Cheating is a metaphor commonly used in behavioral ecology to describe organisms that receive a benefit at the cost of other organisms. Cheating is common in many mutualistic and altruistic relationships. Natural selection favors cheating, but there are mechanisms to regulate cheating.
The producer/scrounger game contains cheaters. Producers search for their own food while scroungers take the food others have found. Scroungers benefit when producers are common. Producers benefit when scroungers are rare. If there are many scroungers and few producers, the producers are easily able to find food since there is much less competition. If there are few scroungers and many producers, the scroungers can easily cheat. The scroungers are no longer competing against each other to take the producer’s food. A bird can be a scrounger. Instead of foraging for its own food, the scrounger will wait until another bird comes back with food. The next day, the scrounger will follow the successful bird to the patch. The cheating bird reaps the benefits without putting in the effort that the producer put in to find the food.
Examples of animals that are known to cheat include cleaner fish, social insects, ungulates, and birds. Cleaner wrasses have a mutualistic relationship, a cleaning symbiosis, with their clients in which the cleaners eat ectoparasites from the integument of other fish ("clients"). The clients benefit by being cleaned and the cleaners benefit by acquiring food. However, the false cleanerfish, which is actually a blenny, cheats by eating tissue, scales and mucus off its clients in addition to parasites. This could be detrimental to the clients and possibly turn the mutualistic relationship into commensalism or parasitism.
In eusocial insects such as some bees, ants and wasps, the queen is usually the only individual that reproduces. On some occasions, however, cheating workers also reproduce disrupting the mutualistic relationship between the queen and the workers.
Vigilance is essential for most animals. When in groups, animals on the periphery will be vigilant, while those within the group forage. The inner animals also monitor the vigilance of the others. A cheater may emerge in groups by continually foraging while the remainder of the group switches between foraging and being vigilant.
The relationships between flowering plants and their animal pollinators and plants and fungi are generally mutualistic, but there are cheaters. Two genera of yucca moth larvae eat yucca seeds and pollinate them, but a third genus does not pollinate the yucca because it lacks the necessary mouthparts, though it lays eggs on the yucca.  The animal pollinators are not the only cheaters though. Some flowers do not produce nectar. Many pollinators are not able to distinguish between which flowers produce nectar and which do not; therefore, some flowers cheat by not making nectar for the pollinator. Examples of nectarless plants include some species of orchids. Orchids are not just cheaters towards pollinators. Some orchids cheat by not providing fixed carbon to mutualistic fungi.
In order to avoid cheating in polyandrous honeybees, worker policing is enforced, which entails the removal of eggs laid by selfish workers. To prevent cheating cleaner fish, the clients chase them or switch partners.
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