Cheating is a term used in behavioral ecology and ethology to describe behavior whereby organisms receive a benefit at the cost of other organisms. Cheating is common in many mutualistic and altruistic relationships. A cheater is an individual who does not cooperate (or cooperates less than their fair share) but can potentially gain the benefit from others cooperating. Cheaters are also those who selfishly use common resources to maximize their individual fitness at the expense of a group. Natural selection favors cheating, but there are mechanisms to regulate it. The stress gradient hypothesis states that facilitation, cooperation or mutualism should be more common in stressful environments, while cheating, competition or parasitms are common in benign environments (i.e nutrient excess).