Chapter 6 Behavioral adaptations for survival

1
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.
• Consequently, organisms have evolved a diverse
  variety of strategies to enhance their ability to
  avoid or deter predators.

2
Anti-predator strategies

• Defensive adaptations include
• Predator avoidance
• Hiding and camouflage
• Group defense
• Fleeing
• Signal unprofitability
• Warnings, deception and honest signals

3
Costs and benefits of camouflage

• Many organisms avoid predators by the use of
  cryptic coloration.
  
• A requirement of camouflage in many cases is that
  the individual choose an appropriate background.
  

4
Peppered moths

• Classic example of evolution in action is that of
  the peppered moth, which occurs in two forms a
  typical white/speckled form and a melanic or
  black form.
• In early 1800s dark form very rare.
• Dark form caused by dominant mutation that occurs
  spontaneously.

5
Peppered moths rest on trees and depend
on camouflage for protection.
6
Peppered moth

• In unpolluted areas trees are covered in lichens
  and the light form of the moth is hard to see.
  
• In mid 1800s air pollution in British cities
  covered trees with soot.
  
• In cities dark form became common and light form
  rare.

7
(No Transcript)
8
Peppered moth

• In mid 1950s pollution controls were introduced
  in Britain and frequency of melanic form has
  declined since then.

9
(No Transcript)
10
Peppered Moth

• Kettlewell carried out famous experiment in which
  he placed moths on dark and pale tree trunks and
  showed that background strongly influenced
  survival.
• In wild, however, moths take much more care about
  where they settle and rarely settle on tree
  trunks.

11

• Instead moths usually choose to rest in shady
  areas where branches join the trunk.
  
• If moths choice of site is adaptive then moths
  in these positions should be taken less often by
  predators than those on tree trunks.

12

• In an experiment in which dead moths were pinned
  to open tree trunks or the underside of branches
  birds consumed fewer of those on the undersides
  of branches.

13
6.17
14

• Other moths also make very specific choices about
  where to rest.
  
• The whitish moth usually perches head up with its
  forewings covering its body.
  
• When given a choice of resting site these moths
  prefer birch trees.

15
(No Transcript)
16

• Pietrewicz and Kamil (1977) tested whether these
  chocies by moths were selectively advantageous.
  
• Trained blue jays to respond to slides of moths
  by pecking a button for a food reward whenever
  they spotted a moth.

17

• Results showed that blue jays spotted moths less
  often on birch trees and especially when moth was
  oriented with its head up.
  
• Thus, moths choices appear to reduce the risk of
  detection by visually hunting predators.

18
6.19
19
Costs and benefits of anti-detection behavior
20
Hiding from predators has costs.

If youre hiding cant be doing something else.
21
Beldings Ground Squirrels, trapped six days
running. Held in trap and fed either peanut b
utter or lettuce. Lettuce eaters lost weig
ht.
22
Subsequently, lettuce eaters when foraging
less likely to stop feeding when predator alarm
call made. Squirrels trade off risk of predatio
n against need to feed.
23
Trinidadian guppies and predation risk
Males must display to attract females.
But, predators can spot them when they display.
24
A major predator is most active at high light
intensities. Male guppies risk is increased in
bright light.
Expect males to reduce displays.
25
(No Transcript)
26
Big males most conspicuous and vulnerable.
Expect large males to be most likely to cease d
isplaying in bright light.
27
(No Transcript)
28
Vigilance and groups.
Flocking and herding behavior widespread.
Several potential advantages. 1. More eyes inc
rease chance of predator detection. 2. Bette
r defense in a group 3. Dilution effect
29
1. More eyes increase chance of predator
detection.
30
Experiments by Kenward using a trained
Goshawk showed that as flock size increased
woodpigeons detected an approaching bird at
greater distances.
31
(No Transcript)
32
(No Transcript)
33
2. Better defense possible as member of a
group.
34
Many animals actively defend themselves
against predators. E.g. Musk oxen form defensiv
e circle facing outwards with calves on inside wh
en attacked by wolves.
Musk Ox
35
Wasps whose nest is disturbed swarm out
and attack the intruder.
36
Sawfly larvae form clusters and defend
themselves using drops of eucalyptus oil,
which they regurgitate and apply to their
enemy.
37
Many colonially nesting birds harass predators
who enter the colony. E.g. Gulls and terns dive
bomb intruders.
38
Such attacks are effective at deterring
intruders. In experiment artificial nests place
d in middle of colony less likely to be destroyed
by predators than nests on the edge.
39
(No Transcript)
40
Non-colonial birds also mob predators.
In mobbing behavior perched hawks and owls are
surrounded by groups of birds that
call loudly and harass the predator.
41
Mobbed bird often flies away to avoid
harassment.
Why does mobbed bird leave?
42
Probably because predators chance of catching
prey is low once discovered by potential prey.
43
Mobbing a predator potentially is dangerous.

