Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time . Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude , elevation , isolation and habitat area . Phytogeography is the branch of biogeography that studies the distribution of plants. Zoogeography is the branch that studies distribution of animals. Mycogeography is the branch that studies distribution of fungi, such as mushrooms .
68-735: The Macaronesian Biogeographic Region is a biogeographic region, as defined by the European Environment Agency , that covers the Azores , the Canary Islands , and Madeira . The name comes from the group of four archipelagos collectively known as Macaronesia that also include Cape Verde , which is not included in the European region. The Macaronesian Biogeographic Region includes the Portuguese archipelagos of
136-523: A refugium (plural: refugia ) is a location which supports an isolated or relict population of a once more widespread species. This isolation ( allopatry ) can be due to climatic changes, geography, or human activities such as deforestation and overhunting. Present examples of refugial animal species are the mountain gorilla , isolated to specific mountains in central Africa, and the Australian sea lion , isolated to specific breeding beaches along
204-476: A combination of historical factors such as: speciation , extinction , continental drift , and glaciation . Through observing the geographic distribution of species, we can see associated variations in sea level , river routes, habitat, and river capture . Additionally, this science considers the geographic constraints of landmass areas and isolation, as well as the available ecosystem energy supplies. Over periods of ecological changes, biogeography includes
272-421: A global scale. GIS can show certain processes on the earth's surface like whale locations, sea surface temperatures , and bathymetry. Current scientists also use coral reefs to delve into the history of biogeography through the fossilized reefs. Two global information systems are either dedicated to, or have strong focus on, biogeography (in the form of the spatial location of observations of organisms), namely
340-419: A great impact on Charles Darwin , who was inspired to consider species adaptations and evolution after learning about botanical geography. De Candolle was the first to describe the differences between the small-scale and large-scale distribution patterns of organisms around the globe. Several additional scientists contributed new theories to further develop the concept of biogeography. Charles Lyell developed
408-492: A measure of geodiversity. Because geodiversity has been shown to be correlated with biodiversity, even as species move in response to climate change, protected areas with high geodiversity may continue to protect biodiversity as niches get filled by the influx of species from neighboring areas. Highly geodiverse protected areas may also allow for the movement of species within the area from one land facet or elevation to another. Conservation scientists, however, emphasize that
476-419: A meteor strike, and global, multiyear effects occur. The sweepstake-winning species happens to already be living in a fortunate site, and their environment is rendered even more advantageous, as opposed to the "losing" species, which immediately fails to reproduce. Ecological understanding and geographic identification of climate refugia that remained significant strongholds for plant and animal survival during
544-413: A number of methods have been developed to produce arguably more complete "predictive" or "modelled" distributions for species based on their associated environmental or other preferences (such as availability of food or other habitat requirements); this approach is known as either Environmental niche modelling (ENM) or Species distribution modelling (SDM). Depending on the reliability of the source data and
612-987: A result of tectonic uplift (or subsidence ), natural damming created by a landslide , or headward or lateral erosion of the watershed between adjacent basins. Biogeography is a synthetic science, related to geography , biology , soil science , geology , climatology , ecology and evolution . Some fundamental concepts in biogeography include: The study of comparative biogeography can follow two main lines of investigation: There are many types of biogeographic units used in biogeographic regionalisation schemes, as there are many criteria ( species composition , physiognomy , ecological aspects) and hierarchization schemes: biogeographic realms (ecozones), bioregions ( sensu stricto ), ecoregions , zoogeographical regions , floristic regions , vegetation types, biomes , etc. The terms biogeographic unit, biogeographic area can be used for these categories, regardless of rank. In 2008, an International Code of Area Nomenclature
680-553: A species inhabits during the period of a glacial/interglacial cycle that represents the species' maximum contraction in geographical range," and "areas where local populations of a species can persist through periods of unfavorable regional climate." In systematic conservation planning , the term refugium has been used to define areas that could be used in protected area development to protect species from climate change . The term has been used alternatively to refer to areas with stable habitats or stable climates. More specifically,
748-614: A volcanic origin, complex landscape and gentle climate, and have rich biodiversity. Biogeography 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 , taxonomy , geology , physical geography , palaeontology , and climatology . Modern biogeographic research combines information and ideas from many fields, from
