When populations of Geospiza fuliginosa and Geospiza fortis are sympatric on Santa María and San Cristóbal, G. fuliginosa has a shallower, smaller beak and G. fortis a deeper, larger one (top graph), adaptations that favor eating different sizes of seeds.

Allopatric populations of these 2 species on other islands have similar beak morphologies (bottom two graphs) and can eat similarly sized seeds.