Symbiosis: Mutualism, Commensalism and Parasitism

The species in an ecosystem will interact in different ways. These interactions may have positive, neutral or negative impacts on the species involved.

The term symbiosis can be used to broadly refer to these types of relationships as it directly translates to mean living together (sym: with; bio: life).

There are many examples in nature of two organisms living in close association with each other. The relationship can consist of two animals, two plants, a plant and an animal, or even a fungus and an algae (such as in lichens). Biologists have tried to give names to and define certain examples of 'living together' such as 'symbiosis' and 'mutualism' and 'parasitism' but it is often difficult to know where one type of association ends and another begins.

Commensalism

One organism benefits and the other is neither harmed nor helped.

Mutualism

Both organisms benefit. An obligate mutualist cannot survive without its partner; a facultative mutualist can survive on its own.

Parasitism

One organism (the parasite) benefits and the other (the host) is harmed.

Mutualism
This is a beneficial relationship to both partners of different species living together. For example a bee and a pollinating flowe. The bee gains nectar from the flower for survival, as it uses the bee to carry its pollen to other flowers. So both organisms living together benefit from their existence.



Commensalism
The association of two or more partners living together, where only one benefits from the partnership and the other remains unharmed.  An example of this is the relationship between a sea anemone with and a clown fish. The anemone travels with the fish on route to its destination and the fish remains unharmed.


Parasitism
Parasites are completely dependent on a host for survival. The relationship is beneficial to one, and harmful to the other.  Parasites may live outside or inside a host; they are called ectoparasites (the prefix ecto means outside) and endoparasites (theprefix endo means inside). An example of the endoparasite is the tapeworms which live in the digestive systems of its host. Examples of ectoparasites are ticks and lice.