Prezygotic barriers impede mating or hinder fertilization if mating does occur.
Two species of garter snakes: one lives mainly in water while the other is mainly terrestrial.		The eastern spotted skunk mates in late winter; the western spotted skunk mates in late summer.		Blue-footed boobies of the Galapagos perform a courtship display unique to the species. Boobies:		These 2 species of snails have opposite spirals in their shells so their genital openings are not aligned.