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#1732772163032816-492: A whole suite of predictor variables for biogeographic analysis, including satellite imaging and processing of the Earth. Two main types of satellite imaging that are important within modern biogeography are Global Production Efficiency Model (GLO-PEM) and Geographic Information Systems (GIS). GLO-PEM uses satellite-imaging gives "repetitive, spatially contiguous, and time specific observations of vegetation". These observations are on
884-424: Is an alternate view than that of Linnaeus. Buffon's law eventually became a principle of biogeography by explaining how similar environments were habitats for comparable types of organisms. Buffon also studied fossils which led him to believe that the Earth was over tens of thousands of years old, and that humans had not lived there long in comparison to the age of the Earth. Following the period of exploration came
952-404: Is in the geological similarities between varying locations around the globe, the geographic distribution of some fossils (including the mesosaurs ) on various continents, and the jigsaw puzzle shape of the landmasses on Earth. Though Wegener did not know the mechanism of this concept of Continental Drift, this contribution to the study of biogeography was significant in the way that it shed light on
1020-473: Is on how the environment and humans affect the distribution of species as well as other manifestations of Life such as species or genetic diversity. Biogeography is being applied to biodiversity conservation and planning, projecting global environmental changes on species and biomes, projecting the spread of infectious diseases, invasive species, and for supporting planning for the establishment of crops. Technological evolving and advances have allowed for generating
1088-614: The Age of Enlightenment in Europe, which attempted to explain the patterns of biodiversity observed by Buffon and Linnaeus. At the birth of the 19th century, Alexander von Humboldt, known as the "founder of plant geography", developed the concept of physique generale to demonstrate the unity of science and how species fit together. As one of the first to contribute empirical data to the science of biogeography through his travel as an explorer, he observed differences in climate and vegetation. The Earth
1156-713: The Global Biodiversity Information Facility (GBIF: 2.57 billion species occurrence records reported as at August 2023) and, for marine species only, the Ocean Biodiversity Information System (OBIS, originally the Ocean Biogeographic Information System : 116 million species occurrence records reported as at August 2023), while at a national scale, similar compilations of species occurrence records also exist such as
1224-550: The Holocene ) was apparently limited or precluded by topographic , streamflow , or habitat barriers —or by the extinction of coevolved animal dispersers . The concern is that ongoing warming trends will expose them to extirpation or extinction in the decades ahead. In anthropology , refugia often refers specifically to Last Glacial Maximum refugia , where some ancestral human populations may have been forced back to glacial refugia (similar small isolated pockets on
1292-552: The Klamath-Siskiyou Ecoregion found that, in addition to old-growth forest, the northern aspects of hillslopes and deep gorges would provide relatively cool areas for wildlife and seeps or bogs surrounded by mature and old-growth forests would continue to supply moisture even as water availability decreases. Beginning in 2010 the concept of geodiversity (a term used previously in efforts to preserve scientifically important geological features) entered into
1360-542: The Last Glacial Maximum ) in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover . Glacial refugia, where human populations found refuge during the last glacial period, may have played a crucial role in shaping the emergence and diversification of the language families that exist in the world today. More recently, refugia has been used to refer to areas that could offer relative climate stability in
1428-411: The southern hemisphere .) Each site becomes a refugium, one as a "cold-surviving refugium" and the other as a "hot-surviving refugium". Canyons with deep hidden areas (the opposite of hillsides, mountains, mesas, etc. or other exposed areas) lead to these separate types of refugia. A concept not often referenced is that of "sweepstakes colonization": when a dramatic ecological event occurs, for example
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#17327721630321496-567: The "living fossil" of a marine dinoflagellate called Dapsilidinium pastielsii , currently found in the Indo-Pacific Warm Pool only. For plants, anthropogenic climate change propels scientific interest in identifying refugial species that were isolated into small or disjunct ranges during glacial episodes of the Pleistocene , yet whose ability to expand their ranges during the warmth of interglacial periods (such as
1564-479: The 36 volume Histoire Naturelle, générale et particulière , in which he argued that varying geographical regions would have different forms of life. This was inspired by his observations comparing the Old and New World, as he determined distinct variations of species from the two regions. Buffon believed there was a single species creation event, and that different regions of the world were homes for varying species, which
1632-509: The Amazon basin, Orinoco basin, and Guianas ) 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
1700-963: The Azores and Madeira, and the Spanish Canary Islands. The Natura 2000 list of sites of Community importance for the region was the first such list to be adopted, in December 2001. It contained 208 sites covering over 5,000 square kilometres (1,900 sq mi) of land and sea. The list is updated every year. As of 14 December 2018 it contained 224 entries ranging from ES0000041 Ojeda, Inagua y Pajonales, 3,527.6 hectares (8,717 acres) at 27°56′38″N 15°41′55″W / 27.9438°N 15.6985°W / 27.9438; -15.6985 to PTTER0018 Costa das Quatro Ribeiras — Ilha da Terceira, 267.63 hectares (661.3 acres) at 38°48′N 27°13′W / 38.80°N 27.21°W / 38.80; -27.21 . The archipelagos all have
