Based on an evolutionary theory that assumes that the attributes of organisms are optimal, i.e., better than others in terms of the ratio of fitness benefits to costs; the theory is used to generate hypotheses about the possible adaptive value of traits in terms of the net fitness gained by individuals that exhibit these attributes.

Ex. Crow/whelk=>optimality model

An evolutionary approach to study of adaptive value in which the payoffs to individuals associated with one behavioral tactic are dependent on what the other members in the group are doing. 

Captures behavior in competition better than optimality model.

See Hawk vs. Dove model

• Scottish deer: territory holder is challenged by outside male who roars, territory holder roars back; sometimes escalates into a "standoff," the "parallel walk," see if they can take one another; either leave or brawl

• Lemurs secrete gross liquid in defense

• Male chimp turns to yawn/bare teeth to deter other males

• Hippos also do this when competing for females

Two Strategies: 

• HAWKS: Always Escalate
• DOVES: Always display, then retreat before contest escalates into fighting

Payoffs: 

• Win: +50
• Lose: 0
• Injury: -100
• Waste time in display: -10

Proportion of time winning or losing times payoff

• Won't work--> not stable
• Number of individuals playing hawk will decrease if all hawk
• All dove could be invaded by strategy involving hawk

A strategy which, if adopted by all members of a population, cannot be invaded by an alternative.

Ex. In terms of Hawk vs. Dove, ESS is at equilibrium, where mean payoff from hawk strategy=mean payoff from dove strategy

Mean payoff for attacker:

Proportion of time winning or losing times payoff.

Hawk vs. Hawk=

1/2(win)+1/2(lose)=1/2(50)+1/2(-100)=25

Hawk vs. Dove=

1(win; always win)=1(50)= +50

Dove vs. Hawk=

1(lose; always lose)= 1(0)= 0

Dove vs. Dove=

1/2 (win minus display cost)+1/2 (loss minus display cost)= 1/2 (50-10)+ 1/2(0-10)= 15

h = frequency you play hawk

= probability of hawk encounter

h-1  = frequency you play dove

= probability of dove encounter

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• Develop linear heirarchy
• Set up 1 male unit w/ high ranking male
• Introduce low-ranking male
• Sometimes compete, sometimes no
• Low ranking male watches females
• If females groom high ranking male a lot, low ranking will not challeng him due to difficulty of challenge

• Defend territory
• Some "floaters" sneak in to mate a little and eat a little sneakily 
• After 3 trials, discovered that as summer went on, there is more food
• ESS in early summer different than later b/c easy to get food as floater in late summer
• Many territory holders abandon territory in late summer to reap benefits of being floater
• Must look for ESS not "optimal strategy"

1) One individual's fighting strategy depends on ____?

2) The ESS depends on ___ and 3)___?

1)What others are doing

2) Other strategies in the game

3) the values assigned to each strategy

Most animal contests don’t escalate into fighting but instead involve displays.

Displays occur because there is no single “best” strategy. Animals must assess their opponents and make decisions based on these assessments.

Natural selection favors individuals

that give displays because...

Dominant animals will win contests

Subordinate animals will avoid costly fights

Size, strength, physical ability--> reliable

Intentions--> unreliable

• Pitch of roar in red deer (Natural selection faors challengers that pay attention to roar that indicates male size so that they know when not to fight)
• Size in Elephants
• Stalk-eyed flies try to figure out who is bigger via display of distance b/t eyes

• some signals have become indicators of aggression--> "intention movements"
• not all displays are intention movements
• when vervet monkeys slapped the ground but did not attack, opponents started to ignore
• the more frequently a display is used, the less effective it is

Threat displays:

1)

2)

3)

1) Giving displays is always adaptive

2) Individuals can display using either reliable or unreliable signals

3) Although signalers will try to bluff, selection will favor recipients that attend only to reliable signals

1)Why are most displays honest indicators?

2) How is this enforced?

3) Example?

1) Because they involve a cost

2)Skeptical recipients enforce this as they weed out unreliable signals

3) male birds with black badge area

• larger black strip=higher status
• correlated with testosterone levels so it is an honest indicator
• tested by taking low ranking male in a new flock and putting larger black stripe on him
• mostly unattacked, but eventually one bird (usually older male) attacks, and false-striped bird loses fight
• rest of flock finds out, and unreliable signal is weeded out

• Tested hierarchy by devocalizing male to test in flocks
• In unestablished flocks, devocalized males fell to bottom of hierarchy
• In established flocks, devocalized males retained status

• High-ranking males call most often and at the highest rates
• All males compete most often against rivals of similar rank
• Contests between similarly-ranked rivals:

- longer

- more calls

- higher calling rates

- more likely to result in fighting

Why Have Badges of Status? 

(Recipient and signaler perspective)

From the signaler’s perspective:

Subordinates avoid costly fights

Dominants can too

You may deceive your opponent

From the recipient’s perspective:

Often a quick, reliable way to assess an opponent without fighting