Chapter 7
Primate Behavior
Chapter Outline
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Primate Field Studies
The Evolution of Behavior
Sympatric Species
Why Be Social?
Primate Social Behavior
Chapter Outline
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Reproduction and Reproductive Behaviors
Mothers, Fathers, and Infants
Issue: Primates in Biomedical Research: Ethics
and Concerns
Behavior
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Anything organisms do that involves
action in response to internal or external
stimuli.
The response of an individual, group, or
species to its environment.
Such responses may or may not be
deliberate and they aren’t necessarily the
results of conscious decision making.
Free-ranging
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Pertaining to non-captive animals living in
their natural habitat.
Ideally, the behavior of wild study groups
would be free of human influence.
Social Structure
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The composition, size, and sex ratio of a group
of animals.
Social structures are the results of natural
selection in specific habitats, and they influence
individual interactions and social relationships.
In many species, social structure varies,
depending on different environmental factors.
Thus, in most primate species, social structure
should be viewed as flexible, not fixed.
Observing Primates
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(a) Rhesus macaques spend much of their time
on the ground and are easier to observe than
(b) black-and-white colobus.
Behavioral Ecology
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An approach that focuses on the relationship
between behaviors, the natural environment,
and biological traits of the species.
Based on the assumption that animals, plants,
and microorganisms evolved together.
Some behaviors are influenced by genes and
are subject to natural selection the same way
physical characteristics are.
The Evolution of Behavior
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Individuals with behavioral phenotypes that
increase reproductive fitness pass on their
genes at a faster rate than others.
Behavior is a product of interactions between
genetic and environmental factors.
Species vary in their limits and potentials for
learning and for behavioral flexibility.
These limits and potentials are set by genetic
factors favored throughout the evolutionary
history of every species.
Primate Social Structure
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Social structures are the results of natural
selection in specific habitats.
They guide individual interactions and
social relationships.
Primates are among the most social of
animals, so social behavior is one of the
major topics in primate research.
Factors That Influence Social
Structure: Body Size
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Larger animals are
better able to retain
heat and their overall
energy requirements
are less than for
smaller animals.
Factors That Influence Social
Structure
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Basal Metabolic Rate (BMR) and Diet
Smaller animals generally have a
higher BMR than larger ones.
Consequently, smaller primates require
an energy-rich diet high in protein, fats,
and carbohydrates.
Metabolism
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The chemical processes within cells that
break down nutrients and release energy
for the body to use.
Factors That Influence Social
Structure
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Distribution of Resources
Leaves can be abundant and will support
large groups of animals.
Fruits and nuts occur in clumps. These can
be efficiently exploited by smaller groups of
animals.
Some species that rely on foods distributed
in small clumps tend to be protective of
resources, especially if their feeding area is
small enough to be defended.
Distribution of Resources
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This male mountain
gorilla has only to
reach out to find
something to eat.
Factors That Influence Social
Structure
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Predation
Primates are vulnerable to many types of
predators, including snakes,birds of prey,
leopards, wild dogs, lions, and even other
primates.
Where predation pressure is high, large
communities are advantageous.
These may be multimale-multifemale groups
or congregations of one-male groups.
Factors That Influence Social
Structure
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Relationships with Other,
Nonpredatory Species
Many primate species associate with
other primate and nonprimate species
for various reasons, including predator
avoidance.
Factors That Influence Social
Structure
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Dispersal
Members of one sex leave the group in which
they were born when they become sexually
mature.
Individuals who leave find mates outside their
natal group, so dispersal is believed to
decrease the likelihood of close inbreeding.
Factors That Influence Social
Structure
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Life Histories
Life history traits are characteristics or
developmental stages that typify members of
a species and influence reproductive rates.
Examples: length of gestation, length of time
between pregnancies, period of infant
dependency and age at weaning, age of
sexual maturity, and life expectancy.
Factors That Influence Social
Structure
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Distribution and Types of Sleeping Sites
Gorillas are the only nonhuman primates that
sleep on the ground.
Primate sleeping sites can be in trees or on
cliff faces, and their spacing can be related to
social structure, predator avoidance, and
how many sleeping sites are available.
Factors That Influence Social
Structure
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Activity Patterns
 Nocturnal species tend to forage for food alone or in
groups of two or three and many use concealment to
avoid predators.
