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Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area.
Knowledge of spatial variation in the numbers and types of organisms is as vital to us today as it was to our early human ancestors, as we adapt to heterogeneous but geographically predictable environments. Biogeography is an integrative field of inquiry that unites concepts and information from ecology, evolutionary biology, geology, and physical geography.
Modern biogeographic research combines information and ideas from many fields, from the physiological and ecological constraints on organismal dispersal to geological and climatological phenomena operating at global spatial scales and evolutionary time frames.
The patterns of species distribution across geographical areas can usually be explained through a combination of historical factors such as: speciation; extinction; continental drift; glaciation, and associated variations in sea level, river routes, and habitat; and river capture; in combination with the geographic constraints of landmass areas and isolation; and the available ecosystem energy supplies.
Over periods of ecological changes, biogeography includes the study of plant and animal species in: their past and/or present living refugium habitat; their interim living sites; and/or their survival locales. As writer David Quammen put it, "...biogeography does more than ask Which species? and Where. It also asks Why? and, what is sometimes more crucial, Why not?."
Modern biogeography often employs the use of Geographic Information Systems (GIS), to understand the factors affecting organism distribution, and to predict future trends in organism distribution. Often mathematical models and GIS are employed to solve ecological problems that have a spatial aspect to them.
Biogeography is most keenly observed on the world's islands. These habitats are often much more manageable areas of study because they are more condensed than larger ecosystems on the mainland. Islands are also ideal locations because they allow scientists to look at habitats that new species have only recently colonized and can observe how they disperse throughout the island, the success they achieve in these places, and they can then apply this information to similar mainland habitats. Islands are very diverse in their biomes, ranging from the tropical to arctic climates. This diversity in habitat allows for a wider range of species study in different parts of the world.
One scientist who recognized the importance of these geographic locations was Charles Darwin, who remarked in his journal "The Zoology of Archipelagoes will be well worth examination". Two chapters in On the Origin of Species were devoted to geographical distribution.
The scientific theory of biogeography grows out of the work of Alexander von Humboldt (1769–1859), Hewett Cottrell Watson (1804–1881), Alphonse de Candolle (1806–1893), Alfred Russel Wallace (1823–1913), Philip Lutley Sclater (1829–1913) and other biologists and explorers.
Wallace studied the distribution of flora and fauna in the Amazon Basin and the Malay Archipelago in the mid-19th century. Wallace and Sclater saw biogeography as a source of support for the theory of evolution. Key findings, such as the sharp difference in fauna either side of the Wallace Line, and the sharp difference that existed between North and South America prior to their relatively recent faunal interchange, can only be understood in this light. Otherwise, the field of biogeography would be seen as a purely descriptive one.
The publication of The Theory of Island Biogeography by Robert MacArthur and E.O. Wilson in 1967 showed that the species richness of an area could be predicted in terms of such factors as habitat area, immigration rate and extinction rate.
This added to the long-standing interest in island biogeography. The application of island biogeography theory to habitat fragments spurred the development of the fields of conservation biology and landscape ecology.
Classic biogeography has been expanded by the development of molecular systematics, creating a new discipline known as phylogeography. This development allowed scientists to test theories about the origin and dispersal of populations, such as island endemics. For example, while classic biogeographers were able to speculate about the origins of species in the Hawaiian Islands, phylogeography allows them to test theories of relatedness between these populations and putative source populations in Asia and North America.
Biogeography continues as a point of study for many life sciences and geography students worldwide however may be under different broader titles within institutions such as ecology or evolutionary biology.
Paleobiogeography goes one step further to include paleogeographic data and considerations of plate tectonics. Using molecular analyses and corroborated by fossils, it has been possible to demonstrate that perching birds evolved first in the region of Australia or the adjacent Antarctic (which at that time lay somewhat further north and had a temperate climate). From there, they spread to the other Gondwanan continents and Southeast Asia - the part of Laurasia then closest to their origin of dispersal – in the late Paleogene, before achieving a global distribution in the early Neogene. Not knowing the fact that at the time of dispersal, the Indian Ocean was much narrower than it is today, and that South America was closer to the Antarctic, one would be hard pressed to explain the presence of many "ancient" lineages of perching birds in Africa, as well as the mainly South American distribution of the suboscines.
Paleobiogeography also helps constrain hypotheses on the timing of biogeographic events such as vicariance and geodispersal, and provides unique information on the formation of regional biotas. For example, data from species-level phylogenetic and biogeographic studies tell us that the Amazonian fish fauna accumulated incrementally over a period of tens of millions of years, principally by means of allopatric speciation, and in an arena extending over most of the area of tropical South America (Albert & Reis 2011). In other words, unlike some of the well-known insular faunas (Galapagos finches, Hawaiian drosophilid flies, African rift lake cichlids), the species-rich Amazonian ichthyofauna is not the result of recent adaptive radiations.