Why do small birds take the risk?
44
Because mobbing may cause predator to
move far away.
European kestrels after being mobbed moved
on average a distance more than twice the
territory diameter of birds doing the
mobbing.
45
3. Dilution effect. Increasing group size redu
ces chance that a particular individual will be c
hosen by a predator. E.g. bird in flock of 10
0 has only 1 chance of being picked by predator
.
46
Extreme example of dilution effect seen in
swamping strategies Many prey synchronize beh
avior in attempt to overwhelm predators ability
to consume them.
47
E.g. Almost all Wildebeest give birth in about a

2-week period.
48
Hyenas and other predators cannot eat all the
babies, so most survive.
49
E.g. Mayflies emerge to breed over a period of
only a few days. Predation risk is lowest for t
hose individuals
that emerge with most others.
50
(No Transcript)
51
Most extreme example of emergence
synchronicity is in periodic cicadas.
In some species all individuals emerge as adult
s to mate at intervals of 13 or 17 years.
52
Mating cicadas
53
Cycle of 13 or 17 years minimizes the
chance of predators cycling their reproduction to
match emergence pattern
of cicadas. Why?
54
13 and 17 are prime numbers. No shorter cycle
can consistently match the emergence times.
55
Optimal group size and selfishness.
Many groups probably are selfish herds. Ind
ividuals join groups for own benefit not
that of group as a whole.
56
If for species X optimal group size is
10 individuals, would you expect to
observe groups of 10 in the wild?
Why or why not?
57
Should expect groups to be larger than
optimal size until they reach size at which
benefit to an individual of joining a group
is equal to that of remaining solitary.
58
Also see selfish behavior in cases where
predator may or may not be present, but no
one in group wants to be the one to find out.

59
E.g. penguins at edge of ice hesitate to enter
sea (and sometimes push one another in)
because of predatory leopard seals.
60
Costs of flocking Major cost is food must be sh
ared. House Sparrows attract others by giving a
chirrup call to signal food availability.
When predation risk low sparrows dont chirrup.
61
(No Transcript)
62
Defense by associating with a protective species
E.g. various tropical birds nest close to
ants, bees or wasps.

63
Experiment Polybia wasp nests moved close
to rufous-naped wren nests. Experimental nests
50 produced young Control nests 10 produced
young.
64
Many caterpillars attract ants who feed on
sugary secretions honeydew produced by
caterpillar. Ants repel parasitic wasps and fli
es.
65
Fleeing from predators
Flight is an important means of escape.
66
The faster you can flee the more likely you
are to escape. Muscular, chunky butterflies fly
fast. Less likely to be caught by birds than
thinner, less muscular butterflies.
67
Body shape, flight speed and escape
probability in tropical butterflies.
68
If being fast is an advantage why arent all
butterflies fast fliers?
69
Because there are costs to fast flight too.
Energy invested in muscle mass cannot be invest
ed in other structures.
What tissue might be more important to
invest in than muscle?
70
Reproductive tissue! Fast flying butterflies have
less ovarian tissue.
They produce fewer young.
71
Signaling Unprofitatbility

• Chemical defenses widely used to deter attackers
• Many plants produce toxic/indigestible
• chemical compounds (allelochemicals) to reduce
  grazing.

72
Monarch butterfly caterpillars
feed on milkweed. Incorporate cardiac glycoside
s from plant into their bodies. These provide
protection against predators.
73
Adult monarch butterflies advertise their
toxicity with bright colors.
74
Many organisms produce sticky substances
to guard against marauding ants (e.g.
Asian honeybees and solitary paper wasps).
75
Lots of animals signal their chemical
defenses/poisons with bright warning
colors. E.g. Monarch butterflies, bees, wasps,
coral snakes, ladybugs all have bright warning
coloration.
76
Coral Snake
77
Bright warning colors are mimicked by
numerous non-toxic/non-dangerous species.
Such mimics are referred to as Batesian mimics
.
78
Coral Snake and mimics. Which is the coral
snake?
79
Some caterpillars mimic vine snakes.
80
Jumping spiders mimicked by a tephritid fly.
81
Fly has leg-like pattern on wings.
Fly Spider
When approached, fly waves wings
mimicking territorial defense display of
jumping spider.
82
Jumping spiders reluctant to approach
displaying flies. Effectiveness of display test
ed experimentally.
House flies and tephritid flies had wings
surgically exchanged.
83
Tephritids with housefly wings and houseflies
with tephritid wings were ineffective at
deterring spiders. Tephritids whose own wings
were removed but reattached deterred 16 of 20 sp
ider attacks.
84
Jumping spiders also are mimics. Mimic
non-dangerous species and inanimate objects.
Ant mimic Beetle mimic
85
Bird dropping mimic.
86
An acoustical Batesian mimic.
Burrowing Owls live in prairie dog burrows.
87
Burrowing Owls make sound like a
rattlesnakes rattle. Deters animals from enter
ing owls burrow.
88
Mullerian mimicry In Mullerian mimicry sever
al toxic or dangerous species all display same or
similar warning
colors. Convergent evolution.
89
Mullerian mimics on left of red line
Batesian on right of line
90
Advertising unprofitabilty to deter pursuit.

