Topic 12. Social Behavior and CooperationSocial behavior can be examined from a cost/benefit standpoint. Some costs and benefits are very obvious, but some are not. For instance, aerodynamic advantage is a benefit of birds flying in a V formation that is not necessarily obvious.Why would animals NOT live in groups? Clearly, some of the COSTS associated with living in groups would be Competition and Disease.COMPETITION: Can limit sociality and group size. There’s a positive correlation between competition for resources and group size. Remember that territoriality and dominance hierarchies can reduce the costs of sociality.Why WOULD animals live in groups? Although there are many benefits of group living (see PP slide #2) two of the most compelling reasons are Evading Predators and Finding Food.EVADING PREDATORS. Groups can use a variety of successful tactics to evadepredators. These categories or descriptions are not mutually exclusive.1. Dilution Effect: Associating with others exponentially reduces the chances of becoming prey as group size increases.2. Selfish Herd: Get behind another conspecific or in the middle of a group to avoid predator attack. This is NOT cooperation. (Shoal=group of fish not moving; School=group of fish that IS moving in a coordinated fashion)3. Confusion Effect: Decreases predation when predators have difficulty in picking out a prey from the crowd.4. Vigilance: This is a major function of sociality, especially among closely related individuals (see Inclusive Fitness and Kin Selection). Vigilance by one species can benefit heterospecifics in a mixed-species flock or group. Another benefit of having a sentinel on lookout (besides predator avoidance) is that the other members of the group can spend more time with their heads down feeding. An example of this is the Redshank.5. Group defense: Decreases predation risk when group actions such as mobbing behavior drives off predators.FINDING FOOD. Living in groups can help individuals find sources of food through a variety of strategies which are not mutually exclusive.1. Local Enhancement: The presence of others foraging for food can be used as an indication of abundant food resources. Local Enhancement does not necessarily mean that the animals are intentionally attracting conspecifics to the site, but remember that animals can, under some circumstances, intentionally communicate the location of resources to conspecifics. A good example of this would be the Leaf-Cutter ants.2. Information Centers: Flocks of animals can serve as centers about information regarding food sources. This is particularly true if the food patches arelarge, but ephemeral.3. Capturing Difficult Prey: Conspecifics can intentionally attract others toassist in capturing or accessing a difficult prey item. Some species can hunt in packs (which would involve a level of cooperation), or some species need help from conspecifics to tear open a prey item. This is the example shown by ravens who are carrion feeders and ordinarily solitary, but a single raven might not be ableto tear open a dead prey item such as moose and require assistance from conspecifics.Why COOPERATE? Remember that cooperation is not synonymous with group living. The “Selfish Herd” is an example of group living without cooperation. In fact, the animals in a selfish herd are actually competing with each other.A definition of cooperation is when the behavior of one individual benefits another.Cooperation is actually a Darwinian dilemma since natural selection criteria favorsurvival and reproduction by individuals, and does not support the idea of helping or cooperating with others. Cooperation is strongly associated with altruism in which an action benefits a recipient at an immediate cost to the actor.So a major question in animal behavior is how can altruism evolve? The presence of altruism in the behavioral repertoire or phenotype of an animal is unexpected given the criteria of natural selection.There is a major difference in the hypotheses regarding altruism evolution between those explanations for this behavior among close relatives vs. non-related individuals.ALTRUISM EVOLUTION IN RELATED INDIVIDUALS. Inclusive fitness and resulting kin selection are evoked as explanations for how altruism can evolveamong groups of closely related individuals.Inclusive fitness = direct + indirect fitnessDirect fitness: an individual’s reproductive/genetic successIndirect fitness: increasing the probability of successful allele survival, due to genetic relatedness, by altruistic behavior. Inclusive fitness models add to models of natural selection by considering the effect of an allele, not only on the individuals that bears it, but on individuals sharing the allele which are identical by common descent.The average percentage of alleles (coefficient of relatedness) an individual can expect to share with genetic relatives is:Parents, offspring = 50%Siblings = 50%Grandparents, grandchildren = 25%Aunts/Uncles, Nieces/Nephews = 25%First cousins = 12/5%Hamilton’s Rule and kin selection involve costs and benefits adjusted by relatedness.Helping behavior can evolve among genetic relatives when:B X r > CWhere: B = Benefit to the recipientr = coefficient of relatedness C = Cost to altruistWE DID NOT COVER HAMILTON’S RULE IN THE 1:00