The New York Times,
November 22, 2005Link
Islands hold a special place in the hearts of evolutionary biologists. When Charles Darwin visited the Galī¿½pagos Islands in 1835, he was stunned by the diversity of birds, which helped guide him to his theory of evolution by natural selection.
Beginning in the middle of the last century, the ornithologist Ernst Mayr laid the foundation for the modern understanding of the way new species evolve, arguing that they mainly emerged when populations became geographically isolated. Mayr based his theory on his studies of birds from Pacific islands.
Yet islands have generally been considered evolutionary dead ends. After animals and plants emigrated from the mainland, it was believed that they became so specialized for island life that they could not leave. They eventually became extinct, only to be replaced by new arrivals from the mainland.
''They were like baubles of the evolutionary past,'' said Christopher E. Filardi, a biologist at the American Museum of Natural History.
But Dr. Filardi and Robert Moyle, a colleague at the museum, have found evidence that islands can act as engines of evolution instead of dead ends.
Animals can spread from island to island, giving rise to an explosion of new species, and even colonizing the mainland again. The results suggest that conserving biodiversity on islands is vital for the evolution of new species in the future.
Dr. Filardi made this discovery by studying a group of Pacific island birds, known as monarch flycatchers, that were among the birds Mayr studied 80 years ago. Dr. Mayr could compare only the anatomy and colors of monarch flycatchers. Dr. Filardi, on the other hand, was able to analyze their DNA.
He collected it from some species by going to remote islands, while Dr. Moyle extracted other samples from preserved flycatchers stored at the museum, going back to the 1800's.
The scientists identified 13 species that shared a common ancestor in Australia or New Guinea between 2 million and 5.6 million years ago. The descendants of that ancient bird spread thousands of miles to islands as far-flung as Fiji and Hawaii. New species arose along the way, undergoing drastic changes at a rapid rate.
In one lineage, the monarch flycatchers tripled their body size in less than a million years. ''This stuff can happen really fast,'' Dr. Filardi said. This evolutionary wave returned to its origins when flycatchers from the Solomon Islands colonized Australia and New Guinea.
Dr. Filardi and Dr. Moyle published their results in the Nov. 10 issue of Nature.
''Many aspects of island bird evolution are going to have to be rewritten,'' said Jon Fjeldsa, an ornithologist at the University of Copenhagen.
Other recent studies suggest that islands may also be engines of evolution for many other animals and perhaps even plants. In the June issue of The Journal of Biogeography, for example, Kirsten Nicholson of Washington University and her colleagues published a study of lizards that live in Central and South America.
The team demonstrated that 123 mainland species are the descendants of an ancestor that lived in the West Indies.
''I have a feeling that in the next 10 years we're going to see a lot more of this,'' Dr. Filardi said.
Today monarch flycatchers and other island species are under serious threat from habitat loss and from rats and other animals introduced by humans. Rising seas from global warming could destroy some islands altogether.
Dr. Filardi argues that the new findings make preserving island biodiversity even more urgent, because islands may be an important source of new biodiversity.
''It's the potential that the earth has to reinvent itself in the future,'' he said. ''Islands may have more to do with that than we ever thought.''
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