Friday, July 14, 2006; Posted: 12:15 p.m. EDT (16:15 GMT)
WASHINGTON (AP) --
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A medium sized species of Darwin's finch has evolved a smaller beak to take advantage of different seeds just two decades after the arrival of a larger rival for its original food source.
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This was certainly a documented case of microevolution, added Fleischer, who was not part of Grant's research.
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In 1982 a breeding population of large ground finches, Geospiza magnirostris, arrived on the island and began competing for the large seeds of the Tribulus plants. G. magnirostris was able to break open and eat these seeds three times faster than G. fortis, depleting the supply of these seeds.
In 2003 and 2004 little rain fell, further reducing the food supply. The result was high mortality among G. fortis with larger beaks, leaving a breeding population of small-beaked G. fortis that could eat the seeds from smaller plants and didn't have to compete with the larger G. magnirostris for large seeds.
That's a form of evolution known as character displacement, where natural selection produces an evolutionary change in the next generation, Grant explained in a recorded statement made available by Science.
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more:
http://www.cnn.com/2006/TECH/science/07/14/darwin.finches.ap/index.html