Prezygotic barriers prevent members of different species from mating to produce a zygote, a single-celled embryo. Some example scenarios are below:
- Two species might prefer different habitats and thus be unlikely to encounter one another. This is called habitat isolation.
- Two species might reproduce at different times of the day or year and thus be unlikely to meet up when seeking mates. This is called temporal isolation.
- Two species might have different courtship behaviors or mate preferences and thus find each other “unattractive”. This is known as behavioral isolation.
- Two species might produce egg and sperm cells that can’t combine in fertilization, even if they meet up through mating. This is known as gametic isolation.
- Two species might have bodies or reproductive structures that simply don’t fit together. This is called mechanical isolation.
These are all examples of prezygotic barriers because they prevent a hybrid zygote from ever forming.
Prezygotic and postzygotic barriers not only keep species distinct, but also play a role in the formation of new species.