One question: how do you know
he is just playing?
• If this is practice for later, real fighting, how do
the participants know this is not the real
thing?
• 1) Order and frequency of play activity not
the same as the real thing: exaggerated and
misplaced
Not the real thing
• 2) Play markers or signals: stereotypic
activities designed to signal intent. Behaviors
of dogs: pawing, bowing, etc.
• 3) Role reversal or self-handicapping
- Here what would normally be a dominate
individual will take a subordinate role, let the
other one “win”.
- Letting your little brother “beat” you or he may
not play with you!
here
General theory
• Some separate/some overlap.
• How about a general theory?
• Main function of all play is to develop physical
and psychological skills to handle unexpected
events were you lose control.
- Increases versatility of movements used to
recover loss of balance
- enhance ability of animals to cope with
unexpected stressful situations
Summary
• Three types of play, based on whether you
play with objects, yourself, or others.
• Each has some unique functions and common
ones
• Overall function is to prepare individual, not
just for adulthood, but for the uncertainties of
adulthood
• Increases your reaction capabilities and coping
skills.
Aggressive behavior (Chap 14)
• Not all fun and games!
• As mentioned, play gets you ready for adult
life, one filled with a lot of aggression
Aggressive behavior (Chap 14)
• Not all fun and games!
• As mentioned, play gets you ready for adult life,
one filled with a lot of aggression
• Saw it in sexual behavior, especially between
males, but can happen between females.
• Occurs often outside of sexual context
• Besides sexual behavior between male and
female, likely the second most frequent behavior
type, and is even found in sexual behavior!
Aggression or agonistic behavior
• Defined: refers to behavior between members
of the same species that is intended to cause
pain or harm
•
•
•
•
Again, lets see how we would define it.
Violent
Resolve conflicts
Establish social order
•
•
•
•
•
Warnings
Defense of resources
Instill fear in others
Communication
Defend offspring
• Excludes predation or predation is a special
form of interspecific aggression!??
• Will deal with this later.
Classification
• Can we classify different types of aggression?
• Aggression can be subdivided into types based
on intended victim, body postures during
aggression, and other factors such as what the
animal may want, estrus status of animals
involved, and location of the aggressive
encounter
Classification
• In each hints at function, so lets look at this.
• supposed function of the aggression can be
used as the basis of classification:
• Dominance (status related) related,
possessive, protective and territorial,
predatory, fear induced, pain
induced, parental, redirected, play, intermale,
interfemale, and pathophysiologic (medical)
in origin.
Communication
• First thing to remember is that aggression is
actually a means of communication.
• Communicating your emotional state
• Communicating your intentions
• Communicating your social rank
• Etc.
Dominance
• One of the best known forms of aggression is
in establishing social rank.
• Solitary animals: territorial aggression.
• Social animals: Dominance Hierarchy.
• Social rank determined by outcomes of
aggression, Alpha male/female, Beta
individuals, etc.
Factors involved
Reasons for aggression
• Ultimate implications:
• used to resolve competitive disputes over
resources (territory, food)
Ultimate implications
• More access to resources
Ultimate implications
• Greater survival of young
Proximate mechanisms
• Testosterone
• The hormone of
winners!
Not just limited to males
• Higher testosterone,
higher rank
• High ranking females
more aggressive
Proximate mechanisms
• Glucocorticoids: hormones related to stress
• The hormone of losers??
• Stress hormone, would expect more stress in
subordinate individuals
• But yet…
• Some propose dominance hierarchy way of
reducing social stress, everyone knows its
place!
Not necessarily!
Enough stress to go around!
• Way of reducing social stress??
• Most cases not
• Dominant individuals stressed about keeping
dominate status
• Subordinate ones stressed because of
aggression in dominant ones and because
they want to advance!
Is it just testosterone?
•
•
•
•
Wide range of hormones figure in
Just starting to unravel it all
serotonin plays a role
In mammals: low levels linked with high
aggression but low status.
• In fish: the opposite
Overall
•
•
•
•
Proximate cause of aggression is hormonal
Testosterone one we know best
Others still working on
Exactly how they “cause” aggression??
Evolution of aggression
• In aggressive encounters, the outcome
depends on the actions of both involved.
