Biogeography deals with the geographical distribution of organisms, species, and ecosystems across geological time. This segment of the study reveals variation in biological communities of organisms in the lines of geographical gradients of elevation, habitat area, isolation, and latitude. Familiarity with the spatial differences in the types and numbers of living organisms is of utmost importance in today’s study of history and geography just as much as it was necessary for our ancestors. This is made manifest as we conform to the heterogeneous environments which in most cases are geographically predictable.
The systemic distribution of species of living organisms over several geographical areas is usually accounted for and explained by integrating and combining different historical factors including extinction, glaciations, extinction, and continental drifts as well as some deviations and variations in sea level, river capture, river routes and habitat (Browne, 36). This is in conjunction with a combination of supplies from ecosystem energies, isolation, geographical constraints, and landmass. On the same note, the theory of evolution stipulates that all the millions of species of living organisms on the face of the earth underwent an evolution process from a common ancestor through a process termed natural selection.
This idea sounded out that the organisms that got immeasurably adapted to their natural habitat managed to pass on their traits to their offspring and as time passed over such traits accumulated in a way that transformed those organisms to be what is currently termed as species. Evolution also sheds light on the formation of the earth about 4.6 billion years. Therefore, this article presents a detailed description of how biogeography supports the theory of evolution.
Objectives
This article aims at discussing how biogeography supports the theory of evolution. To fulfill this objective, this article would be intended;
- To show how biogeography defines the history of species that evolved
- To indicate how ecological biogeography supports evolution
- To use the study of biogeography to justify plate tectonic theory
- To explain how Island biogeography of species depicts the theory of evolution
- To describe Continental discontinuity of species about evolution
- To distinguish how evolution theory affirms the biogeography of distribution of islands
- To highlight how Darwin’s discovery was fostered by biogeography
How biogeography defines the history of species that evolved
Amazingly, from the definition of the duo fields of studies, it is crystal clear that one can not form lines of distinctions between biogeography and evolution. However, one thing that strikes me is that without the theory of evolution, biogeography has no basis. In other words, biogeography explains and affirms the theory of evolution in a greater dimension.
First, biogeography discusses the geographical distribution of species and how those living organisms interact with the environment while the theory of evolution analyses the origin of those species and their traits that make them behave or respond to different environmental conditions. It is also important to note that the theory of evolution underlies the core reasons for variations in environmental conditions on the surface of the earth such as on oceans, lakes, winds, seas, hills, mountains, snows, ice among others.
Therefore, to begin with, biogeography defines the history of species in their evolution process along with time scales. This is made possible by the use of evidence from other disciplines of history, especially archaeology. In this case, the fossils extracted from the earth from different places are rich in information that are necessary for the determination of the distribution of living organisms across the surface of the earth as well as the past interactions of various species.
In the bid to understand the sediments and relays facts from the fossils, biogeographers normally employ molecular biology. In the bid to come to terms with the evolutionary history of species with help of molecular biology, biogeographers normally use a tool referred to as area cladogram. Cladogram uses a taxonomic tree to show similarities between different species. The names of the species in the diagram are also replaced with geographical locations where different species are found. This enables these scientists to be in a position of determining environmental influence on the history of the evolution of various species of the same origin. The cladogram is as shown below;
Ecological biogeography and evolution
Ecology is another aspect of biogeography that affirms the theory of evolution. In this case, the current information that is gotten from the population is used explaining how those species might have evolved. This information depicts the behaviour of organism at different locations. In many instances, island communities for the basis of study in formation of hypothesis about development of species. Unlike other bigeographers who use cladogram, in this segment of study, richness equilibrium model is used. It presents uninhabited island that is characterized to be surrounded by other habitats that are not inhabited by other species of living organisms.
All the colonizing species are referred to as species pool. With increase in the number of species in the new area, there is a relative decrease in species pool which in turn translates to decrease in the rate of immigration (Dansereau, 65). Consequently, crowding of the island would be an issue to talk about due to scarcity of supplies and resulting into an elevation in the rate of extinction. The model is meant to predict deviations in the rates of immigration and extinction towards the equilibrium. This normally vary depending on the how much the island is endowed with resources as well as the degree at which it is separated from other islands. This can be illustrated in the figure below;
Biogeography and Plate tectonic theory of evolution
Biogeography justifies the plate tectonic theory which is a stronger part of the evolution theory. Examination of fossils had given a hint on how the evolution of certain species took place in various regions of the world such as the Antarctic. These areas during those times were characterized to be on the further north where the climate was characterized by high temperatures. It is from these points that they spread to other parts namely South Asia and Gondwanan continents, Laurasia during the late stages of Paleogene, and then the global distribution. During that dispersal time, it is said that the Indian Ocean was much narrower as compared to its nature today.
The Antarctic was also much close to South America. Nevertheless, to this point, it would be hard to account for the presence of several ancient lineages of perching birds across the continent of Africa. Therefore, one can easily note that the entire process of evolution impacted greatly on the distribution of some sets of species in different parts of the earth thus unveiling a correlation between biogeography and the theory of evolution.
Island biogeography of species
All and sundry can notice that there is no even spread of life and islands across the surface of the earth. The occurrence of this phenomenon is owed to the process of evolution and biogeography acts as the tool that lightens this phenomenon. Data concerning the availability of certain species in different islands and continents revealed through biogeography aid gives out information of almost the same descent and also distinguishes specific patterns of the process of speciation.
