衝突 ( conflict ) ─ 動物行為學 (ethology) 鄭先祐 (ayo) 國立臺南大學...

衝突 (Conflict) ─ 動物行為學 (Ethology)

鄭先祐 (Ayo)

國立臺南大學環境與生態學院生態科學與技術學系教授

Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/

大學部生態學與保育生物學學程 ( 必選 ) 2010 年秋冬

Ayo 教材 (動物行為學 2010) 2

Part 3. 個體間的互動

生殖行為 (Reproductive Behavior) 親代照顧與交配體系 (Parental Care and Mating

Systems) 溝通：管道與功能 (Communication: Channels and

Functions) 溝通的演化 (The Evolution of Communication) 衝突 (Conflict) 團體生活，利他和合作 (Group Living, Altruism,

and Cooperation)


16 衝突 (conflict)

Aggression and conflict Why do animals fight?

As evolutionary view of conflict The evolution of fighting behavior Game theory Asymmetries in contests

Conflict among group members How dominance is determined The benefits of being dominant The benefits of being subordinate

Conflict over space Home ranges, core areas, and

territories The ideal free distribution and

space use

The economics of holding a territory

The economics of territory size Strategies for reducing the cost

of territorial defense A proximate view of conflict

Aggression and testosterone Stress, aggression, and

dominance


Some fights end peaceably, others do not

Male ibex are mountain goats with long, curved horns They fight for access to females The confrontation begins with an assessment

They push and shove each other Sometimes fights end with the loser’s death

Speckled wood butterflies spiral up and up Until one flies off unharmed

Even when animals have weapons Contestants often exhibit restraint ( 克制 )


Aggression and conflict

Aggression: 給予對方有害的刺激或傷害的行為 Includes predation Behaviors in response to aggression are not included (i.e.

fleeing) Agonistic behavior: encompass the behavior of both the

aggressor and the animal that is the focus of the aggression Includes all conflict between conspecifics Threats, submissive behavior, chasing, and physical combat Only includes interactions between conspecifics Excludes aggressive acts between species (i.e. predation)


Why do animals fight?

Conflict is potentially dangerous And metabolically costly (it requires energy)

Enough resources (food, shelter, mates) decreases conflict But resources are frequently limited So conflict occurs

Conflict between parents and offspring The amount of energy and time a parent has available for a

particular offspring Versus investing in other offspring or its own survival

Conflict is extremely common But it manifests itself differently in manner and intensity


Evolution of fighting behavior: game theory

Why don’t animals always fight with maximum effort? Natural selection favors the individual that passes on

more of its genes Game theory can help to understand the evolution of

conflict Game theory: predicts an animal’s optimal behavior

While taking into account the behavior of other animals


The game-theory model

Players: the combatants Strategies: Different decisions available to players

Assumed to be heritable Successful strategies increase in the population

Payoff: measures the costs and benefits for each strategy

Currency: used to measure the payoff Relates to fitness (number of offspring produced or

number of calories acquired) A payoff matrix: organizes the values of the payoffs

of each strategy against the other strategies


One game theory model: hawk-dove

The simplest game-theory model of aggression Two players fight over a resource Each opponent can play one of two strategies: hawk

and dove Hawk strategy: immediately attack its opponent Dove strategy: flee immediately if confronted by a

hawk Display if confronted by another dove

If a hawk meets a hawk or a dove meets a dove Each opponent has a 50% chance of winning


The payoff matrix for the hawk-dove game Three variables measure a currency that relates to

fitness: V = the value of the resource being contested W = the cost of being wounded in a fight D = the cost of displaying to an opponent

Add some numbers: V = 30 W = 60 D = 5


Payoff for hawk – hawk interaction

If an animal playing the hawk strategy meets another hawk Both attack immediately One hawk wins the resource: its payoff is V The other hawk will be wounded: its payoff is –W

The average payoff for a hawk vs. hawk interaction Payoff for the winning hawk + the payoff for the losing

hawk Divide by 2 to get the average V – W

2


Payoffs for other interactions

Hawk against dove The hawk immediately attacks The dove flees Hawk wins the resource, so its payoff is V

Dove against hawk The dove immediately flees The dove does not get injured Nor does it win anything - its payoff is 0


The payoff for dove vs. dove

One wins the resource The other walks away

Both pay the cost of display The payoff for the winning dove is V-D The payoff for the losing dove it is just –D

Sum these and divide by 2 V ─ D ─ D V ─ 2D V

= = ─ D 2 2 2


Box18.1 How many hawks and doves?