Cheetahs hunt Thompsons gazelles.
91
Cheetah
Thompsons gazelle
92
Gazelle that spot cheetahs frequently stot.
They bounce in a stiff-legged gait and display
their white rump to the cheetah.
93
Display apparently advertises that predator has
been spotted and prey is too quick so a chase
would be pointless.
94
Stotting appears to be an honest signal of
uncatchability as cheetahs fail to catch
stotting individuals and usually abandon the
hunt
95
A similar honest signal is given by Anolis
lizards which perform pushups when they
spot an approaching snake.

96
The number of pushups an Anole performs
closely matches the lizards endurance in
running and so appears to honestly signal its
ability to flee.
97
Because signal is honest it appears to
benefit both prey and predator to exchange
information.
98
Avoiding consumption after capture
As a last-ditch defense captured animals
may attempt to force the predator to release
them.
99
Several approaches tried.
(i) Chemical deterrence. (ii) Misdirection of
attack. (iii) Startle predator (iv) Attract comp
eting predators

100
(i) Chemical deterrence.
Many insects spray defensive chemicals
such as formic acid when gripped.
101
Some salamanders release toxic secretions
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 afte
r eating.
102
(ii) Misdirection of attack
Common defensive tactic is to divert attack
to non-critical part of the body.

Examples include
103
False eyespots on fish. Direct attention away f
rom vulnerable
head.
104
Prominent detachable tails in lizards.
Tail often held high above body to induce
an attack there.
105
Tail can be shed if grabbed and regrown.
Regrown Tail.
106
Dark tail tip in stoats
107
In experiments predatory birds strike at
dark tail tip rather than stoats head.
108
Also, some butterflies have fake heads
on their wings.
False head has been bitten off
109
(iii) Startle predator. Underwing moths flash
bright hindwings when pecked. Many animals s
cream. Loud cries may Induce predator to let go
.
110
(iv) Attract competing predators
Fear screams may also attract other
predators which may interfere with attacking
animal allowing prey to escape.
111
Minnows use chemicals to scream
Fathead minnows release skin chemicals when bi
tten.
These attract predatory fish.
112
In presence of extra predators handling time
is longer. Prey sometimes escapes.
One pike Two pike
113
Optimality Theory

• Cost-benefit ratios are important and when costs
  and benefits can be measured accurately we can
  make precise predictions about the behavioral
  choices we would expect organisms to make.
• One way we can study such decisions is by using
  optimality theory.

114
Optimality Theory

• Optimality theory assumes that organisms attempt
  to maximize their benefits while simultaneously
  minimizing their costs.
  
• Thus, we predict organisms should behave in such
  a way that the benefit to cost ratio is maximized.

115
Fig 6.30
Four different phenotypes X,X,Y and Z).
Phenotype X has largest benefitcost ratio and s
hould increase in frequency as a result.
116
Optimality Theory and Bobwhites

• Bobwhite Quail form flocks (called coveys) in
  winter.
  
• Coveys appear to provide anti-predator benefits.
  Percentage time at least one individual is
  scanning for predators increases with covey size
  up to a flock size of about 10 and then levels
  off.
• Increased competition for food among flock
  members is likely cost of increased flock size.

117
Optimality Theory and Bobwhites

• In Bobwhites individual daily survival rate peaks
  at a covey size of about 10.

118
Fig 6.31 a
119
Optimality Theory and Bobwhites

• Mean daily movement of coveys is minimized for
  coveys of 10 or 11 birds.
  
• Small coveys may move a lot trying to find
  another covey to join and large coveys move to
  find more food.

120
Fig 6.31B
121
Optimality Theory and Bobwhites

• Benefitcost ratio is maximized for coveys of
  10-11 birds and these are the commonest covey
  size found.

122
Fig 6.31C
123
Game Theory

• Game theory is another way of analyzing
  behavior.
  
• Game theory focuses on the strategies organisms
  choose and the best strategies depend on what
  other individuals are playing. Recall the
  Hawk-Dove model from Dawkins.