Islands—we are talking about real islands now, rather than “islands” of habitat—tend to be species-poor, or, to use the term of art, depauperate. This is true of volcanic islands situated in the middle of the ocean, and it is also, more intriguingly, true of so-called land-bridge islands that are located close to shore. Researchers who have studied land-bridge islands, which are created by fluctuating sea levels, have consistently found that they are less diverse than the continents they once were part of.
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