Island Biogeography

TWSchoener, University of California, Davis, CA, USA © 2008 Elsevier B.V. All rights reserved.

The MacArthur-Wilson Equilibrium Theory Effect of Elevation

Tests of Species Equilibrium Effect of Habitat

Tests of Turnover Extinction and Conservation

Effect of Area Further Reading

Effect of Distance

As MacArthur and Wilson note in their revolutionary book The Theory of Island Biography, Charles Darwin was among the first to call attention to islands as a crucial subject for scientific study. As he was departing the Galapagos Islands in 1835, Darwin wrote when I see these Islands in sight of each other, & possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties ... If there is the slightest foundation for these remarks the Zoology of Archipelagos will be well worth examination; for such facts would undermine the stability of species.

Of course Darwin's main interest was in evolution; we know now that islands can contribute enormously to our understanding of ecology as well. There are at least seven reasons why this should be so:

1. Islands are 'simple', with relatively few species and habitats so that the often notoriously complex web of ecological relationships is manifested in a more easily understood state.

2. Islands are 'discrete' and often small, providing a well-defined, manageable spatial unit for study.

3. Islands are 'isolated', so that they are relatively immune from outside fluxes, much as a laboratory tank or greenhouse.

4. Islands are 'natural', so unlike those human-constructed containers have biotas adjusted in at least the moderately long term to a confined state.

5. Islands are 'combinatorial', so that species occur in various combinations, often with absences and presences of key species varying as if in experimental removals or introductions, allowing comparative inference of those species' effects.

6. Islands are 'replicated' so that often a number are available with a given set of species or environmental conditions, allowing statistical analysis and experimentation.

7. Islands are 'ubiquitous', not being limited to areas of land surrounded by bodies of water but generalizing to any patch of one type of habitat surrounded by another - mountaintops, river systems, hosts for parasites, etc. Indeed, as MacArthur and Wilson also pointed out, natural habitat is becoming increasingly fragmented, that is, insularized by human activities so that many areas of conservation interest are effectively archipelagal.

Finally, were such scientific rationale not enough, islands are esthetically pleasing, enamoring us all, scientists or not, with their charm and beauty (could this be the real reason many ecologists work on islands?).

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