To better understand the scope of organisms and how they react with the world around them, we need to step back from mutualistic relationships to look at the broader category of Symbiosis.
Symbiosis simply refers to the interaction of two (or more) different species of biological organisms. However, symbiosis is subdivided into categories based upon the effect this interaction has upon each of its members or the species in general:
Mutualism: A symbiotic relationship in which both symbionts gain benefit from the interaction.
Example: Bees transfer pollen between flowers and fertilize them as they gather nectar and pollen as a food source.
Commensalism: A symbiotic relationship in which one organism benefits from the relationship, while the other is not significantly helped or harmed.
Example: A group of fish called remoras are equipped with modified fins along the top of their heads, Which acts as suckers. Remoras attach to larger fish and marine mammals. In most cases the symbiont gain nothing from the interaction. The remoras not only get a free ride, but also feast on stray bits of food dropped by the host.
Parasitism: A symbiotic relationship in which only one member of the association benefits, whereas the other is harmed.
Example: Tapeworms are flat segmented parasites that live in the digestive tracts of some animals, including humans. The tapeworm gets its nutrition as the host is digesting food. The host receives no positive advantage from the tapeworm.
There are also a few other types of interactions which don’t exactly fit into the above categories, but do play a significant role in the welfare of the species and survival of individuals within that species.
Competition: Groups or individuals within a species battle for available food or territory, with those from another species.
Predation: The predator/prey relationship entails the consumption of individuals from one species by those of another. This may seem to be the same as parasitism, in that one species receives a benefit while the other is harmed, but in general, a parasite receives the benefit while the host is alive. Of course, there are exceptions. And if we look past the individuals, to the species as a whole, in many cases both the predator and prey groups are strengthened by this struggle for survival, with the weakest among them being weeded out.
It is not always easy or even entirely possible to clearly sort some relationships into a particular category. Disputes often arise among scientists as to which group certain interactions belong to. There are also those who believe that symbiosis should only refer to persistent mutualism. Without ignoring the possible validity of such a view, for the purpose of this site, we will include the other types of subcategories as part of symbiosis.