• There are two possible actions: fight or flee
and if your willing to fight, it now depends on
what your opponent decides
• Similar to cooperation models brings us to
game theory as a way of modeling evolution
of fighting behavior: betting on other’s action
Three prominent models
• Hawk-dove
• War of attrition
• Sequential assessment
Commonalities
• There is a cost to fighting
- opportunity costs (cost associated with not
doing something else
- physical injury
• Includes a variable represents the value of
resource being contested.
- access to food
- access to reproductive opportunities
Resource value
- Often will value the resource differently.
- This sets the stage for level of motivation to
fight or not.
- If your hungrier,
you may fight
harder than if
your not.
Hawk and dove
• Game theory model proposed by Maynard
Smith and others in the 70’s-80’s
• Setting: individuals can adopt one of two
behavioral strategies when faced with possible
aggressive situation
Hawk and dove model
• - Hawk: player will continue to escalate until it
either is injured or the opponent gives up.
• Like poker, the person who will always raise
the bet.
• - the Dove: player will attempt to escalate but
will retreat and give up if opponent escalates
• Poker: the person who is “bluffing”!
Conditions (stakes)
•
•
•
•
•
•
•
V = value of the contested resource (the “pot”
C = cost of fighting (what you have to lose)
Envision 4 possible combinations
Hawk-hawk
Hawk-dove
Dove- hawk
Dove-Dove
here
Combinations and outcomes
Dove
Hawk
Easiest: hawk-dove
- Hawk wins
(V – C)/2
Hawk
V
0
(V – C)/2
V/2
0
Dove
V
V/2
Dove-Dove?
Dove
Hawk
• Assume
each
“wins” half
Hawk
the time
• No cost
because
other
leaves.
Dove
(V – C)/2
V
0
(V – C)/2
V/2
0
V
V/2
Hawk-hawk?
Hawk
• -only loser
pays the
cost.
• 50% chance Hawk
of winning
• 50% chance
of paying
cost (injury)
(V – C)/2
V
0
(V – C)/2
V/2
0
Dove
V
V/2
What is evolutionary stable strategy?
•
•
•
•
•
Depends on relative value of V and C
If V > C, then being a hawk is the ESS.
Hawk meets dove, hawk wins
Hawk meets hawk, win ½ time
Only time dove wins anything is when it meets
another dove, ¼ of the time this happens!
• Reason: Price paid (C ) is low compared to V
and you only pay it if you loose!
ESS
• IF V < C, becomes more complex
• Now not necessarily beneficial to be a hawk in
a hawk world. Price of fighting not worth the
cost, which you will pay ½ the time!
• Now some combination of hawks and doves
becomes the ESS.
Real animals?
• If value of resource is high, e.g. mating
opportunities, we can see how aggression
would be selected for. Fighting over the
resource is only way to win.
• If resource value is low, not worth fighting for,
better to be a dove.
• Example of speckled wood butterflies.
• Resource: open forest patch
• If you come across a territory that is occupied, you
leave.
• Only a hawk If you
have territory.
Why?
Resource patch
ephemeral, why fight
ever it.
Another example
• Case: when value of resource might be high
but resource is not limited.
• Here inherent value might outweigh cost BUT
relative value/availability becomes low.
• Mexican spiders: establish territory but if
intruder comes, they leave rather than fight.
Costs less to go and find new territory than to
fight.
Rules of engagement
• So not just a model on how aggression might
arise in a population.
• Model for decision making as to when to be
aggressive or not
• Determining factors are V and C.
War of Attrition model
• Often aggressive interactions settled by
displaying rather than fighting
• One who displays the longest wins
• For this type of aggressive encounters, we can
use war of attrition model.
• War of attrition scenarios refer to the
situation where fighters attempt to grind
down the opponent's defenses. There is no
fixed cost associated with losing or contesting,
but as the encounter wears on, each player
accumulates incremental costs. A decision to
give up arises when one individual backs
down, relinquishing access to the contested
resource, rather than continuing to sustain
further insults
Model assumptions
• Three assumptions.
• 1) individuals can choose to display
aggressively for any duration of time.
• 2) Display behavior is costly, the longer the
display, the more energy expended
• 3) no clear cues such as size, territory, etc. that
contestants can use to settle a contest
Let the game begin
• Basic standoff situation, the first one to blink
loses.
