抗掠食行為 (Antipredator behavior) ─ 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: hycheng

抗掠食行為 (Antipredator

behavior)

─ 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

12 抗掠食行為 (Antipredator behavior)

Camouflage ( 偽裝 ) Polymorphism ( 多型性 ) Warning coloration ( 警告色 ) Batesian mimicry ( 擬態 ) Diverting coloration, structures, and behavior Intimidation ( 恫嚇 ) and fighting back Pronouncement of vigilance ( 警戒 ) Group defense Maintenance of antipredator behavior


Butterflies are eaten by many predators

They have developed ways to outsmart their enemies Using a combination of color pattern and behavior to avoid

being eaten Warning potential predators that they taste bad

Caterpillars eat milkweed and incorporate toxins in their tissues Birds that eat butterflies vomit and avoid them in the future Poisons, stolen from plants, may deter some predators

No defense system works all the time Its effectiveness varies with season, species of predator, and

context of the predator-prey encounter


Animals have antipredator abilities

In summer and autumn, monarch butterflies migrate to Mexico

Black-backed orioles and black-headed grosbeaks eat monarchs Despite their chemical defenses

Butterflies converge in enormous numbers at their overwintering colonies Tens of millions of individuals dilute the predation risk to

any one individual


Camouflage: “I am not here”

Animals have several forms of camouflage Coloration matching the visual background Disruptive coloration ( 斷裂顏色 ) Countershading ( 反差陰影 ) Transparency ( 透明 ) Masquerade ( 化裝舞會 ) : prey animals appear

inedible to predators (i.e. a leaf, twig, or bird dropping)


Animals can match their background

Reduces the risk of detection by visually hunting predators Animals blend with the background upon which they

are resting

Animals, such as this grouse( 松雞 ), that blend with their background are often described as cryptic.


Coloration matching the visual background

Concealment( 隱藏 ) that results from an animal’s resemblance to a random sample of the visual background Background matching is maximized when coloration

visually matches a random sample of the background Great tits had to search longer for the prey that was

more difficult to detect


Animals select “correct backgrounds”

Prey coloration matching a random visual sample of the background may only maximize background matching on simple backgrounds

There is more to background matching than color and pattern Once on the “correct” background, animals exhibit

behavior that maximizes their camouflage California yellow-legged frogs lies motionless against

a background to which they are perfectly matched Boulders( 卵石 ) covered by a yellow-brown layer of

algae


California yellow-legged frogs


Matching and selecting the correct background is adaptive

Stoneflies ( 石蠅 ) select dark brown resting spots during daylight hours No selection was observed in the dark They are vulnerable to predation by rainbow trout ( 紅

鱒魚 ) when resting on light substrates

rainbow trout Stoneflies


Selecting the correct background

Resting on dark resting spots by stoneflies has been naturally selected It reduces the risk of being found and eaten by visually

hunting fish Animals need to be cryptic only when they are most

vulnerable to predation by visual hunters Substrate choice by stoneflies may also conceal them

from their own prey


Animals are camouflaged in certain areas

Animals using background matching occur in areas where they are best concealed

Species can get around this restriction by changing color as they change backgrounds

A cuttlefish ( 烏賊 ) swiftly and dramatically changes color and pattern When resting on the bottom: it adjusts its color to the

substrate Within seconds, the dorsal color can change from gray

to brown Bold elements are part of disruptive coloration.


cuttlefish ( 烏賊 )


Cuttlefish can rapidly change color

Cuttlefish change color to match their background They can even display bold contrasting elements


Disruptive coloration

Animals avoid being seen by matching their background But visual predators may recognize prey by their body outline

Animals break up their body outline by through bizarre projections or bold contrasting markings

Bold patches prevent or delay visual recognition of the prey Drawing attention away from the prey’s body Patches at the periphery of the prey’s body break up the

body’s outline Disruptive coloration: prevents perception of a prey

animal’s form


Patterns at the periphery enhance survival

Disruptive coloration enhances survival


High contrast patterns enhance survival

Disruptive coloration enhances survival


Disruptive coloration vs. habitat specialization

There is a relationship (tradeoff) between the types of coloration and habitat specialization

Species that rely on background matching evade detection by predators as long as they are living in a particular habitat They are habitat specialists

Disruptive( 斷裂的 ) coloration works on a greater variety of visual backgrounds It may be a strategy employed by habitat generalists


Countershading: self-shadow concealment

Countershading: animals with dark backs and light bellies Makes animals hard to detect They obscure their own shadows

