As a result of these different rates, we expect the traits of those groups with high speciation or low extinction to be common among species and the traits of those groups with low speciation or high extinction to be rare. Species selection is thus a way to explain the patterns noted above. To understand species selection, we will consider different possible reasons for different rates of speciation and extinction. We have discussed speciation in some detail already. We need to make sure we understand extinction before we continue to study species selection.
Extinction occurs when all members of species die out leaving no descendents.
So there are currently no descendents of species that have really gone extinct. We can contrast this with something called pseudoextinction, which occurs after speciation, when we consider that the ancestral species no longer exists, but that the descendents of that species still exist. To understand species selection, we will consider possible reasons for high rates of speciation or low rates of extinction in some groups. Adaptive radiation occurs when there is a high rate of speciation because there is the potential for each new evolving species to adapt to use a different aspect of the environment. Adaptive radiation occurs in situations in which the environment is relatively empty of potentially competing species.