Cozumel | Critically endangered or Extinct |
Non-ruminant ungulates
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Malagasy hippopotamuses | Choeropsis madagascariensis Hippopotamus lalouema H. lemerlei | Madagascar | Extinct (c. AD 1000) | Pygmy hippopotamus Common hippopotamus |
Bumiayu dwarf hippopotamus[20] | Hexaprotodon simplex | Bumiayu Island (now Java) | Extinct (Early Pleistocene) | Asian hippopotamuses |
Cretan dwarf hippopotamus | Hippopotamus creutzburgi | Crete | Extinct (Middle Pleistocene) | European hippopotamus |
Maltese dwarf hippopotamus | Hippopotamus melitensis | Malta | Extinct (Pleistocene) | European hippopotamus |
Cyprus dwarf hippopotamus | Hippopotamus minor | Cyprus | Extinct (c. 8000 BC) | |
Sicilian hippopotamus | Hippopotamus pentlandi | Sicily | Extinct (Pleistocene) | |
Cozumel collared peccary[11] | Pecari tajacu nanus | Cozumel | Unknown | Collared peccary |
Philippines rhinoceros[29] | Rhinoceros philippinensis | Luzon, Philippines | Extinct (Middle Pleistocene) | Javan rhinoceros |
Bovids
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Sicilian bison[18] | Bison priscus siciliae | Sicily | Extinct (Late Pleistocene) | Steppe bison |
Sicilian aurochs[30] | Bos primigenius siciliae[18] | Sicily | Extinct (Late Pleistocene) | Eurasian aurochs |
Cebu tamaraw | Bubalus cebuensis | Cebu, Philippines | Extinct | Wild water buffalo |
Lowland anoa | Bubalus depressicornis | Sulawesi and Buton, Indonesia | Endangered | |
Tamaraw | Bubalus mindorensis | Mindoro, Philippines | Critically endangered | |
Mountain anoa | Bubalus quarlesi | Sulawesi and Buton, Indonesia | Endangered | |
Balearic Islands cave goat | Myotragus balearicus | Majorca and Menorca | Extinct (after 3000 BC) | Gallogoral |
Dahlak Kebir gazelle[31] | Nanger soemmerringi ssp. | Dahlak Kebir island, Eritrea | Vulnerable | Soemmerring's gazelle |
Nesogoral[32] | Nesogoral spp. | Sardinia | Extinct | Gallogoral |
Cervids and relatives
Example | Binomial Name | Native Range | Status | Continental relatives |
---|---|---|---|---|
Cretan dwarf megacerine deer | Candiacervus spp. | Crete | Extinct (Pleistocene) | Praemegaceros verticornis[9] |
Ryukyu dwarf deer[33] | Cervus astylodon | Ryukyu Islands | Extinct | Sika deer (?) Cervus praenipponicus (?) |
Jersey red deer population[34] | Cervus elaphus | Jersey | Extinct (Pleistocene) | Red deer |
Corsican red deer | Cervus elaphus corsicanus | Corsica and Sardinia | Near Threatened | |
Pleistocene Sicilian deer[18] | Cervus siciliae | Sicily | Extinct (Late Pleistocene) | |
Hoplitomeryx | Hoplitomeryx spp. | Gargano Island | Extinct (Early Pliocene) | Pecorans |
Sicilian megacerine deer[18] | Megaloceros carburangelensis | Sicily | Extinct (Late Pleistocene) | Irish elk |
Key deer | Odocoileus virginianus clavium | Florida Keys | Endangered | Virginia deer |
Sardinian megacerine deer[9] | Praemegaceros cazioti | Sardinia | Extinct (c. 5500 BC) | Praemegaceros verticornis |
Svalbard reindeer | Rangifer tarandus platyrhynchus | Svalbard | Unknown | Reindeer |
Philippine deer | Rusa marianna | Philippines | Vulnerable | Sambar deer |
See also
Wikinews has related news: Bones of "small-bodied humans" found in cave |
Notes
- ↑ An example of noninsular phyletic dwarfism is the evolution of the dwarfed marmosets and tamarins among New World monkeys, culminating in the appearance of the smallest example, Cebuella pygmaea.[2]
References
- ↑ Prothero, D. R.; Sereno, P. C. (Winter 1982). "Allometry and Paleoecology of Medial Miocene Dwarf Rhinoceroses from the Texas Gulf Coastal Plain". Paleobiology. 8 (1): 16–30. JSTOR 2400564.
