The distribution of modern and ancient plant and animal species — the realm of biogeography — is an essential line of evidence that Darwin methodically built up to support his theory of evolution via variation and natural selection. Indeed, his extensive field observations on the Beagle trip alerted him to such a possibility. The distribution of organisms is anything but uniform.
For starters, species separated by physical barriers are frequently highly different, even though they share the same habitat. Second, identical or highly related species are frequently found in widely apart locations. There are no examples of these species in the intermediate area.
Palaearctic region represents old world and Nearctic region represents North America. The world has been split into six biogeographical zones based on similarities and contrasts in fauna and flora distribution.
Europe and Asia north of the extensive mountain ranges — the Himalayas-arid the Nan Ling, Africa north of the Sahara Desert, and North America north of the Mexican Plateau — are considered part of the Holarctic area. Bears and foxes of the species Vulpes are two of the most common creatures in this vast region.
Africa south of the Sahara Desert is included in the Ethiopian region. This area is home to mammals like gorillas, giraffes, lions, and hippopotamuses.
The Oriental area includes Asia south of the Himalayas and the Nan Lings and is characterised by the gibbon, the orangutan, the Indian elephant, and the flying fox.
The Neotropical area comprises South and Central America, home to animals such as tapirs, sloths, prehensile-tailed monkeys, and vampire bats.
Australia is included in the Australian area, distinguished mainly by marsupial animals, bats, and certain rodents. All of the aforementioned areas have related islands.
These biogeographical zones are divided by long-standing obstacles such as deserts, mountains, and seas. Finally, there are fewer species on oceanic islands, most unique to each island. There is one more thing we need to think about here. Physical circumstances in one place are similar to those in another. As a result, one would anticipate plants and animals from one region to have little trouble surviving in the other.
They share just a few creatures in common, which may represent isolated survivors from formerly widespread groupings. This disparity in flora and fauna of identical places can only be explained by evolutionary theory, which holds that evolution has taken a distinct path in various locations.
As previously stated, similarly related creatures can be found in disparate environments. Take the black gum tree Nyssa as an example. Nyssa and several closely related species are found exclusively in South East Asia and Eastern North America. The physical and biotic environments in these locations are comparable. The broad space that divides these two places lacks naturally occurring Nyssa.
According to fossil data, Nyssa and the allied species were dispersed throughout a continuous range that included most of the northern hemisphere during a warmer epoch. The environment became too harsh for these plants throughout much of this range during the glacial period. As a result, Nyssa became extinct in most locations and survived only in areas with warmer climates. If they arose independently in widely different places, one would expect them to be present in other areas with similar circumstances. A vicariant distribution is one in which populations of the same species are far apart.
Darwin discovered that oceanic islands outside continents account for significantly fewer naturally existing animals. He discovered 26 species of terrestrial birds in the Galapagos archipelago, 21 to 23 of which were endemic. However, only two of the 11 marine bird species discovered there were endemic. This distinction is connected to varied eating patterns, which allowed them to occupy diverse ecological niches within a limited region.
Human-introduced flora and animals have thrived and flourished on these islands, demonstrating that these islands are well adapted to supporting a considerably broader range of creatures. Amphibians and terrestrial animals, but not bats, are typically absent from maritime islands, but when introduced, they can spread fast, becoming a nuisance. If all species had evolved in the regions where they now exist, amphibians and terrestrial mammals would be as common on oceanic islands as on roughly comparable continental areas.
Oceans, like lands, contain unique biotic areas that support a variety of ecosystems.
The intertidal zone is the area on every coast that is constantly exposed to tides.
The continental shelf extends beyond the littoral zone, with the higher sections forming continental islands.
Neritic zone is located over the shallow continental shelf and is no deeper than 600 feet (183 metres). The ocean bottom descends swiftly to vast depths at the edge of the continental shelf, creating new zones.
The pelagic zone is defined as water extending to a depth of 600 feet. The water is well-oxygenated and well-lit. Furthermore, the water at this level is prone to wave action.
The bathyal zone has water to a depth of 6000 feet. The sea is silent and dimly lit here.
The abyssal zone is located under the bathyal zone and receives no sunshine. The water is usually excellent and silent here.
Bio-geography is an essential line of evidence supporting Darwin's evolution theory via variation and natural selection. The world has been divided into six biogeographical zones based on similarities and contrasts in fauna and flora distribution, which can only be explained by evolutionary theory. Nyssa and other closely related species are found exclusively in South East Asia and Eastern North America.
Darwin discovered that oceanic islands have a smaller number of naturally existing animals. Human-introduced flora and animals have thrived on these islands, demonstrating that they are well adapted to supporting a broader range of creatures. Oceans contain unique biotic areas that support a variety of ecosystems, such as the littoral, continental shelf, neritic, pelagic, bathyal, and abyssal zones.
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