Why Does Adaptive Radiation Occur? Let’s Know!
Adaptive radiation is an evolutionary process in which an ancestral form gives rise to new species adapted to new habitats and new ways of life.
In adaptive radiation, a population of ancestral species can separate itself into a new habitat, new lifestyle, and new resources to form many separate descendant species populations over the period of millions of years of evolution.
Adaptive radiation usually occurs when the ancestral population of a species gets new exploitable resources. These new exploitable resources usually occur due to change in the environment, formation of new habitat, destruction of old habitat, change in resource availability, creation of new challenges, or due to the introduction of new environmental niches.
In adaptive radiation, adaptive simply means “adaptation” and radiation simply means “diversification.”
Adaptive radiation usually means how the species will adapt itself to the environment and in doing so it will diversify itself into many different species with each species being adapted differently.
This causes a rapid increase in the diversity of the clade of ancestral species into many descendent species with various phenotypic adaptations exhibiting different morphological and physiological traits.
Adaptive Radiation Occurs Due To The Following Broad Reasons
Due to the change in environment
Adaptive radiation can occur due to the change in the environment of any species which may force those species to try to adapt to its new environment.
Such a change can be due to the destruction of the old environment because of various natural calamities, deforestation, geographical isolation, etc. Or maybe, due to the excessive competition the species changes its environment. Or maybe, the species were forcefully thrown out of their old environment by nature.
The environment is the surroundings or conditions in which a person, animal, or plant lives or operates. And, the environment demands that species are well and fit enough in order to compete for its survival and reproduction.
And so, in order to survive and reproduce, all living organisms must adjust to the conditions imposed on them by their environments. This makes the organism better able to survive in its new environment.
Example: Genetic interchange between Finches is prevented when a flock becomes isolated from the rest on an island. Eventually, the isolated group emerges as a completely separate species.
Due to the availability of new or different resources
The availability of new or different resources in an environment causes better options for the inhabiting species to diversify their way of living and survival.
As new resources get available they don’t need to stick themselves to the same-old resources as their ancestors did.
And so, they try new things in their environment, and in doing so they develop better ways and hacks to better survive and thus get better adapted gradually over time.
This reason states that the availability of new or different resources in the environment can affect the outcomes of evolutionary diversification thus leading to adaptive radiation and so speciation.
Example: The finches (small black birds) in the Galapagos Island are well-known for adaptive radiation. It is seen that those species that eat large seeds tended to have large-tough beaks, while those that eat insects have thin-sharp beaks. All have originated from their ancestral seed-eating finches.
Due to the occurrence of new challenges
Another prominent reason for adaptive radiation is the occurrence of new challenges for the species to survive and reproduce in any environment.
As new challenges occur, nature only selects those individuals who are with favorable variations and are best adapted to the environment to take those challenges. Those less fit and unfit organisms are destroyed over time.
The challenges in an environment can be due to loss of habitat, less availability of food, introspecific or interspecific struggle for existence, volcanic eruptions, flood, or damaging effect due to heat, cold, etc.
Those species that have passed the challenges remain alive and those that haven’t passed become extinct. That’s the way of how the natural selection process of evolution works.
Example: The Pseudoxyrhophiinae sub-family of Lamprophiid snakes of Madagascar have evolved into land-burrowing, tree-living, terrestrial, and semi-aquatic forms that converge with the Colubridae family of snakes in the rest of the world.
Adaptive Radiation can occur because of the following:
All of the reasons you will read below seem to be somewhat similar, but they aren’t. In fact, these are distinct from each other with only a few differences.
All of these mentioned below are some of the profound reasons for the occurrence of Adaptive radiation. So, keep reading…
1. Loss of habitat: When organisms lose their natural habitat (where it was born and had learned to survive and reproduce), may soon become extinct if they don’t find any new habitat and get adapted to it. And it is likely that those organisms who used to live in the destroyed region will recolonize without evolving and adapting themselves greatly. And, if they have found new habitat and got adapted then, they will soon evolve via. adaptive radiation.
2. Formation of new habitats: As new habitats become available in the environment it remains isolated for many years, and gradually new random and uncommon arriving species will colonize it. And after colonizing it, they will soon learn and determine various ways to better adapt themselves to their new habitat. This can lead to adaptive radiation over the millions of years of evolution.
3. Adaptation to new environment: As a new species enter a new environment they get new surroundings and the impact of the surroundings on the species is also new and highly challenging. Now while passing through the various challenges, the organism will learn and develop new adapting characteristics phylogenetically over the course of its evolutionary history. The finches in Galapagos Island are the fine examples of this reason.
