Symbiosis is a relationship between two or more organisms that live closely together. There are several types or classes of symbiosis:
- Commensalism
- One organism benefits and the other is neither harmed nor helped.
- Mutualism
- Both organisms benefit. An obligate mutualist cannot survive without its partner; a facultative mutualist can survive on its own.
- Parasitism
- One organism (the parasite) benefits and the other (the host) is harmed.
To be successful, a symbiotic relationship requires a great deal of balance. Even parasitism, where one partner is harmed, is balanced so that the host lives long enough to allow the parasite to spread and reproduce.