BIOLOGY Life on Earth
WITH PHYSIOLOGY Tenth Edition
Audesirk Audesirk Byers
25
Animal Behavior
Lecture Presentations by
Carol R. Anderson
Westwood College, River Oaks Campus
© 2014 Pearson Education, Inc.
Chapter 25 At a Glance
▪ 25.1 How Do Innate and Learned Behaviors Differ?
▪ 25.2 How Do Animals Communicate?
▪ 25.3 How Do Animals Compete for Resources?
▪ 25.4 How Do Animals Find Mates?
▪ 25.5 Why Do Animals Play?
▪ 25.6 What Kinds of Societies Do Animals Form?
▪ 25.7 Can Biology Explain Human Behavior?
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Behavior is any observable activity of a living animal
– Some examples of behavior include
– Moths fly to a light
– Honeybees fly to a cup of sugar-water
– Bluebirds sing
– Wolves howl
– Frogs croak
– Humans dance, play sports, and wage wars
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25.1 How Do Innate and Learned Behaviors Differ?
▪ Innate behavior can be performed without prior
experience
– Innate behaviors are performed in reasonably
complete form the first time an animal of the right age
and motivational state encounters a particular
stimulus
– For example, a red squirrel will attempt to bury a nut
when presented with it for the first time
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25.1 How Do Innate and Learned Behaviors Differ?
▪ Innate behavior can be performed without prior
experience (continued)
– Some innate behaviors can be recognized by their
occurrence immediately after birth, before any
opportunity for learning presents itself
– The female cuckoo birds lay their eggs in the nests of
other bird species to be raised by the unwitting adoptive
parents
– After a cuckoo egg hatches, the cuckoo chick will
display the innate behavior of shoving the nest owner’s
eggs out of the nest to eliminate competition for food
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Figure 25-1 Innate behavior
A cuckoo chick ejects an egg
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A foster parent feeds a cuckoo
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience
– Natural selection may favor innate behaviors in many
circumstances
– A gull chick pecks at its parent’s bill after hatching
– The capacity to make changes in behavior on the
basis of experience is called learning
– An example of learning is the process by which a
human learns language
– Another example is a sparrow’s use of stars for
navigation
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25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Habituation is a decline in response to a repeated
stimulus
– A common form of learning is habituation, defined as a
decline in response to a repeated stimulus
– The ability to habituate prevents an animal from wasting
its energy and attention on irrelevant stimuli
– For example, a sea anemone will retract its tentacles
when touched, but will stop retracting if the touch is
repeated frequently
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Figure 25-2 Habituation in a sea anemone
After many touches, the
anemone habituates and
no longer responds
Touched for the first time,
the anemone withdraws
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Habituation is a decline in response to a repeated
stimulus (continued)
– The ability to habituate is generally adaptive
– Humans habituate to nighttime traffic sounds, as country
dwellers do to choruses of crickets and tree frogs
– Each may initially find the other’s habitat unbearably
noisy at first, but eventually stops responding to the
novel sounds
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Conditioning is a learned association between a
stimulus and a response
– A more complex form of learning is called trial-anderror learning in which new and appropriate responses
to stimuli are acquired through experience
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Conditioning is a learned association between a
stimulus and a response (continued)
– Animals are faced with naturally occurring rewards and
punishments and can learn to modify their behavior in
response to them
– A hungry toad that captures a bee quickly learns to avoid
future encounters with bees
© 2014 Pearson Education, Inc.
Figure 25-3 Trial-and-error learning in a toad
A naive toad is
presented
with a bee.
While trying to eat
the bee, the toad is
stung painfully on
the tongue.
The toad is presented
with a dragonfly.
The toad immediately
eats the dragonfly,
demonstrating that the
learned aversion is
specific to bees.
© 2014 Pearson Education, Inc.
