1. Reproductive Isolation

2. Prezygotic Barriers: impedance or the hindering of fertilization
Postzygotic Barriers: Ovum is fertilized after overcoming a prezygotic barrier producing a non-viable fertile adult

3. Prezygotic Barriers
Habitat Isolation: 2 species that occupy Different habitats in the same biome

4. Prezygotic Barriers
Temporal Isolation: Breeding schedule is different … time of day / season / years etc

5. Prezygotic Barriers
Behavioral Isolation: Courtship rituals and other behaviors

6. Prezygotic Barriers
Mechanical Isolation: Morphological differences prevent success

7. Prezygotic Barriers
Gametic Isolation: inability of the sperm to fertilize the egg of different species. Thickness of the eggs outer membrane or the inhospitable environment of the reproductive track.

8. Postzygotic Barriers
Reduced Hybrid Viability: incompatible genes in the genome may impair development (become frail)

9. Postzygotic Barriers
Reduced Hybrid Fertility: When chromosomes do not match in number or structure meiosis will not produce gametes a vigorous organism but infertile

10. Postzygotic Barriers
Hybrid Breakdown: Hybrid is fertile and reproductive but the next generation is feeble and sterile.

11. –Crickets Gryllus pennsylvanicus and Gryllus firmus both inhabit the Eastern US, where they are allopatric. They are separate in that G. pennsylvanicus prefers loamy soils and G. firmus prefers sandy soils. At times they exist in close proximity, but still remain confined to the preferred soil type.