Adaptive radiation is a process in evolutionary biology where organisms rapidly diversify from an original species into a plethora of new forms, especially when a change in the environment makes new resources available. These also include changes in biotic interactions or the creation of new environmental niches. Starting with a single ancestor, this process leads to the speciation and phenotypic adaptation of a diverse range of species with various morphological and physiological characteristics. Finch speciation in the Galapagos Islands (Darwin’s finches) is the prototypical example of adaptive radiation.
Definition of adaptive radiation
In simple words, adaptive radiation is an evolutionary process in which several species in a given area begin from a single species and radiate to other forms.
Characteristics of Adaptive Radiation
Adaptive radiation can be distinguished by four characteristics:
Shared Ancestry: A shared ancestry of component species, a particularly recent one. Note that this is not the same as monophyly, which includes all descendants of a single ancestor.
Phenotype-environment correlation: A considerable link between surroundings and the morphological and physiological features needed to exploit those circumstances is known as a phenotype-environment correlation.
Trait Utility: Trait utility refers to the benefits of trait values in their respective settings in terms of performance or fitness.
Rapid Speciation: Rapid speciation is defined as the appearance of one or more bursts of new species around the time that ecological and phenotypic divergence takes place.
Illustrations of Adaptive Radiation
Darwin’s Finches
- Adaptive radiation was demonstrated by finches, also known as Darwin’s Finches. Natural selection has allowed species that have descended from a common ancestor to successfully adapt to their environment over time.
- The finches had previously occupied the South American mainland, but they had also managed to colonise the Galapagos Islands, which are almost 600 miles away. They occupied a sparsely populated ecological niche.
- Intraspecific competition became an issue as the population grew in these favourable conditions, and resources on the islands were scarce, unable to sustain the finch population for long.
- The finches were more suited to the environment as a result of natural selection, mechanisms and changes in the gene pool.
Marsupials
The marsupial mammals live in Australia and are distinguished from placental mammals by the fact that they give birth to their young in a pouch. Long ago, Earth’s landmass was made up of only one continent, Pangaea, which was home to all species. The geographical barrier created by the fragmentation of this continent into smaller continents meant that the mammals of the period could no longer breed with one another. From this point forward, the gene pool of these mammalian groupings would become increasingly diverse, until they could no longer breed with one another. This is true of the marsupial family of mammals that live in Australia.
All marsupials in modern-day Australia are thought to have descended from a single ancestor. However, many marsupial species such as the kangaroo and koala have inhabited their ecological niche and evolved accordingly over time and through natural selection. Kangaroos have long, muscular legs that allow them to cover a large area of ground, whereas koalas have a smaller structure and a more concentrated centre of gravity that allows them to climb trees and collect the eucalyptus they eat.
Humans
Humans, as the most evolved species in the world, have undergone several changes since their forefathers. Here are several examples:
- Humans are bipedal, which means we walk on two legs. Our other limbs, arms, and hands have evolved to do precision activities like typing or tying shoelaces, which are typical chores in our daily lives.
- The amount of melanin in our skin reflects the climate we live in; for example, dark-skinned people dwell in hotter and sunnier climes.
- Our body structure also provides information about the temperature in our environment.
- Humans who have successfully produced offspring can live in cold climates, and are broader and smaller in size, whereas those who dwell in hotter environments are thinner and taller.
Conclusion
Adaptive radiation is defined by a rapid increase in the number of species that share a common ancestor, as well as a high level of ecological and morphological diversity. The adaptation of organisms to new ecological situations is the driving force behind it. When Charles Darwin first visited the Galapagos Islands, one of the first things he observed was the diversity of finches that could be found on each island, each with its beak form and size. This is adaptive radiation in action, as well as natural selection. However, apart from these, there are several other illustrations of adaptive radiation that we can see throughout history.