Adaptive radiation in evolution

Introduction to Adaptive Radiation

Adaptive radiation is pivotal for evolution to bring in changes as the species grow through generations. Every individual must adapt themselves in accordance with the changes in the external conditions such as weather changes, food pattern and increase in the number of predators. In evolutionary biology, one should clearly understand whether adaptive radiation is a necessity or a random act presented by the system. It is true that the mechanisms like mutation and radiation provide individuals - the strength and abilities to change their body according to the external factors exist in the environment from time to time.

1. Introduction to Adaptive Radiation

2. Darwin`s theory of evolution

3. Features of adaptive radiation

4. Examples of adaptive radiation among species

Darwin`s theory of evolution

As per Darwin’s theory of evolution, over a period of time, all living organisms modify their physical and anatomical structures that help them to adjust to the changing environments. Such change is really necessary, for instance, when we look at the global temperature, there is a rise in at least 1Celsius every year. Keeping this in mind, the organisms living in the tropical regions must exhibit specific changes over a period of time.  In order for the organisms to survive and reproduce, they need to exploit the other organisms in their ecological range. But how is this possible? Evolution by mutation, speciation, and the adaptive radiation helps the species to redesign their bodies through structural manipulations. As a result, the organisms get split and adapt to the variety of versions of the environment for their better survival. One such example is the extreme threat from the living zone of the habitants. For instance, a volcano formed in an aquatic ecosystem leading to the formation of a large new lake habitat. This could serve as an alternative for the species to survive during volcanoes.  In simpler terms, adaptive radiation is one of the evolutionary process resulting in the formation of many different species from their common ancestors. Have you ever observed, the cat is a family that looks like many similar animals such as domestic cat, leopard, lion; they all look similar because of their common ancestors from which they got radiated into many types of animals with a variety of similarities.  Another example is the diversity of Galapagos finches as a result of their adaptive radiation from their common ancestors. Finches, during the course of evolution, have modified their beaks in terms of size, shape and length which eventually classified them into many subcategories. Because of such change in their beaks, some eat animals (e.g. insects), and a few other consume seeds or plants. Similarly, because of bodily changes as a result of radiation, some feed on the trees, and few of them find their food on the ground.  There are many such examples where the species survive because of the evolutionary process like adaptive radiation. So, the word radiation refers to the expression of the taxonomic diversity via bodily changes which are also a result of a great diversity in the species. Adaptive radiation is an evolutionary pattern rather than an independent phenomenon by itself. When we look at  14 or 15 species of Galapagos finches, they have emerged into what they are in a span of 2 million years hence, the  14 or 15 species what we see today are an observable result of an evolutionary adaptation. The process of adaptive radiation was first observed by Darwin as he travelled through Galapagos Island where he found a variety of finches with their varied beaks hence these finches have become well-known as  Darwin’s finches.

 

Features of adaptive radiation

  1. There must be a common ancestry specifically in a recent ancestry.

  2. There is evidence of a correlation between the phenotype( morphological features ) with the environment

  3. There should be trait utility, in other words, the morphological changes must be exercised to survive in an adverse situation. For instance, the beers in the polar region use their thick fur to safeguard from the extremely cold environment.

  4. There is rapid speciation with a high frequency of emergence of new species around the time that ecological and phenotypic divergence is underway.

 

Examples of adaptive radiation among species

  1.  A classic example of adaptive radiation is the evolution of Darwin`s Finch population as explained above.

  2. One of the typical examples of adaptive radiation is the development of different Australian Marsupials out of a single ancestral stock as shown in the image below. This, in fact, one of the example of divergent evolution. Marsupials species have diverged into different orders and species from their original order Euaustralidelphia.

 

  1.  Radiation of Hawaiian tetragnathid spiders to build orb webs that help in predation.

  2. Radiations of Caribbean Anolis lizards have repeatedly evolved chameleon-like ectomorphs.

  3.  The limb structure (mode of locomotion) of placental mammal provides the best example of adaptive radiation. The ancestor of the present-day placental mammal was a five-toed short-legged terrestrial insectivore. From such stem mammals, various modern types of mammals have evolved by the modification of limbs



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