Ecological Character Displacement in Darwin's Finches.

Character displacement resulting from interspecific competition has been extremely difficult to demonstrate. The problem was addressed with a study of Darwin's ground finches (Geospiza). Beak sizes of populations of G. fortis and G. fuliginosa in sympatry and allopatry were compared by a procedure that controls for any possible effects on morphology of variation among locations in food supply. The results provide strong evidence for character displacement. Measurement of natural selection in a population of G. fortis on an island (Daphne) lacking a resident population of G. fuliginosa shows how exploitation of G. fuliginosa foods affects the differential survival of G. fortis phenotypes.