Encyclopedia of the World's Biomes - Chapter: Island Biogeography Revisited

Elsevier, Encyclopedia of the World's Biomes, 2020. 
Helmus, M., Behm, J.

For centuries, naturalists have been intrigued by islands. Patterns in island biodiversity are the basis for fundamental theories in ecology such as island biogeography theory (IBT). Under this theory, the biodiversity of islands is a function of three processes: immigration, evolution and extinction. Immigration from source pools and subsequent evolution adds biodiversity to islands. Evolution allows immigrants to adapt to island habitats and evolve into new species. In contrast, extinction subtracts species. In a natural context, these three processes are a function of island area and isolation. Larger islands have more immigration, more evolution, and less extinction and thus more biodiversity than smaller islands. Isolated islands have more evolution, but less immigration and higher extinction resulting in lower biodiversity than proximate islands. Understanding how geography influences these three processes is the focus of IBT. Here, we review the history of island biogeographic study, discuss main themes of IBT, and place IBT in the context of the Anthropocene where humans are greatly impacting island immigration, evolution and extinction.