Island biogeography is the study of past and present animal and plant distribution patterns on islands and the processes that created those distribution patterns. Historically, island biogeographers mainly studied geographic islands—continental islands close to shore in shallow water and oceanic islands of the deep sea. In the last several decades, however, the study and principles of island biogeography have been extended to ecological islands such as forests and prairie fragments isolated by human development. Biogeographic "islands" may also include ecosystems isolated on mountain-tops and landlocked bodies of water such as Lake Malawi in the African Rift Valley. Geographic islands, however, remain the main laboratories for developing and testing the theories and methods of island biogeography.

Equilibrium Theory

Until the 1960s, biogeographers thought of islands as living museums—relict (persistent remnant of an otherwise extinct species of plant or animal) scraps of mainland ecosystems in which...