Islands have always had a great influence on the natural sciences, far out of proportion to the tiny fraction of Earth's surface that they cover. The reason for this is straightforward: Islands and other insular habitats, such as lakes, caves, springs, and mountaintops replicate natural experiments. Island biogeography is a field within biogeography that attempts to describe and understand the innumerable patterns in the distribution of species arising from these natural experiments.
Islands can be divided into two broad types: (1) true islands, land wholly surrounded by water, and (2) habitat islands, other forms of insular habitat, that is, discrete patches of habitat surrounded by strongly contrasting (hostile) habitats.
In terms of geology, geography, and biology, true islands can be subdivided into two types:
Oceanic Islands. These ...