Neither hawk nor dove is an evolutionarily stable strategy.

Rather, the stable equilibrium composition of the population is some combination of hawks and doves in a mixed ESS.

The stable proportion of hawks and doves occurs when the average payoff for the hawk strategy equals the average payoff for the dove strategy.

Assume: p = the proportion of hawks in a population 1- p = the proportion of doves


Box18.1 How many hawks and doves?

(V-W) Payoff for dove strategy = p ----------- + (1 - p) V 2

Payoff for hawk strategy = p (0) + (1 – p) (V/2 – D)

-15p + (1-p)30 = 0 + (1-p) 10 -15p + 30 -30p = 10 – 10p 30 – 45p = 10 – 10p 20 = 35 p p = 0.57


Understanding the game

The currency = units of fitness These strategies are heritable

Successful doves have offspring That also play the dove strategy

Hawks give rise to hawks Game-theory models predict whether strategies in a

population Increase in frequency Remain stable Or disappear


An evolutionarily stable strategy (ESS)

A strategy that, when played by all members of the population Cannot be invaded by another strategy

If the dove strategy is an ESS All members of the population play the dove strategy

If an animal playing hawk entered All of its opponents would be doves

The hawk strategy will do well The hawk’s genes increase The hawk strategy increases in frequency


Is the hawk strategy an ESS?

Will the population eventually become all hawks? If the population is comprised of all hawks The average payoff drastically decreases

If a dove enters the population It won’t win But it won’t be wounded during half its battles The frequency of the dove strategy would increase

Neither a “pure hawk” strategy nor a “pure dove” strategy is an ESS


A mixed ESS is stable

A mixed ESS: some combination of hawk and dove strategies that is stable

The stable proportion of hawks and doves occurs When the average payoff for the hawk strategy equals

the average payoff for the dove strategy A certain proportion of animals always plays hawk

And another proportion always plays dove Or all animals play both hawk and dove


Can a hawk or dove strategy be stable?

If the value of a resource (V) is greater than the cost of being wounded (W) A pure hawk strategy is an ESS

If V < W, a mixed ESS will result A pure dove strategy is never an ESS


Game-theory models generate predictions One prediction: the ferocity of a contest depends on

the value of the resource Relative to the cost of injury

In some species, the prize for winning a fight is incredibly valuable i.e. a lifetime’s worth of reproductive success Animals should risk everything, even fighting to the

death


A valuable resource is worth fighting for

Male elephant seals have brutal( 粗暴的 ) and bloody fights Duels are so strenuous( 費力的 ) that a male can be harem master

for only a year or two before he dies


Another reason for hawk-like fighting

Game theory predicts that fights are more likely to escalate( 增加 ) Not only because the value of the

resource is high But if fight costs are low

Toads have no real weapons against conspecifics Fights rarely end in serious injury

or death Toads engage in lively battles

over females


Some species display

In species that have serious weapons Battles are generally

restricted to displays Game theory reminds us

that it is the cost of battle relative to the benefit of winning that drives fight intensity


Resource value influences fight intensity

If the value of the resource changes over time or in different places Fighting intensity correlates with

resource value For example, the value of a female to a

male is not always the same Red deer stags fight most fiercely and

are wounded most frequently during the period when most calves are conceived


As predicted by game theory, male red deer fight harder when the value of the resource is greater


Asymmetries in contests

In the basic hawk-dove model All animals value the contested resource to the same extent All individuals have the same ability to fight

In real life, rivals are rarely true equals Contests are usually asymmetric

Inequalities (asymmetries) are grouped into categories The ability of each contestant to defend the resource The experiences of each contestant in previous fights The value of the resource to each contestant Arbitrary asymmetries unrelated to either resource value

or the ability to defend the resource


Asymmetry in fighting ability

One combatant may be larger or heavier Have bigger weapons Be a more skilled fighter

