Sociality and Social Behaviour
(Part 2)
Altruism by non-relatives
Reciprocity - incur a cost now in anticipation
of receiving a benefit later
Modelling - use Game Theory - John Nash
Altruism by non-relatives
Prisoner’s Dilemma
2 prisoners - caught and jailed for a petty crime
- suspected of having committed a
more serious crime
Altruism by non-relatives
Prisoner’s Dilemma
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
Altruism by non-relatives
Prisoner’s Dilemma
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)
Altruism by non-relatives
Prisoner’s Dilemma
This relationship of payoffs must hold
T > R > P > S
Temptation > Reward > Punishment > Sucker’s
Altruism by non-relatives
Maximum sentence - 12 years (10 for major, 2 for minor)
What are the years saved by each strategy?
Player B
Plays first
Cooperate
Defect
Player A
Cooperate
R = 10
S=0
Defect
T = 12
P=2
Altruism by non-relatives
Prisoner’s Dilemma
How should they behave?
-should defect - always saves something
Player A
-if B cooperates - T > R
-if B defects - P > S
Player B
If both defect do worse than if they
cooperate
R > P
Altruism by non-relatives
Prisoner’s Dilemma
How should they behave?
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
Altruism by non-relatives
Prisoner’s Dilemma
Benefits of tit-for-tat
1. Initially cooperative
2. Quick to retaliate
3. Quick to forgive
Altruism
Does this work in nature?
Kin Selection
Reciprocity
Altruism
Kin Selection
- in mate acquisition
Wild turkeys
- male progeny of a single brood
- group for life
-dominance hierarchy - only dominant male
mates
Altruism
Kin Selection
- in mate acquisition
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
Altruism
Reciprocity
- in mate acquisition
Long tailed manakins
Altruism
Reciprocity
- in mate acquisition
Long tailed manakins - only dominant male mates
Courtship dance
Subordinate
Dominant
Altruism
Reciprocity
- in mate acquisition
Does subordinate male assume role of dominant?
predicted
•
•
•
Copulations per hour:
New alpha male
•
• •
observed
•
•
Copulations per hour: previous alpha male
Altruism
Reciprocity
- in mate acquisition
Why have 2 males?
- females are attracted to 2-male courtship groups
Altruism
Reciprocity
- in predator detection
Meerkats - sentinels
Altruism
Reciprocity
- in predator detection
Meerkats - sentinels
-forage in groups - not related
-every so often - one animal stands
to look for predators
-sentinel warns of approaching predator
Altruism
Reciprocity
- in predator detection
Meerkats - sentinels
This behaviour is adaptive if:
Chance of being
preyed on while
acting as a sentinel
<
Survivorship while
others are sentinels
Altruism
Reciprocity
- in predator detection
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.
Altruism
But is this really reciprocity?
Some predictions from reciprocity hypothesis:
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