Transcript Hawk strategy

大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
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/
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
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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)
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16 衝突(conflict)
 Aggression and conflict
 The economics of holding a
territory
 Why do animals fight?
 The economics of territory size
 As evolutionary view of conflict
 The evolution of fighting behavior
 Strategies for reducing the cost
of territorial defense
 Game theory
 A proximate view of conflict
 Asymmetries in contests
 Aggression and testosterone
 Conflict among group members
 Stress, aggression, and
 How dominance is determined
dominance
 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
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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
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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)
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Aggression and conflict
 Aggression: 給予對方有害的刺激或傷害的行為
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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
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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)
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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
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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
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While taking into account the behavior of other animals
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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
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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
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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
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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
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The payoff matrix for the hawk-dove
game
 Three variables measure a currency that relates to
fitness:
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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
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Payoff for hawk – hawk interaction
 If an animal playing the hawk strategy meets another
hawk
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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
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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
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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
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V─D─D
2
=
V ─ 2D
2
=
V
─D
2
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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:
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p = the proportion of hawks in a population
1- p = the proportion of doves
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Box18.1 How many hawks and doves?
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(V-W)
 Payoff for dove strategy = p ----------- + (1 - p) V
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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
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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
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Increase in frequency
Remain stable
Or disappear
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An evolutionarily stable strategy (ESS)
 A strategy that, when played by all members of the
population
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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
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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
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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
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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
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Can a hawk or dove strategy be stable?
 If the value of a resource (V) is greater than the cost of
being wounded (W)
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A pure hawk strategy is an ESS
 If V < W, a mixed ESS will result
 A pure dove strategy is never an ESS
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Game-theory models generate
predictions
 One prediction: the ferocity of a contest depends on
the value of the resource
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Relative to the cost of injury
 In some species, the prize for winning a fight is
incredibly valuable
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i.e. a lifetime’s worth of reproductive success
Animals should risk everything, even fighting to the
death
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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
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Another reason for hawk-like fighting
 Game theory predicts that fights
are more likely to escalate(增加)
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Not only because the value of
the resource is high
But if fight costs are low
 Toads have no real weapons
against conspecifics
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Fights rarely end in serious
injury or death
Toads engage in lively battles
over females
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Some species display
 In species that have serious
weapons
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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
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Resource value influences fight intensity
 If the value of the resource changes
over time or in different places
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Fighting intensity correlates with
resource value
 For example, the value of a female to a
male is not always the same
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Red deer stags fight most fiercely and
are wounded most frequently during
the period when most calves are
conceived
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As predicted by game theory, male red deer fight
harder when the value of the resource is greater
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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
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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
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Relative to their own
And adjusting their fighting strategy
 Conditional strategy: adjusted according to the
conditions of the particular fight
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A conditional strategy: assessor strategy
 Assessor strategy:
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if one’s RHP is greater than the opponent’s , Play hawk
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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
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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
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Asymmetry in experience
 Experience of winning or losing influences the outcome of
future encounters
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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
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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
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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
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Because the food was more important to the lean birds
They were more highly motivated to win
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 copperheads (銅頭蝮)
 northern harriers
hawks
 bluethroat birds
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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
harder2010)if they are an attacker
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 red-winged blackbird
 Hermit crabs (寄居蟹)
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Arbitrary asymmetries
 Arbitrary (uncorrelated) asymmetries: rules or
conventions used to settle conflicts
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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
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The second male was deferring ownership
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 hamadryas baboon (阿拉伯狒狒)
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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
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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
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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
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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
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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(動物行為學
rank 2010)
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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
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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
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All birds of one flock rank above those of the other
Subordinate birds ride the coattails(衣尾) of the highestranking bird
Highest-ranking individuals behave differently towards
familiar birds
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Dominance may be a birthright
 Dominance may also be a birthright based on the
status of one’s parents
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Adult female rhesus monkeys have a linear dominance
hierarchy
Offspring assume a dominance position just below their
mother
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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
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Reproductive benefits go to the best competitor
 In some social groups, all or nearly all the reproductive
benefits in a group
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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
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In eusocial species (social insects, naked mole rats) only a
single female reproduces
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Dominants have a reproductive advantage
 More commonly, dominant animals have a clear
reproductive advantage
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But they don’t completely suppress reproduction by
subordinates
 A pack of African wild dogs has a clear dominance
hierarchy in each sex
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More dominant females gave birth than subordinate
females
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The benefits of being subordinate
 If subordinates have no other choice but to stay in a
group
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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
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When the dominance hierarchy in chickens is stable
Hens fight less and lay more eggs
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Subordinates avoid the costs of
dominance
 Dominant great tits or pied flycatchers have a higher
resting metabolic rate
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And require more food
 In some species, dominant individuals have increased
glucocorticoid levels
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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
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But mortality rates of dispersers is also very high
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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
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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
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A subordinate Rocky Mountain bighorn sheep may win
and mate with a female
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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
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Male side-blotched lizards, plainfin midshipman fish
 Satellite males intercept females who are attracted to a
dominant male
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Natterjack toads
 The underlying strategy: avoid the costs of achieving
and maintaining dominance
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And still enjoy some reproductive success
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Rocky Mountain bighorn sheep
side-blotched lizards,
Natterjack toads
plainfin midshipman fish
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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
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 savanna baboons
 White-winged
trumpeter birds
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Conflict over space
 Home range of an individual: the area in which it carries
out its normal activities
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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
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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
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May be used solely for feeding, mating or raising young
Or used for a variety of purposes: multipurpose
territories
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The ideal free distribution and space use
 Ideal free distribution: the pattern by which animals
settle into different areas
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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
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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
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 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.
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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
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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
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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
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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
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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
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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
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Optimal territory size: the benefits outweigh the costs by the
greatest amount
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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
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A bird adjusts the size of its territory to gain weight as
quickly as possible
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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
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 Anolis lizard
 Red-capped cardinals
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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
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 (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.
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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
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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
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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
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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
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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
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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
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 A model of the possible interactions between
glucocorticoids, serotonin, and dopamine over the
course of an interaction.

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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
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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
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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
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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





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問題與討論
[email protected]
 Ayo 台南 NUTN 站
http://myweb.nutn.edu.tw/~hycheng/
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