1768-597: The Gómez Farias Region, Tamaulipas, Mexico , which has been described as "ground-breaking" and "a classic treatise in historical biogeography". Martin applied several disciplines including ecology , botany , climatology , geology , and Pleistocene dispersal routes to examine the herpetofauna of a relatively small and largely undisturbed area, but ecologically complex, situated on the threshold of temperate – tropical (nearctic and neotropical) regions, including semiarid lowlands at 70 meters elevation and
1836-619: 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
1904-452: The Origin of Species were devoted to geographical distribution. The first discoveries that contributed to the development of biogeography as a science began in the mid-18th century, as Europeans explored the world and described the biodiversity of life. During the 18th century most views on the world were shaped around religion and for many natural theologists, the bible. Carl Linnaeus , in
1972-482: The Theory of Continental Drift in 1912, though it was not widely accepted until the 1960s. This theory was revolutionary because it changed the way that everyone thought about species and their distribution around the globe. The theory explained how continents were formerly joined in one large landmass, Pangea , and slowly drifted apart due to the movement of the plates below Earth's surface. The evidence for this theory
2040-603: The Theory of Uniformitarianism after studying fossils. This theory explained how the world was not created by one sole catastrophic event, but instead from numerous creation events and locations. Uniformitarianism also introduced the idea that the Earth was actually significantly older than was previously accepted. Using this knowledge, Lyell concluded that it was possible for species to go extinct. Since he noted that Earth's climate changes, he realized that species distribution must also change accordingly. Lyell argued that climate changes complemented vegetation changes, thus connecting
2108-639: The U.K. National Biodiversity Network , the Atlas of Living Australia , and many others. In the case of the oceans, in 2017 Costello et al. analyzed the distribution of 65,000 species of marine animals and plants as then documented in OBIS, and used the results to distinguish 30 distinct marine realms, split between continental-shelf and offshore deep-sea areas. Since it is self evident that compilations of species occurrence records cannot cover with any completeness, areas that have received either limited or no sampling,
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2176-414: The anticipated effects of climate change can also be used to show potential changes in species distributions that may occur in the future based on such scenarios. 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
2244-540: The area may have been a refugium. Moreover, the current distribution of species with narrow ecological requirements tend to be associated with the spatial position of glacial refugia. One can provide a simple explanation of refugia involving core temperatures and exposure to sunlight. In the northern hemisphere , north-facing sites on hills or mountains, and places at higher elevations count as cold sites . The reverse are sun- or heat-exposed, lower-elevation, south-facing sites: hot sites . (The opposite directions apply in
2312-421: The biotic and abiotic features of the Earth in his book, Cosmos . Augustin de Candolle contributed to the field of biogeography as he observed species competition and the several differences that influenced the discovery of the diversity of life. He was a Swiss botanist and created the first Laws of Botanical Nomenclature in his work, Prodromus. He discussed plant distribution and his theories eventually had
2380-614: The coast are predicted to experience overall less warming than areas toward the interior of the US State of Washington . Other research has found that old-growth forests are particularly insulated from climatic changes due to evaporative cooling effects from evapotranspiration and their ability to retain moisture. The same study found that such effects in the Pacific Northwest would create important refugia for bird species. A review of refugia-focused conservation strategy in
2448-475: The development of biogeography as a science. The scientific theory of biogeography grows out of the work of Alexander von Humboldt (1769–1859), Francisco Jose de Caldas (1768–1816), 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. The patterns of species distribution across geographical areas can usually be explained through
2516-420: 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
2584-504: The environmental surroundings to varying species. This largely influenced Charles Darwin in his development of the theory of evolution. Charles Darwin was a natural theologist who studied around the world, and most importantly in the Galapagos Islands . Darwin introduced the idea of natural selection, as he theorized against previously accepted ideas that species were static or unchanging. His contributions to biogeography and
2652-597: The extremes of past cooling and warming episodes largely pertain to the Quaternary glaciation cycles during the past several million years, especially in the Northern Hemisphere . A number of defining characteristics of past refugia are prevalent, including "an area where distinct genetic lineages have persisted through a series of Tertiary or Quaternary climate fluctuations owing to special, buffering environmental characteristics", "a geographical region that
