What is Adaptive Radiation | Factors causing Adaptive Radiation

Introduction

Evolution is an intricate and slow process. Various organisms constantly adapt by changing their morphological and anatomical characteristics in response to the change in the environmental conditions of their habitat. They make minor changes in their genetic composition to adapt to their surroundings and thrive in their niche. These, minor alterations in their genes are responsible for the formation of new species. Adaptive radiation is one such process by which organisms of a single species rapidly transform into distinct forms to propagate successfully and thrive in their niche.

Factors causing adaptive radiation

Various factors are causing adaptive radiation some of them are-

• Geographical isolation– Geographic isolation of organisms from the mainland due to the formation of valleys, mountains, earthquakes, etc. becomes one of the main reasons for adaptive radiation to take place. This sudden separation causes organisms to rapidly adapt to new changes and hence evolve.
• Exposure to new habitat– When organisms are exposed to new habitats, they are exposed to lots of new resources which are available abundantly. This abundance of resources forces them to diversify and adapt in a way that they can exploit those resources to the maximum and thus cause the evolution of new features.
• Changes in environmental conditions- Change in environmental conditions can occur due to floods, volcanic eruptions, deforestation, weather changes, etc. These changes are sudden and hence force the organisms living in particular habitats to change rapidly and hence lead to adaptive radiations.

All of the above factors cause a change in the genetic composition of the organisms and hence lead to the formation of new and permanent changes in their genotype which then in turn leads to the formation of newer species.

Distinctive features of Adaptive radiation

Distinctive features of adaptive radiation which separate it from other evolutionary changes are as follows-

• Common ancestry- Organisms that undergo adaptive radiation belong to the same ancestor. 
• Phenotype-environment correlation- The changes in the phenotype of the species are with the change in the environmental conditions. 
• Trait utility-The new trait thus formed due to adaptive radiation helps the organisms to survive in the new environment. For eg-Darwin’s finches.
• Rapid speciation-This adaptation is a very rapid process as the organisms need to quickly adapt to the changing environment for their survival.

Adaptive radiation in mammals

Adaptive radiation can be studied by various examples once such as limb structure in mammals which is used for locomotion.

• Modern placental mammals are incredibly diverse in terms of size, behavior, and many other features. They may be found practically anywhere in the world.
• These mammals are descended from a little, short-legged, terrestrial predecessor that consumed insects.
• The pentadactyl (five-fingered) small legs belonged to the insectivorous ancestor. Despite being terrestrial, the appendages cannot move the creature.
• The extinction of dinosaurs suddenly caused the remaining mammals to undergo fast diversification. This gave rise to a variety of modern mammals through the process of adaptive radiation.

Mammals followed five separate evolutionary lines and evolved features to fit their respective surroundings, these adaptations are-

• Arboreal placental animals- These are climbers and are generated by growing appendages with grabbing capabilities. Example: Monkeys and tree-dwelling squirrels.
• Aerial placental mammals- These mammals can fly. They evolved limbs into flying wings. Examples- are gliding squirrels and bats.
• Aquatic placental mammals- These can swim in the water. They have appendages that are designed specifically for swimming and surviving in water. Examples- Whales, dolphins, seals, polar bears, sea lions, and walruses.
• Fussorial placental mammals- These are burrowing mammals and bear strong pentadactyl limbs allowing them to dig down far into the ground. Example- moles and badgers.

Cursorial placental mammals- These mammals evolved limbs to allow for swift ground movements such as running, climbing, walking, etc. Examples-wolves, are horses, pigs, antelopes, and lions.

Even though each of the aforementioned groups of placental animals has limbs that are specific for particular habitat, they all shared a common ancestor that had pentadactyl limbs. These evolutionary lines that radiated out in different directions served the purpose of locomotion in their respective habitat.

Summary

Understanding adaptive radiation aids in the comprehension of how organisms interact within a given habitat. Although the food web provides clear knowledge of species interactions, examining adaptive radiation evolution might help us understand how species are dependent on one another. Adaptive radiation enables us to gain new insights into the environmental changes which influence evolution.

Frequently Asked Questions

1. Does adaptive radiation favor biodiversity?
Ans: When a common ancestor diversifies into various forms to fit into the new environment it is known as adaptive radiation. The newly developed adaptive species then gradually diverge from their ancestor until they no longer resemble them. Since adaptive radiation occurs quickly and in multiple directions at once, it leads to biodiversity.

2. How does adaptive radiation operate?
Ans: As a result of being exposed to new ecological conditions, organisms constantly diversify. They do this to take full advantage of the environmental conditions. Therefore, the process of adaptive radiation has been continuously driven by the formation of new ecological niches which increase the availability of newer resources for survival.

3. Is it accurate to say that only species with the ability to move can benefit from adaptive radiation?
Ans: Moving to a new environment is not the only way for an organism to adapt or experience a different environment. Adaptive radiation can also affect sessile plants. For instance, a single common ancestor gave rise to 28 species of Hawaiin silverswords. They belong to three distinct genera and fill various niches.