1. Alcock, Chapter 6
Behavioral Adaptations for Survival

2. Hans Kruuk & Black-Headed
Gulls (Alcock, p. 177-181)
• Kruuk wanted to know whether the mobbing response of
black-headed gulls was an adaptive product of natural
selection.
• Kruuk’s hypothesis was that mobbing behavior distracted
certain predators, reducing the chance that they would find
the mobbers’ offspring which would boost the fitness of
mobbing parents gulls.
• Given the variation always exists in populations, some
gulls would be better mobbers than others.
• Does the cost to mobbers (time and energy spent in
screaming, diving, and flapping about, plus the chance that
they, themselves, might be grabbed and eaten) outweigh
the benefit of saving their young from predation?

3. Kruuk’s Research)
(Cont’d
---The question is: do mobbers leave more surviving
progeny than non-mobbers? Do they have a higher fitness?
And what about the cost and benefits?
• Because distracted crows are probably less likely to find
prey eggs or gull hatchlings, Kruuck established
that a probable benefit existed for mobbing.
• The benefit of crow mobbing exceeds the cost, given that
rarely are mobbing gulls caught and killed by crows.
• Kruuk counted surviving eggs in his research, assuming
that they would become surviving offspring and carry on
their parents’ genetic lines (he did not measure full
reproductive success by counting the number of surviving
offspring produced by individuals over their lifetimes).

4. Alcock, p. 184, Fig. 6.7
Comparing Gull Species
• Members of the same evolutionary gull lineage share a
common ancestry, and therefore share many of the same
genes, and thus tend to have similar traits, such as
mobbing behavior.
• But the effects of shared ancestry can be overridden by a
novel selection pressure.
• Reduction in predation pressure has led to divergent
evolution by the cliff nesting gull called the kittiwake,
which no longer mobs potential enemies.
• The various ground-nesting gulls, including the black-
headed gull, mob nest predators as do some colonial
swallows, including the bank swallow, even though gulls
and swallows are not related, having come from different
ancestors long ago.

5. Comparing Gull
Species and Swallows
 Kittiwake Bank Swallow 
--The kittiwake no longer mobs, but
the bank swallow does mob, like
black-headed and other ground-
nesting colonial gulls.
--Even though gulls and swallows are not related, they have
converged on a similar antipredator behavior in response
to shared selection pressure from predators that have fairly
easy access to nesting colonies.
--Cliff-nesting kittiwakes, although clearly relatives of the
black-headed gulls, no longer need to mob as potential
predators cannot prey effectively on their precarious
nesting areas.

6. Ground Squirrel Mobbing
(Alcock, p. 185-86; Figs. 6.8 & 6.9)
• California ground squirrels mob rattlesnakes.
• These squirrels live in groups and dig burrows in the
ground, and react to a hunting rattlesnake by gathering
around it and kicking sand in its face, thereby preventing
the snake from exploring nest burrows for newborns and
infants.
• Given the costs of a rattlesnake bite, researchers predicted
that the squirrels would be able to adjust their behavior in
relation to the level of risk of snakebite, which could be
assessed by listening carefully to the rattling buzzes made
by the snakes.
• The rattler’s sounds vary according to size and body
temperature—larger snakes and warmer snakes (which can
move quickly) present a greater risk.

7. Ground
Squirrels (Cont’d)
• Ground squirrels, as predicted, were less eager to approach
speakers playing the rattles of large and warmer snakes.
• The ability to assess the risk would enable squirrels to
reduce the cost of their mobbing.
• Also, as their offspring matured and became better able to
avoid snakes on their own, mother squirrels were less
likely to mix it up with rattlers, as measured by the
reduced time they spent close to a tethered snake.
• In other words, as the benefits of mobbing behavior fell,
the benefit-to-cost ratio of the activity, declined, and as
one would predict, the willingness of adult squirrels to
engage in the behavior also decreased.

8. Costs and Benefits of
Anipredator
Behavior (Alcock, p. 187,
Fig. 6.10)
• Mud-puddling = Why do butterflies aggregate in large,
packed groups around mud puddles on tropical riverbanks
where they suck up fluid containing valuable nutrients?
• Possible answer = to dilute the risk of one specific
individual being attacked and eaten.
• The risk of death for a member of a group of 1000
butterflies is 1% per day, whereas it is 10x higher for
members of a group of 100 butterflies.
• The dilution effect provides a benefit for individual
butterflies that tend to mud-puddle with many others.
• Thus the benefit to cost ratio for the tendency to aggregate
could well be positive, facilitating the evolution of the
behavior.

