Oceanic dispersal is a type of biological dispersal that occurs when terrestrial organisms transfer from one land mass to another by way of a sea crossing. Often this occurs via large rafts of floating vegetation such as are sometimes seen floating down major rivers in the tropics and washing out to sea, occasionally with animals trapped on them. Dispersal via such a raft is sometimes referred to as a "rafting event".
Colonization of land masses by plants can also occur via long-distance oceanic dispersal of floating seeds.
Rafting has played an important role in the colonization of isolated land masses by mammals. Prominent examples include Madagascar, which has been isolated for ~120 million years (Ma), and South America, which was isolated for much of the Cenozoic. Both land masses, for example, appear to have received their primates by this mechanism. According to genetic evidence, the common ancestor of the lemurs of Madagascar appears to have crossed the Mozambique Channel by rafting between 50 and 60 Ma ago. Likewise, the New World monkeys are thought to have originated in Africa and rafted to South America by the Oligocene, when the continents were much closer than they are today. Madagascar also appears to have received its tenrecs (25–42 Ma ago), nesomyid rodents (20–24 Ma ago) and euplerid carnivorans (19–26 Ma ago) by this route and South America its caviomorph rodents (over 30 Ma ago). Simian primates (ancestral to monkeys) and hystricognath rodents (ancestral to caviomorphs) are believed to have previously rafted from Asia to Africa about 40 Ma ago.
Among reptiles, several iguanid species in the South Pacific have been hypothesized to be descended from iguanas that rafted 10,000 kilometres (6,200 mi) from Central or South America (an alternative theory involves dispersal of a putative now-extinct iguana lineage from Australia or Asia). Similarly, a number of clades of American geckos seem to have rafted over from Africa during both the Paleogene and Neogene. Skinks of the related genera Mabuya and Trachylepis also apparently both floated across the Atlantic from Africa to South America and Fernando de Noronha, respectively, during the last 9 Ma. Skinks from the same group have also rafted from Africa to Cape Verde, Madagascar, the Seychelles, the Comoros and Socotra. (Among lizards, skinks and geckos seem especially capable of surviving long transoceanic journeys.) Surprisingly, even burrowing amphisbaenians and blind snakes appear to have rafted from Africa to South America.
Colonization of groups of islands can occur by an iterative rafting process sometimes called island hopping. Such a process appears to have played a role, for example, in the colonization of the Caribbean by mammals of South American origin (including caviomorphs and monkeys).
A remarkable example of iterative rafting has been proposed for spiders of the genus Amaurobioides. Members of this genus inhabit coastal sites and build silken cells which they seal at high tide; however, they do not balloon. DNA sequence analysis suggests that ancestors of the genus dispersed from southern South America to South Africa about 10 million years (Ma) ago, where the most basal clade is found; subsequent rafting events then took the genus eastward with the Antarctic Circumpolar Current to Australia, then to New Zealand and finally to Chile by about 2 Ma ago. Another example among spiders is the species Moggridgea rainbowi, the only Australian member of a genus otherwise endemic to Africa, with a divergence date of 2 to 16 Ma ago.
However, oceanic dispersal of terrestrial species may not always take the form of rafting; in some cases, swimming or simply floating may suffice. Tortoises of the genus Chelonoidis arrived in South America from Africa in the Oligocene; they were probably aided by their ability to float with their heads up, and to survive up to six months without food or fresh water. South American tortoises then went on to colonize the West Indies and Galápagos Islands. The dispersal of anthracotheres from Asia to Africa about 40 Ma ago, and the much more recent dispersal of hippos (relatives and probably descendants of anthracotheres) from Africa to Madagascar may have occurred by floating or swimming.
The first documented example of colonization of a land mass by rafting occurred in the aftermath of hurricanes Luis and Marilyn in the Caribbean in 1995. A raft of uprooted trees carrying fifteen or more green iguanas was observed by fishermen landing on the east side of Anguilla – an island where they had never before been recorded. The iguanas had apparently been caught on the trees and rafted two hundred miles across the ocean from Guadeloupe, where they are indigenous. Examination of the weather patterns and ocean currents indicated that they had probably spent three weeks at sea before landfall. This colony began breeding on the new island within two years of its arrival.