Factors That Influence Social
Structure
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Human Activities
 Virtually all nonhuman primate populations are
impacted by human hunting and forest clearing.
 These activities disrupt and isolate groups, reduce
numbers, reduce resource availability, and eventually
can cause extinction.
Matrilines
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Groupings of females who are all descendants
of one female (e.g., a female, her daughters,
granddaughters, and their offspring).
Matrilines also include dependent male
offspring.
Among macaques, some matrilines are
dominant to others, so that members of
dominant matrilines have greater access to
resources than do members of subordinate
ones.
Types of Nonhuman Primate
Social Groups
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One male-multifemale.
Am adult male, several adult females, and
offspring.
The most common structure, typically formed
by a male joining a kin group of females.
Females usually form the permanent group.
Examples: guenons, gorillas, some pottos,
some spider monkeys, patas, some langurs,
and some colobus.
Types of Nonhuman Primate
Social Groups
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Multimale-multifemale
Several adult males, several adult females,
and their young.
The presence of several males may lead to a
dominance hierarchy.
Examples: some lemurs, macaques,
mangabeys, savanna baboons, vervets,
squirrel monkeys, some spider monkeys, and
chimpanzees.
Types of Nonhuman Primate
Social Groups
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Monogamous pair
The least common breeding structure among
nonhuman primates.
Extra-pair matings aren’t uncommon.
Species that form pairs are usually arboreal,
show minimal sexual dimorphism, and are
frequently territorial.
Examples: siamangs, gibbons, indris, titis,
sakis, owl monkeys, and pottos.
Types of Nonhuman Primate
Social Groups
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Polyandry
One female and two males.
This social group is seen only in some
New World monkeys (marmosets and
tamarins).
Males participate in care of infants.
Types of Nonhuman Primate
Social Groups
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Solitary
Individual forages for food alone.
This group is seen in some nocturnal
prosimians (aye-ayes, lorises, and galagos).
In some species, adult females may forage in
pairs or may be accompanied by offspring.
Also seen in orangutans.
Philopatric
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Remaining in one’s natal group or home
range as an adult.
In most species, members of one sex
disperse from their natal group as young
adults, and members of the philopatric
sex remain.
In most of the nonhuman primate species,
the philopatric sex is female.
Life History Traits
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Characteristics and developmental stages
that influence rates of reproduction.
Examples include longevity; age at sexual
maturity; length of time between births,
etc.
Strategies
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Behaviors or behavioral complexes that
have been favored by natural selection to
increase individual reproductive fitness.
Sympatric
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Living in the same area.
Pertaining to two or more species whose
habitats partly or largely overlap.
Primate Social Strategies
Home Range
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The total area exploited by an animal or
social group.
Usually given for 1 year—or for the entire
lifetime—of an animal.
Predators
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When a baboon
strays too far from its
troop, it’s more likely
to fall prey to
predators.
Leopards are the
most serious
nonhuman threat to
terrestrial primates.
Primate Social Behavior:
Dominance
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Many primate societies are organized into
dominance hierarchies.
These impose order by establishing parameters
of individual behavior.
Higher-ranking animals have greater access to
preferred food and mating partners than lower
ranking individuals.
Dominance hierarchies are sometimes called
“pecking orders.”
Breeding and Suppressed
Males
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Fully mature, breeding male orangutan with
well-developed cheek pads (a) compared to a
suppressed adult male without cheek pads (b).
Factors that Influence
Dominance Status
Sex
Age
Aggression
Time
in the group
Intelligence
Motivation
Mother’s social position
Dominance
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One young male savanna baboon mounts another as
an expression of dominance.
Primate Social Behavior:
Communication
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Raised body hair is an example of an
autonomic response.
Vocalizations and branch shaking are examples
of deliberate communication.
Reassurance is communicated through hugging
or holding hands.
The fear grin, seen in all primates, indicates
fear and submission.
Displays communicate emotional states.
Threatening Behavior
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An adolescent male
savanna baboon
threatens with a
characteristic “yawn” that
shows the canine teeth.
Note that the eyes are
closed briefly to expose
light, cream colored
eyelids.
This has been termed
the “eyelid flash.”
Question
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Dominance hierarchies
a)guarantee that dominant males are
more reproductively successful.
b)result in dominant individuals having
priority access to food.
c)don't guarantee a reproductive
advantage in dominant males.
d)are permanent.