9. Synchronized
Metamorphosis
• Mayflies (Alcock, p. 187-88, Fig.6.11)
• Some mayflies synchronize their metamorphosis
from aquatic nymphs to flying adults so that most
individuals emerge from the water during just a
few hours on a few days each year.
• Fig. 6.11 presents data indicating that the more
female mayflies that emerged together on a June
evening the less likely that any individual mayfly
could be eaten by a predator

10. Social Insects and Group Attacks
(Alcock, p. 188-89, Fig. 6.12)
• Benefits of group livingthe potential for group attack on
a shared enemy (termites, ants, wasps, and bees).

11. Australian Sawfly Grubs
(Alcock, p. 189-90, Fig. 6.13)
• Communal defense by sawfly larvae: these larvae form circular
clusters that rest with their heads facing outward during the day.
• When threatened the raise their heads in warning while regurgitation
droplets of repellent eucalyptus oils, which the hold in their moths to
spew out onto an attacking enemy.

12. Costs/Benefits of
Camouflage: The
Melanic Moths
Story (p. 190-94)
• The peppered moth in the U.K. & U.S.A. and the spread of
the melanic (black) phenotype as industrial soot darkened
tree trunks (Fig. 6.16).
• Although most of these moths rest next to tree limb joints,
of those that rest on the trunks, the melanic forms were
less often discovered by birds in polluted (darkened)
woods, while the typical peppered (largely whitish) forms
survived better in unpolluted woods where tree trunks
were not darkened (Fig. 6.17).
• Consider here that the benefit vs. costs changes (for each
phenotype) when a critical environmental variable
changes.

13. Cryptic Coloration and
Body Orientation
(p. 192-193;
Figs. 6.18 & 6.19)
• The orientation of the another whitish moth Catocala
relicta usually perches head-up, with its forewings over its
body, on white birch and other light-barked trees with
narrow, intermittent black bands (Fig. 6.18).
• The orientation of the resting C. relicta determines
whether the dark lines in its wing pattern match up with
the dark lines in birch bark.
• Lab experiments with blue jays indicate that a C. relicta,
when properly oriented head-up, with wing patterns
aligned horizontally with bark bands, was very likely to be
overlooked by blue jays.
• Any C. relicta perched not-head up or on a non-matching
substrate were targeted much more (again the cost of not
using camouflage properly).

14. The Assassin Bug’s “Backpack”
• Assassin bugs cover themselves with sand, dust, and/or organic debris
such as the carcasses of their own prey to build a “backpack to
camouflage themselves.)
• Bugs that retain the dust and debris that they apply to themselves are
typically ignored by predatory army ants.
• Those bugs that have lost a portion of all of their camouflage are
subject to predation (p. 193, Fig. 6.20).
• Again, an example of the necessity to properly use camouflage or face
predation.

15. Darwinian Puzzle: Why would
a Prey Animal become
Conspicuous to its Predators?
• This would seem to be a cost-benefit dilemma, but
the monarch butterfly provides a good answer (p.195-96).
• The monarch’s conspicuous coloration warns predators of
its chemical toxin (monarch larvae feed on poisonous
milkweeds and retain the plants poison in their tissues)
• A naïve predator attempts to eat just one monarch, vomits
and avoids this species for life.
• Although a dead animal cannot pass on its genes, a dead
monarch educates a predator who will never prey on the
monarch’s close relatives (a terrible cost = great benefit).
• So the dead one is a sacrifice that helps genetically similar
monarchs survive to pass on shared genes to the next
generation.

16. Why Behave
Conspicuously?
• The tephritid fly habitually waves its banded wings as if
trying to catch the attention of predators.
• The fly’s wing markings resemble the legs of jumping
spiders which prey on them.
• Researchers hypothesized that when the fly waves its
wings, it creates a visual effect similar to the aggressive
leg-waving displays of the spiders—and this deters an
attack by the spiders.
• Experiments confirmed the hypothesis: the fly mimics the
spider’s own aggressive signal and this mimicry “releases”
escape behavior on the part of the jumping spider.

