A Look at Symbiosis:

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:

Mutualistism: A symbiotic relationship in which both symbionts gain benefit from the interaction. Familiar examples include flowering plants and pollinators; ants and aphids.

Commensalism: A symbiotic relationship in which one organism benefits from the relationship, while the other is not significantly helped or harmed. Examples include barnacles on a whale; moss that grows on a tree.

Parasitism: A symbiotic relationship in which only one member of the association benefits, whereas the other is harmed. Examples include: fleas on a dog; parasitic wasps and the caterpillars they lay their eggs in.

There are also a few other types of interactions that 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. Examples include corals and sponges; cheetahs and lions. 

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. Examples include the lion and the zebra; the eagle and the fish. 

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 those who believe that the word, symbiosis should only refer to persistent mutualism, as it once did. 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.