Systems are structured by countless interactions between components, which are driven by the felt or experienced degree of profit of a relation with an other component, expressed as beneficial (+), unfavourable (-) or neutral (0). Seven types of interactions can be defined, grouped in symbiotic, oppositional and neutral.
Mutualism + +
Components benefit from each other.
Commensalism + o
One component benefits from another that is not affected.
Amensalism o –
One component inflicts harm to another without any costs or benefits received by itself.
Parasitism + –
One component, the parasite, benefits from the interaction, while the other (host) is harmed. It is a form of symbiosis which comes with a price. It actually is a predator but rather than kill quickly, it consumes its host in small pieces. Some types of parasites manage to live permanently inside their host (Wilson et al.).
Competition – –
More components compete for the same resources or between them.
Predation + –
One component hunts (being predator or herbivor) and eats the other (being prey or plant). Within one type of component it is called cannibalism.
Two components that interact but do not affect each other, where interactions are negligible or insignificant.