Biogeography also explains the process of evolution well when the situation in Australia is analyzed. Before the arrival of human species about over 40, 000 years, Australia was inhabited by over 100 species of animals including; marsupials, Koalas and Kangaroo. However, there were no traces of terrestrial mammals whose line of species is advanced with the likes of horses, wolves, bears, lions, and wolves. Considering the case of isolated islands such as New Zealand and Hawaii, there was a habitation for land animals.
Nevertheless, each of these isolated islands and areas habited several species of birds, plants, and insects which could not be seen in any part of the world except in such like places. Therefore, the existence of extreme and unique environmental conditions in Hawaii, Australia, and New Zealand can best be explained as the formation of life through evolution in isolation from other parts of the planet for millions of years elapsing.
Continental discontinuity of species
Continental biogeography further makes the whole process of evolution understandable. It depicts that all living organisms/creatures have specific adaptations to biotic and abiotic factors in their surrounding habitat (Holly, 112). Even though one can expect that the modes of adaptation influence the same species of organisms to be found in the almost same geographical area such as in Asia, South America, and Africa, all species of living things are distributed discontinuously all around the planet earth.
This kind of discontinuous distribution of species of animals and plants is easily noted in South America as well as in Africa instance, in Africa, there are short-tailed giraffes, monkeys, lions, and elephants while in South America, the story changes due to the presence of long-tailed llamas, monkeys, jaguars, and cougars. It is also in the same way that discontinuity can be observed in the flora of South America as well as North America. This is depicted by the presence of cacti in both cases while in Asia, Africa, and Australia, deserts are characterized by the presence of succulent native kinds of euphorbia that are similar in appearance to cacti but are distinct in several ways. It is in the same way that cacti randomly planted by humans also thrive especially in Australian deserts.
Biogeography best accounts for continental discontinuity of species of living organisms as evolution was underway. We come to note that the major group of mammals seen in the modern world originated from the Northern Hemisphere after which they migrated in three distinct directions. The first direction was to South America through places known as Bering Strait (across the land bridge) and Panama. However, some families of marsupials in South America got extinct due to scarcity of food and competition with their counterparts from Northern America. The second direction was towards Africa through the Strait of Gibraltar while the third direction was to Australia through South Eastern side of Asia (these areas were at one time connected by a mass of land).
Passage through the first direction is illustrated by the fact that Bering Strait was very shallow hence could ease passing of animals as they shifted between the northern continents. Besides, it also shades more light on the current similarity noted in Faunas.
However, after movement to the continents located to the south, a number of barriers isolated them and with time they developed ways of adaptation to their new habitats in a way that show their differences to the present day. Some of those barriers include; Isthmus of Panama which submerged and later isolated the fauna in South America, African fauna was also isolated by Mediterranean Sea and the Northern African desert and also the connection that existed between South East Asia and Australia got submerged leading to isolation of Australian Fauna. After isolation, most of the animals across all the outlined continents have been able indicate an adaptive radiation capability to evolve.
Distribution of islands
Evolution process that led to formation and distribution of islands is also best explained with the aid of biogeography. This study depicts that islands can be categorized into two and this is; continental islands such as Japan and Britain that are traced to have belonged to one continent at one time. The next category is known as oceanic islands such as the islands of Hawaii and Galapagos (Whittaker, 95). Oceanic islands are characterized by distribution of indigenous plants and native animals. Actually, terrestrial mammals are not present in oceanic islands with exception of seals and bats.
Others include fresh water fish and amphibians and in some instances, terrestrial reptiles can be found in oceanic islands but this barely happens (Wallace, 68). Amazingly, evolution of these species exclusively found in oceanic islands happened in such a way that they are not present in any other location on the surface of the earth (endemic). Nevertheless, these species have a number of similarities with other species in other highlands.
Darwin’s discovery through biogeography
In the study of evolution or in attempts to seek to understand certain things that seem like mysteries on the surface of the earth such as striking difference in flora and fauna and reason for the presence of polar bears in Arctic and penguins in Antarctica. Actually, this brings an important point in the context of this article that biogeography provided foundational basis for understanding the real details underlying the entire process of evolution. In case where island species were so different from others, Darwin came to a conclusion that the inhabitants of the island must have come from the mainland just the same as other species.
This then become the literal explanation of why species present in Galapagos island takes after the ones in mainland (South America) while those found in Cape Verde so much resemble the ones in West African mainland. Darwin also came to infer that deviations in location of climatic zones with time accounts for variation in patterns habitat of various animals. Moreover, Darwin’s claims or evolution theory is even more eminent with continuous finding of fossils in the same parts of the globe which are traced to have belonged to the ancestors.
Conclusion
In conclusion, this article explains how the study of distribution of species, organisms and geographical ecosystems affirms the theory of evolution. From this article, one thing that is evident is the fact that biogeography provided the basis for discovery and foundational basis for Darwin’s theory of evolution. This is supported by a number of factors thus making biogeography as a study a very powerful tool of insight as far as evolution is concerned.
Works Cited
Browne, Janet. The Secular Ark: Studies in the History of Biogeography. New Haven: Yale University Press, 1983. Print.
Dansereau, Pierre. Biogeography: An Ecological Perspective. New York City: Ronald Press Company, 1957. Print.
Hollry, Dennis. Biogeography as Evidence of Evolution: Understanding the Discontinuity of Species Distribution. London: Blackwell Publishing, 2009. Print.
Wallace, Arisson. The Geographical Distribution of Animals. London: Macmillan publishers, 1876. Print.
Whittaker, Right. Island Biogeography: Ecology, Evolution, and Conservation. New York: Oxford University Press, 1998. Print.