A more pronounced difference in a particular character occurring where two similar species coexist than where their populations do not overlap. A classic example involves two species of Galápagos finch, Geospiza fortis and G. fuliginosa (see also darwin’s finches). On islands occupied exclusively by one or the other species, the beak of either species tends towards an intermediate size. But where these two species occupy the same island, they can easily be distinguished by beak size, the beak of G. fortis being noticeably larger than that of G. fuliginosa. This is an effect of competition between the two coexisting species, which has caused the finches to evolve different-sized beaks to exploit seeds of different sizes more effectively. Other types of character that affect the competitive ability of overlapping species, including physiological and behavioural characters, may also be displaced. This ecological character displacement is driven by competition, whereas reproductive character displacement reinforces reproductive barriers and prevents mating between closely related species.