| Concept/Content |
reciprocity / vampire bats |
| Information caption |
Roosting vampire bats (Desmodus rotundus). The bats cannot survive without food more than a few days. But on any given night, 7-30% of the bats fail to find a meal. A bat may then turn to a roostmate and nuzzle its throat. On roughly 5 of 8 occasions, the second bat regurgitates a small amount of blood for the first bat. Such sacrifices are not isolated acts, however. Eventually the donor bat fails to find food. Because bats frequently return to the same roost, the same behavior can occur again, with the roles reversed. The "debt" is repaid (Wilkinson 1984, 1988, 1990). Reciprocity, or the potential for such, is critical. Exchanges (as in other cooperative mutualisms) are simply be displaced in time. Namely, the recipient later reciprocates, essentially closing an unstated deal (Trivers 1971).
See also FRAME 22.
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| Inquiry caption |
Vampire bats (Desmodus rotundus) cannot survive without food more than a few days. But on any given night, 7-30% of the bats fail to find a meal. A bat may then turn to a roostmate and nuzzle its throat. On roughly 5 of 8 occasions, the second bat regurgitates a small amount of blood for the first bat. This occurs even among non-kin (Wilkinson 1984, 1988, 1990). Can you imagine a context in which this costly helping behavior might evolve?
[Note: bats frequently return to the same roost — and roostmates.]
[Vampire bat sharing behavior is not an isolated act. Eventually, the donor bat fails to find food. Roles of beggar and potential donor are then reversed. Here, exchanges (as in other cooperative mutualisms) may simply be displaced in time. Namely, the recipient may later reciprocate, essentially closing an unstated deal (Trivers 1971).]
Grooming is not critical to survival, but it occurs frequently in many primate species, even among unrelated individuals. It is typically reciprocated by later grooming or other social "favors." In one study of food sharing in a chimpanzee troop, based on over 7,000 observed interactions, exchange was ultimately balanced for each chimp pair (de Waal 1989).
Target Concept: Some cases of costly helping are explained by reciprocity. |
| Photographer |
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| Credit |
Photo from the Centre for the Conservation of Specialized Species, conservationcentre.org. |
| SIZE in pixels [file size] |
544x408 |
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