- ↑ Perelman, P.; et al. (2011). "A Molecular Phylogeny of Living Primates". PLOS Genetics. 7 (3): 1–17. doi:10.1371/journal.pgen.1001342. PMC 3060065. PMID 21436896.
- 1 2 3 4 5 Van Den Bergh, G. D.; Rokhus Due Awe; Morwood, M. J.; Sutikna, T.; Jatmiko; Wahyu Saptomo, E. (May 2008). "The youngest Stegodon remains in Southeast Asia from the Late Pleistocene archaeological site Liang Bua, Flores, Indonesia". Quaternary International. 182 (1): 16–48. doi:10.1016/j.quaint.2007.02.001. Retrieved 2011-11-27.
- 1 2 3 4 Raia, P.; Meiri, S. (August 2006). "The island rule in large mammals: paleontology meets ecology". Evolution. 60 (8): 1731–1742. doi:10.1111/j.0014-3820.2006.tb00516.x. Retrieved 2011-11-27.
- 1 2 Keogh, J. S.; Scott, I. A. W.; Hayes, C. (January 2005). "Rapid and repeated origin of insular gigantism and dwarfism in Australian tiger snakes". Evolution. 59 (1): 226–233. doi:10.1111/j.0014-3820.2005.tb00909.x.
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- ↑ "Dwarf dinosaur island really did exist, scientists claim". Telegraph Media Group. 2010-02-22. Retrieved 2010-02-26.
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- ↑ Dyke, G. (2011-09-20). "The Dinosaur Baron of Transylvania". Scientific American. 305 (4): 80–83. doi:10.1038/scientificamerican1011-80. PMID 22106812.
- 1 2 3 4 Cuarón, A. D.; Martínez-Morales, M. A.; McFadden, K. W.; Valenzuela, D.; Gompper, M. E. (2004). "The status of dwarf carnivores on Cozumel Island, Mexico" (PDF). Biodiversity and Conservation. Kluwer Academic Publishers. 13: 317–331. doi:10.1023/b:bioc.0000006501.80472.cc. Retrieved 2017-07-31.
- ↑ Parker S (1984) The extinct Kangaroo Island Emu, a hitherto-unrecognised species. Bulletin of the British Ornithologists' Club 104: 19–22.
- ↑ Heupink, T. H.; Huynen, L.; Lambert, D. M. (2011). "Ancient DNA Suggests Dwarf and 'Giant' Emu Are Conspecific". PLoS ONE. 6 (4): e18728. doi:10.1371/journal.pone.0018728. PMC 3073985. PMID 21494561.
- ↑ Glaw, F.; Köhler, J.; Townsend, T. M.; Vences, M. (2012-02-14). "Rivaling the World's Smallest Reptiles: Discovery of Miniaturized and Microendemic New Species of Leaf Chameleons (Brookesia) from Northern Madagascar". PLoS ONE. 7 (2): e31314. doi:10.1371/journal.pone.0031314. PMC 3279364. PMID 22348069. Retrieved 2012-02-17.
- ↑ Auliya, M.; Mausfeld, P.; Schmitz, A.; Böhme, W. (2002-04-09). "Review of the reticulated python (Python reticulatus Schneider, 1801) with the description of new subspecies from Indonesia". Naturwissenschaften. 89 (5): 201–213. doi:10.1007/s00114-002-0320-4. Retrieved 2012-04-08.
- ↑ Schirber, Michael. Surviving Extinction: Where Woolly Mammoths Endured. Live Science. Imaginova Corporation. Retrieved 2007-07-20.
- ↑ The mammoths of Wrangel Island, north of Siberia, are no longer considered dwarfs. See: Tikhonov, Alexei; Larry Agenbroad; Sergey Vartanyan (2003). Comparative analysis of the mammoth populations on Wrangel Island and the Channel Islands. DEINSEA 9: 415–420. ISSN 0923-9308
- 1 2 3 4 5 Sondaar, P. Y.; A.A.E. van der Geer (2005). "Evolution and Extinction of Plio-Pleistocene Island Ungulates" (PDF). International Journal of the French Quaternary Association. 2: 241–256. Retrieved 2017-07-31.
