Symbiosis

Mutualism is a symbiosis between species in which both partners benefit. Mutualism is considered by some biologists to be the archetypal form of symbiosis. The examples of symbiosis that are discussed in the next section are all mutualisms.

Parasitism is another type of symbiotic association, in which one organism obtains nourishment from a host, usually without killing it. In most parasitisms, the parasite has a close and sometimes obligate relationship with the host. However, to be healthy, the host by no means needs the parasite, and in fact usually suffers a detriment from the symbiosis. Commensalism is a relationship in which one symbiont benefits from the interaction, while the host species is neither positively or negatively affected. For example, small epiphytic plants derive a substantial ecological benefit from living on larger plants, but the latter are not usually affected to a meaningful degree.