| Commensalism is a situation in which two organisms are associated in a relationship in which one benefits from the relationship and the other is not affected much. The two animals are called commensals.
An example is vermiliads (plants living on trees in rainforests) and frogs; the frogs get shelter and water from the vermiliad but the vermiliad is unaffected. Commensalism is a type of symbiosis.
Commensalism:
One organism uses another to get a better position in the environment
neither organism is harmed-- there is usually no physiological interaction between the two organisms
most often for photosynthesis advantages in shaded areas -- very common in rainforests
may also be for reproductive advantages-- some fungi “climb” up trees and vines (while not gaining nutrition from them) in order to release their spores from as high a perch as possible. | 
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