Presented with a harmless robber fly, which
resembles a bee, the
toad cringes.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Conditioning is a learned association between a
stimulus and a response (continued)
– Trial-and-error learning is an important factor in the
behavioral development of many animal species
– This type of learning plays a key role in human behavior
– For example, a child learns which foods taste good
or bad, that a stove can be hot, and not to pull a cat’s
tail
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Insight is problem solving without trial and error
– In certain situations, animals seem to solve problems
suddenly, without prior experience
– This kind of sudden problem solving is called insight
learning, because it is superficially similar to how
humans mentally manipulate concepts to arrive at a
solution
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ Learned behaviors require experience (continued)
– Insight is problem solving without trial and error
(continued)
– In certain situations, animals seem to solve problems
suddenly, without prior experience (continued)
– In 1917, Kohler showed that a hungry chimpanzee,
without any previous training, could stack boxes to reach
a banana suspended from the ceiling
– Epstein and colleagues performed an experiment
showing that pigeons may be capable of insight learning
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25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors
– No behavior is totally innate or learned
– All behaviors are a mixture of the two
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Seemingly innate behavior can be modified by
experience
– Behaviors that seem to be performed correctly on the
first attempt without prior experience can later be
modified by experience
– For example, a newly hatched gull chick is able to peck
at a red spot on its parent’s beak, an innate behavior that
causes the parent to regurgitate food for the chick to eat
© 2014 Pearson Education, Inc.
Figure 25-4 Innate behaviors can be modified by experience
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25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Seemingly innate behavior can be modified by
experience (continued)
– Habituation can also fine-tune an organism’s innate
responses to environmental stimuli
– For example, young birds crouch down when a hawk
flies over but ignore harmless birds such as geese
– Early scientists hypothesized that only the very specific
shape of predatory birds provoked crouching
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Seemingly innate behavior can be modified by
experience (continued)
– Using an ingenious model, Tinbergen and Lorenz, two
of the founding fathers of ethology, tested and
confirmed the hypothesis
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25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Learning may be governed by innate constraints
– Learning always occurs within boundaries that help
increase the chances that only the appropriate behavior
is acquired
– Example of this concept includes a robin, whose ability to
learn songs is limited to those of its own species; the
songs of other species are excluded
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25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Learning may be governed by innate constraints
(continued)
– The innate constraints on learning are perhaps most
strikingly illustrated by imprinting
– Imprinting is a form of learning in which an animal’s
nervous system is rigidly programmed to learn a certain
thing only during a certain period (sensitive period) of
development
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– Learning may be governed by innate constraints
(continued)
– Imprinting is best known in geese, ducks, and chickens
– These birds learn to follow the animal or object that they
most frequently encounter during an early sensitive
period
– In the laboratory, these birds may imprint on a toy train or
other moving object
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Figure 25-5 Konrad Lorenz and imprinting
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25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– All behavior arises out of interaction between genes
and the environment
– Ethologists realize that no behavior can be caused
strictly by genes or strictly by the environment
– The relative contributions of heredity and learning vary
among animal species and among behaviors within an
individual
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– All behavior arises out of interaction between genes
and the environment (continued)
– The nature of the link between genetics and
environmental components is not well understood, but
some evidence exists
– Bird migration is learned by experience through
navigation with celestial cues
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– All behavior arises out of interaction between genes
and the environment (continued)
– Naive migrating birds, hatched only months earlier,
travel properly from one location to another without any
previous experience
– The birds, thus, appear to be born with the ability to
migrate; it must be in their genes
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– All behavior arises out of interaction between genes
and the environment (continued)
– Genetically controlled ability to migrate is supported by
hybridization experiments with blackcap warblers
– This species breeds in Europe and migrates to Africa
– Birds from western Europe travel in a southwesterly
direction to reach Africa
– Birds from eastern Europe travel to the southeast
© 2014 Pearson Education, Inc.
25.1 How Do Innate and Learned Behaviors Differ?
▪ There is no sharp distinction between innate and
learned behaviors (continued)
– All behavior arises out of interaction between genes
and the environment (continued)
– If birds from the two populations are crossbred in
captivity, however, the hybrid offspring migrate due
south—the intermediate between the orientations of the
two parents
– This suggests that parental genes—of which offspring
inherit a mixture—influence migratory direction
© 2014 Pearson Education, Inc.
Figure 25-6 Genes influence migratory behavior
breeding range
winter range
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25.2 How Do Animals Communicate?
▪ Animals frequently broadcast information
– Sounds uttered
– Movements made
– Chemicals emitted
– Level of aggression
– Readiness to mate
▪ If this information evokes a response from other
individuals, and if that response tends to benefit the
sender and the receiver, then a communication
channel can form
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25.2 How Do Animals Communicate?
▪ Communication is the production of a signal by one
organism that causes another organism to change
its behavior in a way beneficial to both
▪ Although animals of different species may
communicate, most animals primarily communicate
with members of their own species
▪ The ways in which animals communicate are
astonishingly diverse
– Visual displays, sound, chemicals, and touch
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25.2 How Do Animals Communicate?
