Social Cooperation and Reciprocal Altruism in Desmodus rotundus
Vampire bats provide a wonderful example of social cooperation in the form of reciprocal altruism.  True reciprocal altruism is very rare, in most cases it is a combination of kin selection and other forms of cooperation.  Thus the vampire bat is an excellent study subject for reciprocal altruism because it fits the definition almost perfectly.  Reciprocal altruism is described as when one animal acts for the benefit of another animal and in doing so decreases its own fitness (Winterhalder 1998).  The reason for this altruism is because in the future the giving animal expects to be able to receive that same service in its own time of need.  Thus, there must be a way for the animals in the group to keep track of these exchanges as well as identify animals that are cheating the system and are only giving, not receiving (Mesterton-Gibbons 1992).  The vampire bat has developed complex behaviors to deal with all of these issues.  First, it is important to understand why vampire bats need to participate in reciprocal altruism in order to increase their ability to survive.  Vampire bats require blood meals every night.  By nature of their sanguivorous diet, they deteriorate rapidly when they miss meals after just two days (Michel 1999).  Failure rates for feeding are much higher than mortality rates would suggest,  vampires fail to successfully feed 7-30% of the time (Winterhalder 1998).   The high failure rate and yet low mortality rate  is explained by the ability for  a vampire that misses a meal to go to other members of its particular group and receive a food transfer that will hold the vampire over until it can go and feed again the next night (Kunz and Pierson 1994).  This allows the vampire a bigger window of leeway for feeding and puts less pressure on finding a meal every night.  Younger bats, especially, are in need of this assistance because they are not yet experienced enough to get meals every night and have much higher failure rates than adults (33% compared to 10% [Kunz and Pierson 1994]).   This high failure rate compounded by the necessity to feed often is what results in the need for reciprocal altruism.  Vampire bats have developed this altruism and maintain it by vigilance to make sure and weed out any would-be cheaters.  Some believe that the vampire bats social interactions, mainly grooming, is the method by which vampires detect cheaters.  Researchers have noted that the social grooming occurs after the night's foraging and is centered around the stomach region (Kunz and Pierson 1994).  When vampire bats feed, they consume so much blood that their stomachs become severely distended and therefore it is easy to detect which members of a social group were successful feeders that particular evening.   Knowing which bats were successful allows the bats to know who is able to share food to any of the group members that were unsuccessful.  The vampire bat thus is able to detect who can give, and also remember who has given in the past.  These are essential in upkeeping the altruism system.
  The vampire bats behavior in these interesting displays of reciprocal altruism can be seen as selfish only in the sense that the reason to give to a group member in need is because in the future the giver is going to be in the same situation and needs to be assured that she will be helped by her group members.  Thus, it is selfish in the ultimate sense because the altruistic act of sharing food with a starving group member is expected to be reciprocated at some point in the future.  This altruism is sometimes based on kin altruism, but only if it happens that the group is comprised of some relatives.  This is not the norm, however, so despite there being individual cases in existence of kin altruism, the overall system is  reciprocal altruism.
 
  • Habitat and habitat utilization
  • General description of Desmodus rotundus and its social system
  • Social spacing
  • Social relationships
  • Summary
  • Bibliography

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