The advent of human civilization has created opportunities for organisms to raft on floating artifacts, which may be more durable than natural floating objects. This phenomenon was noted following the 2011 Tōhoku tsunami in Japan, with about 300 species found to have been carried on debris by the North Pacific Current to the west coast of North America (although no colonizations have been detected thus far).
- Mittermeier, R.A.; et al. (2006). Lemurs of Madagascar (2nd ed.). Conservation International. pp. 24–26. ISBN 1-881173-88-7.
- Won, H.; Renner, S. S. (2006). "Dating dispersal and radiation in the gymnosperm Gnetum (Gnetales) – clock calibration when outgroup relationships are uncertain". Systematic Biology. 55 (4): 610–622. PMID 16969937. doi:10.1080/10635150600812619.
- Roos, Christian; Schmitz, Jürgen; Zischler, Hans (July 2004). "Primate jumping genes elucidate strepsirrhine phylogeny" (PDF). PNAS. 101 (29): 10650–10654. Bibcode:2004PNAS..10110650R. PMC . PMID 15249661. doi:10.1073/pnas.0403852101.
- Sellers, Bill (2000-10-20). "Primate Evolution" (PDF). University of Edinburgh. pp. 13–17. Retrieved 2008-10-23.
- Ali, J. R.; Huber, M. (2010-01-20). "Mammalian biodiversity on Madagascar controlled by ocean currents". Nature. Nature Publishing Group. 463 (4 Feb. 2010): 653–656. Bibcode:2010Natur.463..653A. PMID 20090678. doi:10.1038/nature08706. Retrieved 2010-01-20.
- Flynn, J. J.; Wyss, A. R. (1998). "Recent advances in South American mammalian paleontology". Trends in Ecology and Evolution. 13 (11): 449–454. PMID 21238387. doi:10.1016/S0169-5347(98)01457-8.
- Flynn, John J.; Wyss, André R.; Charrier, Reynaldo (2007). "South America's Missing Mammals". Scientific American (May): 68–75.
- Chaimanee, Y.; Chavasseau, O.; Beard, K. C.; Kyaw, A. A.; Soe, A. N.; Sein, C.; Lazzari, V.; Marivaux, L.; Marandat, B.; Swe, M.; Rugbumrung, M.; Lwin, T.; Valentin, X.; Zin-Maung-Maung-Thein; Jaeger, J. -J. (2012). "Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa". Proceedings of the National Academy of Sciences. 109 (26): 10293. PMC . PMID 22665790. doi:10.1073/pnas.1200644109.
- Gibbons, J. R. H. (Jul 31, 1981). "The Biogeography of Brachylophus (Iguanidae) including the Description of a New Species, B. vitiensis, from Fiji". Journal of Herpetology. Society for the Study of Amphibians and Reptiles. 15 (3): 255–273. JSTOR 1563429. doi:10.2307/1563429.
- Noonan, B.P.; Sites, J. W., Jr. (2009-11-24). "Tracing the origins of iguanid lizards and boine snakes of the Pacific". The American Naturalist. University of Chicago Press. 175 (1): 61–72. PMID 19929634. doi:10.1086/648607.
- Gamble, T.; Bauer, A. M.; Colli, G. R.; Greenbaum, E.; Jackman, T. R.; Vitt, L. J.; Simons, A. M. (2010-12-03). "Coming to America: Multiple origins of New World geckos" (PDF). Journal of Evolutionary Biology. 24 (2): 231–244. PMC . PMID 21126276. doi:10.1111/j.1420-9101.2010.02184.x.