2720-483: The face of modern climate change . As an example of a locale refugia study, Jürgen Haffer first proposed the concept of refugia to explain the biological diversity of bird populations in the Amazonian river basin . Haffer suggested that climatic change in the late Pleistocene led to reduced reservoirs of habitable forests in which populations become allopatric. Over time, that led to speciation : populations of
2788-659: The face of the continental ice sheets ) during the last glacial period . Going from west to east, suggested examples include the Franco-Cantabrian region (in northern Iberia ), the Italian and Balkan peninsulas, the Ukrainian LGM refuge , and the Bering Land Bridge . Archaeological and genetic data suggest that the source populations of Paleolithic humans survived the glacial maxima (including
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2856-597: 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 invasive species have only recently colonized and can observe how they disperse throughout
2924-402: The formation of regional biotas. For example, data from species-level phylogenetic and biogeographic studies tell us that the Amazonian teleost fauna accumulated in increments 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
2992-483: The former Lifemapper project at the University of Kansas (now continued as a part of BiotaPhy ) and AquaMaps , which as at 2023 contain modelled distributions for around 200,000 terrestrial, and 33,000 species of teleosts , marine mammals and invertebrates, respectively. One advantage of ENM/SDM is that in addition to showing current (or even past) modelled distributions, insertion of changed parameters such as
3060-655: The geographical distribution of organisms around the globe. Alfred Russel Wallace studied the distribution of flora and fauna in the Amazon Basin and the Malay Archipelago in the mid-19th century. His research was essential to the further development of biogeography, and he was later nicknamed the "father of Biogeography". Wallace conducted fieldwork researching the habits, breeding and migration tendencies, and feeding behavior of thousands of species. He studied butterfly and bird distributions in comparison to
3128-411: The importance of environmental and geographic similarities or differences as a result of climate and other pressures on the planet. Importantly, late in his career Wegener recognised that testing his theory required measurement of continental movement rather than inference from fossils species distributions. In 1958 paleontologist Paul S. Martin published A Biogeography of Reptiles and Amphibians in
3196-559: The island and change it. They can then apply their understanding to similar but more complex mainland habitats. Islands are very diverse in their biomes , ranging from the tropical to arctic climates. This diversity in habitat allows for a wide 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
3264-409: The late 1990s and early 2000s. The most recent efforts have used the idea of land facets (also referred to as geophysical settings , enduring features , or geophysical stages ), which are unique combinations of topographical features (such as slope steepness, slope direction, and elevation ) and soil composition, to quantify physical features. The density of these facets, in turn, is used as
3332-659: The literature of conservation biologists as a potential way to identify climate change refugia and as a surrogate (in other words, a proxy used when planning for protected areas) for biodiversity. While the language to describe this mode of conservation planning hadn't fully developed until recently, the use of geophysical diversity in conservation planning goes back at least as far as the work by Hunter and others in 1988, and Richard Cowling and his colleagues in South Africa also used "spatial features" as surrogates for ecological processes in establishing conservation areas in
3400-488: The mid-18th century, improved our classifications of organisms through the exploration of undiscovered territories by his students and disciples. When he noticed that species were not as perpetual as he believed, he developed the Mountain Explanation to explain the distribution of biodiversity; when Noah's ark landed on Mount Ararat and the waters receded, the animals dispersed throughout different elevations on
3468-515: The most important and consequential developments in biogeography has been to show how multiple organisms, including mammals like monkeys and reptiles like squamates , overcame barriers such as large oceans that many biogeographers formerly believed were impossible to cross. See also Oceanic dispersal . Biogeography now incorporates many different fields including but not limited to physical geography, geology, botany and plant biology, zoology, general biology, and modelling. A biogeographer's main focus
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#17327721630323536-505: The mountain. This showed different species in different climates proving species were not constant. Linnaeus' findings set a basis for ecological biogeography. Through his strong beliefs in Christianity, he was inspired to classify the living world, which then gave way to additional accounts of secular views on geographical distribution. He argued that the structure of an animal was very closely related to its physical surroundings. This
3604-683: The nature of the models employed (including the scales for which data are available), maps generated from such models may then provide better representations of the "real" biogeographic distributions of either individual species, groups of species, or biodiversity as a whole, however it should also be borne in mind that historic or recent human activities (such as hunting of great whales , or other human-induced exterminations) may have altered present-day species distributions from their potential "full" ecological footprint. Examples of predictive maps produced by niche modelling methods based on either GBIF (terrestrial) or OBIS (marine, plus some freshwater) data are
