Animal Contests Flashcards
What do animals compete for? And what are the types of contests
Animals compete for limited resources such as food, territories, nest sites and mates. This can take the form of scramble competition in which the first to get the resource takes it or in the form of contest which takes on the form of agonistic encounters ie combative.
Discuss contests and what they are
Contests may involve displays without contact. Or escalated fights or both. Both will have costs but these are likely to b e much higher in escalated contests. eg jumping spiders wave legs at each other, (non-aggressive contests) and butterflies. However, elephant seals - aggressive contests.
Animals will have different tactics that they can follow in these contests and which one is selected may influence the outcome ie determine which contest wins. The winner gets the resource! Thus the understanding of contests is important because they determine fitness and hence drive natural selection- contests are a fundamental driver of natural selection and sexual selection as they influence fitness and will interact with evolutionary and selectional pressures
What is game theory?
Game theory was initially developed by economists to study rationale human decision-making. Professor john nash developed this theory. It is a theoretical framework for conceiving social situations amount competing players. The best strategy depends not only about yourself but what the rest of the group is likely to do.
what is the most studied game in game theory?
The prisoners dilemma.
Case A
- P1- remain silent (20 years)
- P2 - confess (released)
Case B
- P1- remain silent (1 year)
- P2 - remain silent (1 year)
Case C
- P1- confess (5 years)
-P2 - confess (5 years)
In these payoff conditions the best choice, know as the Nash equilibrium is to confess. Frequency dependent selection- ie the best strategy depends on what others in the population are doing. Like at a concert- behavioural pattern depends on the rest of the population ie if people at the front stand up then everyone will stand up
Who applied game theory to animal contests?
John Maynard Smith- read this article
Lethal weapons may not be used eg poisonous snakes. Previously explained as acting for the good of the species (ie group selection). This is not true as they are selfish to some degree. Natural selection acts on individual genes within individuals, doesn’t act at the species level. By applying game theory and the concept of frequency dependent selection we can analyse the fitness gain from different strategies for individuals.
what does frequency dependent selection mean
the direction of selection being dependent on which options are used in the rest of the population
what is an evolutionarily stable strategy
a strategy that, if all members of the population adopt, cannot be bettered by an alternative strategy a strategy is a mode or option that is genetically determined
what is the hawk dove game
hawk- always fight and may injure their opponents
dove- simply display and never engage in fights. Two doves will spend some time displaying. They do not attack and run away immediately if attacked and avoid injury. ie activist vs pacifist
Imagine a population of doves in which a mutant hawk is produced. How will the hawk fare? the hawk will win all its encounters because it attacks cause the dove to run away. However, if the mutant allele spreads (they get the resources) hawks will start to encounter other hawks and thus some will be injured. ie more fights more injuries
which is better: hawk or dove
lets consider
v- value of the resource
w- cost of the wound
T- cost of time spent displaying
- So in the scenario hawk against dove= 0.5V - 0.5w. This is because 1/2 hawks will receive the resource and 1/2 will experience costs for the wound
- For Hawk vs dove= V as the dove will run away leaving the hawk with the resource
- For Dove vs Hawk- 0 as the dove will run away. doesn’t gain or loose anything
- For Dove vs Dove= 0.5v-t - both the doves play the cost in displaying
if we fill in values we can work out the fitness gain in these strategies.
what is the conclusion of the hawk dove theory
- hawks do well when they met doves (+10) but badly when they meet hawks (-5)
- doves get a higher fitness gain when they meet a hawk(0) than does a hawk meeting a hawk (-5) (the cost of the contest weighs more than obtaining no resource)
- doves meeting doves do better (+2) than when they meet hawks(0)
there should be a population mix when the two do equally well (ie their average fitness is equal) - this is the ESS.
discuss hawk dove and ESS.
point where the fitness of the hawk is equal to the dove is the evolutionarily stable strategy- each strategy has equal fitness. 61.5% hawks and 38.5% doves in the population. if all the animals decided to play the dove strategy it would have a higher fitness. therefore group selection does not occur.
what happens to the ESS of hawk and dove theory if the resource has a higher value
If we increase V from 10 to 15, whilst keeping the other values the same, the ESS is now 80.77% hawks. If it is to increase further to 20 then the ESS is for the whole population to comprise hawks. that is, with high value resources doves may be eliminated from the population.
what happens if the average cost of wounds increases as might happen if weapons are developed, infection is prevalent, or predators take injured contestants
if we increase W from 20 to 30 and keep the other original values we see that ESS shifts to 44.44% hawks. As W increases, the utility of fighting decreases
What happens if the average cost of display increases as might happen if predators are more common and prey on displaying animals?
If T increases from 3 to 10 then the ESS is for 75% hawks. That is, increased display of costs increase the utility of fighting
What is a mixed strategy
so far we have spoke on hawks and doves- pure strategy
a mixed strategy is also possible. Here animals will play hawk with probability x and dove with probability x-1. these probabilities will have the same frequencies as set by the ESS calculation for particular costs and benefits.
