When most people hear the term adaptive radiation, they might think about nuclear radiation adapting to our environment. However, adaptive radiation is one of the greatest evolutionary mechanisms that we know of.
Britannica.com defines, adaptive radiation, as evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life. Adaptive radiations are best exemplified in closely related groups that have evolved in a relatively short time.
However, for the common layperson adaptive radiation is a relative short burst of evolution among a species, which creates a variety of species. Despite that, adaptive radiation usually takes place after a mass extinction or on islands.
An example of adaptive radiation occurring after a mass extinction is the extinction that killed off the dinosaurs. What caused this mass extinction was when a massive comet hit earth, off the Yucatan Peninsula. However, the University of Colorado states, that mammals survived this catastrophic event for the most part, because they could burrow in holes for shelter. Regardless, about 90% of all life on earth was destroyed. This led to an opportunity for the surviving plants and animals to disperse to new environments. When these animals dispersed to new environments, they evolved within these new ecosystems. These animals were pressured to to adapt quickly if they were going to survive. As these animals became more adapted to their new environments, they changed so much that they became totally different species. This is what adaptive radiation is.
It is easy to study adaptive radiation taking place today on islands. Some factors that contribute to this are few predators, little food, and small habitat. It is due to this extreme selective pressure that allows adaptive radiation to take place.
Charles Darwin observed this first hand on the Galapagos Islands. When Darwin first arrived on the Galapagos Islands, he discovered finches that looked astonishingly similar to the finches that were found in South America. However, these finches were different in size, diet, and habitat preferences. After years of studying, Darwin figured that these finches on these islands all had a common ancestor that came from the continent of South America and got stranded. After the ancestor finches got stranded, they quickly ate the available-food supply. However, the finches with stronger beaks could eat the seeds that had hard to crack shells. Over a short period, these finches mated with finches that had similar hard beaks. These finches then started to display a much larger beak when compared to the original ancestors. In fact, they soon became their own distinct species. Other finches adapted in similar ways to find new food resources. With the adaptive radiation that occurred by the time Darwin arrived, there were 13 different species of finches, each with their respective niche on the islands, according to pbs.gov.
This discovery also played a vital role for Darwin when he formulated the theory of evolution.
The main cause of adaptive radiation is high pressure from the new environment. Since islands are limited in their resources, a species has to adapt quickly or die.
A few things to remember about adaptive radiation are animals do not consciously decide to make changes. If certain traits are better suited for an environment, then that species will have a better chance to reproduce and create offspring with that trait.
While adaptive radiation does occur relatively fast, it still can take many generations to see any actual changes. This can make things extremely difficult when learning about extinct species. Also, plants undergo adaptive radiation, as well. However, it is more rare for plants to do this, because they cannot disperse to new territory as animals can.