Adaptation in Darwin's Finches
Beak depth, which is correlated with body size and
the ability to crack larger seeds, varies according to drought
conditions, which produce fewer, harder seeds in dry years and more and
softer seeds in wet years. The change is ±5% in extreme years.
The graph shows a pattern of stabilizing selection, in which beak depth
fluctuates around a mean of about 9.6mm.
Consistent environmental differences in different
habitats on different islands in the Galapagos, as well as the
availability of different foods sources, have produced more than a
dozen distinct species of finches, all unique to the archipelago.
Text
material
© 2004 by Steven M. Carr
