Transcript ppt檔案 - 國立臺南大學

大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
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/
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
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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
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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
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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)
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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.
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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
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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
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 California yellow-legged frogs
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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
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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
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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.
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 cuttlefish (烏賊)
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Cuttlefish can rapidly change color
 Cuttlefish change color to match their background
 They can even display bold contrasting elements
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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
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Disruptive coloration enhances survival
Patterns at the periphery enhance survival
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Disruptive coloration enhances survival
High contrast patterns enhance survival
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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)
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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
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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
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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
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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
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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
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Apostatic selection (變節的選擇)
Prey switching
 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
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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
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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
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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
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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
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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.
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 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.
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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
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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
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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
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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
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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
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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
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 Hoverflies (食蚜蠅)是食蚜蠅科
 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。
（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。
Ayo 教材
(動物行為學 2010)
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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
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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
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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
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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
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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)
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 An opossum playing dead.
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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
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 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.
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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
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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)
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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
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 Intimidation
displays in
several species
of animals.
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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
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 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。
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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
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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
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Bombardier beetles deter
predators by emitting a hot,
irritating spray
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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
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 coyotes
 kit foxes
 Texas horned lizard
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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
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 gray squirrels
 Chipmunks (花栗鼠)
 wood thrush
(畫眉鳥)
 Timber
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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
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 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.
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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
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驚嚇
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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
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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
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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
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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
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 meerkats(狐獴)
 Dwarf mongooses (侏獴)
 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。
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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
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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
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 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.
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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
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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
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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”
Silverside fish
seabass
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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
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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
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For all four predators, attack success per encounter
decreased as the size of the school of prey increased
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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
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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
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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
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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
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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
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 Marine iguanas
 wallabies
 kangaroos
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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
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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
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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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