L5 Flashcards
Inclusive fitness theory: Hamilton’s rule
- Shifted focus away from individual to gene level
-Individuals can gain fitness by assisting reproduction of close relatives
-Animals expected to be more helpful to close relatives than non-relatives
What is the equation for a favoured behaviour in Hamilton’s rule?
C - cost to actor of social behaviour
B - benefit to recipient of social behaviour
R - genetic relatedness between actor and recipient
sibling relatedness = 0.5
cost < r x b
Examples of social actions and their cost and benefits, giving food to recipient
- C is positive as is B
Food is worth more to recipient than actor eg recipient could not find food and was hungry
Cost has to be less than benefit x relatedness for it to occur
Cannibalism
- Cost to actor is negative
-Benefit to recipient is also negative - Recipient loses out
-For it to occur cost < r x b
- Favours little to no relatedness
Tiger salamanders are more likely to develop into cannibals if they are in groups containing:
- Many conspecifics (other salamanders)
- Variation in larval size
- Mostly unrelated individuals
Game theory
- Optimal way to behave can sometimes depend upon other individuals
Eg time trial vs race
If others are producing sons (or daughters), it’s better to produce daughters (or sons) to maximise number of grand-offspring
If the sex ratio is even its better to produce an even ratio of sons and daughters
= evolutionary stable strategy (ESS)
Evolutionary stable strategy (ESS)
If others are producing sons (or daughters), it’s better to produce daughters (or sons) to maximize number of grand-offspring
If the sex ratio is even its better to produce an even ratio of sons and daughters
Sex ratios P1
- Two daughters each produce 4 offspring
- Each matriarch female ends up with 8 grand offspring
-If an equal sex ratio then each son will have one mate producing 4 grand offspring - 9 grand offspring again
- Each matriarch female ends up with 8 grand offspring
Sex ratios P2
If twice as many females, each son mates with two females producing twice as many grand offspring as daughters
If the sex ratio is male biased a female having daughters will have a higher fitness than the male having sons
Selection tends to favour an even sex ratio
Oscillation till equilibrium at an even sex ratio
Sons and daughters are equally as good at passing on genes
Animal contests - Pairwise contests examples
-The hawk dove game
-Rock paper scissors game
The hawk dove game
Two individuals contest ownership of a resource in pairs
Hawk- dove game
Hawk
* Never shares, always fights
* Big win vs large loss
* High risk
Dove
* Will share, never fights, retreat if opponent fights
* Low risk
* Never get whole resource
* Little gain
Payoffs
value of resource = v
Cost of fighting to loser = c
Payoff matrix =
Payoff matrix
- Each dove gets half of resource - Each hawk vs hawk wins half and loses half (v-c)/2 - Hawk gets entire resource vs dove, but pays a fighting cost against other hawks - Dove gets nothing against a hawk but doesn’t incur a cost - Dove shares so gets some pay-off against other doves
Invasion of rare strategies
Lone dove strategy
* Doves payoff is nothing
Hawks is costly
- Dove invade when 0 is greater than doves cost
- Dove theory can invade population
Hawk will:
- With a hawk population a dove can push population towards dove strategy
- Doesnt have to be 50/50 for each strategy
- Both strategies create evolutionary stability
- We can get a pure ESS of hawks or invasion from both ends producing a mixed ESS
Bourgeois
- Individual plays hawk when resident and dove when intruder
- Resident wins (convention)
- Bourgeois always invades dove
- Bourgeois can invade hawk and resists hawks if v< c
Bourgeois butterflies
Sit on sun spots waiting for females
Unoccupied spot they will take over it
Occupied spots they try and take it over
Resident always wins
Eg once owner is gone a new resident comes and will always win
