Darwin explored the Galapagos Islands and observed variations of certain species. For example, he saw that the mockingbirds on three different islands were distinct but still similar to the mockingbirds found on the mainland. The level of diversity in an ecosystem can be determined by the frequency of speciation and extinction. Describe speciation and identify two possible prezygotic barriers of the mockingbirds that contribute to speciation. If the mockingbirds became extinct, explain how this could lead to adaptive radiation.