Chapter 6 Behavioral adaptations for survival. Evolutionary success is measured in offspring produced or genetic contribution to the next generation, but to reproduce it is necessary to survive long enough to do so.
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on camouflage for protection.
If you’re hiding can’t be doing something
Held in trap and fed
either peanut butter
Lettuce eaters lost
less likely to stop feeding when predator alarm
Squirrels trade off risk of predation against
need to feed.
Males must display to attract females.
But, predators can spot them when they display.
Male guppies risk is increased in bright light.
Expect males to reduce displays.
Expect large males to be most likely to
cease displaying in bright light.
Flocking and herding behavior widespread.
Several potential advantages.
1. More eyes increase chance of
2. Better defense in a group
3. Dilution effect
Goshawk showed that as flock size increased
woodpigeons detected an approaching bird at
E.g. Musk oxen form defensive circle facing
outwards with calves on inside when attacked
and attack the intruder.
themselves using drops of eucalyptus oil,
which they regurgitate and apply to their
who enter the colony.
E.g. Gulls and terns dive bomb intruders.
In experiment artificial nests placed in middle
of colony less likely to be destroyed by
predators than nests on the edge.
In mobbing behavior perched hawks and
owls are surrounded by groups of birds that
call loudly and harass the predator.
Why does mobbed bird leave?
Probably because predator’s chance of catching prey is low once discovered by potential prey.
Why do small birds take the risk?
move far away.
European kestrels after being mobbed moved
on average a distance more than twice the
territory diameter of birds doing the
Increasing group size reduces chance that
a particularindividual will be chosen
by a predator.
E.g. bird in flock of 100 has only 1% chance
of being picked by predator.
Many prey synchronize behavior in attempt
to overwhelm predators ability to consume
babies, so most survive.
Predation risk is lowest for those individuals
that emerge with most others.
synchronicity is in periodic cicadas.
In some species all individuals emerge as
adults to mate at intervals of 13 or 17years.
chance of predators cycling their reproduction to match emergence pattern
13 and 17 are prime numbers. No shorter cycle can consistently match the emergence times.
Many groups probably are “selfish herds”.
Individuals join groups for own benefit not
that of group as a whole.
10 individuals, would you expect to
observe groups of 10 in the wild?
Why or why not?
optimal size until they reach size at which
benefit to anindividual of joining a group
is equal to that of remaining solitary.
predator may or may not be present, but no
one in group wants to be the one to find out.
sea (and sometimes push one another in)
because of predatory leopard seals.
Major cost is food must be shared.
House Sparrows attract others by giving a
“chirrup” call to signal food availability.
When predation risk low sparrows don’t
E.g. various tropical birds nest close to
ants, bees or wasps.
to rufous-naped wren nests.
Experimental nests: 50% produced young
Control nests: 10% produced young.
sugary secretions “honeydew” produced by
Ants repel parasitic wasps and flies.
Flight is an important means of escape.
are to escape.
Muscular, chunky butterflies fly fast.
Less likely to be caught by birds than
thinner, less muscular butterflies.
probability in tropical butterflies.
butterflies fast fliers?
Energy invested in muscle mass cannot be
invested in other structures.
What tissue might be more important to
invest in than muscle?
Fast flying butterflies have less ovarian tissue.
They produce fewer young.
Chemical defenses widely used to deter attackers
Many plants produce toxic/indigestible
chemical compounds (allelochemicals) to reduce grazing.
feed on milkweed.
Incorporate cardiac glycosides
from plant into their bodies.
These provide protection
toxicity with bright colors.
to guard against marauding ants (e.g.
Asian honeybees and solitary paper wasps).
defenses/poisons with bright warning
E.g. Monarch butterflies, bees, wasps, coral
snakes, ladybugs all have bright warning
numerous non-toxic/non-dangerous species.
Such mimics are referred to as Batesian
When approached, fly waves wings
mimicking territorial defense display of
Effectiveness of display tested experimentally.
House flies and tephritid flies had wings
with tephritid wings were ineffective at deterring
Tephritids whose own wings were removed
but reattached deterred 16 of 20 spider attacks.
non-dangerous species and inanimate objects.
Ant mimic Beetle mimic
Burrowing Owls live in prairie dog burrows.
Deters animals from entering owl’s burrow.
In Mullerian mimicry several toxic or dangerous
species all display same or similar warning
colors. Convergent evolution.
Batesian on right of line
Cheetahs hunt Thompson’s gazelles.
They bounce in a stiff-legged gait and display
their white rump to the cheetah.
Display apparently advertises that predator has been spotted and prey is too quick so a chase would be pointless.
uncatchability as cheetahs fail to catch
stotting individuals and usually abandon the
lizards which perform pushupswhen they
spot an approaching snake.
closely matches the lizard’s endurance in
running and so appears to honestly signal its
ability to flee.
benefit both prey and predator to exchange
As a last-ditch defense captured animals
may attempt to force the predator to release
(i) Chemical deterrence.
(ii) Misdirection of attack.
(iii) Startle predator
(iv) Attract competing predators
Many insects spray defensive chemicals
such as formic acid when gripped.
when grabbed by garter snakes.
In one California population arms race
between salamanders and snakes has
produced salamanders so toxic that
snakes are paralyzed for hours after
Common defensive tactic is to divert attack
to non-critical part of the body.
Direct attention away from vulnerable
Tail often held high above body to induce
an attack there.
dark tail tip rather than stoat’s head.
on their wings.
False head has been bitten off
Underwing moths flash bright hindwings
Many animals scream. Loud cries may
Induce predator to let go.
Fear screams may also attract other
predators which may interfere with attacking
animal allowing prey to escape.
Fathead minnows release skin chemicals
These attract predatory fish.
is longer. Prey sometimes escapes.
One pike Two pike
Four different phenotypes X,X,Y and Z). Phenotype X has largest
benefit:cost ratio and should increase in frequency as a result.