Light usually comes from above Being darker dorsally and paler

ventrally obscures the body outline

Self-shadow concealment: the mechanism by which countershading achieves camouflage


Countershading: background matching

Countershading makes animals difficult to detect Common in aquatic animals

With light coming from above and a light belly: the animal matches the bright background when viewed from below The dark back matches the deep waters when viewed

from above


Countershading in the naked mole-rat

Naked mole-rats live in underground colonies Containing a breeding female (the queen),

breeding males, and non-breeding workers Colony members display countershading

A darker dorsal coloration A lighter (pink) ventral coloration

Exceptions to the countershaded pattern Queens, newborns, breeding males, and

very old individuals are pink


Why do naked mole-rats have countershading?

Hypotheses for countershading in this species Protects individuals from ultraviolet light Facilitates thermoregulation The pigment melanin protects skin from abrasions ( 擦傷 ) Provides camouflage for individuals dispersing above

ground It has no current function

Data were most consistent with the camouflage hypothesis The age of dispersal coincides with the time when naked

mole-rats have well-developed countershading


Transparency ( 透明 )

Some animals are camouflaged by being transparent Cnidarians ( 刺胞動物門 ) (hydroids ( 水螅 ) and

jellyfish( 水母 )), ctenophores ( 櫛水母 ) (comb jellies), and the pelagic (open ocean) larval stages of many fish are almost transparent The high water content of tissues Small size Reduced number of light-absorbing molecules or pigments

Transparency is the dominant form of camouflage in aquatic environments In pelagic( 遠洋的 ) habitats where organisms have no

surfaces to match or places to hide


Transparency is rare in terrestrial organisms

In aquatic organisms the refractive index (angle of light traveling from the water into the watery tissues of an aquatic animal) is unchanged The animal appears to be transparent

In a terrestrial environment, light passes from air into the water-filled tissues of an animal Creating an obvious body outline and reducing transparency

To protect terrestrial animals from harmful ultraviolet radiation Animals need protective pigments While ultraviolet radiation is filtered in aquatic habitats


Masquerade ( 化裝舞會 )

Prey may be detected but deemed ( 視為 ) inedible by predators

Leaf resemblance is a common disguise ( 偽裝 ) Insects have green or brown coloration, leaf-like patterns of

venation, and flattened shapes They also behave like leaves: remaining still or swaying

Leaf resemblance also occurs in some small vertebrates


Masquerade in vertebrates

Leaf resemblance also occurs in amphibians and fish

Amphibians that inhabit the leaf litter of the forest floor

A nocturnal catfish ( 鯰魚 )


Animal color and pattern may act together or in opposition

Evading( 迴避 ) predators is not the only function of color pattern

Color affects heat balance and plays a role in thermoregulation It is also important in communication, mate recognition,

courtship, male-male competition, and territorial defense How can animals communicate and yet be inconspicuous?

Animals evolve auditory or olfactory signals to communicate But many still rely on visual cues

Color patterns may be a compromise between camouflage and conspicuousness ( 顯而易見 )


Mate acquisition vs. camouflage in wild guppies ( 孔雀魚 )

Females favor brighter colored, more visible patterned males Selection by predators favors less colorful and

conspicuous patterns As predation increases, males have

Less conspicuous colors Fewer number and size of spots Reduced diversity of patterns

As predation decreases Colors and patterns become more conspicuous to attract

mates


Polymorphism

Background matching is not foolproof Predators may develop a search image for a species And systematically search out and consume individuals

Predators that rarely encounter individuals forget the search image Species that occur at widely spaced locations use

background matching Species avoid the problem of search images by exhibiting

polymorphism Species occurring in several different shapes and/or color

forms


Melanistic polymorphism in fox squirrels

Fox squirrel color varies among and within populations Dorsal coloration ranges from gray or tan to black

Melanistic (black) and nonmelanistic young occur in a litter Melanism is correlated with the frequency of wildfires Both are more common in the southeastern United States

Variable coat color in fox squirrels Matches the background of an environment

that periodically burns and regenerates


Squirrel polymorphism is maintained by fire

Wildfires blacken the ground and tree trunks Dark squirrels are less conspicuous to

hawks New plant growth causes fox squirrels

with variable amounts and patterns of black to be more difficult to see

When the forest has regrown, the advantage shifts to light squirrels


Being different can save lives

Some polymorphic species do not match their background They rely on their diverse

appearance to evade detection Predators search for individuals

with a specific appearance Species that occur at high densities

exhibit extreme polymorphism Different appearances prevent

formation of search images


Apostatic selection ( 變節的選擇 )

