Explain the concept of "adaptive radiation". Why have adaptive radiations proceeded mass extinction events?

Adaptive radiation is a process that occurs due to environmental changes and cause organisms to rapidly diversify from an ancestral species into a lot of new different forms. Simply saying, organisms evolve into a wide variety of new types that are adapted to new modes of life. For example, if certain animals from the same species, occupy different habitats with different environmental conditions, different morphological features or adaptations will be formed.

When mass extinction occurs, consequently number of species decrease and biodiversity is reduced. Many niches are left abundant, so they can be occupied by new species.