recap

483

22.5 recap

Dietary specialization, pollinator specialization, sexual selection, and poor dispersal abilities are correlated with high rates of speciation. Open ecological niches present opportunities for adaptive radiations.

learning outcomes

You should be able to:

  • Explain the factors that commonly affect speciation rates.

  • Describe the conditions that favor adaptive radiation.

Question 1

How can pollinator specialization in plants and sexual selection in animals increase rates of speciation?

If a pollinator specializes on one particular flower type, that will reduce opportunities for cross-fertilization among different flower types. Any polymorphism in flowers can thus lead to rapid genetic divergence between individuals that express each flower type. A similar process occurs with sexual selection in animals. If some females prefer to mate with males that have a certain trait and other females prefer a different male trait, then the population can quickly lead to genetic isolation and differentiation in the two groups.

Question 2

Why do adaptive radiations often occur when a founder species invades an isolated geographic area?

A new immigrant to an isolated area may encounter no competition for a particular feeding strategy or life style. Under these conditions, there are many “open niches” that can be co-opted by the invading species, leading to a rapid increase in speciation.

The result of 3.8 billion of years of evolution has been many millions of species, each adapted to live in a particular environment and to use environmental resources in a particular way. In the next chapter we will look at the molecular processes that gave rise to that diversity.