Resource-holding potential (RHP): characteristics that bear on an opponent’s ability to defend a resource

Contestants increase their fitness by assessing their opponent’s RHP Relative to their own And adjusting their fighting strategy

Conditional strategy: adjusted according to the conditions of the particular fight


A conditional strategy: assessor strategy

Assessor strategy: if one’s RHP is greater than the opponent’s , Play hawk If one’s RHP is smaller, Play dove

Assessor strategy is an ESS when the cost of assessing the opponent’s RHP is less than the cost of losing a fight

How do animals assess RHP? Displays convey an impression of size and strength to an

opponent. Animals assess one another accurately

But bluff convincingly when possible


Some traits are difficult to bluff

Such traits are used in assessment A male mountain sheep with small horns defers to a

competitor with larger horns Male red deer judge each other’s size by interlocking

their antlers and pushing Size of the male shore crab claw is more important than

its body size Some species may not be able to judge their opponent’s

RHP


Asymmetry in experience

Experience of winning or losing influences the outcome of future encounters Important in insects, spiders, molluscs, fish, birds, mammals

Winners are more likely to win subsequent fights Losers become more likely to lose

Spiders fight fiercely for their prey Spiders experienced as winners beat size-matched opponents

Loser effects can be long-lasting Larger male copperheads ( 銅頭蝮 ) win fights for access to a

female When rematched: prior losers gave up without even

challenging the competitor


Asymmetry in the value of a resource

A contested resource may be more valuable to one contestant

Food is more precious to a starving animal The hungry contestant fights harder for it

Once northern harriers hawks have eaten The value of the remaining prey decreases Harriers are not as aggressive toward intruders

Leaner bluethroat birds were able to chase away larger birds Because the food was more important to the lean birds They were more highly motivated to win


copperheads ( 銅頭蝮 )

northern harriers hawks

bluethroat birds


One animal may value a resource more

An animal that knows about a resource values it more Than an animal that knows less about it

Territory is more important to a resident than an intruder A resident knows the location of food, escape routes, refuges

Individuals value a territory more as it becomes familiar If red-winged blackbird territory owners were removed

New residents fight harder as the territory becomes more valuable

Knowledge about a resource influences fighting behavior Hermit crabs ( 寄居蟹 ) attempt to steal shells from

conspecifics Owners of poor shells fight harder if they are an attacker


red-winged blackbird Hermit crabs ( 寄居蟹 )


Arbitrary asymmetries

Arbitrary (uncorrelated) asymmetries: rules or conventions used to settle conflicts i.e. fipping a coin, pulling straws Rules that are mutually agreed upon

Prior ownership (or residency) Animals adhere to the principle that “possession is

nine-tenths of the law” A hamadryas baboon male permitted to associate

with a female was perceived as the “owner” by a newly introduced male The second male was deferring ownership


hamadryas baboon ( 阿拉伯狒狒 )


The bourgeois( 中產階級者 ) strategy is an ESS

To add the possibility of prior ownership, a variation of the hawk-dove model includes a third strategy: bourgeois Sets rules for dealing with prior ownership: Play hawk if you had possession first; otherwise, play dove

If the bourgeois strategy is added to hawk and dove strategies in a population, it does better than either So it is an ESS

If all animals play the bourgeois strategy The owner always wins the outcome of any dispute Can be reversed by switching ownership


An uncorrelated asymmetry

Male speckled wood butterflies defend spots of sunlight That serve as mating territories

Males fight by flying upward together At the top of the spiral, one flies away

When a male resident butterfly is removed The sunspot is instantly claimed by another male When the original male is released again It always loses the fight to regain its spot Wood butterflies follow the rule that the “owner wins”

Butterfly fights may be determined by intrinsic aggression Or fighting ability, or prior experience


Dominance hierarchies in groups

Conflict exists among group members Animals encounter the same individuals repeatedly The animals don’t usually fight each time they meet

