Generally, in evolutionary biology, adaptive radiation refers to a type of process in which the organisms are diverged rapidly from an ancestral species to a multitude new form especially when there is a change in an environment and the available resources for them such as alteration in the biotic interactions or new environmental niches.
However, starting from a single ancestor evolution in the speciation and their adaptations in the species shows different morphological and physiological traits.
One of the prototypical examples of adaptive radiation is Galapagos based on finch speciation. It is often known as Darwin’s finches.
What is Adaptive Radiation?
Adaptive radiation is generally defined as the adaptation of an organism that enables them to serve successfully in varying environmental regions.
According to Darwin theory of evolution, all the living organisms change their physical and anatomical structures for a longer period of time for improving their adaptations according to the changing environment.
The starting point of evolution is when organisms wanted to exploit a niche so that they are not able to exist with the same body designs and the structural components.
According to the changing environment organisms started to split themselves and adapts various versions for their better survival.
Else more, adaptive radiation is one of the evolutionary process in which the organism originates from one species in a particular are and radiate to different species at different areas.
The phenomenon of adaptive radiation was first identified by Darwin when he was travelling to Galapagos island. There he observed finches with various types of beaks.
On observing those finches, he concluded that all of them are radiated from the single individuals in the same island from their single ancestor finch.
Where all of these Finches has developed beaks accordingly to the kind of food that are available for them.
Hence it is said that they are evolved from the conventional seed eating finches, which is later known as Darwin’s finches
Cause of Adaptive Radiation
Adaptive radiation most commonly occurs due to major changes in the environmental factors and other physical disturbances.
It helps an organism to spread successfully in the other environmental regions.
Further it also leads to speciation which leads to phenotypically dissimilar and related species.
There are few reasons for the cause of adaptive radiation and they are listed below.
I. Ecological Opportunities
On entering into a new environment which has lot of ecological opportunities, organisms tend to adapt themselves according to it, which results in adaptive divergence.
An adaptive zone is generally an unexploited area which has various ecological opportunities.
Example: Nocturnal flying to catch insects and small flies, grazing on grass while migrating across Savana, swimming on the surface of the ocean to filter the planktons, etc.
Vacant adaptive areas are more commonly found on islands, because only few species inhabit in the islands compared to that of main lands.
When these adaptive zones are empty, they will be get filled by the species which diversifies quickly.
For example: Cichlids of African great Lakes, Darwin’s Finches of Galapagos Islands, Hawaiian honeycreepers, etc.
II. Mass Extinction
When there comes a mass extinction due to major environmental conditions or other physical disturbances, it also leads to adaptive variations with variety of reasons.
Extinction in a particular area produces empty adaptive zones which provides a new opportunity for a species that exists.
For example: After the extinction of dinosaurs, mammals get diversified quickly by exploiting various zone of adaptiveness.
As a result of these extinction competitions, species which remains flourishes.
For example: Mammals which has coexisted with the reptiles, but now they are considerably small so that they can hide and save themselves form great creatures like dinosaurs.
Acquisition of Novel Adaptive Traits
Evolutionary innovations trigger various adaptive radiations.
Evolutionary novelties are the variations in the pre-existing creatures which are known as preadaptation’s. A change in the basic pattern of the certain species produces unique creatures which adapts to a different role.
Examples of such preadaptation’s includes, Feathers wings on birds which are evolved from reptilian scales represents the preadaptation of flight.
Flowers on the plants has speeded up the ability to engage in the sexual reproduction which has turned into a great advantage of terrestrial animals for pollination which increases the reproduction rate.
Amniotic eggs and wings on insects are also some of the examples of proadaptive variations.
Area of Adaptive Radiation
Adaptive radiation can also be defined as an evolutionary process in any of the groups either in plants or animals into a wide variety of types which are adapted to specialized modes of life.
Adaptive radiations are often seen in the closely related groups which has been evolved in a shorter period of time.
A good example that can be sorted for adaptive radiation is in beginning of the Paleogenic era, approximately 66 million years ago of a basal stock of mammalian which are adapted for running, leaping, climbing, flying and swimming.
Other examples that are includes such as Australian marsupials, cichlif fish, Darwin’s finches or Galapagos finches, etc.
Many types of examples for this type of radiation are mostly found in archipelagoes removed from the main land.
In addition to the Galapagos Islands it can also be seen in Hawaiian archipelago along with its several volcanic islands and the relatively small area hosts a great number of plant and animal species are endemic, which means that they are evolved there and cannot be found anywhere.
Almost 90% of the native species of Hawaii island including flowering plants, land mollusks, birds and insects are found to be endemic.
Examples of Adaptive Radiation
Adaptive radiation helps in understanding the biodiversity. The concept of adaptive radiation can be made clear through the upcoming examples,
1. Let us consider a family consisting of about four children. Now these four children’s have a same parents and origin, and they four grow under the same circumstances and on growing each moved in different regions for the better opportunities.
And now, each of them has their own adaptations depending on their environmental conditions and the region they are living and their lifestyles. In this case, lineage splits and radiates different characteristics.
2. Considering another example, where adaptive radiation is different from the development.
Taking an account of Australian Marsupials which are all from a single ancestral stock from which various species has raised.
But according to the given geographical area, several adaptive radiations take place in various species, which gives rise to convergent evolution.
Marsupials are considered as one of the most commonly known examples for the adaptive radiation.
The marsupials have been diverted into different orders and species where each order gets diversified from its order Euaustralidelphia.
Adaptive Radiation Citations
- The tale of the finch: adaptive radiation and behavioural flexibility. Philos Trans R Soc Lond B Biol Sci . 2010 Apr 12;365(1543):1099-109.
- Mega-evolutionary dynamics of the adaptive radiation of birds. Nature . 2017 Feb 16;542(7641):344-347.
- Comparative landscape genetics and the adaptive radiation of Darwin’s finches: the role of peripheral isolation. Mol Ecol . 2005 Sep;14(10):2943-57.
- Cranial shape evolution in adaptive radiations of birds: comparative morphometrics of Darwin’s finches and Hawaiian honeycreepers. Philos Trans R Soc Lond B Biol Sci . 2017 Feb 5;372(1713):20150481.
- Adaptive Radiation Genomics of Two Ecologically Divergent Hawai’ian Honeycreepers: The ‘akiapōlā’au and the Hawai’i ‘amakihi. J Hered . 2020 Feb 5;111(1):21-32.
- Ecological and evolutionary determinants for the adaptive radiation of the Madagascan vangas. Proc Natl Acad Sci U S A . 2012 Apr 24;109(17):6620-5.