Adaptive Radiation Evolution

Introduction

Evolution is a complex process. Studying different organisms (both living and extinct) with respect to their physical, and functional characters for a long duration makes an understanding of how present-day species have evolved. Sometimes the environment and living conditions force organisms to acquire new features essential for them. Without which, the particular organism can find it difficult to survive in that environment.

Suppose some organisms are introduced into a new environment and their body makeup does not fit them into the niche. They adapt to the environment by undergoing small changes so that they can succeed in their niche. They are small and rapid changes that can lead to the diversification of species into different forms. The process of rapid adaptation of organisms of one species into different forms so that they can spread successfully is called Adaptive Radiation. Adaptive radiation results in the rapid diversification of species. It involves genetic mutations resulting in multiple different phenotypic variations that are best adapted to the environment.

Factors Leading to the Evolution of Adaptive Radiation

• Adaptive radiation occurs when the species is exposed to new environmental conditions. It can occur if there occurs a geographic separation due to the formation of new landforms like mountains, islands etc.

• When a population is exposed to new habitats with unexploited resources, members of the population experience ample resources for utilization. They diversify intensely and adapt themselves to exploit the available resources. Species undergo diversification in morphology for utilizing the resources to the maximum possible extent. This takes place most commonly in islands where there are limited terrestrial species because of geographic isolation.

• Exposure to the new environment solely does not represent separation from own habitat.

• Changes in environmental conditions obviously change the availability of resources.

• Sometimes major changes in environmental conditions can lead to the extinction of some species. The lack of competitors leaves unexploited resources for other species inhabiting there allowing them to diversify and utilize the resources intensely.

Importance of Adaptive Radiation Evolution

Studying adaptive radiation helps to understand the species' interaction in a particular niche. Though the food web makes a clear understanding of species interrelation, their dependency rate can be understood by studying adaptive radiation evolution. Particularly in cases of mass extinction, when there are ample open new opportunities for the existing members. Since the existing species undergo adaptations to exploit resources, adaptive radiation opens new understandings about the environmental factors contributing to evolution.

Let us understand adaptive radiation by examples

Example 1

There are many classic examples of Adaptive radiation. Some of them are Darwin's finches of Galapagos, African great lake cichlids, Honeycreeper birds, and mammals.

Let us consider the adaptive radiation evolution of mammals with respect to limb structure as a primary locomotor appendage. Mammals of the Mesozoic era were rare and very small.

• The present-day placental mammals inhabit almost all parts of the globe and are extremely diverse in terms of size, behaviour, and many other aspects. They are descendants of a small insectivorous, short-legged, terrestrial ancestor.

• The insectivorous ancestor had five-fingered (pentadactylic) short legs. Though it is terrestrial, the appendages cannot serve locomotor functions.

• The sudden extinction of dinosaurs led to rapid speciation of existing mammals allowing them to adaptively radiate into different forms of present-day mammals.

• They developed traits to suit the environment and followed five different evolutionary lines.

Climbing placental mammals are arboreal − They are radiated by developing appendages that are able for grasping. For example, monkeys, and squirrels that live on trees.

Flying placental mammals are aerial − They developed limbs for flying. Examples like bats and gliding squirrels.

Swimming placental mammals are aquatic − Their appendages are specialized for swimming and surviving in the aquatic environment. Whales, dolphins, seals, polar bears, sea lions and walruses are aquatic mammals with pentadactylic appendages.

• Fussorial placental mammals are burrowing mammals − Mammals like moles and badgers have strong pentadactyl limbs for digging deep into the ground.

• Cursorial placental mammals − These mammals developed limbs to facilitate rapid movement on the ground. Lions, horses, pigs, antelopes, and wolves are some examples of cursorial mammals.

Although all the above categories of placental mammals have limbs specialized for different tasks, they originated from a common ancestor with pentadactyl limbs. The evolutionary lines radiated out in different directions to serve the locomotion in their respective niche.

Example 2

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Distinctive Attributes of an Adaptive Radiation Evolution

Adaptive radiation evolution can be distinguished from other evolutionary phenomena by checking for the presence of its distinctive features.

They are explained below −

• Considering ancestry − When the descendent species under study share a common ancestor.

• Correlating phenotype with the existing environment − When there is a relation between the environment with morphology or physiology of species.

• Utility of traits − When the species under study share some morphological or physiological traits that are necessary for survival in that particular environment.

• Rapid speciation − Adaptive radiation is a rapid process by originality.

So when the descendent species under study showed rapid speciation with a common ancestor and utilize traits that have a relation with the niche environment, they can be considered to have emerged through adaptive radiation evolution.

Conclusion

Adaptive radiation is a process by which organisms rapidly speciate into new forms by undergoing certain adaptations to environmental changes. Over a period of time, the resultant variants appear morphologically and phenotypically distinctive from the original species. Adaptive radiation can occur if organisms are exposed to a new environment or in the absence of competitors due to some mass extinctions. In either of the cases, organisms rapidly diverge to exploit the available resources and adapt to the living conditions.

Adaptive radiation has many distinctive features from other evolutionary processes. The main distinctive feature is that all the descendants have a common ancestor and have rapidly speciated from it by developing traits that are much needed for survival. Darwin's finches of Galapagos, cichlids of African great lakes, honeycreeper birds, Hawaiian silverswords, and Australian marsupials are some commonly known examples of adaptive radiation.

FAQs

Q1. Can you relate adaptive radiation to biodiversity?

Ans: Adaptive radiation occurs when a common ancestor diversifies into different forms of variants that undergo adaptations to fit into a new environment. Over a period of time, the newly formed adapted species diverge to an extent that it appears entirely different from their ancestor. Since adaptive radiation is a rapid process in different directions at a time it adds flavour to biodiversity.

Q2. Is it true that adaptive radiation can only work on motile organisms able to migrate?

Ans: Migration is not the only means for an organism to experience a new environment. Sessile plants can also experience adaptive radiation. For example, twenty-eight species of Hawaiin silverswords have evolved from a single common ancestor. They occupy three different genera and inhabit different niches.

Q3. What drives adaptive radiation?

Ans: When organisms are exposed to new ecological opportunities they constantly diversify in order to utilize them to the fullest. So it is the new ecological opportunities that have been constantly driving the process of adaptive radiation.

Q4. What is the reason for calling it adaptive radiation?

Ans: Since the descendants arise from a common ancestor by adaptation and radiate in different directions colonizing varied habitats by harnessing different resources, it is called adaptive radiation.

Q5. Does adaptive radiation affect speciation?

Ans: Adaptive radiation results in different species formation from a primitive common ancestor adding its impact positively to speciation.