One form of frequency-dependent selection Members of a population look as different as possible

When two morphs are equally camouflaged The rare morph has a selective advantage Predators develop a search image for the common

morph Predators do not need to hunt by search image to

cause apostatic selection in prey Some predators may have an aversion to rare or

unfamiliar prey

Prey switching


Being different pays off

Painted mussel shells with pieces of meat were offered to carrion crows Some shells were monomorphic (all the same color) Others were trimorphic (red, yellow and black) Crows took fewer trimorphic prey

When prey populations occur at the same density Individuals in polymorphic populations experience

less predation than those in monomorphic populations


Warning coloration (aposmatism)( 警告色 )

Aposematism (warning coloration): a conspicuous appearance that advertises dangerous or unpleasant attributes Discourages a predator’s attack

Bright colors and contrasting patterns Bold (black, white, red, or yellow) markings A skunk’s black and white color warns predators A wasp’s yellow and black body warns of its painful sting


Warning coloration in dendrobatid frogs

Dendrobatid frogs ( 箭毒蛙 ) have bright coloration and toxic skin secretions Species are red, yellow, blue, or some combination The colors may contrast with black markings

The most notorious is Phyllobates terribilis It has enough toxin in its skin to kill 100 humans

The bright coloration of these frogs is an example of aposematic coloration The more toxic species were the most colorful


Toxicity and brightness can be decoupled

In some dendrobatid frogs the most toxic species was not the most conspicuous And the most conspicuous was only moderately toxic

The relationship between conspicuousness and toxicity varies under different ecological conditions A negative relationship might occur if the costs of

conspicuousness are so high That prey are better off decreasing their investment in

bright colors And increasing their investment in toxins


Learned predator responses to aposematism Predators learn to avoid unpalatable prey if the prey are

conspicuously colored They sample the prey Discover its unpleasantness And avoid prey of similar appearance

Predators learn more quickly to avoid distasteful prey that are conspicuous.


Garter snake were first offered pieces of fish on aposematic (yellow and black) or on nonaposematic (green) forceps.

The snakes were then made ill by an injection of lithium chloride.

The post-treatment attack latencies to (a) pieces of fish or (b) earthworms indicate that snakes in the aposematic treatment group had a stronger aversion to fish than did snakes in the nonaposematic treatment group.


Mullerian mimicry

Two warningly colored species can look alike The two noxious species benefit from a shared pattern

Predators consume fewer of each species while learning to avoid all animals of that general appearance


Innate predator responses to aposematism Some predators display innate avoidance of

aposematic prey An innate response to warning coloration might be

favored over a learned response When prey can be fatal to the predator Learning at the moment of death is of little value


Sometimes warning coloration is ignored

A predator that is starving Wolves will attack skunks ( 臭鼬 ) and porcupines ( 豪

豬 ) when other prey is scarce Some predators are specialists

They can eat certain animals As long as an antipredator device confers a net

advantage in survival and reproduction It will continue in the population


Batesian mimicry

A palatable species adopts the warning characteristics of a noxious or harmful species

The harmless species is called the mimic The noxious one is the model

By resembling a noxious species, the mimic gains protection from predators The mimic does better when it is rare and less likely to

be detected by the predator than the noxious model The more distasteful the model, the better the mimic

fares


Mimics experience various degrees of protection

Other factors play a role in protection of mimics depending on The memory of predators Availability of alternate prey If mimics and models are encountered together or

separately Animals associated unpleasantness not just with the

model But also with the place where it was experienced

A mimic gains the most if its habits and activity overlap the model species


Mimics do not have to match models perfectly

Hoverflies ( 食蚜蠅 ) mimic wasps ( 黃蜂 ) Pigeons rank hoverflies according to their similarity to

wasps The two most common types of hoverflies least resemble

wasps Yet pigeons rank them as being very similar to wasp The wasps have some key feature used by pigeons in

pattern recognition When studying the defenses of prey animals, consider the

cognitive and perceptual abilities of their predators


Hoverflies ( 食蚜蠅 ) 是食蚜蠅科（ Syrphidae ）的昆蟲。牠們經常會停留在花朵上，成年的食蚜蠅主要吃花蜜及花粉，而幼蟲則吃不同種類的食物。一些物種的幼蟲是腐生生物，吃腐化的植物及動物。另外一些物種的幼蟲是食蟲動物，獵食蚜蟲、牧草蟲及其他吮食植物的昆蟲。已知有約 6000 種共 200 屬的食蚜蠅。牠們在世界各地都很普遍，除了南極洲外，各大洲都可以找到牠們的蹤跡。