Dominance: the ability of one animal to assert itself over others in acquiring access to a limited resource Food, a mate, a display or nesting site

A submissive animal predictably yields to a dominant one Hierarchies vary among species, conditions and time Despotism ( 專制君主統治 ) : the simplest form of a

dominance hierarchy One individual rules over all others in the group Subordinates are equal in rank


Dominance hierarchies may also be linear A is dominant over all B is dominant over all but A

A ––> B ––> C ––> D ––> E Often called a pecking order Dominance hierarchies can be more complicated

A is dominant over B B is dominant over C But C is dominant over A

Hierarchies can shift as circumstances change


Dominance is attained through associations

Dominance in social groups may also be attained through an association with a high-ranking individual

When two flocks of dark-eyed juncos merge All birds of one flock rank above those of the other Subordinate birds ride the coattails( 衣尾 ) of the highest-

ranking bird Highest-ranking individuals behave differently towards

familiar birds


Dominance may be a birthright

Dominance may also be a birthright based on the status of one’s parents Adult female rhesus monkeys have a linear dominance

hierarchy Offspring assume a dominance position just below their

mother


The benefits of being dominant

Being dominant translates into increased fitness Two fitness-related benefits: access to food and mates

Dominant individuals get more food than subordinates In brown hyenas each sex has a linear dominance hierarchy The male and female at the top have equal rank Top-ranking animals have more feeding time at carcasses Subordinates leave without feeding if a dominant animal is

present


Reproductive benefits go to the best competitor

In some social groups, all or nearly all the reproductive benefits in a group Go to a single individual that is the best competitor

In some species, the dominant female (or male) suppresses reproduction by other members of the group In eusocial species (social insects, naked mole rats) only a

single female reproduces


Dominants have a reproductive advantage

More commonly, dominant animals have a clear reproductive advantage But they don’t completely suppress reproduction by

subordinates A pack of African wild dogs has a clear dominance

hierarchy in each sex More dominant females gave birth than subordinate

females


The benefits of being subordinate

If subordinates have no other choice but to stay in a group Repeatedly challenging other individuals to fights would

lead to a risk of injury in conflicts they would lose In many groups, both subordinates and dominants suffer

from a shake-up in the hierarchy When the dominance hierarchy in chickens is stable Hens fight less and lay more eggs


Subordinates avoid the costs of dominance

Dominant great tits or pied flycatchers have a higher resting metabolic rate And require more food

In some species, dominant individuals have increased glucocorticoid levels A steroid hormone associated with stress

Subordinates may leave and join another group But this can be risky

Subordinate red foxes usually don’t live long enough to become dominant in their natal group But mortality rates of dispersers is also very high


Staying vs. leaving

The benefits of staying may outweigh the costs of leaving For a subordinate animal

The situation in the group could get better for a subordinate The dominant animal could die or be displaced

Subordinates may gain some fitness through kin selection By helping to raise siblings

A subordinate can occasionally win a fight to briefly gain access to a resource A subordinate Rocky Mountain bighorn sheep may win

and mate with a female


Subordinates can use subversive ( 破壞性的 ) techniques Such as alternative reproductive strategies Sneaky males mimic a female to get past a dominant

male Male side-blotched lizards, plainfin midshipman fish

Satellite males intercept females who are attracted to a dominant male Natterjack toads

The underlying strategy: avoid the costs of achieving and maintaining dominance And still enjoy some reproductive success


Rocky Mountain bighorn sheep side-blotched lizards, Natterjack toads plainfin midshipman fish


Subordinates may form alliances

Band together to challenge dominant individuals Lowest-ranking male savanna baboons form alliances

To oppose a single higher-ranking male Alliances gained reproductive access to the female

But alliances do not always overturn the current hierarchy Some female Old World monkeys band together

And “gang up” on other lower-ranking monkeys Alliances occur in other animals besides primates

White-winged trumpeter birds Subordinate males collaborate to interrupt copulation by the

dominant male


savanna baboons

White-winged trumpeter birds


Conflict over space

Home range of an individual: the area in which it carries out its normal activities Space it defends from others Space that is used by others

