An adaptive radiation is a burst of evolution, creating several new species out
of a single parent species. A population of species, 1, moves into a new
habitat and establishes itself in a niche, or role, in that habitat. While
there, it adapts to its new environment and becomes different from the parent
species. Next, a new population of the parent species, 2, moves into the area,
trying to occupy the same niche as 1. Because of the niche rule, which states
that only one of a group of closely related species may occupy the a niche in a
given habitat, competition between 1 and 2 places pressure on both groups to
adapt to separate niches. In this process, each becomes further distinguished
from each other and the parent species. A third or even more populations of the
parent species may move into the area, causing several different species to
arise from the same parent species.