[ISL] "Three Island Stories"

[rfmcdonald]

3 Quarks Daily recently featured an essay by Kevin Baldwin describing islands, useful for--among other things--providing small-scale, easily-managed models of the sorts of ecological and geological trends of continents.

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.

Island biogeography is one thing Baldwin examines. Put simply, the amount of land area determines the diversity of species supported in a given territory (the larger the island, the more ecologically diverse it is). This has serious implications for non-island environments.

If we think of large patches of undeveloped habitat as large islands, then we can understand that initially they should support a high diversity of species. As development occurs within large plots, they will be effectively divided ad isolated into smaller and smaller islands. What is an ordinary road to us can present an impassable obstacle to some species. A superhighway could be a barrier to all except birds. Even some forest-dwelling birds will not cross open areas. Something as seemingly innocuous as a lawn may be as forbidding as a paved parking lot to some species.

The equilibrium number of species on an island is a balance between colonization and extinction. Smaller islands of habitat will have higher rates of extinction because they will support smaller populations that are more likely to go extinct due to chance. They also are likely to be structurally simpler with fewer habitat types that can support fewer species. Small islands also have more perimeter relative to their area, and this increased edge allows more incursions by predators and parasites. As development continues, the habitat patches will get smaller and more isolated from one another. Isolation makes it less likely that new colonization will make up for higher extinction rates. Habitat fragmentation can continue in this manner until only small patches of habitat with few species remain. Small species may live out their entire lives within one patch and thus be less likely to suffer these effects. Large ones may not be so lucky. Fragmentation is one reason why large predators like bears, panthers and wolves are especially susceptible to extinction.

One partial solution to the fragmentation problem may be to connect island reserves to one another with corridors of habitat. However, some worry that narrow corridors may increase mortality (by increasing "edge") and/or act as corridors for disease as well. Currently, most people think that large reserves are the best bet for preserving species diversity because as large "islands" they intrinsically have lower extinction rates. Having large reserves near or connected to one another could increase colonization rates. Buffer zones of less dense development around reserves may also increase their effective size and connectedness.

Meanwhile, besides islands providing examples in miniature of geological processes--volcanic islands, with their cataclysms, comes particularly to mind--Baldwin notes the example of Baldwin island, once barren but then--thanks to Charles Darwin, among others--made into a productive cloud forest.

Read the whole essay. Baldwin gets islands, at least their non-human aspects.