▪ Visual communication is most effective over short
distances
– Animals with well-developed eyes use visual signals
to communicate
– Visual signals can be active, in which a specific
movement or posture conveys a message
– Visual signals may be passive, in which the size,
shape, or color of the animal conveys important
information, commonly about its sex and reproductive
state
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Figure 25-7 Active visual signals
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Figure 25-8 A passive visual signal
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25.2 How Do Animals Communicate?
▪ Visual communication is most effective over short
distances (continued)
– Active and passive signals can be combined
– Like all forms of communication, visual signals have
both advantages and disadvantages
– On the plus side, visual signals are instantaneous and
can convey a variety of messages in a short period, and
they are quiet and unlikely to alert distant predators
© 2014 Pearson Education, Inc.
25.2 How Do Animals Communicate?
▪ Visual communication is most effective over short
distances (continued)
– Like all forms of communication, visual signals have
both advantages and disadvantages (continued)
– On the negative side, visual signals are generally
ineffective in dense vegetation or in darkness, and they
are limited to close-range communication
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Figure 25-9 Active and passive visual signals combined
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25.2 How Do Animals Communicate?
▪ Communication by sound is effective over longer
distances
– As with visual signals, sound signals are almost
instantaneous
– But unlike visual signals, sound can be transmitted
through darkness, dense forests, and murky water
– Acoustic signals can also be effective over longer
distances than visual signals
– The low, rumbling calls of an African elephant can be
heard by elephants several miles away
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25.2 How Do Animals Communicate?
▪ Communication by sound is effective over longer
distances (continued)
– Different messages can be conveyed by variations in
sound pattern, volume, and pitch
– For example, ethologist Thomas Struhsaker, studying
vervet monkeys in Kenya, found that they produced
different calls in response to threats from each of their
major predators: snakes, leopards, and eagles
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25.2 How Do Animals Communicate?
▪ Communication by sound is effective over longer
distances than visual signals (continued)
– The use of sound is not limited to birds and mammals
– Male crickets produce species-specific songs that
attract female crickets of the same species
– The high-pitched whine of a female mosquito, as she
prepares to bite, alerts nearby males that she may soon
have the blood meal necessary for laying eggs
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25.2 How Do Animals Communicate?
▪ Communication by sound is effective over longer
distances than visual signals (continued)
– The use of sound is not limited to birds and mammals
(continued)
– Male water striders vibrate their legs, sending speciesspecific patterns of vibrations through the water,
attracting mates and repelling other males
– Many species of fish produce croaks, grunts, or other
sounds
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Figure 25-10 Communication by vibration
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25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary
– Chemicals produced by individuals that influence the
behavior of other members of the same species are
called pheromones
– Pheromones can carry messages over long distances
and take little energy to produce
– They are typically not detectable by other species, and
so do not attract predators
© 2014 Pearson Education, Inc.
25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Chemicals produced by individuals and that influence
the behavior of other members of the same species
are called pheromones (continued)
– They can act as a signpost, persisting over time and
marking an animal’s boundaries
– While chemicals convey critical information, fewer and
simpler messages can be conveyed than with sight- or
sound-based systems
© 2014 Pearson Education, Inc.
25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Pheromones can cause immediate changes in the
behavior of the detecting animal
– For example, foraging termites that discover food lay a
trail of pheromones from the food to the nest, and other
termites follow the trail
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Figure 25-11 Communication by chemical messages
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25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Pheromones can also cause physiological changes in
the detecting animal
– For example, the queen honeybee produces a
pheromone, queen substance, which prevents other
females in the hive from becoming sexually mature
© 2014 Pearson Education, Inc.
25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Pheromones can also cause physiological changes in
the detecting animal (continued)
– Mature males of some mouse species produce urine
containing a pheromone that influences female
reproductive physiology
– The pheromone stimulates newly mature females to
become fertile and sexually receptive to the male
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25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Humans have harnessed the power of pheromones to
combat insect pests
– Controlling pests with pheromones has major
environmental advantages over conventional
pesticides, which kill beneficial as well as harmful
insects and foster the evolution of pesticide-resistant
insects
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25.2 How Do Animals Communicate?
▪ Chemical messages persist longer but are hard to
vary (continued)
– Humans have harnessed the power of pheromones to
combat insect pests (continued)
– In contrast, each pheromone is specific to a single
species and does not promote the spread of resistance,
because insects resistant to the attraction of their own
pheromones do not reproduce successfully
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25.2 How Do Animals Communicate?