Core area: within the home range An area in which most activities are concentrated Immediately surrounding the nest site, food or water


Territory

A defended area Other definitions downplay( 貶低 ) defense And emphasize exclusive use of space

It is virtually impossible to state with any certainty That the exclusive use of an area is maintained by active

defense Territories have different uses, depending on the

resource being contested May be used solely for feeding, mating or raising young Or used for a variety of purposes: multipurpose

territories


The ideal free distribution and space use

Ideal free distribution: the pattern by which animals settle into different areas It’s “ideal” because the animals know the value of each

habitat and can instantly choose the best one And “free” because every animal is free to choose its

location without interference


The ideal free distribution and ducks

Two habitats A = higher quality

As ducks arrive in the area They should select habitat A As the number of animals in A increases The number of resources available declines The quality of A declines to the point that a new arrival

gets the same benefits Regardless of which habitat it selects


The ideal free distribution. Illustrated is a case with two habitats, with habitat A of higher quality than habitat B. Thus, as animals arrive , they should select habitat A. As the number of animals in habitat A increases, the number of resources available to each animal declines. Finally, the quality of A declines to the point that a new arrival will get the same benefits regardless of which habitat it selects.


Animals are not always ideal or free

An “ideal” animal has perfect knowledge of a site’s quality But that’s not always true

Animals need time to gather information Before they assess the quality of their environment

An animal is not always “free” Others constrain them from behaving optimally Some animals may be better competitors and grab more

than their fair share of the food


The economics of holding a territory

What influences an animal to hold or share a territory? Benefits of having a territory:

Exclusive access to resources (shelter, food, safety, mates, site to raise offspring)

Costs of holding a territory: Energy to patrol territory boundaries and display to or evict

intruders Boundary fights can be dangerous A “lost opportunity” cost: acquisition and defense takes

time away from other essential activities


Costs and benefits of holding a territory: resource abundance

Territoriality occurs only if The fitness benefits from enhanced access to a resource Exceed the fitness costs of defending the resource

Resource abundance: territoriality is favored when resources are moderately abundant If resources are scarce: not enough benefits to pay the

defense bill If there are more than enough resources, it’s unnecessary

to defend a territory


Resource abundance affects territoriality

Scarce resources don’t provide enough benefits Golden-winged sunbirds abandon a territory when it no

longer contains enough food to meet the energy costs of activities and defense

Chickadees in habitats disturbed by logging were less likely to defend their territories

Territoriality is unnecessary with abundant resources Female marine iguanas only defend territories with few

nest sites


Costs and benefits of holding a territory: resource distribution and intruders Resource distribution: animals are more likely to be

territorial if resources are moderately clumped A pile of food is easier to defend As long as there aren’t too many competitors

Intruder pressure: the number of other individuals willing to compete for a territory The more competitors, the greater the cost of defense Male fruit flies are less likely to hold territories when

there is a higher density of males


The economics of territory size

Costs and benefits influence not only whether a territory is held But also its size

Benefits increase as territory size increases An animal uses certain resources More resources are not necessary

Costs of defense also increase with territory size More borders to patrol More intruders to drive off


Optimal territory size: the benefits outweigh the costs by the greatest amount


Territory size maximizes energy gains

Rufous hummingbirds stop in California during migration To build fat reserves

Each bird defends a group of flowers as a territory More flowers provide more energy But requires more energy for defense

Reducing territory size cuts defense costs And maximizes weight gain


A bird adjusts the size of its territory to gain weight as quickly as possible


Reducing the costs of territorial defense

Animals can band together and share a territory The faster an intruder is detected, the easier it is to drive away

Good vantage points and high trees Juvenile Anolis lizards living in habitats without a barrier

Defended compact territories They did not include barriers in their territories

Some birds pay attention to visibility when choosing territories Red-capped cardinals defend territories along rivers and lakes They defend territories on opposite shores They easily see intruders on the opposite shore


Red-capped cardinals

Anolis lizard


Reducing the costs of territorial defense

Some animals use natural boundary markers to mark a territory i.e. Cicada killer wasps

Wasps use dowels (wooden sticks) as landmark cues And shift their territories so the boundaries align with the

dowels


(a) cicada killer wasp (b) the original placement of the territories (c) wooden dowels were laid on the ground

so that none of them aligned with territory boundaries

(d) the next day, the wasps shifted their territory boundaries so that they aligned with the dowels.