For freshwater organisms, landscapes are divided naturally into discrete drainage basins by watersheds, episodically isolated and reunited by erosional processes. In regions like the Amazon Basin with an exceptionally low (flat) topographic relief, the many waterways have had a highly reticulated history over geological time. In such a context stream capture is an important factor affecting the evolution and distribution of freshwater organisms. Stream capture occurs when an upstream portion of one river drainage is diverted to the downstream portion of an adjacent basin. This can happen as a result of tectonic uplift (or subsidence), natural damming created by a landslide, or headward or lateral erosion of the watershed between adjacent basins.
Some fundamental concepts in biogeography include:
- evolution – change in genetic composition of a population
- extinction – disappearance of a species
- dispersal – movement of populations away from their point of origin, related to migration
- endemic areas
- geodispersal – the erosion of barriers to biotic dispersal and gene flow, that permit range expansion and the merging of previously isolated biotas
- range and distribution
- vicariance – the formation of barriers to biotic dispersal and gene flow, that tend to subdivide species and biotas, leading to speciation and extinction
- Bibliography of biology
- Biome (biogeographic realm)
- Continental drift
- Distance decay
- Charles Darwin
- Ecological land classification
- Landscape ecology
- Sky island
- Systematic and evolutionary biogeography association
- Tectonic plates
- Miklos Udvardy
- Alfred Russel Wallace
- Max Carl Wilhelm Weber
Notes and references
- Martiny JBH et al. Microbial biogeography: putting microorganisms on the map Nature: FEBRUARY 2006 | VOLUME 4
- Quammen, David (1996). Song of the Dodo: Island Biogeography in an Age of Extinctions. New York: Scribner. p. 17. ISBN 978-0-684-82712-4.
- Cavalcanti, Mauro. (2009). Biogeography and GIS. http://digitaltaxonomy.infobio.net/?Software:Biogeography_and_GIS
- Whittaker, R. (1998). Island Biogeography: Ecology, Evolution, and Conservation. New York: Oxford University Press. ISBN 0-19-850021-1.
- MacArthur R.H.; Wilson E.O. 1967. The theory of island biogeography. 
- von Humboldt 1805. Essai sur la geographie des plantes; accompagne d'un tableau physique des régions equinoxiales. Levrault, Paris.
- Watson H.C. 1847–1859. Cybele Britannica: or British plants and their geographical relations. Longman, London.
- de Candolle, Alphonse 1855. Géographie botanique raisonnée &c. Masson, Paris.
- Wallace A.R. 1876. . The geographical distribution of animals. Macmillan, London.
- Browne, Janet (1983). The secular ark: studies in the history of biogeography. New Haven: Yale University Press. ISBN 0-300-02460-6.
- This work expanded their 1963 paper on the same topic.
- This applies to British and American academics; landscape ecology has a distinct genesis among European academics.
- Jønsson, Knud A. & Fjeldså, Jon (2006). Determining biogeographical patterns of dispersal and diversification in oscine passerine birds in Australia, Southeast Asia and Africa. Journal of Biogeography 33(7): 1155–1165. doi:10.1111/j.1365-2699.2006.01507.x (HTML abstract)
- Lovejoy, N. R., S. C. Willis, & J. S. Albert (2010) Molecular signatures of Neogene biogeographic events in the Amazon fish fauna. Pp. 405-417 in Amazonia, Landscape and Species Evolution, 1st edition (Hoorn, C. M. and Wesselingh, F.P., eds.). London: Blackwell Publishing.
- Albert, J. S., & R. E. Reis (2011). Historical Biogeography of Neotropical Freshwater Fishes. University of California Press, Berkeley. 424 pp. 
- Albert, J.S., & W.G.R. Crampton (2010). The geography and ecology of diversification in Neotropical freshwaters. Nature Education 1(10): 3.
- Dansereau, Pierre (1957). Biogeography: An Ecological Perspective. New York City: Ronald Press Company. ISBN 0-8260-2330-4.
- Cox C.B. and Moore P.D. 2010. Biogeography: an ecological and evolutionary approach. 8th ed, Wiley. ISBN 0-470-63794-3 (standard text)
- MacArthur, Robert H. (1972). Geographic Ecology. New York: Harper & Row.
- McCarthy, Dennis (2009). Here be dragons : how the study of animal and plant distributions revolutionized our views of life and Earth. Oxford & New York: Oxford University Press. ISBN 978-0-19-954246-8.
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