▪ Communication by touch helps establish social
bonds
– Physical contact is used to establish and maintain
social bonds among group members, as seen in
humans and other primates
– Gestures include kissing, nuzzling, patting, petting, and
grooming
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25.2 How Do Animals Communicate?
▪ Communication by touch helps establish social
bonds (continued)
– Communication by touch is not limited to primates
– In many other mammal species, close physical contact
helps cement the bond between parent and offspring
– Species in which sexual activity is preceded or
accompanied by physical contact can be found
throughout the animal kingdom
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Figure 25-12 Communication by touch
Bab
oon
s
© 2014 Pearson Education, Inc.
Lan
d
snai
ls
25.3 How Do Animals Compete for Resources?
▪ The contest to survive and reproduce stems from
the scarcity of resources relative to the reproductive
potential of populations
▪ The resulting competition underlies many of the
most frequent types of interactions between animals
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25.3 How Do Animals Compete for Resources?
▪ Aggressive behavior helps secure resources
– A manifestation of competition for food, resources, or
mates is aggression, or antagonistic behavior,
between members of the same species
– Aggressive behaviors include physical combat between
rivals, which can injure or kill the participants
– As a result, natural selection has favored the evolution
of symbolic displays or rituals for resolving conflicts
© 2014 Pearson Education, Inc.
25.3 How Do Animals Compete for Resources?
▪ Aggressive behavior helps secure resources
(continued)
– A manifestation of competition for food, resources, or
mates is aggression, or antagonistic behavior,
between members of the same species (continued)
– These displays allow competitors to assess each other
on the basis of size, strength, and motivation, thus
determining a winner without injury or death
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25.3 How Do Animals Compete for Resources?
▪ Aggressive behavior helps secure resources
(continued)
– During aggressive displays, animals may exhibit
weapons, such as claws and fangs, and often make
themselves appear larger
– Competitors often stand upright and erect their fur,
feathers, ears, or fins
– These visual displays are typically accompanied by
vocal signals such as growls, croaks, roars, or chirps
– Fighting is usually a last resort
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Figure 25-13 Aggressive displays
A
mal
e
bab
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Sar
cast
ic
frin
25.3 How Do Animals Compete for Resources?
▪ Aggressive behavior helps secure resources
(continued)
– In addition to aggressive visual and vocal displays,
many animals engage in ritualized combat
– Deadly weapons may clash harmlessly or may not be
used at all
– The ritual allows contestants to assess the strength and
the motivation of their rivals
– The loser slinks away in a submissive posture that
minimizes the size of the body
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Figure 25-14 Displays of strength
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25.3 How Do Animals Compete for Resources?
▪ Dominance hierarchies help manage aggressive
interactions
– In a dominance hierarchy, each animal in a group
establishes a rank that determines access to
resources
– Though aggressive encounters occur frequently while
the dominance hierarchy is being established, once
each animal learns its place, disputes are infrequent
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25.3 How Do Animals Compete for Resources?
▪ Dominance hierarchies help manage aggressive
interactions (continued)
– In a dominance hierarchy, each animal in a group
establishes a rank that determines access to
resources (continued)
– Dominant individuals obtain most access to the
resources needed for reproduction, including food,
mates, and space
– Among male bighorn sheep, dominance is reflected in
horn size
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Figure 25-15 A dominance hierarchy
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources
– In many animal species, competition for resources
takes the form of territoriality, the defense of an area
where important resources—such as mates, food,
and shelter—are located
– Territorial behavior is most commonly seen in adult
males, and territories are usually defended against
members of the same species, who compete most
directly for the resources being protected
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Territories are as diverse as the animals defending
them, and examples include
– A tree where a woodpecker defends acorn storage sites
– A small depression in the sand used as a nesting site
by a cichlid fish
– A hole in the sand that is home to a crab
– An area of forest providing food for a squirrel
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Figure 25-16 A feeding territory
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Territoriality reduces aggression
– Acquiring and defending territory requires considerable
time and energy, yet territoriality is seen in animals as
diverse as worms, arthropods, fish, birds, and
mammals
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Territoriality reduces aggression (continued)
– Territoriality provides some important advantages
– As with dominance hierarchies, once a territory is
established through aggressive interactions, relative
peace prevails as boundaries are recognized and
respected
– Niko Tinbergen demonstrated this principle in an
experiment using stickleback fish
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Figure 25-17 Territory ownership and aggression
Two sticklebacks
establish territories
in an aquarium
A
Both fish are
placed in
A’s territory; A
attempts
to attack B, which
assumes a
submissive
posture
B
A
A’s
territo
ry
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Responses reverse
when
both fish are
placed in B’s
territory
B’s
territo
ry
A’s
territo
ry
B
A
B’s
territo
ry
A’s
territo
ry
B’s
territo
ry
B
25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Competition for mates may be based on territories
– For males of many species, successful territorial
defense has a direct impact on reproductive success
– Males who successfully defend the best territories have
the greatest chance of passing on their genes
– Females may choose males whose territories are large in
size, and have abundant food and secure nesting areas,
thus increasing survival chances of her offspring
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Animals advertise their occupancy
– Territories are advertised through sight, sound, and
smell
– If a territory is small enough, its owner’s presence—
along with aggressive displays—is sufficient defense
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Animals advertise their occupancy (continued)
– Vocal displays are a common form of territorial
advertisement
– Male sea lions and crickets using vocal displays
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Animals advertise their occupancy (continued)
– The husky trill of the male seaside sparrow is part of an
aggressive display, warning other males to steer clear
of his territory
– The importance of singing to seaside sparrows’ territorial
defense was demonstrated by ornithologist M. Victoria
McDonald, who captured territorial males and operated
on them in a way that left them unable to sing
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25.3 How Do Animals Compete for Resources?