- Carranza, S.; Arnold, N. E. (2003-08-05). "Investigating the origin of transoceanic distributions: mtDNA shows Mabuya lizards (Reptilia, Scincidae) crossed the Atlantic twice". Systematics and Biodiversity. Cambridge University Press. 1 (2): 275–282. doi:10.1017/S1477200003001099. Retrieved 2008-04-04.
- Vidal, N.; Azvolinsky, A.; Cruaud, C.; Hedges, S. B. (2007-12-11). "Origin of tropical American burrowing reptiles by transatlantic rafting". Biology Letters. 4 (1): 115–118. PMC . PMID 18077239. doi:10.1098/rsbl.2007.0531.
- Vidal, N.; Marin, J.; Morini, M.; Donnellan, S.; Branch, W. R.; Thomas, R.; Vences, M.; Wynn, A.; Cruaud, C.; Hedges, S. B. (2010-03-31). "Blindsnake evolutionary tree reveals long history on Gondwana". Biology Letters. 6 (4): 558–561. PMC . PMID 20356885. doi:10.1098/rsbl.2010.0220.
- Mayr, G.; Alvarenga, H.; Mourer-Chauviré, C. C. (2011-10-01). "Out of Africa: Fossils shed light on the origin of the hoatzin, an iconic Neotropic bird". Naturwissenschaften. 98 (11): 961–966. PMID 21964974. doi:10.1007/s00114-011-0849-1.
- Hedges, S. Blair (2006-08-23). "Paleogeography of the Antilles and Origin of West Indian Terrestrial Vertebrates1". Annals of the Missouri Botanical Garden. 93 (2): 231–244. doi:10.3417/0026-6493(2006)93[231:POTAAO]2.0.CO;2.
- Kukso, F. (2016-11-08). "Seafaring Spiders Made It around the World—in 8 Million Years". Scientific American. Retrieved 2016-11-10.
- Kuntner, M.; Ceccarelli, F. S.; Opell, B. D.; Haddad, C. R.; Raven, Robert J.; Soto, E. M.; Ramírez, M. J. (2016-10-12). "Around the World in Eight Million Years: Historical Biogeography and Evolution of the Spray Zone Spider Amaurobioides (Araneae: Anyphaenidae)". PLOS ONE. 11 (10): e0163740. PMC . PMID 27732621. doi:10.1371/journal.pone.0163740.
- Kuntner, M.; Harrison, S. E.; Harvey, M. S.; Cooper, S. J. B.; Austin, A. D.; Rix, M. G. (2017). "Across the Indian Ocean: A remarkable example of trans-oceanic dispersal in an austral mygalomorph spider". PLOS ONE. 12 (8): e0180139. doi:10.1371/journal.pone.0180139.
- Le, M.; Raxworthy, C. J.; McCord, W. P.; Mertz, L. (2006-05-05). "A molecular phylogeny of tortoises (Testudines: Testudinidae) based on mitochondrial and nuclear genes". Molecular Phylogenetics and Evolution. 40 (2): 517–531. PMID 16678445. doi:10.1016/j.ympev.2006.03.003.
- Lawrence, E. (1998-10-15). "Iguanas ride the waves". Nature. doi:10.1038/news981015-3.
- Censky, E. J.; Hodge, K.; Dudley, J. (1998-10-08). "Over-water dispersal of lizards due to hurricanes". Nature. 395 (6702): 556. doi:10.1038/26886.
- Yoon, C. K. (1998-10-08). "Hapless iguanas float away and voyage grips biologists". The New York Times.
- Chown, S. L. (2017). "Tsunami debris spells trouble". Science. 357 (6358): 1356–1356. doi:10.1126/science.aao5677.
- Carlton, J. T.; Chapman, J. W.; Geller, J. B.; Miller, J. A.; Carlton, D. A.; McCuller, M. I.; Treneman, N. C.; Steves, B. P.; Ruiz, G. M. (2017). "Tsunami-driven rafting: Transoceanic species dispersal and implications for marine biogeography". Science. 357 (6358): 1402–1406. doi:10.1126/science.aao1498.