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Sociality and Social Behaviour (Part 2). Reciprocity - incur a cost now in anticipation of receiving a benefit later. Altruism by non-relatives. Modelling - use Game Theory - John Nash. Prisoner ’ s Dilemma. Altruism by non-relatives. 2 prisoners - caught and jailed for a petty crime.
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Reciprocity - incur a cost now in anticipation of receiving a benefit later Altruism by non-relatives Modelling - use Game Theory - John Nash
Prisoner’s Dilemma Altruism by non-relatives 2 prisoners - caught and jailed for a petty crime - suspected of having committed a more serious crime
Prisoner’s Dilemma Altruism by non-relatives Each prisoner (player) has a choice cooperate - deny all knowledge of the serious crime defect - accuse the other of the more serious crime Reward for defecting - forgiven minor crime
Prisoner’s Dilemma Altruism by non-relatives Each strategy has a payoff Payoff depends on behaviour of the opponent 1. Both cooperate - both get a reward - R 2. Both defect - both get punished - P 3. One cooperates & one defects - defector set free - T (temptation payoff) - cooperator jailed - S (sucker’s payoff)
Prisoner’s Dilemma Altruism by non-relatives This relationship of payoffs must hold T > R > P > S Temptation > Reward > Punishment > Sucker’s
Maximum sentence - 12 years (10 for major, 2 for minor) What are the years saved by each strategy? Altruism by non-relatives Player B Plays first Cooperate Defect Player A S = 0 R = 10 Cooperate T = 12 P = 2 Defect
Prisoner’s Dilemma How should they behave? Altruism by non-relatives -should defect - always saves something Player A • if B cooperates - T > R -if B defects - P > S If both defect do worse than if they cooperate R > P Player B
Prisoner’s Dilemma How should they behave? Altruism by non-relatives After a number of simulations with more than one move, Best strategy is a tit-for-tat -cooperate on first move and then do what opponent did on previous move
Prisoner’s Dilemma Benefits of tit-for-tat Altruism by non-relatives Initially cooperative Quick to retaliate Quick to forgive
Does this work in nature? Altruism Kin Selection Reciprocity
Kin Selection - in mate acquisition Altruism Wild turkeys - male progeny of a single brood - group for life -dominance hierarchy - only dominant male mates
Kin Selection - in mate acquisition Altruism Reproductive success of non-mating males -realized through RS of brother How? If brother mates with four females -non-maters RS = 4 x relatedness x .5 (to account for female’s contribution) = 4 x 0.5 x 0.5 = 1.0
Reciprocity - in mate acquisition Altruism Long tailed manakins
Reciprocity - in mate acquisition Altruism Long tailed manakins - only dominant male mates Courtship dance Subordinate Dominant
Reciprocity - in mate acquisition Altruism Does subordinate male assume role of dominant? predicted • • Copulations per hour: New alpha male • observed • • • • • Copulations per hour: previous alpha male
Reciprocity - in mate acquisition Altruism Why have 2 males? - females are attracted to 2-male courtship groups
Reciprocity - in predator detection Altruism Meerkats - sentinels
Reciprocity - in predator detection Altruism Meerkats - sentinels -forage in groups - not related -every so often - one animal stands to look for predators -sentinel warns of approaching predator
Reciprocity - in predator detection Altruism Meerkats - sentinels This behaviour is adaptive if: Chance of being preyed on while acting as a sentinel Survivorship while others are sentinels <
Reciprocity - in predator detection Altruism But is this really reciprocity? Alternative hypothesis (selfish): “Sentinels” are really just animals who have finished feeding and are looking for predators to protect themselves.
But is this really reciprocity? Some predictions from reciprocity hypothesis: Altruism Prediction Observation Regular rotation of sentinel duty Sentinel duty appears to be haphazard Sentinel duty has risk of succumbing to predator Sentinels are usually closer to an escape burrow Less time is spent in predator detection in groups No difference in sentinel time when solitary