▪ Animals may defend territories that contain
resources (continued)
– Animals advertise their occupancy (continued)
– The husky trill of the male seaside sparrow is part of an
aggressive display, warning other males to steer clear
of his territory (continued)
– The males unable to sing could not defend territories or
attract mates, but regained their lost territories when they
recovered their singing ability
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Figure 25-18 Defense of a territory by song
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25.4 How Do Animals Find Mates?
▪ In many sexually reproducing animal species,
mating involves copulation or other close contact
between males and females
– Before animals can successfully mate, they must
identify one another as
– Members of the same species
– Members of the opposite sex
– Being sexually active
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
– Individuals that waste energy and gametes by mating
with members of the wrong sex or wrong species are
at a disadvantage in the contest to reproduce
– Natural selection favors behaviors by which animals
communicate their sex and species to potential mates
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Many mating signals are acoustic
– Animals often use sounds to advertise their sex and
species
– Male grasshoppers, crickets, frogs, and birds all
produce mating calls
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Many mating signals are acoustic (continued)
– Females may compare the songs of rival suitors to
assess the relative quality of the males
– For example, the male bellbird uses its deafening song to
defend large territories and to attract females from great
distances
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Many mating signals are acoustic (continued)
– Females may compare the songs of rival suitors to
assess the relative quality of the males (continued)
– A female flies from one male to another to listen to its
earsplitting song, and compare the songs between
different males, perhaps choosing the loudest as a mate
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Visual mating signals are also common
– Displays are used by males to attract the attention of
females
– For example, the elaborate construction projects of the
male gardener bowerbirds and the scarlet throat of the
male frigate bird advertise sex, species, and male quality
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Visual mating signals are also common (continued)
– These signals may be risky, making it easier for
predators to find the males, but are necessary because
females won’t mate with males that lack the appropriate
signal
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Figure 25-19 Sexual displays
A bowerbird bower
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A male frigate bird
25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Visual mating signals are also common (continued)
– Females, in contrast, typically do not need to attract
males or assume the risk of a conspicuous signal, and
so in many species are drab in comparison to the males
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Figure 25-20 Sex differences in guppies
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25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Visual mating signals are also common (continued)
– The intertwined functions of sex recognition and
species recognition, advertisement of individual quality,
and synchronization of reproductive behavior
commonly require a complex series of signals, both
active and passive, by both sexes
© 2014 Pearson Education, Inc.
Figure 25-21-1 Courtship of the three-spined stickleback
A male, inconspicuously colored,
leaves the school of males and
females to establish a breeding
territory.
As his belly takes on the red color
of the breeding male, he displays
aggressively at other red-bellied
males, exposing his red underside.
Having established a territory, the
male begins nest construction by
digging a shallow pit that he will fill
with bits of algae cemented together
by a sticky secretion from his kidneys.
After he tunnels through the nest to
make a hole, his back begins to take on
the blue courting color that makes him
attractive to females.
© 2014 Pearson Education, Inc.
Figure 25-21-2 Courtship of the three-spined stickleback
An egg-carrying female displays her
enlarged belly to him by assuming a
head-up posture. Her swollen belly
and his courting colors are passive
visual displays.
After she enters, he stimulates her to
release eggs by prodding at the base of
her tail.
© 2014 Pearson Education, Inc.
