Commensalism (ecology).

Commensalism is a term used to characterize a particular type of relationship between organisms. Organisms may exist in relation to one another in a variety of ways. Some have a parasitic relationship, where one organism lives by harming another. An example of this can be seen in the leech, which attaches itself to another creature and consumes some of its blood for sustenance. Another type of relationship is mutualism. In a mutualistic relationship, both organisms derive some type of benefit An example of this is the scarlet cleaner shrimp, which obtains its food by cleaning the teeth and skin of other undersea creatures. The shrimp benefits by receiving food, and the other creature benefits from a thorough cleaning. A less common type of relationship between organisms is called amensalism, and it involves one organism being harmed while the other is neither harmed nor benefitted. A counterintuitive example of amensalism would be a herd of cows leaving a path through tall grass—the grass is trampled down day after day as the cows travel to and from their pasture, but the cows are unaffected by the grass or the harm it suffers.