Symbiosis is the interaction between two different organisms living in close physical association. Typically these relationships last for a long period of time and impact the fitness of at least one of the animals. There are three main distinctions of symbiosis; Mutualism, Commensalism, and parasitism.
Mutualism Symbiosis is a relationship in which both species benefit from the interaction with the other. This kind of relationship can be seen between the Rhinoceros and a small bird called an Oxpecker. These birds land on the backs of the beasts and eat off the ticks and parasites living there, giving the bird a free meal and freeing the Rhino from the small pests. Oxpeckers also help in times of danger by flying up and screaming a warning to the rhino-acting as a live alarm system for the animal. Most times this relationship is by choice, to give organisms advantages that they would not have had alone. Other times, though,through obligatory Mutualistic relationships, organisms are completely interdependent on the other. This is shown through ants and the Umbrella thorn Acacia tree, in which the tree gives the ants shelter and the ants protect the tree from other herbivores wanting to dine on the tree. Without the shelter the tree provides for the ants, the ants would perish and without the protection that the ants provide the tree, the tree would suffer. Thus exemplifying obligatory mutualism.
Commensalism Symbiosis, on the other hand, is when, in a relationship of two organisms, only one benefits from the other while the other isn't affected either negatively or positively by the relationship. This is shown by the birds that rest in the Acacia tree. They're benefited by the protection and shade that the tree provides, but the tree isn't in any way affected by the birds in it's boughs.
Completely different from the other two symbiotic relationships is parasitism symbiosis. In this parasitic relationship, which is only slightly similar to commensalism as only one of the two organisms rake in the benefit. But it differs from commensalism and mutualism in the way that the other organism in the relationship actually suffers negative consequences from the relationship. A fantastic example of this type of relationship is between an Elephant and the ticks living on the skin of the animal. The tick has a benefit from sucking the elephants blood and creating a lifestyle for itself, but the Elephant suffers due to the small irritating bites that the ticks continually leave.