Using a zigzag dance, he
leads her to the nest.
He enters the nest as she leaves and
deposits sperm, which fertilize the eggs.
25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Chemical signals can bring mates together
– Pheromones can also play an important role in
reproductive behavior
– A sexually receptive female silk moth, for example, sits
quietly and releases a chemical message that can be
detected by males up to 3 miles away
© 2014 Pearson Education, Inc.
25.4 How Do Animals Find Mates?
▪ Signals encode sex, species, and individual quality
(continued)
– Chemical signals can bring mates together
(continued)
– Water is an excellent medium for dispersing chemical
signals, and fish commonly use a combination of
pheromones and elaborate courtship movements to
ensure the synchronous release of gametes
– Mammals often rely on pheromones released by the
female during her fertile periods to attract males
© 2014 Pearson Education, Inc.
Figure 25-22 Pheromone detectors
Antennae detect
pheromones
© 2014 Pearson Education, Inc.
Noses detect pheromones
25.5 Why Do Animals Play?
▪ Many animals play
– Pygmy hippopotamuses push one another, shake and
toss their heads, splash in the water, and pirouette on
their hind legs
– Otters delight in elaborate acrobatics
– Bottlenose dolphins balance fish on their snouts,
throw objects, and carry them in their mouths while
swimming
– Baby vampire bats chase, wrestle, and slap each
other with their wings
© 2014 Pearson Education, Inc.
25.5 Why Do Animals Play?
▪ Animals play alone or with other animals
– Play can be solitary or within a group
– Often, young of the same species play together, but
parents may join in
– Play can be social
– Social play typically includes chasing, fleeing, wrestling,
kicking, and gentle biting
© 2014 Pearson Education, Inc.
25.5 Why Do Animals Play?
▪ Animals play alone or with other animals (continued)
– Play seems to lack any clear function and is
abandoned in favor of feeding, courtship, and
escaping from danger
– Play typically borrows movements from other
behaviors (attacking, fleeing, stalking, and so on)
– Play is potentially dangerous
– Many young humans and other animals are injured,
and some are killed, during play
© 2014 Pearson Education, Inc.
Figure 25-23 Young animals at play
Polar bears
Chimpanzees
© 2014 Pearson Education, Inc.
Red foxes
25.5 Why Do Animals Play?
▪ Play aids behavioral development
– It is likely that play has survival value and that natural
selection has favored those individuals who engage in
playful activities
– One of the best explanations for the survival value of
play is the practice hypothesis
© 2014 Pearson Education, Inc.
25.5 Why Do Animals Play?
▪ Play aids behavioral development (continued)
– The practice hypothesis suggests
– That play allows young animals to gain experience in
behaviors that they will use as adults
– That by practicing these acts in play, the animal gets
skills that will later be important in hunting, fleeing, or in
social interactions
© 2014 Pearson Education, Inc.
25.5 Why Do Animals Play?
▪ Play aids behavioral development (continued)
– Play is most intense early in life when the brain
develops and crucial neural connections form
– John Byers, a biologist at the University of Idaho,
suggests that species with larger brains are more
playful than those with small brains
– Because larger brains are linked to greater learning
ability, this relationship supports the idea that adult
skills are learned during juvenile play
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Sociality is a widespread feature of animal life
– Most animals interact at least a little with other
members of their species
– Many spend the bulk of their lives in the company of
others, and a few have developed complex, highly
structured societies
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Group living has advantages and disadvantages
– Living in a group has both costs and benefits
– Benefits to social animals include
– Increased ability to detect, repel, and confuse predators
– Increased hunting and food-finding efficiency
– Potential for division of labor
– Increased likelihood of finding a mate
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Group living has advantages and disadvantages
(continued)
– On the negative side, social animals may encounter
– Increased competition within the group for limited
resources
– Increased risk of infection from contagious diseases
– Increased risk of offspring being killed by other
members of the group
– Increased risk of being spotted by predators
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Sociality varies among species
– The degree to which animals of the same species
cooperate varies from one species to the next
– Some types of animals are solitary, where interactions
between adults consist of brief aggressive encounters
and mating; an example is the mountain lion
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Sociality varies among species (continued)
– Other types of animals are either occasionally or
permanently part of simple social groups
– For example, coyotes are solitary when food is
abundant, but hunt in packs when food becomes scarce
– Musk oxen form herds that function as a unit when
threatened by predators such as wolves
– In this case, male oxen form a circle with horns pointed
outward around the females and the young
© 2014 Pearson Education, Inc.
