Friday, July 14, 2006

 

Evolution caught in the act

Competition between two species of finch in the Galapagos has caused the beak size of one species to shrink, and scientists have watched it happen. Detailed observations of the birds, which Darwin famously studied while formulating his theory of evolution, have provided one of the best descriptions of a characteristic trait evolving in the wild.

In a paper appearing in this week's issue of Science, Peter and Rosemary Grant, both biologists at Princeton University, New Jersey, describe the struggle between the medium ground finch (Geospiza fortis) and the large ground finch (Geospiza magnirostris).

In the harsh environment of the tiny Galapagos island Daphne Major, the medium ground finch subsists mainly on small seeds. Members of the population with sufficiently large beaks, however, have been able to tackle the bigger seeds of a low herbaceous plant called Tribulus cistoides.

These larger-beaked birds met with competition upon the arrival of the bigger G. magnirostris, a few members of which flew to the island in 1982 and set up a colony. Their universally large beaks made cracking into big seeds an easy job.

A Tribulus seed is like 'an orange wedge with two great big long spines sticking out the back of it,' says Dolph Schluter, a zoologist at the University of British Columbia in Vancouver, Canada, who worked with the Grants when he was a graduate student. 'The medium ground finches twist off the ends, but it takes a lot of force to do it. G. magnirostris has no problem with it.'

The two species lived fairly happily together for many years, until two factors forced the birds into harsh competition.

The above news report is also available here

Abstract of the Science report (Evolution of Character Displacement in Darwin's Finches) available here

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