Final answer:
Prezygotic barriers prevent fertilization, while postzygotic barriers affect the survival or fertility of hybrids.
Step-by-step explanation:
Reproductive isolation is divided into two groups: prezygotic barriers and postzygotic barriers. Prezygotic barriers prevent fertilization from taking place, while postzygotic barriers occur after fertilization and affect the survival or fertility of hybrid organisms. For example, prezygotic barriers can include gametic barriers where the gamete cells of different species do not allow fertilization, or mechanical barriers where reproductive structures do not fit together. On the other hand, postzygotic barriers can lead to hybrid inviability, where hybrid organisms do not survive past the embryonic stage, or hybrid sterility, where hybrid organisms are born sterile and unable to reproduce offspring of their own.