Figure 25-24 Cooperation in loosely organized social groups
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Sociality varies among species (continued)
– A small number of species, most of which are insects
or mammals, form highly integrated cooperative
societies
– Some cooperative societies are based on behavior that
seems to sacrifice the individual for the good of the
group
– Young, mature Florida scrub jays may remain at their
parents’ nest and help them raise subsequent broods
instead of breeding
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Sociality varies among species (continued)
– Some cooperative societies are based on behavior
that seems to sacrifice the individual for the good of
the group (continued)
– Worker ants often die in defense of their nest
– Ground squirrels may sacrifice their own lives to warn
the rest of their group about an approaching predator
– These behaviors are examples of altruism—behavior
that decreases the reproductive success of one
individual to benefit another
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Forming groups with relatives fosters the evolution
of altruism
– When individuals perform self-sacrificing deeds,
alleles that contribute to this behavior are not
eliminated
– Other members of the group are close relatives of the
altruistic individual
– Because close relatives share alleles, the altruistic
individual may promote the survival of its own alleles
through behaviors that maximize the survival of family
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Forming groups with relatives fosters the evolution
of altruism (continued)
– This concept is called kin selection
– Kin selection helps explain the self-sacrificing
behaviors that contribute to the success of
cooperative societies
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies
– Scientists have long struggled to explain this social
structure where most individuals never breed, but
instead labor to feed and protect the offspring of
another individual
– Honeybees, ants, and termites are examples
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– Honeybees have a rigidly organized caste system
based on functional position in the colony
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– They emerge from their larval stage into one of three
preordained roles
1. Queen: There is only one queen per hive, and her role
is to produce eggs and regulate the lives of the workers
2. Drones: All drones are males, and serve as mates to
the queen
3. Workers: All workers are sterile females; they perform
a variety of functions depending on age
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– A worker’s tasks are determined by her age and by
conditions in the colony
– A newly emerged worker starts life as a waitress,
carrying food such as honey and pollen to the queen, to
other workers, and to the developing larvae
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– A worker’s tasks are determined by her age and by
conditions in the colony (continued)
– As she matures, special glands begin to produce wax,
and she becomes a builder, constructing perfectly
hexagonal cells of wax in which the queen deposits her
eggs and where the larvae develop
– Her final role in life is that of a forager, gathering pollen
and nectar as food for the hive
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– Forager worker bees communicate sources of nectar
to other foragers by using a waggle dance
© 2014 Pearson Education, Inc.
Figure 25-25 Bee language: the waggle dance
40°
If the dance is performed
on a vertical wall inside
the hive, the angle (from
vertical) of the waggle run
represents the angle
between the sun and the
food source
up
40°
If the dance is performed
on a horizontal surface
outside, the waggle run is
aimed at the food source
The rate of circling communicates
the distance to the food source
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Honeybees live together in rigidly structured
societies (continued)
– Pheromones play a major role in regulating the lives
of social insects
– Honeybee drones are drawn irresistibly to the queen’s
sex pheromone (queen substance), which she releases
during her mating flights
– This substance is also licked off her body by the
workers, rendering them sterile and leaving only one
reproductive queen in each hive
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Naked mole rats form a complex vertebrate society
– The nervous systems of vertebrates are for more
complex than those of insects, and we might expect
vertebrate societies to be proportionately more
complex
– With the exception of human society, they are not that
much more complex
– One of the most unusual societies among non-human
mammals is that of the naked mole rat
© 2014 Pearson Education, Inc.
25.6 What Kinds of Societies Do Animals Form?
▪ Naked mole rats form a complex vertebrate society
(continued)
– The queen is the largest individual in the colony, and
prevents ovulation in rival females by physically
stressing rival females
– A division of labor among workers exists based on
size
– Small, young rats clean the tunnels, gather food, and
tunnel
– Larger mole rats fling the dirt into the air, adding it to a
cone-shaped mound
© 2014 Pearson Education, Inc.
Figure 25-26 Naked mole rat workers
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ The behaviors of humans, like those of all other
animals, have an evolutionary history
▪ The techniques and concepts of ethology can help
us understand and explain human behavior
▪ Human ethology is less rigorous science than animal
ethology
▪ People cannot be treated as laboratory animals,
devising experiments that control and manipulate
the factors that influence their attitudes and actions
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ The behavior of newborn infants has a large innate
component
– Because newborn infants have not had time to learn,
we can assume that much of their behavior is innate
– Sucking, which can be observed in a human fetus, is
innate
– Other behaviors include grasping with the hands and
feet and making walking movements when the body is
held upright and supported
© 2014 Pearson Education, Inc.