Wasp ( 黃蜂 ) ，又稱為胡蜂或螞蜂，分布廣泛、種類繁多、飛翔迅速的昆蟲。

雌蜂身上有一根長螫針，在遇到攻擊或不友善干擾時，會群起攻擊，可以致人出現過敏反應和毒性反應，嚴重者可導致死亡。


Mimics gain protection from their enemies

A system of Batesian mimicry involves the juvenile stage of a snail (the mimic) And the tubes of a polychaete worm( 多毛綱蟲 )(the

model) White-spiral phase juveniles are indistinguishable from

worms Fewer were eaten by fish


Diverting a predator’s attention: false heads

Many predators attack the head of the prey

Some prey species have evolved false heads at their posterior end Misdirecting predators

Lycaenid butterflies ( 小灰蝶 ) deflect predator attacks toward a false head Complete with dummy antennae


Diverting a predator’s attention: autotomy

Some prey hand over a “disposable” body part to their attacker Autotomy ( 自割 ): the ability to break off a body part when

attacked Has evolved in both vertebrates and invertebrates

Tail autotomy in lizards, salamanders The prey breaks away from its attacker The detached tail moves, distracting the attacker

When attacked, sea cucumbers ( 海蔘 ) expel their guts The predator feeds on the sea cucumber’s offering

In most autotomy cases, the body part is regenerated


Costs of tail autotomy

May lead to reduced speed, balance, swimming, climbing, or mating ability

When the tail is used as a display Declines in social status occur

Regeneration of the tail entails costs in energy and materials Lizards have fat deposits in their tails that are lost with

the tail Once used, autotomy cannot be employed again, at least

for a while


Diverting a predator’s attention: feigning injury or death Ground-nesting birds (i.e. killdeer) may feign( 假裝 )

injury to divert a predator’s attention away from its nest and young An adult drags its wing as it flutters away from its nest The predator follows The killdeer suddenly recovers and flies away The predator wanders off

May cause a predator to lose interest i.e. opossums ( 負子鼠 ) and juvenile caimans ( 美洲鱷 )


An opossum playing dead.


Hognose snakes ( 豬鼻蛇 ) have a complex antipredator repertoire

When first disturbed, the hognose bluffs ( 嚇唬 ) It flattens and expands the front third of its body and

head to look larger It then coils and hisses( 發出嘶嘶聲 ) , making false

strikes When further provoked it writhes( 扭動 ) violently and

defecates ( 排便 ) Then it rolls over, belly up, with its mouth open and

tongue lolling If the predator loses interest and moves away, the snake

rights itself and crawls off


Hognose snakes ( 豬鼻蛇 ) The hognose snake is a type of colubrid

snake ( 無毒蛇類 ) characterized by an upturned snout. They are notorious for playing dead( 裝死 ) when threatened.


Young hognose snakes

Young snakes use cues from predators to adjust their antipredator behavior Assessing the degree of threat

Recovery from feigning death ( 裝死 ) of newly hatched snakes under various conditions An owl and a direct human gaze( 凝視 ) caused longer

recovery times


Death feigning( 裝死 ) involves immobility

Prey immobility may function to mimic death Immobility may also enlarge a prey’s functional body size

When grasped by a frog, a pygmy grasshopper ( 菱蝗 ) assumes a rigid T-shape

The posture is an adaptation for avoiding frog predation The size-enhancing rigid posture of grasshoppers is

ineffective against praying mantises ( 螳螂 ) These predators gnaw ( 啃咬 ) on prey rather than

swallowing it whole ( 整個吞 )


Prey can intimidate ( 威嚇 ) predators or fight back

The size-maximization principle A cat hunches its back and erects its fur Toads and fishes inflate themselves

Intimidation ( 威嚇 ) does not need to be visual Calls, hisses, or growls deter a predator

Animals display weapons Ungulates display their horns and paw at the ground Porcupines ( 豪豬 ) erect their spines Cats display their teeth


Intimidation displays in several species of animals.


