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Adaptive Radiation

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Adaptive Radiation - Lesson Summary

Charles Darwin carried out several interesting studies on the Galapagos Islands, what amazed Darwin most was the extensive variety of finches on these islands. These species of finches differed from each other with respect to the shape of their beaks and their overall size. These finches also known as Darwin’s finches demonstrated the concept of adaptive radiation. It is a type of evolution in which species in the same geographic area, derived from a common ancestor, successfully adapt themselves to their natural environment due to natural selection.
Adaptive radiation is of two types: adaptive divergence and adaptive convergence. In adaptive divergence, animals of the same or closely related group exhibit great divergence in their morphology when found in a different habitat. For example, the finches of the Galapagos Islands. These finches had originally come from the South American mainland to the Galapagos Islands. With the passage of time, they multiplied and began to compete with each other for food. As a result, all the food resources on the islands were used to the optimum. To take advantage of all the available food sources on the islands, the finches adapted themselves to the different varieties of food. One observable trait that pointed to this adaptation was the altered beaks of different species of finches. Their beaks divided them into specialised insectivorous and vegetarian varieties respectively. Another type of adaptive radiation is adaptive convergence, where animals of unrelated groups occupying same habitat exhibit common features. For example, Australian marsupials such as the kangaroo, marsupial rat, banded anteater, tiger cat, Tasmanian wolf and Koala. Marsupial mammals are characterised by their pouch in which the female carries the young through the initial days of infancy. On tracing the evolution of these marsupials, it was found that the drifting of the continents had shaped their history. When the ancient landmasses of Laurasia and Gondwana broke apart to form separate continents, the marsupials were also divided into two groups. While one group of marsupials was isolated on the Australian island, the other group remained in South America. Thereafter, the marsupials on both these continents evolved in a parallel manner and hence this is also known as parallel evolution. Interestingly, on comparing marsupials and placental mammals of Australia, we find similar adaptive radiations between them. Although they have separate lineages, they resemble each other physically. Studies show that the impelling causes of adaptive radiation are the need for food, safety and for better breeding grounds. Thus the process of adaptive radiation illustrates how life forms have modified and evolved into new forms.


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