Biogeography

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 the mid-18th century, initiated the ways to classify organisms through his exploration of undiscovered territories. 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 the mountain. This showed different species in different climates proving species were not constant.[4] 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.[10] He argued that the structure of an animal was very closely related to its physical surroundings. This was important to a George Louis Buffon's rival theory of distribution.[10]

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, 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 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.[10] 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.[4]

Following the period of exploration came 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",[4] 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 was divided into regions which he defined as tropical, temperate, and arctic and within these regions there were similar forms of vegetation.[4] This ultimately enabled him to create the isotherm, which allowed scientists to see patterns of life within different climates.[4] He contributed his observations to findings of botanical geography by previous scientists, and sketched this description of both the biotic and abiotic features of the earth in his book, Cosmos.[10]

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.[16] He discussed plant distribution and his theories eventually had 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.[10]

Several additional scientists contributed new theories to further develop the concept of biogeography. Charles Lyell developed 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.[17] 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.[18] 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 the environmental surroundings to varying species. This largely influenced Charles Darwin in his development of the theory of evolution.[10]

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 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 the geographical distribution of organisms around the globe.[10]

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 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.[10] 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 was similar to a record of species inheritance.[10] 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.[4]

Schematic distribution of fossils on Pangea according to Wegener

Moving on to the 20th century, Alfred Wegener introduced the Theory of Continental Drift in 1912, though it was not widely accepted until the 1960s.[4] 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 is in the geological similarities between varying locations around the globe, fossil comparisons from different 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 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.[19]

In 1958 paleontologist Paul S. Martin published A Biogeography of Reptiles and Amphibians in the Gómez Farias Region, Tamaulipas, Mexico, which has been described as "ground-breaking"[20]^{: 35 p.} and "a classic treatise in historical biogeography".[21]^{: 311 p.} 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 the northernmost cloud forest in the western hemisphere at over 2200 meters.[20][21][22]

Biologist Edward O. Wilson, coauthored The Theory of Island Biogeography which helped in stimulating much research on this topic in the late 20th and 21st. centuries.

The publication of The Theory of Island Biogeography by Robert MacArthur and E.O. Wilson in 1967[23] 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.[24]

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.[15]

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 the most important and consequential developments in biogeography has been to show how multiple organisms, including mammals like monkeys and reptiles like lizards, overcame barriers such as large oceans that many biogeographers formerly believed were impossible to cross.[25] See also Oceanic dispersal.

The study of comparative biogeography can follow two main lines of investigation:[31]

• Systematic biogeography, the study of biotic area relationships, their distribution, and hierarchical classification
• Evolutionary biogeography, the proposal of evolutionary mechanisms responsible for organismal distributions. Possible mechanisms include widespread taxa disrupted by continental break-up or individual episodes of long-distance movement.