Animal Behavior
Ch 39.3 through 39.6
Behavior
• Behavior can be fuzzily defined as “actions
an animal takes,” but there’s no one definition
that makes everyone happy. Phenomena
studied by behavioral ecologists include:
– The function of peacock tail symmetry
– How a songbird came to sing a particular tune
– The circumstances under which a moth produces
pheromones
Behavior
• And it’s important to avoid what I just
did (>_>), anthropomorphization - the
attribution of human characteristics to
non-human subjects
Questions about
Behavior
• Ethologist Niko Tinbergen outlined four
questions that can be asked about any
behavior, and a full understanding of the
behavior therefore demands multiple
approaches.
– Two search for proximate causes of the behavior
• “How” questions that probe the mechanism
– Two search for ultimate causes
• “Why” questions that probe the reasons for it
Tinbergen’s Four Questions
• 1. What are the genetic/developmental
mechanisms? (Proximate cause)
• 2. What are the anatomical/physiological
mechanisms? (Proximate cause)
• 3. What historical pathways led to the current
behavioral trait? (Ultimate cause)
• 4. What selective processes shaped the
behavioral trait? (Ultimate cause)
Discussion: Ask Four Questions
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Sources of Behavior
• Behaviors can be:
– Innate - has a genetic or
developmental basis
• Instinct, “born with it”
• Example: fixed action
patterns, sequences of
unlearned, unchangeable
behaviors
– Kelp Gull chicks peck at a red spot if
they see one, even just on the end
of a stick. Here’s what their
mother’s head looks like.
• Another fixed
action pattern:
Male stickleback
fish will attack a
fake fish of any
weird size or
shape, if it has a
red underside. A
perfectly-shaped
fake fish that
doesn’t have a
red underside
goes unmolested.
Sources of Behavior
• Another example,
imprinting.
– Ethologist Konrad Lorenz
found, in studying Greylag
Geese, that 13-16 hours
after hatching, goslings
would “imprint” on whatever
was predominately moving
nearby, and thereafter
mimic its behavior.
– In the wild, this is almost
always the mother. In the
case of Lorenz’s
incubators …
Sources of Behavior
– Behaviors can be learned - Acquired as a
consequence of experience
• 1999, researchers trained some ravens how to
open a trick box with food, then released them
into their flock. Soon, many untrained
members of the flock had learned to copy the
trick and could easily open the boxes
themselves.
Discussion
• Suppose you notice that birds from
Island A preferentially hunt green crabs,
and birds from Island B preferentially
hunt blue crabs.
• What are methods/study designs you
could employ to determine whether this
behavior is innate, learned, or both?
Sources of Behavior
• Both genetic and environmental factors
often is the answer
– An example from humans: alcohol and
drug addiction. What causes someone to
become an addict?
Discussion
• This is analogous to the age-old “nature
vs. nurture” debate.
– Some argue that behaviors exist on a
spectrum, and can be purely natural,
purely nurtured, or some mixture.
– Others argue that no behaviors are strictly
one or the other, or that there is
functionally no such thing as “nurture.”
• Where do you stand? Why?
Types of Behaviors
• Behaviors can be broken down into (broad,
not all-inclusive) categories such as:
–
–
–
–
–
–
–
–
Antipredation
Foraging
Habitat selection/territoriality
Migration
Communication
Mating
Parental care
Sociality
Discussion
• Think back, back, baaaack in time to
your freshman year… and explain
natural selection as clearly as possible.
Put another way, explain how natural
selection can lead to a population’s
acquisition of a particular trait.
Adaptation
• A trait that is adaptive is one that gives
its bearer a reproductive advantage.
– This is conceived of in terms of number of
successful descendants. For instance,
number of healthy great-grandchildren.
• A trait that is maladaptive is one that
confers a reproductive disadvantage.
Not Discussion
• What does an organism need to be, to
do, or to have in order to successfully
produce great-grandchildren?
Optimality in Behavior
• Focusing on one of Tinbergen’s ultimate
causes, the adaptive nature of behavior
• Behavioral adaptations can be summed up as
a “quest for optimality”
– Traits that maximize benefits while minimizing
costs to the greatest extent possible are
considered optimal
– Evolutionary trade-offs
Optimality in Behavior
• Think of it like efficiency.
– It’s time for your first car! Are you a Formula One
Racing enthusiast? How about an F1 Ferrari, then?
What would be the benefits?
