by Kevin Baldwin
Islands have always been fascinating places. The old story-tellers, wishing to recount a prodigy, almost invariably fixed the scene on an island — Faery and Avalon, Atlantis and Cipango, all golden islands just over the horizon where anything at all might happen. And in the old days at least it was rather difficult to check up on them. Perhaps this quality of potential prodigy still lives on in our attitude towards islands.
— John Steinbeck, from The Log from the Sea of Cortez, 1941
Introduction
In addition to providing great settings for stories, islands have also been a source of fascination and inspiration to biologists. They have had an influence on biology, ecology, and conservation that is far greater than their small areas would suggest. Because they frequently occur in groups called archipelagos, they provide separate but similar environments that have in effect, acted as replicated natural experiments for both nature and the scientists who study it. In the 19th century, Darwin and Wallace's explorations of the Galapagos Islands and Malay Archipelago clearly demonstrated patterns in nature that begged for explanation. It is doubtful that the they would have made their intellectual leaps to the elucidation of natural selection without having experienced those sites first-hand. Islands are like conceptual models: They offer simplified versions of reality. Smaller and less diverse than continents, patterns on islands were easier to see and comprehend.
I. Island Biogeography
In the 20th century, islands were important in advancing our understanding the origin and maintenance of diversity of species. In 1967, Robert MacArthur and Edward Wilson published a book entitled “The Theory of Island Biogeography” that revolutionized the study of ecology and biogeography. MacArthur and Wilson's approach was radical in that it deliberately avoided historical explanations for species diversity and sought to identify and explain more general patterns based upon current organisms' attributes and their relationships to current environments. It also refocused ecological inquiry from simply describing patterns to generating and testing theories that could account for those patterns.
The three island patterns that were linked together by a common theory were:
1. Species-area relationships: Larger islands have more species than smaller ones (there are more places to live, and species are less likely to go extinct if there are more individuals spread over a large area).
2. Isolation: Islands that are farther away from the mainland have fewer species than ones close to land.
3. Species turnover: The number of species on an island tends to remain constant although the identity of the species may change through a process called species turnover.

