PREZYGOTIC BARRIERS
Most reproductive isolating mechanisms are prezygotic barriers: that is, they prevent fertilization between members of different species from occurring.

Temporal isolation is a prezygotic barrier in which the two species reproduce at different times of the day, season, or year. Wood and leopard frogs are an example of two similar species whose ranges overlap.

Habitat isolation is a prezygotic barrier in which two species whose ranges overlap live in different habitats. As a result, potential mates from the two species do not encounter one another. During the breeding season in eastern North America, five species of small birds known as flycatchers are found in different habitats in the same area. One species prefers open woods and farmland; one frequents beech trees; one is found in alders, one in conifer woods, and one in willowy thickets.