Transcript predators

Chap.11
Antipredator Behavior
鄭先祐 (Ayo) 教授
國立台南大學 環境與生態學院
生態科學與技術學系
環境生態研究所 + 生態旅遊研究所
Antipredator behavior
Avoiding predators
 Blending into the environment
 Being quiet
 Choosing safe habitats
What to do when prey encounter
predators
 Fleeing, approaching predators,
 feigning death, signaling to predators
 Fighting back
Predation and foraging trade-offs
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Snake and ground squirrels
 Approximately a million years.
 Strongly selected for ground squirrels to be able to
identify their predators and to respond to them
with fine-tuned behaviors.
 Squirrel antipredator behavior includes
throwing dirt, pebbles, and roots at putative
predators, as well as emitting alarm calls that
are specifically made when snakes, but not
other predators, are present. (Fig. 11.1)
 and also immunological defenses (Fig. 11.2)
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Ground squirrel pups
emerge from their
burrows at about
forty days. Shortly
before this, there is
an increase in their
immunological
defenses against
snakes.
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Ground squirrel pups often face serious predation threat
on their first emergence from their burrow.
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Avoiding predators
 Blending into the environment
 Cryptic, hidden through camouflaging,
making their detection by predators unlikely.
(Fig. 11.4 Cuttlefish (烏賊) camouflaging)
 (A) using uniform color to camouflage itself
against the rocks
 (B) using a “mottled (斑駁的) ” camouflage pattern,
with small dark splotches resembling the dark
patches or rocks and sand
 (C) a “disruptive(破裂的)” camouflage pattern
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Uniform color to camouflage
Mottled camouflage pattern
Disruptive camouflage pattern
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Being quiet
Gulf toadfish (prey) (Fig. 11.5)and
bottlenose dolphins (predator)
Dolphins orient toward the “boatwhistle”
sound produced by male toadfish during
breeding season.
Dolphins produce two kinks of sounds,
high-frequency whistle for social
communication, low-frequency “pops”
for foraging.
Fig. 11.6 Gulf toadfish become silent.
 Playback test
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Wax moth and bat
Subtle differences between male moth
sounds and bat echolocating sounds.
Females were indeed able to
distinguish between these types of
calls and responded appropriately.
(playback test)
 Fanning their wings when they heard
male calls
 But dramatically decreasing this
behavior when they heard bat
echolocation calls.
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Choosing safe habits
 Predation and choice of nesting sites in parrots
 Phylogenies examination showed the ancestral
state was tree cavity nesting.
 Why the nesting in other cavities had evolved
independently many time in both Australian
and Amazonian parrot species?
 Whether predation was the key selecting for
the shift away from tree cavity nesting?
 101 North American species found that a
correlation between the nest predation rate and
the length of nesting period.
 Therefore, OC nesters should have longer nesting
periods.
 The data on both Amazonian and Australian parrot
species do.
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What to do when prey encounter predators?
Encounters with predator’s dangers are,
over the lifetime of an organism (prey),
inevitable (Fig. 11.8).
Fig. 11.8 encounter with a predator.
 A scavenging skua gull descends from the
air in search of penguin eggs or
unattended chicks, while these two gentoo
penguins attempt to fend it off.
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What to do when prey encounter predators?
1. Fleeing
 A meta-analysis of flight initiation behavior
 Tree frog embryos and snakes
2. Approaching predators
 Thomson’s gazelles
 minnows
3. Feigning death
4. Signaling to predators
 Warning coloration in monarch butterflies
 Tail flagging as a signal
5. Fighting back
 Chemical defense in beetles
 Social learning and mobbing in blackbirds
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Fleeing
 The most common response of prey that have
spotted a predator is to flee for safety. (Fig.
11.9)
 Flight initiation distance, how close a predator
can approach before prey flee.
 Gathered published data from 61 studies of
flight initiation in mammals, fish, birds, and
reptiles. (meta-analysis)
 Animals far from of their refuge initiated fleeing
from a predator sooner than animals closer to
their refuge.
 Animals involved in foraging, mating, or fighting
were slower to flee from predators than animals
were not currently involved in such behaviors
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Tree frog embryos and snakes
 Fig. 11.11 predators that feed on treefrog
eggs
 (A) here a wasp forages on treefrog eggs
 (B) Snakes are another dangerous predator on
red-eyed treefrog eggs.
 If terrestrial predation is weak, eggs hatch late
I the season.
 Warkentin predicted that treefrog eggs would
hatch sooner if predation in the terrestrial
environment increased.
 Fig. 11.12 wasp predation and the development
time of treefrog eggs
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Treefrogs respond
to wasp predation
by hatching early.
Green bar represent
hatching rate of
clutches that
suffered wasp
predation, while
orange bars indicate
undisturbed clutches.
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Snake predation and development time
Fig. 11.13 Snake predation and
development time of treefrog eggs.
 Treefrogs also respond to snake predation
by hatching earlier than normal. Clutches
attacked by the snake at (A) five days old
and (B) six days old. (C) clutches that
were undisturbed by predation.