Another way to reduce costs of territorial defense Paying attention to the early-warning system provided

by neighboring territory holders Peruvian red-capped cardinals evict( 驅逐 ) an

intruder Chasing and calling This behavior alerts neighbors that there is an intruder

lurking nearby Territory holders detect and evict an intruder if their

neighbor has just evicted it


A proximate view of conflict

Aggressive tendencies involve genetics, hormones and the nervous system

Seasonal changes in testosterone levels are correlated with the intensity of territorial aggression In winter, both testosterone levels and territorial defense

are low Testosterone may increase after there is an aggressive

response to an intruder A territory holder maintains its high aggression levels Especially in the face of a persistent intruder


Hormones may influence behavior

The presence of a hormone does not mean a particular behavior will follow An animal primed by testosterone will not fight if a

predator is nearby Hormones increase the likelihood of a behavior


Stress, aggression, and dominance

Aggression and stress are linked by the neurotransmitter serotonin And hormones called glucocorticoids

Physiological changes accompany conflict and other stressful situations

The fight-or-flight response: increased heart rate, rapid breathing, sweating Digestion, growth and reproduction are shut down Under the control of short-term bursts of glucocorticoids


Serotonin and glucocorticoid levels during aggression

Baseline levels establish an animal’s tendency to be aggressive In dominant animals: high glucocorticoids, low serotonin Serotonin holds aggressive tendencies in check

When a social interaction begins Glucocorticoids, serotonin, and dopamine (another

neurotransmitter) increase in dominant individuals As the fight increases

Both dominant and subordinates have increased serotonin and corticosterone levels

And show stress responses


Interactions between glucocorticoids, serotonin, and dopamine

When dominance is established and the fight ends: Serotonin remains high in subordinates Which are then less likely to initiate fights

The winner effect: winners are more likely to win future fights


A model of the possible interactions between glucocorticoids, serotonin, and dopamine over the course of an interaction.


Being subordinate is not always more stressful Subordinate baboons have higher levels of

glucocorticoids But dominant animals also spike with unstable

dominance hierarchies The effect of glucorticoids varies by species

Glucocorticoid levels can be positively correlated, negatively correlated, or uncorrelated with rank

Or even vary in their correlation with rank during the day


Stress responses can both help and harm

Cortisol level vary according to the social situation Subordinates without close social support have higher

levels Stress responses are adaptive in the short term

But persistent, long-term stress can lead to health problems

Increased susceptibility to disease, shorter lifespan


Summary

Conflict occurs when resources are limiting Aggression: inflict noxious stimulation or destruction on another Agonistic behavior: behaviors of the aggressor and the object of

aggression Animals can limit conflict to displays and other low-cost actions Game theory examines when conflicts escalate and when they

don’t In the hawk-dove model, hawks escalate and doves flee A strategy’s payoff depends on the value of the resource, cost of

being wounded, and the cost of display Contests can be asymmetrical (different sizes, experience, etc.) Arbitrary asymmetries are conventions that fighters follow


Summary

Dominance may be determined by fights or as a birthright Dominant animals get resources and access to mates Subordinate animals stay: no other options are available

Ideal Free Distribution: how animals should distribute themselves Territoriality can be energetically costly and even dangerous

Is favored when resources are moderately abundant, moderately clumped and the number of intruders is moderate

To reduce costs of territoriality: select territories with good visibility and landmarks, obey warnings of neighbors

In some species, dominant animals exhibit higher stress levels In others, subordinate animals do


問題與討論

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Ayo 台南 NUTN 站 http://myweb.nutn.edu.tw/~hycheng/

衝突 ( conflict ) ─ 動物行為學 (ethology) 鄭先祐 (ayo) 國立 臺南大學...

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衝突 ( conflict ) ─ 動物行為學 (ethology) 鄭先祐 (ayo) 國立臺南大學...