Conflict and agression: Agression Flashcards
What is agression
Agression is a social behavior with fitness consequences for both the actor and recipient.
Even when it pays to be agressive there is still huge variation in how long and hard individuals fight -> can’t be explained by relatedness
What explains variation in agression?
Agression is determined by the benefit cost ratio
Benefit of being aggressive depends on benefit/cost ratio (V/c)
V = value of resource
c = cost of fighting (giving + receiving aggression)
Aggression favoured if V/c > 1
This means that the level of agression between non related individuals varies depending on the cost of fighting and the value of the resources. -> huge variation
Does not take into consideration -rB as the actor is not related to the recipient so does is not influenced by the costs to the recipient.
Models for optimal levels of agression: game theory
Hawk-dove game was first model for understanding aggressive behavior
Two strategies:
- Hawk: Always fight
- Dove: retreat if attacked
H vs H
- 50% chance of winning and 50% chance of losing and incurring a cost
D vs D
- 50% chance of winning and 50% of losing but no cost.
H vs D
- Hawk always wins
There can evolutionary stable strategy as long as fighting cost exceeds the value of the resources (then would always pay to be a hawk)
Frequency dependent selection -> lots of hawks then doves do well, lots of doves then hawks do well
Example: Finches
- Red is more agressive then black
- Red is rare = greater fitness as more success in cotests over breeding sites
- Red is common= lower fitness due to negative effect of agression
- Assumes assortative mating
Continuus variation in agression is more likely -> how can this be modelled?
Models for optimal level of agression: War of attrition
A reward is obtained by whichever of two opponents displays longer, each individual incurring the same cost associated with the length of the contest -> Giving up time is taken from a negative disitrbution of t*
c= r x t
C: cost of conflict (those incurred from own actions like display)
r: rate at which costs are incurred
t: time
Individual gives up when costs exceed c* -> occurs at t*
There is no pure ESS (single value of t*) as mutants persisting for a tiny bit longer would invade.
Mixed ESS: be unpredictable
- t* value picked at random from a negative exponential disibtrution (meam=v/t)
- The negative disitrbution changes depending on the value of the resource and the cost of fighting (mean will change)
- High value = higher t* and longer fights.
- High cost = lower t* and shorter fights
Assumptions:
- Individuals have the same resource holding potential (fighting ability)
- This is unrealistic and individual with lower RHP will give up first.
Example: Dung Beatles
- Study looking at struggle persistance time between males for female dung beatles found superficial concordance with war of attriction model (time taken from negative distribution)
- Further investigation showed that there are clearly assymetric contests
- Assesment strategy used instead.
SPider
- Correlation between losing RHP and giving up time
- No correlation between winner RHP and firght duration
This is pure self assesment
Model for optimal level of aggression: Sequential assesment
Rivals differ in resource holding potential, and at any time rivals sample own and other’s performance to estimate difference in RHP.
RHPA- RHPB
With more time steps rivals get more precise infromation about the potential of the component and it get more accurate (pV more precise) but the longer they spend assessing the greater the cost of angaging (C decreases)
ESS: persist as long as…
pV>C
Probability of being victorious x value is greater than the cost
When the esitmate tell the indvidual that pV<c it gives up
Normally the individual with higher RHP wins (not always case e.g. trip up so have low ability assesment)
Nature of fights:
- Fights tend to increase in intensity to attempt to determine RHP difference
- So when RHP are roughly even fights will be longer and escalate to be more aggressive
Another parameter: Perception on how dangerous it is to fight
- Study tested how predation risk effected the cychlids fish
- Increased predation lead to slower fight escalation (longer time til mouth contact) and greater use of low intensity behaviors (tail beating and visual assesment) -> longer fight
- Individuals want to acoid expensive behvaiors and spend more time assessing environment
- Individuals may vary in boldness to risk of predation and this also effects fight outcome (not just RHP)
Prediction from sequenctial assesment model
Fight duration will increase with losing RHP and decrease with winner RHP
- shorter fights with larger RHP differences
Fights will be structured into discrete phases with escalation between phases
- Example: Red deer fighting
Fights escalate further when RHP differences are small
- Example: jumping spiders difference in body size
Fight dynamics are inflienced by information about the rival
- Example: grey fish with blocked urination
- Individuals couldn’t gain as much information about each other so there was greater escalation
Model for optimal levels of agression: Cumulative model
Similair to sequential assesment but rather than testing RHP difference at each time point with increase accuracy, individuals are testing the stamina of the other individual against a set threshold
Example: Hermit crabs fighting over shells
- Attacker taps the shell of defender
- Defender compares tapping to absolute threshold rather than relative threshold
- Reducing oxygen of defender does not change rates of eviction
- Reducing oxygen of attacker changes tap vigour and rates of eviction
P v and C
p
- Cues of fighting ablity (e.g. body size)
- Signals that communicate RHP (e.g. croak of frog)
- Learning through repeated encounters
V
- Levels of agression vary depending on resource (intrinsic value, abundance, spatial distribution, and controllability)
- Example: fish upregulate aggression when offsrping at v vulnerable stage of developement
- Example: Agression is correlated with rank in paper wasps (higher rank = greater future reproductive potential)
C
- What effects the rate they incure costs?
- Characteristics of an oragnisms which determine how they fight in turn effects how agression leads to risk of physical injury or death, energetic depletion, exposure to predation, psychological and physiological stress, or damage to social relationships
When does fatal fighitng evolve?
Fatal fighting evolves when victory more than doubles current fitness
value of resource is greater than value of the future
Example: Lions fighting over hierarchy
- If lose they lose their rank and ability to reproduce so V is over double value of the future