3672-476: The northernmost cloud forest in the western hemisphere at over 2200 meters. 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
3740-583: The origins of species in the Hawaiian Islands , phylogeography allows them to test theories of relatedness between these populations and putative source populations on various continents, notably in Asia and North America . Biogeography continues as a point of study for many life sciences and geography students worldwide, however it may be under different broader titles within institutions such as ecology or evolutionary biology. In recent years, one of
3808-495: The physiological and ecological constraints on organismal dispersal to geological and climatological phenomena operating at global spatial scales and evolutionary time frames. The short-term interactions within a habitat and species of organisms describe the ecological application of biogeography. Historical biogeography describes the long-term, evolutionary periods of time for broader classifications of organisms. Early scientists, beginning with Carl Linnaeus , contributed to
3876-448: The presence or absence of geographical barriers. His observations led him to conclude that the number of organisms present in a community was dependent on the amount of food resources in the particular habitat. Wallace believed species were dynamic by responding to biotic and abiotic factors. He and Philip Sclater saw biogeography as a source of support for the theory of evolution as they used Darwin's conclusion to explain how biogeography
3944-420: 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 that at the time of dispersal,
4012-643: The same species that found themselves in different refugia evolved differently, creating parapatric sister-species . As the Pleistocene ended, the arid conditions gave way to the present humid rainforest environment, reconnecting the refugia. Scholars have since expanded the idea of this mode of speciation and used it to explain population patterns in other areas of the world, such as Africa , Eurasia , and North America . Theoretically, current biogeographical patterns can be used to infer past refugia: if several unrelated species follow concurrent range patterns,
4080-412: The south-west coast of Australia, due to humans taking so many of their number as game. This resulting isolation, in many cases, can be seen as only a temporary state; however, some refugia may be longstanding, thereby having many endemic species , not found elsewhere, which survive as relict populations. The Indo-Pacific Warm Pool has been proposed to be a longstanding refugium, based on the discovery of
4148-428: 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
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#17327721630324216-495: The term in situ refugium is used to refer to areas that will allow species that exist in an area to remain there even as conditions change, whereas ex situ refugium refers to an area into which species distributions can move to in response to climate change. Sites that offer in situ refugia are also called resilient sites in which species will continue to have what they need to survive even as climate changes. One study found with downscaled climate models that areas near
4284-416: The theory of evolution were different from those of other explorers of his time, because he developed a mechanism to describe the ways that species changed. His influential ideas include the development of theories regarding the struggle for existence and natural selection. Darwin's theories started a biological segment to biogeography and empirical studies, which enabled future scientists to develop ideas about
4352-447: 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 (or more generally Greater Amazonia,
4420-400: Was divided into regions which he defined as tropical, temperate, and arctic and within these regions there were similar forms of vegetation. This ultimately enabled him to create the isotherm, which allowed scientists to see patterns of life within different climates. He contributed his observations to findings of botanical geography by previous scientists, and sketched this description of both
4488-529: Was important to a George Louis Buffon's rival theory of distribution. Closely after Linnaeus, Georges-Louis Leclerc, Comte de Buffon observed shifts in climate and how species spread across the globe as a result. He was the first to see different groups of organisms in different regions of the world. Buffon saw similarities between some regions which led him to believe that at one point continents were connected and then water separated them and caused differences in species. His hypotheses were described in his work,
4556-667: Was proposed for biogeography. It achieved limited success; some studies commented favorably on it, but others were much more critical, and it "has not yet gained a significant following". Similarly, a set of rules for paleobiogeography has achieved limited success. In 2000, Westermann suggested that the difficulties in getting formal nomenclatural rules established in this field might be related to "the curious fact that neither paleo- nor neobiogeographers are organized in any formal groupings or societies, nationally (so far as I know) or internationally — an exception among active disciplines." Refugium (population biology) In biology,
4624-502: Was similar to a record of species inheritance. 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. Moving on to the 20th century, Alfred Wegener introduced
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