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Special Relationships between Animals and Plants

Organisms do not live in isolation. Every organism is linked in some way to at least one other living thing. Plants are closely associated with herbivores which depend on all kinds of vegetation for their survival. All predators are dependent on their prey.

Organisms are in constant competition with each other for space and food. A few organisms have very close associations with each other. In many cases the organisms in the association are so dependent on one another that they are unable to survive on their own.

This is true for organisms in a mutualistic relationship. Mutualism is the term used for two organisms which are associated with each other in some way. In a symbiotic relationship both of the organisms gain benefits from their association.

Lichen on rocks, Antarctica © Shirley Burchill

In other associations only one of the organisms benefits. This is true in a parasitic relationship. Here the parasite gains some advantage from the other organism but the other organism does not benefit from any advantage; in fact, the parasite does harm to the second organism in some way.

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