• If V = value of resource and C is cost, what is
the length of a contest involving displays (x)?
• How long do you remain engaged in this?
• Basically depends on V because cost is equal
between the two.
Probability of length of display?
• Instead of asking how long they should stay,
we can ask, what is the probability of them
staying a given x length of time.
•
• At the ESS, the probability that a contest lasts
x units of time = (2/V) e-2x/V
• Ok….
Visually
• Three different values of V, calculate
probability of each x via:
• (2/V) e-2x/V
• Longer x, less
probability.
Higher possibility
contest lengths
will be short.
Who’s blinking and why?
• Said that costs to display should be equal but
why would one give in so often at a low
contest length??
• Basically how much are you willing to pay?
• Prior experience, food resources for example,
how hungry you are!
• Seems to be some support of this in the wild.
Sequential assessment model
• Model to realistically analyze how animals
fight.
• Authors felt other game models not based on
realistic behavioral mechanisms. So much
behavioral diversity in fighting behavior
cannot be analyzed with them.
So how is it different?
• Designed to analyze fights where individuals
continually assess each other via series of
bouts or mini fights.
• So how does model attempt to do this?
Assessing opponent’s ability
• Authors argue similar to statistical sampling.
• One “sample”, a “bout” gives the individual an
idea BUT is prone to random error (how
realistic is it?)
• Increase the sample, reduces the error rate
and have better idea of the “mean” fighting
ability
Once you sampled!
• Once you have sampled sufficiently, you now
can gauge your opponent’s ability against
yours.
• If your chances of winning are low, you leave
• If your chances are high, you fight in ernest!
Sampling process
• So how should you go about sampling fighting
ability?
• Obviously different levels of aggression/
fighting = costs.
• So, start out with the lower levels and
gradually work to higher, more dangerous
levels, until one gives up
• More similar they are, the more aggressive
the behavior
Sequence
• This model also predicts that if there are
numerous behaviors, they should be used in
the same sequence across all fights.
• So if #1 is lowest and #2 progressively more,
etc.
• #2 should always follow #1, #3 - #2 etc.
• Until one breaks away.
• Only the length of contest and thus number of
behaviors will change.
Evidence for this?
•
•
•
•
•
•
•
Sounds good but is there support for it?
Mixed support
Best is with fighting fish.
Males form hierarchies
Range of aggressive behaviors
Color changing (lowest)
To circling to bite each
other (highest)
The study
• Videos of encounters to see how far each
would go based on respective rank.
• Seem to match prediction.
1) More evenly matched,
the longer and more
escalated the fight.
2) Sequence was the same
every time.
Summary of the three models
• Each designed to model different aspects of
aggressive encounters.
• Designed to predict how aggressive behavior
might evolve.
• Rules of engagement, when should you fight,
• With whom you should fight,
• How to avoid physical combat or at least more
dangerous encounters
Summary
• Evolutionarily designed to increase your
access to resources, without getting killed!
• Does result in winners and losers
Winners, losers, and others!
• Can ask how winning or losing may affect your
performance in future encounters.
• Also what is the effect on those that are
watching? (bystanders)
• Lastly, what effect does the audience have on
encounter outcomes??
Winner and loser effects
• Know that in sports winning or losing can
influence how well you do the next time
(pumps you up or breaks your self confidence)
• Similar in animals: winner effects: If you win
an encounter, probability you will win the next
is higher. And visa versa.
• Why?
Winners and losers
• Losers seem to have more glucocorticoid
stress hormones for a longer time after the
fight.
• Testosterone levels related to winning and
losing
Evidence?
• Lots of field evidence: Blue-footed boobies
Snakes
• Copperhead snakes
Mice
• Fig. 4. Testosterone and
Corticosterone levels across the
five conditions. Testosterone
increases significantly in males
that win more than two previous
encounters compared to
controls, and in male winners
that win three previous
encounters compared to male
winners that have won zero
previous encounters.
Bystander effects
• Ok, lots of support for winner and loser effects
• How about bystanders?
• What affect does seeing another win or lose
have on YOUR chances of winning or losing?
• What does watching give you?
Interspecific aggression
• Predators against prey but
• Non-predator situations.