What would be the costs?
Optimality in Behavior
– Examples of optimality-driven hypotheses: Great
Black Backed Seagulls preferentially select the
rare Jonah Crab over the more common Green
Crab. There are competing hypotheses as to why,
including:
• Deriving greater nutritional benefit from a Jonah than a
Green Crab
• Competitive displacement, many other seabirds are
already hunting Green Crabs
• Jonah Crabs may be easier to crack open than Green
Crabs, saving energy
• Jonah Crabs may be less likely to be carrying harmful
parasites
• Can you think of any others?
Optimality
• The majority of the time, what we’re
looking at is optimizing free energy.
Energy optimization is at least
tangentially involved in nearly any
adaptive behavioral study.
– What, specifically, do organisms need free
energy for that makes it so important for
understanding the origins of behaviors?
Optimality
• Free energy is necessary for
The behavior that results in the
most free energy = the behavior
that will be favored by natural
selection
Discussion
• Why does reproduction require
additional energy beyond baseline
requirements? (There’s more than one
reason; come up with as many as you
can)
Parental Investment
• Pre-zygotic sources of investment
• Post-zygotic sources
Optimality
• There are many ways to optimize, to attempt
to obtain maximum energy at minimum cost.
We’ll look at just a few examples:
– Migration
– Mate choice
– Signaling
– Cooperation/
Social grouping
Migration
• Migration is a form of dispersal, the
annual movement away from and return
to the same location.
– Seen in animals ranging from crabs to
whales
• Costs
–
–
–
–
Migration
Physically demanding, requires excess free energy
Difficulty finding shelter from adverse weather
Exposure to predation
Exposure to different pathogen profile
• Benefits
– Avoid harsh seasonal
changes
– Resource availability
Optimizing Migration
• Example: Red-eyed vireo
– Migrates from Eastern U.S. to Central & South
America
– Two possible routes:
• Directly across Gulf of Mexico. Shorter distance,
nonstop flying, absolutely no food, but no predators
either.
•West to Texas, then down
through Mexico. Shelter and
some food available, longer
distance, predators present.
Discussion
• Which route would you predict a vireo
with more fat reserves would generally
take? Which route would a vireo with
fewer fat reserves generally take?
Why?
Optimizing Migration
• Researchers caught vireos in Alabama,
measured their body fat, then measured
which direction they flew off.
– Vireos with < 5 g body fat showed a mean
orientation toward the west-northwest
– Those with ≥ 5 g body fat showed a mean
orientation toward the south
– Does this support or refute our hypothesis?
Mate Choice - Discussion
• Why would a trait be the basis for
choice (i.e. attractive)? Remember: it’s
all about optimizing the success of your
genes several generations down the
line.
• Suppose you’re a bird. In order to have
the most numerous and reproductively
successful great-grandchildren, what
should you look for in a mate?
Mate Choice
• Reframing in terms accurate to actual
selection processes:
– “Good Genes” hypothesis: Individuals predisposed
towards mates with physical characteristic A,
where physical characteristic A correlates with
survival success, will have greater reproductive
success themselves because their kids will inherit
those survival-conferring genes. That
predisposition becomes more common over time.
– But there’s more than that…
• “Healthy Mate Hypothesis” Predisposition towards mates
with characteristics that…
– Correlate with foraging success,
so that s/he can feed you and
the kids
– Correlate with high parental
investment, so you don’t have to
risk as much taking care of
things yourself
– Correlate with low parasite load,
so they don’t pass on
parasites/diseases to you and/or
the kids
• There’s also runaway sexual
selection, but that’s a topic for
another day
Mate Choice
• Classic
example:
Peacocks
Discussion
• Classic example: Peacocks
– Studies showed that female preference for males
placed the highest value on the symmetry of their
tail spots, second highest value on # of spots
• Could this be a case of the “Good Genes” hypothesis? If
this hypothesis is true, what could spot symmetry have to
do with optimizing reproductive success?
• Could this be a case of the “Healthy Mate” hypothesis? If
this hypothesis is true, what could spot symmetry have to
do with optimizing reproductive success?
• What tests could you do to determine which hypothesis is
most accurate?
Signaling
• Animals use visual, audible, tactile, electrical,
and chemical signals to indicate dominance,
find food, establish territory, and achieve
reproductive success.
• Signaling can significantly help optimize an
animal’s resources!
