LIFESCI 3C03 Chapter Notes - Chapter 5: Evolutionarily Stable Strategy, The Selfish Gene, Gie

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Ecology Selfish Gene Reading Chapter 5
Aggression: Stability and the Selfish Machine
To one survival machine, another survival machine (not its close relative) is part of its
environment.
- “oe other surial ahies do ot ipige o eah others lies (e.g. blackbird and
mole, who may interact indirectly in that they both eat worms but otherwise remain
contactless)
- Different species may interact in that they are predators to prey, parasites to hosts,
competitors for a scarce resource
- Same species survival machines are potential mates (if they are the opposite sex),
compete for mates (if they are the same sex), and compete for resources
Animals do not often kill conspecifics they are competing against
- Noble tournament, in which one animal eventually backs down
There are both costs and benefits to pugnacity (aggressive behaviour)
- If you kill one rival, there are still plenty others left, so there is not much point in
wasting that effort
- The death of one rival may benefit another rival
- If the benefit of killing a rival outweighs the cost, killing will be favoured (e.g. death of a
rival male means you get to keep his harem of females)
In this situation though, fighting may result in being mauled so hard that you will
not be able to benefit from having his hare, i hih ase ou ouldt fight
him
- Costs of fighting: time, energy, risk of hurt
Maynard: Game Theory approach to aggression
- Evolutionarily stable strategy: a strategy which, if most members of a population adopt
it, cannot be bettered by an alternative strategy
The best strategy for an individual depends on what the majority of the
population are doing
Selection penalizes deviation from an evolutionarily stable strategy
- Hypothetical hawk and dove example:
Note: these terms are not based on the animals themselves!
Hawk: always fight hard and unrestrainedly, retreat only when seriously injured
Dove: standoff until the other backs down
Poits a e aarded + to idiiduals ho i, ad take aa -) from
individuals who lose or waste time
o Poits: currency of gene survival
Whe a doe fights a doe, the ill aste eah others tie ut ood ill get
hurt.
o Winner: +50 for winning, -10 for wasting time
o Loser: -10 for wasting time
o Average individual: +15
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