4. Mass Extinction: Adaptive radiation is a universal occurrence after mass extinctions because the surviving species gradually evolve themselves over time and try to acquire the available resources that once the extinct species had utilized and used. In doing so, they try to dominate over other species while at the same time adapt themselves to better withstand the environment.
5. Increase in new resources: The increase in the availability of new or different resources in an environment can lead to better options for the inhabiting species to diversify their way of living and survival. This causes adaptive radiation more profoundly and gradually.
6. Geographical Isolation: Geographic isolation is a type of reproductive isolation that occurs when a geographic barrier separates two populations of a species who were reproducing amongst themselves, causing them to reproduce with other populations with whom they haven’t reproduced before. This eventually stops gene flow from other groups of the same species. Thus isolated group evolves by accumulating new mutations not to be found in members of related groups. They adapt with such mutations and overtime forms many new species by adaptive radiation.
7. Natural Selection: Nature selects the fittest ones that have better variations and adaptation to survive in its harsh environment. Adaptive radiation actually leads to the relatively fast evolution of many species from a single common ancestor by natural selection. It generally occurs when an organism enters a new area and different traits affect its survival.
Why do adaptive radiations often occur after mass extinctions? Explained in detail
Mass extinction is the massive destruction and wipe-out of a large number of species on earth within a relatively short period of geological time.
This occurred due to various damaging global events or widespread environmental change that occurs too rapidly for most species to adapt.
Large-scale destruction of habitat, unfavorable environment conditions, massive natural disasters, increase of predators and competitors, etc. are some of the causes of mass extinction.
The organisms that were best adapted to the environment survive and the unfit or upadapted ones get destroyed and become extinct.
Mass extinction is the fact of modern life and its how we all are today. Meaning that our ancestors have survived such a devastating event of extinction and had gradually lead to the present-day speciation.
At least five mass extinctions have been identified in the fossil record, coming at or toward the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods.
Mass extinctions affect biological diversity by permanently removing species with advantageous features as well, and this literally changes the course of evolution.
After extinction, it can take about 5-10 million years or even longer for the diversity of life to return to its previous levels as it was before the mass extinction.
The organisms like those of our ancestors who had survived the mass extinctions got better adapted to life and their environment in order to better survive and reproduce. That’s the natural selection of evolution which with time had lead to Adaptive radiation.
Adaptive radiation is a universal occurrence after mass extinctions because the surviving species gradually evolve themselves through the periods of evolutionary changes thus forming many new species that get better adapted differently to the various ecological roles, or niches, in their communities.
We have previously learned that the availability of new or different resources in an environment causes better options for the inhabiting species to diversify their way of living and survival. This causes adaptive radiation more profoundly.
Over the course of many generations, natural selection will act on these species, allowing them to take better advantage of the new and different available resources that were previously used by the extinct species before the mass extinction. As earlier, it was not possible for these surviving species to take over those resources.
Now, after the mass extinction lineages invade different niches and become isolated from one another, they split, regenerating some of the diversity that was wiped out by the mass extinction. This can lead to rapid diversification and adaptive radiation.
Example: Fossil record indicates that mammals underwent dramatic adaptive radiation after the extinction of terrestrial dinosaurs, about 65 million years ago.
How does adaptive radiation lead to speciation?
Speciation is the evolutionary process by which ancestral populations evolve over time to become distinct species.
And during the process of adaptive radiation, an ancestral form gives rise to new species that are better adapted to new habitats and new ways of life.
Also note that, adaptive radiation is not just evolution that creates only a single new species. In fact, Adaptive radiation is an evolutionary process that produces multiple new species from a single, rapidly diversifying lineage. So, don’t ever confuse with other types of evolution.
In simple words, it is the diversification of a group of organisms in a population into new forms filling different ecological niches and forming new adapted populations over time. These newly evolved and adapted populations are the many new species.
It’s when the population of a species enters into a new habitat and establishes itself in a niche of that habitat. In so doing, it adapts to its new environment and becomes different from the parent species over the course of evolution.
Adaptive radiation actually leads to the relatively fast evolution of many species from a single common ancestor. It generally occurs when an organism enters a new area and different traits affect its survival.
A notable example of adaptive radiation is the presence of finches (small black birds) in the Galapagos Island. These birds have originated from a common ancestral seed-eating bird and then radiated to different geographical areas and have gradually undergone adaptive radiation, especially in their type of beaks.