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five days old
six days old
undisturbed by predation
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Proximate cues?
Vibrational cues associated with snake
attacks as the proximate cue for when
to switch from terrestrial habitats to
aquatic ones.
To test the hypothesis, using three
kinds of sounds (Fig. 11.14) (playback
test)
 Two kinds of the vibrations associated with
snake attacks and One kind of rainfall
 The cues associated with snakes resulted
in treefrogs that hatched earlier.
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Snake attack and eats
an entire clutch of eggs
A rainstorm
Snake eats one or two eggs
in s short series of bites
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Approaching predators
 This approach behavior allows prey to gather
important information about putative
predators and hence reduces their chances of
mortality.
 Approach behavior is often undertaken by
healthy adults.
 This type of behavior has been extensively
documented in vertebrates, particularly in fish,
birds, and mammals.
 Prey typically approach a potential predator
from a distance in a tentative(嘗試的), jerky(急
動的) manner.
 Fig.11.15 Gazelle antipredator behavior. (A)
Gazelles are constantly vigilant (警戒的) for
potential predators (B) many different
species, including the cheetah hunt gazelles.
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Approach behavior in gazelles (Fig. 11.16)
(A) the probability of approach
behavior occurring in gazelles is a
function of group size, as indicated by
the logistic curve.
(B) cheetahs respond to gazelle
approach behavior. The distance a
cheetah move away in response to
gazelle approach behavior is also a
function of the gazelles’ group size.
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Interpopulational differences in approach
behavior in minnows (Fig. 11.17)
 Two different populations of minnows
(from the Dorset area and Gwynedd area)
 Dorset population is under strong predation
pressure from pike predators
 While pike are absent from the Gwynedd
population of minnows
 Both populations of minnows increased their
group size when faced with predators in the
laboratory, but the Dorset population tended
to maintain larger groups.
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(A) Dorset minnow
respond to predators
by decreasing their
predator inspection
behavior
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(B) No statistically significant decrease in inspections
occurs in the Gwynedd minnow population.
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Feigning death
Faking, or feigning, death is an
antipredator behavior seen across a
spectrum of species.
Adzuki bean beetle
 Either fly away or feign death
 Hypothesized that a negative genetic
correlation existed between the intensity
of death feigning and the ability to fly
 Artificial selection, longer duration of feign
death vs. shortest duration of feign death
• After 8 generations
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The long duration lines are in
green and the short duration
lines are in orange.
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Signaling to predators
 Warning coloration in monarch butterflies
 Monarch butterflies ingest milkweed plants, which
contain chemicals called cardiac glycosides.
• These chemicals, which are toxic to birds, do not harm
the monarchs.
 When a naïve predator eats a monarch, the toxins
in the butterfly make the predator violently illtemporarily (Fig. 11.21)
• The color patterns of monarchs act as warning coloration
for that predator who now avoids feeding upon monarchs.
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Tail flagging as a signal
Some animals send signals that may
serve to notify a predator that is has
been spotted.
When the predator is an ambush hunter
that relies on surprise, such a signal
often cause it to move on the leave the
area, and hence clearly benefits the
prey.
Fig. 11.22 Tail raising event in Whitetailed deer.
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Fighting back
Chemical defense in beetles
Fig. 11.23 bombardier defense. When
the bombardier beetle is threatened, it
releases chemicals that ward off
predators.
 This bombardier beetle is being attacked
from the front, and so it is directing its
chemical spray forward.
 They fire the spray backward, when
attacked from the rear.
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Social learning and mobbing in blackbirds
Blackbirds undertake a form of attack
called predator mobbing.
 Once a flock of blackbirds spots a predator,
they join together, fly toward the danger,
and aggressively attempt to chase it away.
 Such group attacks often work well enough
to force predators to leave the blackbirds’
area.
 Mobbing is a form of cultural transmission.
 Animals Raised in captivity failed to have
mobbing behavior.
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Predation and foraging trade-offs
 Fig. 11.24 foraging-predation trade-off.
 When animals are being vigilant for predators, it is
often at the cost of other activities. The starlings
here can’t be foraging for insects while they scan
the sky of hawks.
 Foraging is one of the behaviors especially
affected by predation.
 Predation pressure affects virtually every aspect of
foraging– everything from when a forager begins
feeding.
 Foraging in the gray squirrel (Fig. 11.25)
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Predation and foraging trade-offs
 Squirrels alter their foraging choices as a
result of predation pressure from redtailed
hawks.
 Squirrels who could either eat their food items
where they found such items or carry the food to
cover were more likely to carry items to an area of
safe cover, particularly as the distance to safe
cover decreased.
 The closer the refuge from predation, the more
likely they would use such a shelter when foraging.
 Squirrels were much more likely to carry larger
items to safe areas before continuing to forage.
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(A) Here a squirrel is foraging at a feeding station
(B) A squirrel heads for cover with a food item (a part of a cookie) in its mouth.
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問題與討論
Ayo NUTN website:
http://myweb.nutn.edu.tw/~hycheng/