The process that occurs when a species introduced into a new ecosystem diversifies into new forms filling different environmental niches.
A change of environment makes new resources available.
When an ancestral species occupies and survives in different environments, the resulting adaptation to these various niches will produce speciation and distinct phenotypes.
How it works:
The classic example of adaptive radiation is what happened to mammals when dinosaurs went extinct.
Mammals had survived for 100 million years before the mass extinction at the end of the Cretaceous, but they were small, insignificant and most likely nocturnal.
When dinosaurs disappeared, mammals were able to fill all the environmental niches left empty by the dinosaurs, which had been the dominant species for millions of years.
Some other examples illustrating the concept of adaptive radiation are the distribution of tenrecs throughout Madagascar; the different subspecies of finches in the Galapagos Islands; the way marsupials populated Australia; and the distribution of crayfish on all continents.