Species & speciation
- According to the biological species concept, organisms belong to the same species if they can interbreed to produce viable, fertile offspring.
- Species are separated from one another by prezygotic and postzygotic barriers, which prevent mating or the production of viable, fertile offspring.
- Speciation is the process by which new species form. It occurs when groups in a species become reproductively isolated and diverge.
- In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation.
- In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation.
The biological species concept
What keeps species distinct?
- 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.
How do new species arise?
- Allopatric speciation—allo meaning other and patric meaning homeland—involves geographic separation of populations from a parent species and subsequent evolution.
- Sympatric speciation—sym meaning same and patric meaning homeland—involves speciation occurring within a parent species remaining in one location.