Figure 25-27 A human instinct
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ The behavior of newborn infants has a large innate
component (continued)
– Another example is smiling, which can occur soon
after birth
– Infants up to 2 months old will smile in response to a
stimulus consisting of two dark, eye-sized spots on a
light background
– As the child’s development continues, learning and
further development of the nervous system interact to
limit the response to more correct representations of a
face
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ The behavior of newborn infants has a large innate
component (continued)
– Newborns in their first 3 days of life can be
conditioned to produce certain rhythms of sucking
when their mothers’ voice is used as reinforcement
– In experiments, infants preferred their own mother’s
voices to other female voices, as indicated by their
responses
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ The behavior of newborn infants has a large innate
component (continued)
– Newborns in their first 3 days of life can be
conditioned to produce certain rhythms of sucking
when their mothers’ voice is used as reinforcement
(continued)
– The infant’s ability to learn his or her mother’s voice and
respond positively to it within days of birth has strong
parallels to imprinting, and may help initiate bonding
with the mother
© 2014 Pearson Education, Inc.
Figure 25-28 Newborns prefer their mother’s voice
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Young humans acquire language easily
– Species have a predilection for specific types of
learning that are important to their mode of life
– Humans have an inborn predilection for the
acquisition of language
– Infants are able to distinguish among consonant sounds
by 6 weeks after birth
– Humans typically acquire a 28,000-word vocabulary by
the age of 8
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Behaviors shared by diverse cultures may be innate
– Another way to study the innate bases of human
behavior is to compare simple acts performed by
people from diverse cultures
– This comparative approach has revealed several
gestures that seem to form a universal, and therefore
probably innate, human signaling system
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Behaviors shared by diverse cultures may be innate
(continued)
– Some gestures include
– Facial expressions for pleasure, rage, and disdain
– Greeting movements such as an upraised hand or the
eye flash, where the eyes are opened widely and the
eyebrows are elevated
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Behaviors shared by diverse cultures may be innate
(continued)
– The evolution of neural pathways underlying these
gestures presumably depended on the advantages
that accrued to both senders and receivers from
sharing information about the emotional state and
intentions of the sender
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Behaviors shared by diverse cultures may be innate
(continued)
– A species-wide method of communication was
perhaps especially important before the advent of
language, and later remained useful during
encounters between people who share no common
language
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Humans may respond to pheromones
– Martha McClintock, in the early 1970s, hinted at the
possible existence of human pheromones
– She found that the menstrual cycles of roommates and
close friends tended to become synchronized
– It was suggested that this synchronization was due to
some chemical signal passed between the women
– The actual molecules that cause effects on menstrual
synchronization remain unknown, as does their function
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Studies of twins reveal that there are genetic
components of behavior
– Twins are an opportunity to examine the hypothesis
that differences in human behavior are related to
genetic differences
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Studies of twins reveal that there are genetic
components of behavior (continued)
– If a particular behavior is heavily influenced by genetic
factors, identical twins are more likely to share the
behavior than fraternal twins
– Identical twins: Arise from the same egg and have
identical genes
– Fraternal twins: Arise from individual eggs fertilized by
different sperm and have different genes
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Studies of twins reveal that there are genetic
components of behavior (continued)
– Studies involving identical twins separated at birth are
particularly revealing, showing that twins reared apart
have personalities just as similar as those reared
together
– The differences in their environment had little influence
on their personality development
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Biological investigation of human behavior is
controversial
– The field of human behavioral genetics is
controversial because it challenges the belief that
environment is the most important determinant of
human behavior
– We now recognize that complex behavior in nonhuman animals combines elements of both innate and
learned behaviors
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Biological investigation of human behavior is
controversial (continued)
– It seems certain that our own behavior is influenced
by both our evolutionary history and our cultural
heritage
– The debate over the relative importance of heredity
and environment in determining human behavior
continues and is unlikely ever to be fully resolved
© 2014 Pearson Education, Inc.
25.7 Can Biology Explain Human Behavior?
▪ Biological investigation of human behavior is
controversial (continued)
– Human ethology is not yet recognized as a rigorous
science, and it will always be hampered because we
can neither view ourselves with detached objectivity,
nor experiment with people as if they were laboratory
rats
– Despite the limitations, there is much to be learned
about the interactions of learning and innate
tendencies in humans
© 2014 Pearson Education, Inc.