– Often by minimizing costs
Signaling
• Visual - the peacock’s tail is an example
– It enhances reproductive success,
advertises suitability as a mate
– Discussion:
• Consider a human smile: What benefits does it
provide, what costs does it avoid?
• Other examples?
• In what conditions is it optimal to use visual
signaling vs. a different kind?
Signaling
• And one of the coolest
signals ever - the
waggle dance!
– Direction of the waggle
relative to the hive
shows the direction of
the food
– Duration of the waggle
part of the dance
indicates distance to the
food
– http://www.youtube.com/
watch?v=-7ijI-g4jHg
Fig. 51-8c
(c) Waggle dance (food distant)
A
30°
C
B
Location A
Beehive
Location B
Location C
Signaling
• Audible - from bird calls to
whale songs to cricket chirps.
Shorter duration but longer
range than visual signals.
– Example: male elephant seals
bellow to establish their territorial
dominance
• Carries a cost: maintaining that
proboscis, and the act of the bellow
• But it can avoid the even greater
cost of a fight
Signaling
• Tactile - signaling by
touch. Very short range
but impossible to ignore.
– Primates grooming each
other – Benefits? Costs?
– Hermaphroditic worms
aligning to indicate
mating interest
• Electrical
Signaling
– Electric eels communicate with pulsing
electrical fields
• Chemical (olfactory)
– Ex: Pheromone production to signal (even
trigger) mating availability
– Long range & duration
Discussion
• For each of four main types of signalling
– visual, auditory, olfactory
(chemical/scent), tactile (touch) – come
up with:
– An example not already mentioned
– An example of how it can be an
evolutionary trade-off… how does it
optimize, maximize benefit vs minimize
cost?
Discussion
• Suppose you are an animal that wants
to maintain a large territory, but is
subject to predation within that territory.
You need a signal to warn rivals to keep
out, but that would minimize your risk of
predators finding you. What would be
an optimal signaling method?
Cooperative Behavior
• Cooperative behaviors can involve if they
increase the fitness of an individual. If so,
they tend to increase the survival of the
population (why do you think that is?)
• What are some examples of what you would
consider cooperative behaviors among
animals?
– How can a cooperative behavior be adaptive?
– How can a cooperative behavior be maladaptive?
Cooperative Behavior
• Cooperative behavior can tend to be
conflated with altruism, a selfless sacrifice
for another’s benefit, but this isn’t the
case.
– There is reciprocal altruism, in which an
individual helps another because it expects to
gain something in return
• For instance, searching for food for a few hours in
the morning with the expectation that another
member of the group will search at night
Inclusive Fitness
• And there is the concept of inclusive fitness,
which is your direct + indirect fitness.
– Direct fitness is your reproductive success
because you reproduced.
– But fitness isn’t truly about the number of your
grandkids three generations from now… it’s about
the amount of your genetic information in the gene
pool three generations from now.
• How can you pull that off without involvement of direct
fitness?
Inclusive Fitness
Discussion
• How can cooperative behavior confer a
benefit in terms of your inclusive
fitness?
• What could be some examples of how
an organism could use cooperative
behavior to benefit its inclusive fitness?
Inclusive Fitness
• This can be quantified! William Hamilton
proposed a measure for predicting when
natural selection would favor altruistic acts
among related individuals
• Three key variables in an altruistic act:
– Benefit to the recipient (B)
– Cost to the altruist (C)
– Coefficient of relatedness (the fraction of genes
that, on average, are shared; r)
Fig. 51-28
Parent A
Parent B

OR
1/
1/
(0.5)
probability
Sibling 1
(0.5)
probability
2
Sibling 2
2
Inclusive Fitness
• Hamilton’s Rule: Natural selection favors
altruism when rBB > rCC
• This form of natural selection is called kin
selection: when altruistic behaviors are
favored because they enhance the
reproductive success of relatives
Inclusive Fitness
• Example:
• If an altruistic act resulted in the loss of
one’s own offspring (C = 1, rC = .5
genetic units, because half of its DNA
was yours), but led to the survival of
three nephews (B = 3, rB = .25), will
altruism be favored by natural selection
in this instance?
Inclusive Fitness
• This has held in a number of
fascinating studies, such as:
– Ground squirrels are more likely to
make alarm calls rather than hide
proportional to their relatedness to the
burrow residents near the intruder.
– Seychelles Warblers become helpers
at their parents’ nests proportional to
the likelihood of being able to obtain a
nest of their own that year.