- ↑ http://www.rhinoresourcecenter.com/pdf_files/129/1291330178.pdf
- 1 2 3 4 5 6 Aziz, F.; van den Bergh, G. D. (September 25, 1995). "A dwarf Stegodon from Sambungmacan (Central Java, Indonesia)" (PDF). Proc. Kon. Ned. Akad. v. Wetensch. 98 (3): 229–241. Retrieved 2017-07-31.
- ↑ Zaim, Y. (20 August 2010). "Geological Evidence for the Earliest Appearance of Hominins in Indonesia". In Fleagle, J. G; Shea, J. J.; Grine, F. E.; Baden, A. L.; Leakey, R. E. Out of Africa I: The First Hominin Colonization of Eurasia. Springer Science & Business Media. p. 106. ISBN 978-90-481-9036-2. OCLC 668096676.
- ↑ http://ro.uow.edu.au/cgi/viewcontent.cgi?article=3055&context=smhpapers
- ↑ http://www.bbc.com/earth/story/20150812-tiny-lemur-may-be-worlds-rarest
- ↑ Scientist to study Hobbit morphing, abc.net.au
- ↑ Tucci, S. et al. (2018-08-03). "Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia". Science. 361 (6401): 511–516. doi:10.1126/science.aar8486.
- ↑ "Ancient Small People on Palau Not Dwarfs, Study Says". National Geographic News. August 27, 2008.
- ↑ Gibbons, A. (2018). "Island living can shrink humans". Science. doi:10.1126/science.aau9750.
- ↑ Mondal, M.; Casals, F.; Xu, T.; Dall'Olio, G. M.; Pybus, M.; Netea, M. G.; Comas, D.; Laayouni, H.; Li, Q.; Majumder, P. P.; Bertranpetit, J. (2016). "Genomic analysis of Andamanese provides insights into ancient human migration into Asia and adaptation". Nature Genetics. 48 (9): 1066–1070. doi:10.1038/ng.3621.
- ↑ Renema, Willem (2007). Biogeography, Time and Place: Distributions, Barriers and Islands. Springer Science & Business Media. p. 334. ISBN 978-1-4020-6374-9. OCLC 228153573.
- ↑ van Vuure, Cis (2005). Retracing the Aurochs: History, Morphology and Ecology of an Extinct Wild Ox. Coronet Books Incorporated. ISBN 978-954-642-235-4. OCLC 472741798.
- ↑ Chiozzi, G.; Bardelli, G.; Ricci, M.; De Marchi, G.; Cardini, A. (2014). "Just another island dwarf? Phenotypic distinctiveness in the poorly known Soemmerring's Gazelle, Nanger soemmerringii (Cetartiodactyla: Bovidae), of Dahlak Kebir Island". Biological Journal of the Linnean Society. 111 (3): 603–620. doi:10.1111/bij.12239.
- ↑ van der Geer, A.; Lyras, G; de Vos, J.; Dermitzakis, M. (14 February 2011). "Sardinia and Corsica". Evolution of Island Mammals: Adaptation and Extinction of Placental Mammals on Islands. John Wiley & Sons. ISBN 978-1-4443-9128-2. OCLC 894698082.
- ↑ Kaifu, Y.; Fujita, M.; Yoneda, M.; Yamasaki, S. (15 February 2015). "Pleistocene Seafaring and Colonization of the Ryukyu Islands, Southwestern Japan". In Kaifu, Y.; Izuho, M.; Goebel, T.; Sato, H.; Ono, A. Emergence and Diversity of Modern Human Behavior in Paleolithic Asia. Texas A&M University Press. ISBN 978-1-62349-277-9. OCLC 985023261.
- ↑ Lister, A. M. (1989-11-30). "Rapid dwarfing of red deer on Jersey in the Last Interglacial". Nature. 342 (6249): 539–542. doi:10.1038/342539a0. PMID 2685610. Retrieved 2011-02-28.