Answer: b
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Dominance hierarchies result in
dominant individuals having priority
access to food.
Primate Social Behavior:
Aggression
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Conflict within a group frequently develops out
of competition for resources, including mating
partners and food items.
Most intragroup aggression occurs in the form
of various signals and displays within the
context of a dominance hierarchy.
Most tense situations are resolved through
various submissive and appeasement
behaviors.
Primate Social Behavior:
Aggression
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Primate groups are associated with a home
range where they remain permanently.
Within the home range is a portion called the
core area, which contains the highest
concentration of predictable resources, and it’s
where the group is most frequently found.
The core area can also be said to be a group’s
territory, and it’s the portion of the home range
defended against intrusion.
Displays
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Sequences of repetitious behaviors that
serve to communicate emotional states.
Nonhuman primate displays are most
frequently associated with reproductive or
agonistic behavior.
Chimpanzee Facial Expressions
Ritualized Behaviors
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Behaviors removed from their original
context and sometimes exaggerated to
convey information.
Primate Social Behavior
Affiliative Behaviors
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Common affiliative behaviors include
reconciliation, consolation, and simple amicable
interactions between friends and relatives.
 Hugging,
kissing and grooming are all forms used in
reconciliation.
 Relationships are crucial to nonhuman primates and
the bonds between individuals can last a lifetime.
 Altruism, behaviors that benefit another while posing
risk to oneself, are common in primate species.
Grooming Primates
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(a) Patas monkeys; female grooming male. (b) Longtail
macaques. (c) Savanna baboons. (d) Chimpanzees
Grooming
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Picking through fur to remove dirt,
parasites, and other materials that may be
present.
Social grooming is common among
primates and reinforces social
relationships.
Question
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Affiliative behaviors
a) arise when there is competition for
resources.
b) enhance group cohesiveness.
c) are rare among primates.
d) may include displays.
Answer: b
• Affiliative behaviors enhance group
cohesiveness.
Patterns of Reproduction
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In most primate societies, sexual behavior
is tied to the female’s reproductive cycle.
Permanent bonding is not common
among nonhuman primates.
Male and female Bonobos may mate
even when the female is not in estrus, a
behavior that is not typical of
chimpanzees.
Estrous Swelling in a Female
Chimpanzee
Reproductive Strategies
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Behavioral patterns that contribute to
individual reproductive success.
Primates produce only a few young in
whom they invest a tremendous amount
of parental care. (k –selected)
Male competition for mates and mate
choice in females are both examples of
sexual selection.
K-selected
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An adaptive strategy whereby individuals
produce relatively few offspring, in whom they
invest increased parental care.
R-selected - An adaptive strategy that
emphasizes large numbers of offspring and
reduced parental care.
K-selection and r-selection are relative (e.g.,
mice are r-selected compared to primates but
K-selected compared to many fish species).
Sexual Selection
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A type of natural selection that operates on one
sex, usually males.
Long-term, this increases the frequency of traits
that lead to greater success in acquiring mates.
Sexual selection in primates is most common in
species in which mating is polygynous and
male competition for females is prominent.
Sexual selection produces dimorphism with
regard to a number of traits, most noticeably
body size.
Infanticide As A Reproductive
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One way males increase their chances of
reproducing is by killing infants fathered by
other males.’
Individuals maximize their reproductive
success, no matter the effect on population or
species.
When an infant dies, its mother resumes cycling
and becomes sexually receptive.
An infanticidal male avoids waiting two to three
years for the infants to be weaned before he
can mate with their mothers.
Mothers, Fathers and Infants
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The basic social unit among primates is the
female and her infants.
Except in species in which monogamy or
polyandry occur, males do help rear offspring.
Monkeys raised without a mother were not able
to form lasting affectional ties.
The mother-infant relationship is often
maintained throughout life.
Primate mothers with young.
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(a) Sykes monkey. (b) Patas monkey.
Primate mothers with young.
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(c) Mongoose lemur. (d) Orangutan. (e) Chimpanzee.
Infant Macaque Clinging to
Cloth Mother
Primate Cultural Behavior
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Cultural behavior is passed from generation to
generation through learning.
Nonhuman primate infants, through observing
their mothers and others, learn about food
items, appropriate behaviors, and how to use
and modify objects to achieve certain ends.
Chimpanzee culture includes tools such as
termite fishing sticks and leaf sponges.