1. COOPERATION
Tit-for-Tat and reciprocal
altruism
By-product mutualism
We’ll save for later:
Kin Selection
Coop in Humans

3. General payoff for costly
Two roads to Cooperation
Coop
Defect
TFT
Defect
Coop
(b-c) -c
TFT
(b-c)
(-c)
Defect b
General payoff for costly
Cooperation
Defect
(b)
Prisoner's Dilemma:
the only ESS is to
Defect
TFT is an ESS when:
(-)  c b
>
Reciprocal altruism OR
Cooperation is an ESS when:
r > c/b
where r = coefficient of relatedness (Kin Selection)

4. Reciprocity – Food sharing in Vampire Bats (Gerald Wilkinson)
Evidence for repeated interactions – unrelated group members may share a
roost for several years

5. Data from natural roosts
1) Bats tend not to be
related to each other
2) Cooperation occurs among
commonly associating bats
Associations
Cooperating Pairs
Associations
All Pairs

6. Benefit of receiving aid outweighs the cost of donating
cost of giving up 5%
of your fed weight
weight
benefit of receiving
that 5%
starvation
time since last meal (hrs)

7. Benefit of receiving aid outweighs the cost of donating
cost of giving up 5%
of your fed weight
weight
benefit of receiving
that 5%
starvation
cost benefit
time since last meal (hrs)

8. Using experimental roosts Wilkinson showed:
-- 12 of 13 regurgitations were between members of the same roost in the field
-- Recipients reciprocated to previous donors more than was expected by chance
probability of future interaction is high
individuals can recognize each other
the benefit of a cooperative act greatly outweighs the cost
potential for future retaliation is one does not cooperate

9. Switching gender roles as reciprocal altruism
Egg trading and reciprocity in sequentially
hermaphroditic fishes, e.g., black hamlet fish
Switching gender roles
as reciprocal altruism

10. Are these guppies
cooperating?
Predator-inspection
behavior in guppies

11. Is c > a ? Payoff matrix in terms of the
probability of not being eaten by
the predator
Is c > a ?
Cooperate
(inspect)
Defect a b c d
Yes, inspection is costly

12. Information is Public This individual reacts
similarly as the lcose individual
when the latter is visible

13. Milinski’s experiments with mirrors and sticklebacks shows retaliation
Mirror projects a fellow inspector
traveling side by side the length of
the aquarium
Mirror projected 32° shows fellow inspector
dropping back and finally disappearing the
closer the focal fish approaches the predator

14. Reciprocal Altruism
and predator mobbing

15. (1)
Defector
Cooperator
(2)

17. Byproduct mutualism Problems with Tit-for-Tat
Tracking debts owed and favors
given requires complex score-keeping
Cooperate
Defect 5 1
Cooperate is the sole ESS

18. Prisoner’s Dilemma and byproduct mutualism in blue jays
Trained blue jays choose a perch that
delivers:
Large rewards to its neighbor Or
(2) Small rewards to itself

19. Prisoner’s Dilemma Byproduct Mutualism Prisoner’s Dilemma
Mutual cooperation
Mutual defection
One coop, one defect
?????
Why don’t they coop
Here
????
Individuals act in concert with the theory (in part)
Individuals learn quickly to respond accordingly
Individuals do not cooperate in the Prisoner’s Dilemma even when iterated
Why the mutual defection even when
the PD game is iterated between jays?

20. It is only through iterated cooperation
that both jays can receive their largest
payoff
Individual play of the game has a large
temptation to cheat – Prisoner’s Dilemma

21. The structure of the Payoff Matrix Matters – organisms learn/have
knowledge of the payoffs and respond accordingly
(Pris Dil vs. Byproduct Mut)
Reciprocal Altruism (TFT) is broadly distributed in the animal world
Its seen in simple organisms (fish) largely and social spp (humans later)
Sex, social foraging, predator avoidance/mobbing, and others for sure

22. The trick is for jays to see their food accumulating in transparent
containers and every 4 turns they get to feed.
Proportion
cooperating
Opponent’s strategy
TFT
Accumulating benefits
(low discount)
Unaccumulating
(high discount)