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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 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) Ayo 教材 (動物行為學 2010) 2 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 Ayo 教材 (動物行為學 2010) 3 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) Ayo 教材 (動物行為學 2010) 4 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) Ayo 教材 (動物行為學 2010) 5 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 Ayo 教材 (動物行為學 2010) 6 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 Ayo 教材 (動物行為學 2010) 7 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 Ayo 教材 (動物行為學 2010) 8 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 Ayo 教材 (動物行為學 2010) 9 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 Ayo 教材 (動物行為學 2010) 10 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 Ayo 教材 (動物行為學 2010) 11 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 Ayo 教材 (動物行為學 2010) 12 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 2 = V ─ 2D 2 = V ─D 2 Ayo 教材 (動物行為學 2010) 13 Ayo 教材 (動物行為學 2010) 14 Ayo 教材 (動物行為學 2010) 15 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 Ayo 教材 (動物行為學 2010) 16 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 Ayo 教材 (動物行為學 2010) 17 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 Ayo 教材 (動物行為學 2010) 18 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 Ayo 教材 (動物行為學 2010) 19 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 Ayo 教材 (動物行為學 2010) 20 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 Ayo 教材 (動物行為學 2010) 21 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 Ayo 教材 (動物行為學 2010) 22 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 Ayo 教材 (動物行為學 2010) 23 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 Ayo 教材 (動物行為學 2010) 24 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 Ayo 教材 (動物行為學 2010) 25 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 Ayo 教材 (動物行為學 2010) 26 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 Ayo 教材 (動物行為學 2010) 27 As predicted by game theory, male red deer fight harder when the value of the resource is greater Ayo 教材 (動物行為學 2010) 28 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 Ayo 教材 (動物行為學 2010) 29 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 Ayo 教材 (動物行為學 2010) 30 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 Ayo 教材 (動物行為學 2010) 31 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 Ayo 教材 (動物行為學 2010) 32 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 Ayo 教材 (動物行為學 2010) 33 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 Ayo 教材 (動物行為學 2010) 34 copperheads (銅頭蝮) northern harriers hawks bluethroat birds Ayo 教材 (動物行為學 2010) 35 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 Ayo 教材 (動物行為學 36 red-winged blackbird Hermit crabs (寄居蟹) Ayo 教材 (動物行為學 2010) 37 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 Ayo 教材 (動物行為學 2010) 38 hamadryas baboon (阿拉伯狒狒) Ayo 教材 (動物行為學 2010) 39 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 Ayo 教材 (動物行為學 2010) 40 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 Ayo 教材 (動物行為學 2010) 41 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) Ayo 教材 42 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 Ayo 教材 (動物行為學 2010) 43 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 highestranking bird Highest-ranking individuals behave differently towards familiar birds Ayo 教材 (動物行為學 2010) 44 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 Ayo 教材 (動物行為學 2010) 45 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 Ayo 教材 (動物行為學 2010) 46 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 Ayo 教材 (動物行為學 2010) 47 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 Ayo 教材 (動物行為學 2010) 48 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 Ayo 教材 (動物行為學 2010) 49 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 Ayo 教材 (動物行為學 2010) 50 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 Ayo 教材 (動物行為學 2010) 51 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 Ayo 教材 (動物行為學 2010) 52 Rocky Mountain bighorn sheep side-blotched lizards, Natterjack toads plainfin midshipman fish Ayo 教材 (動物行為學 2010) 53 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 Ayo 教材 (動物行為學 2010) 54 savanna baboons White-winged trumpeter birds Ayo 教材 (動物行為學 2010) 55 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 Ayo 教材 (動物行為學 2010) 56 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 Ayo 教材 (動物行為學 2010) 57 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 Ayo 教材 (動物行為學 2010) 58 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 Ayo 教材 (動物行為學 2010) 59 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. Ayo 教材 (動物行為學 2010) 60 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 Ayo 教材 (動物行為學 2010) 61 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 Ayo 教材 (動物行為學 2010) 62 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 Ayo 教材 (動物行為學 2010) 63 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 Ayo 教材 (動物行為學 2010) 64 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 Ayo 教材 (動物行為學 2010) 65 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 Ayo 教材 (動物行為學 2010) 66 Optimal territory size: the benefits outweigh the costs by the greatest amount Ayo 教材 (動物行為學 2010) 67 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 Ayo 教材 (動物行為學 2010) 68 A bird adjusts the size of its territory to gain weight as quickly as possible Ayo 教材 (動物行為學 2010) 69 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 Ayo 教材 (動物行為學 2010) 70 Anolis lizard Red-capped cardinals Ayo 教材 (動物行為學 2010) 71 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 Ayo 教材 (動物行為學 2010) 72 (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. Ayo 教材 (動物行為學 2010) 73 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 Ayo 教材 (動物行為學 2010) 74 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 Ayo 教材 (動物行為學 2010) 75 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 Ayo 教材 (動物行為學 2010) 76 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 Ayo 教材 (動物行為學 2010) 77 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 Ayo 教材 (動物行為學 2010) 78 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 Ayo 教材 (動物行為學 2010) 79 A model of the possible interactions between glucocorticoids, serotonin, and dopamine over the course of an interaction. Ayo 教材 (動物行為學 2010) 80 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 Ayo 教材 (動物行為學 2010) 81 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 Ayo 教材 (動物行為學 2010) 82 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 Ayo 教材 (動物行為學 2010) 83 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 Ayo 教材 (動物行為學 2010) 84 問題與討論 [email protected] Ayo 台南 NUTN 站 http://myweb.nutn.edu.tw/~hycheng/ Ayo 教材 (動物行為學 2010) 85