What are the motifs in The Song of the Dodo: Island Biogeography in an Age of Extinctions by David Quammen?

The importance of extinction is a recurring idea in the book. The equilibrium theory of island biogeography was initially proposed by the scientists Edward Wilson and Robert MacArthur. It predicts that every island ecosystem will eventually approach a balance where the number of new species that arrive or evolve on the island will be roughly equal to the number that go extinct. Quammen makes much of this theory as it drives a good deal of the research into island ecosystems after its appearance.