| Type | Characteristic |
|---|---|
| Prezygotic | Mechanisms that act before a zygote has formed |
| Ecological | Differences in habitat; individuals do not meet |
| Temporal | Reproduction takes place at different times |
| Mechanical | Anatomical differences prevent copulation |
| Behavioral | Differences in mating behavior prevent mating |
| Gametic | Gametes are incompatible or not attracted to each other |
| Postzygotic | Mechanisms that act after a zygote has formed |
| Hybrid inviability | Hybrid zygote does not survive to reproduction |
| Hybrid sterility | Hybrid is sterile |
| Hybrid breakdown | F1 hybrids are viable and fertile, but F2 are inviable or sterile |