17. Stotting in Thomson’s Gazelle
and in other African Gazelles
• Leaping into the air, stiff legged, while flaring your white
rump patch--another case of why behave conspicuously!?
• Four hypotheses are listed on p. 197, and one by one each
is shot down, until only number four remains—the Pursuit
Deterrent Hypothesis.
• Gazelles stot to announce to a predator that they will be
hard to capture; thus the cheetah will waste energy and
time—and this allows the cheetah to make a wise decision.
• Cheetahs get the message, since they are more likely to
abandon hunts when gazelles stot than when a potential
victim does not stot (p. 198, Fig. 6.26)

18. Optimality Theory and
Antipredator Behavior
• Adaptations have to do more than merely confer a benefit
if they are to increase in frequency in a population (p.
201).
• An adaptation, by definition IS better than the alternatives;
in other words: the net benefit associated with a true
adaptation is greater that that associated with the non-
adaptive alternatives.
• If one can measure the fitness costs and benefits associated
with four alternative behavior phenotypes in a population,
then one can determine which trait confers the greatest net
benefit on individuals in that population (see Fig. 6.30).
• This trait would be considered an adaptation—an optimal
trait that would replace the alternatives given sufficient
evolutionary time.

19. Optimal Covey Size for
Northern Bobwhite Quail
P. 202-02, Fig. 6.31.
• Optimal winter covey size for northern bobwhite quail is a
function of the costs and benefits of belonging to groups of
different sizes.
• Winter coveys range from 2-22 individuals, but with a
strong mean at 10-11 individuals.
• Individuals in smaller groups are less safe from attack;
individuals in larger groups are more safe.
• Yet very large groups must suffer from increased
competition for food among its members.
• So an effective, optimal cost and benefit ratios are found in
mid-sized groups, around 11 individuals.

20. Game Theory
(Costs and Benefits)
• The fundamental competition of life revolves around
getting more of one’s genes into the next generation than
one’s fellows (p. 202-04).
• Game theory comes into play when the benefit of a
behavioral option to one individual depends on what the
other members of its population are doing.
• Game theory views evolution as a game in which the
players are armed with different strategies that are in
competition with one another, with the winners creating a
population over time that cannot be invaded by a player
with an alternative strategy.
• What’s the flaw with this logic? Mutations? A competitive
behavioral arms race spiraling out of hand?

21. The “Selfish Herd” Notion in the
Game Theory Model
• W. D. Hamilton originated the idea that in a “selfish herd”
all the individuals were trying to hide behind others to
reduce the probability of being selected out by a predator.
• Eventually all the members of this population will be
aggregated, with individuals jockeying for the safest
position within their groups, actively attempting to
improve their odds at some else's expense (p. 204).
• The result would be a selfish herd, whose members would
actually be safer if they all could agree to spread out and
not try to take advantage of one another.
• Individuals employing a solitary strategy would be
vulnerable to a social mutant that uses a hide-behind-
another strategy to take fitness from its companions—thus
the exploitative tactic could spread through a species.

22. Are Adelie Penguins
a Selfish Herd?
• Adelie penguins often wait on the ice near open water until
a group assembles, and only then do they all jump into the
water more or less together to minimize the possibility that
any one individual will be caught by a leopard seal.
• The seal can only kill and eat a certain small number of
penguins in a short time, so by swimming in group, many
birds will escape while the seal is engaged in eating one or
two of their unfortunate fellows (p. 204-05, Fig. 6.32).
• If you had to run a seal gauntlet, you would do you best
not to be the first or the last into the water, so the penguins
assembling at the water’s edge qualify as a selfish heard,
whose members are engaged in a game whose winners are
better than others a judging when to plunge into the sea.

23. It’s Not Just Leopard Seals!

24. In Short (p. 206)
• An adaptation is the product of natural selection,
which means that it is a hereditary trait that does a
better job at promoting individual reproductive or
genetic success than any available alternative form
of that trait.
• An adaptation has a better ratio of fitness benefits
to fitness costs than any alternative characteristic
that has happened to appear in a species’ history.

25. In Short (Cont’d)
• Traits that intrigue adaptationists are those that
have substantial fitness costs, which must
therefore generate major fitness benefits if they
are to spread and persist in a population under
natural selection.
• Traits whose costs seem to exceed their benefits
constitute Darwinian puzzles; the solution to these
puzzles are prized by adaptationists (note:
monarch butterflies, tephritid fly wing waving,
and gazelle stotting).

26. In Short (Cont’d)
• The Comparative Method of testing adaptationist
hypotheses is based on two key assumptions:
• (1) that related species will exhibit differences in their
attributes if they face different selection pressures, despite
their having a common ancestor and thus a similar genetic
heritage (black-headed gulls vs. kittiwakes), and
• (2) that unrelated species that share similar selection
pressures will converge on the same adaptive response,
despite their having a different genetic heritage (black-
headed gulls & bank swallows).