Eyespots

Some animals have spots that resemble eyes Small eyespots misdirect a predator

Similar to false heads Located on nonvital portions of the body Prey escape with less than fatal damage

Suddenly flashed spots can startle a predator A disturbed peacock butterfly suddenly opens its wings

Exposing bright colors and large eyespots And emitting a hissing sound


peacock butterfly ( 美眼蛺蝶 ) ，鱗翅目、錘角亞目，蛺蝶科。是香港一種常見的蝴蝶。


Eyespots increase butterfly survival

Researchers presented wild blue tits with palatable peacock butterflies

Butterflies survived better when they had eyespots than when the eyespots were colored over Or when they had eyespots and hissed

Eyespot displays can be very effective in deterring a predator Hissing might deter other predators



Chemical repellents

Many insects discharge noxious chemicals when they are captured Powerful toxins or irritants In some species they can be shot with accuracy

The assassin ( 刺客 ) bug spits fluid in the direction of the attacker The saliva causes intense local pain


Bombardier beetles deter predators by emitting a hot, irritating spray


Vertebrates also use chemical deterrents

One of the most famous examples: skunks When disturbed by canid ( 犬科的 ) predators such as

kit foxes and coyotes the Texas horned lizard spatters ( 濺 ) its attacker with a stream of blood Ejected from the sinus surrounding its eyes The ejected blood contains noxious ( 有毒的 )

components


kit foxes

Texas horned lizard

coyotes


Pronouncement of vigilance ( 警戒 )

Vigilant prey ( 警戒的獵物 ) scan their surroundings for potential predators

Prey reactions communicate to the predator the prey is alert and aware Sit-and-wait predators might leave

Timber rattlesnakes spend hours or days at an ambush site Chipmunks ( 花栗鼠 ) , gray squirrels and wood thrush

( 畫眉鳥 ) harass( 持續騷擾 ) them Harassment displays had visual (tail-flagging) and auditory

components The snakes abandoned their site


Timber rattlesnakes

Chipmunks ( 花栗鼠 )

wood thrush ( 畫眉鳥 )

gray squirrels


Detected predators abandon the hunt

Stotting: a stiff-legged bounding display performed by pronghorn, deer and antelope

Signals to a predator that it has been detected Cheetahs ( 印度豹 ) abandoned hunts when their prey

stotted Two other functions of stotting

To distract a predator from offspring Fawns inform their mother that they have been

disturbed at their hiding place


Stotting is when a quadruped jumps into the air, lifting all four feet off the ground simultaneously.

Stotting (also pronking or pronging) is a gait of quadrupeds, particularly gazelles (e.g. Thomson's Gazelles), involving jumping high into the air by lifting all four feet off the ground simultaneously. This may occur during pursuit by a predator. It might also occur during play.


Stotting

The type of predator When hunted by predators that rely on stamina( 耐力 ),

gazelles ( 瞪羚 ) use stotting to signal their ability to outrun predators

Coursing (奔馳 ) predators chase stotting individuals at lower rates

The antiambush hypothesis: stotting is not a signal but allows the animal to gain a better view of its surroundings When approached by a human, black-tailed deer stotted more

often in taller vegetation Stotting also occurs during intraspecific encounters


驚嚇


Group Defense

Membership in a group Alarm signals: given when a predator approaches a

group of prey One or more individuals give a signal that alerts other

members to the predator’s presence May be visual, auditory, or chemical Inspire retreat by prey to a safe location

The alarm may aid the signaler or its relatives Or everyone in the area, including other species


The western toad’s chemical alarm system

Injured western toad tadpoles produce an alarm substance Functions as an effective

antipredator device Tadpoles exposed to the alarm

substance from an injured conspecific were less vulnerable to predation


Improved detection

Early detection of a predator translates into escape for prey Groups are superior to lone animals in spotting

predators Increases in the number of group members (and eyes,

ears, noses, etc.) Allow earlier detection of predators The escape response of a vigilant ( 警戒的 ) individual

can alert others to approaching danger


Florida scrub jays coordinate vigilance

If a predator is spotted, the sentinel哨兵 sounds the alarm Family members mob a ground predator Or monitor the movements of an aerial attacker

Sentinel 哨兵 systems have also been reported for mammals Dwarf mongooses (侏獴 ) and meerkats (狐獴 )

Members of temporary groupings at foraging locations benefit from improved detection of predators

Members of mixed-species groups also benefit from improved detection Communicating predator detection to other group members


Dwarf mongooses (侏獴 ) meerkats(狐獴 )

獴科（學名 Herpestidae ），哺乳綱食肉目的一科，包括各種獴，外形較象貓。最新的分類方法只包括獴亞科一個亞科。


Dilution effect (稀釋效應 )

