Isolation Barriers

• Reproductive isolation


  Barriers that prevent two populations from interbreeding, keeping their gene pools separate
• Categories of reproductive isolation barriers


  • Prezygotic isolation
  • Postzygotic isolation
• Prezygotic isolation


  • Occurs before fertilisation can occur (no offspring are produced)
• Postzygotic isolation


  • Occurs after fertilisation (offspring are either not viable or infertile)
• Prezygotic isolation barriers

  • Temporal isolation
  • Behavioural isolation
  • Geographic / ecological isolation
  • Mechanical isolation
• Postzygotic isolation barriers


  • Inviability of hybrid organisms
  • Infertility of hybrid organisms
  • Breakdown of hybrid organisms
• Temporal isolation


  Two populations differ in their periods of activity or reproductive cycles
• Temporal isolation


  • Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed
• Behavioural isolation


  Two populations exhibit different specific courtship patterns
• Behavioural isolation


  • Certain populations of crickets may be morphologically identical but only respond to specific mating songs
• Geographic isolation


  Two populations occupy different habitats or separate niches within a common region
• Geographic isolation


  • Lions and tigers occupy different habitats and do not interbreed (usually)