Symbiosis can vary between mutualism, commensalism, and parasitism, though these grade into each other, and it is often difficult to tell which is involved in a given relationship. In mutualism, both organisms benefit. In commensalism, one benefits and the other is unaffected; in parasitism, one benefits and the other is harmed.
Some of these relationships are so close that we speak of the composite of two species as one unit; for example, we speak of the composite of algae and fungi as lichens.
Mutualism
A type of symbiotic interaction in which both organisms benefit from the relationship in some way.
Commensalism
An interaction in which one organism benefits from the relationship without causing benefit or harm to the other organism.
Parasitism
A type of symbiotic interaction in which one organism benefits and the other is harmed.
Cleaning symbiosis
Many species are involved in cleaning symbiosis, though claimed symbioses grade into commensalism, scavenging and parasitism. A clearly symbiotic example is the cleaner wrasse Labroides, a small fish conspicuously shaped and marked, being longitudinally striped with blue. It eats only ectoparasites at "cleaning stations" from the bodies of larger fish such as puffers, sweetlips and groupers.
Endosymbiosis
Autotrophic endosymbioses
Digestive endosymbioses
- Humans and intestinal bacteria
- Ruminants such as cows and their intestinal bacteria and protists
- Termites and their intestinal bacteria and protists
- Aphids and Buchnera bacteria
See also
- Interspecies friendship
- List of symbiotic organisms