08 December 2009

Galapagos Finches

The Galapagos Islands were apparently colonized by at least a male and a female finch from the mainland of South America. There are now 13 closely related species of finch on the islands. (Perhaps not coincidentally, there are about 13 major islands in the archipelago.) The thought is that these birds built up numbers on the first island and then spread out to the others, only to become reproductively isolated on them. When isolated, they built up barriors to reproduction with the birds they left behind. So, from one species, there evolved 13. Because they have been isolated for a relatively short time, they look pretty much the same except for bill size. Events like this of multiple speciation are called adaptive radiation.

A similar adaptive radiation is thought to have happened with the Hawiian Honeycreepers in the family Drepanidae. Because these islands were colonized long before the Galapagos were, the various honeycreepers show a whole lot more diversity than do the Galapagos Finches.


Large-billed Ground Finch
 
Medium and Small-billed Ground Finches

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