Individuals in groups are safer because they detect predators But also because of the dilution effect: each individual has

a smaller chance of becoming the next victim As group size increases, the dilution effect becomes

more effective Predators aggregate in areas where their prey are

abundant Some grouped prey may suffer higher predation rates


The dilution effect vs. aggregating predators

Aphids( 牙蟲 ) benefit by forming groups in the presence of predators

Ladybird beetles( 瓢蟲 ) gather at aphid groupings They also increase their feeding rate

Grouping reduces predation risk for aphids The dilution effect occurs despite aggregation of predators

If parasitoids and pathogens increase rapidly in aphid groups It may eliminate the antipredator advantages of the

dilution effect


The tendency for prey individuals to form large groups and thereby dilute their chances of becoming the next victim by be countered by the tendency by their predators . Predatory lady bird beetles gather in larger number at aphid colonies that contain the most individuals.


Selfish herd (自私群 )

Centrally located animals are safer than those at the edges Lower chances of being attacked Increased probability that a peripheral animal will be

eaten Selfish herd: a group is composed of selfish individuals

Each trying to position as many others as possible between itself and the predator

Differs from the dilution effect and improved detection because it considers the spatial arrangement of individuals within a group


The center of a group is not always best

A location’s safety depends on the predator’s method of attack Schools of fish cope with a number of predators Each uses a different attack strategy

The center is sometimes the most dangerous place to be Silverside fish at the center of a school suffered the most

attacks from seabass Seabass split the school, striking the tail end of group Which contains individuals that were in the center


Optimal positions

Optimal positions within a school are also affected by Foraging efficiency: those in the front see the food first Energetics of locomotion: fish in the front have more

“drag”

seabassSilverside fish


Confusion effect (困惑效應 )

Predators that direct their attacks at a single animal in a group May hesitate or become confused when confronted with

several potential meals at once Any delay operates in favor of the prey

Confusion effect: predators are less successful in attacking prey because they are unable to single out and attack individuals


The confusion effect in schooling fish

One of the primary antipredator advantages of schooling

When fish scatter, it’s hard for visual predators to focus on a single one

Squid, cuttlefish, and pike are ambush predators Perch chase their intended victims

To succeed, predators restrict their attacks to individuals That have strayed (走散 ) from the school or are

conspicuous


For all four predators, attack success per encounter decreased as the size of the school of prey increased


Mobbing (暴衝 )

Sometimes prey attack predators Mobbing: approaching, gathering around, and harassing

one’s enemies This strategy involves visual and vocal displays and

even direct hits Initiated by an individual, conspecifics, or members of

another species


The functions of mobbing

The functions of mobbing include Confusing the predator Discouraging the predator through harassment (煩擾 ) or

announcing that it has been spotted Alerting others


Mobbing is a selfish act

Mobbing is not performed to protect the group It is the selfish act of individuals trying to protect

themselves and their mates, offspring, and relatives Mobbing is costly

It takes time and energy away from other activities Mobbers have a greater chance of being preyed on

As more individuals join the mob, the risk to any one of them is reduced through dilution or confusion effects


Maintenance of antipredator behavior

If an animal freezes or flees when it detects a predator It’s not doing something else: foraging, looking for mates,

or resting Responding to everything as if it were dangerous

decreases an animal’s fitness Costly antipredator behavior should be lost when it is no

longer needed


Maintenance of antipredator behavior

Animals on islands are free of predators Marine iguanas on the Galapagos Islands have been free of

predators for the last 5-15 million years Until feral cats and dogs were introduced 150 years ago After exposure, they became more fearful, but not fearful

enough Marsupials (kangaroos, wallabies, and their relatives)

also lost some (but not all) of their antipredator behaviors after they were isolated on islands

Animals can lose their fear of predators


Marine iguanas

kangaroos wallabies


Summary

Antipredator mechanisms decrease the probability of an encounter with a potential predator

Prey may go undetected if it matches the visual background Or through disruptive coloration

Prey exhibit polymorphism to prevent formation of search images by predators

Prey are recognized as inedible through warning coloration Or be unrecognized through masquerade and Batesian

mimicry


Summary

Other defenses operate during an encounter with a predator Prey divert the predator’s attention, inform the predator that

it has been spotted or fight back Group membership has antipredator advantages

Prey can detect, confuse, and discourage predators An individual has a lower probability of being selected

(dilution effect) Other group members are used as a shield (selfish herd)

Antipredator behaviors have costs Such behaviors are lost when its predators disappear


問題與討論

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

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抗掠食行為 (Antipredator behavior) ─ 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: hycheng

抗掠食行為 (Antipredator behavior) ─ 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: hycheng