AR103 - Readings pgs. 153-181 Week 3 Notes - Oct. 3, 2011
Chapter Seven: Primate Behaviour
Pages # 153 - 181
- Behaviour is 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
- In mammals and birds, behaviour is extremely complex because it’s been shaped over
evolutionary time by interactions between genetic and environmental factors.
The Evolution of Behaviour
- Scientists study behaviour in free-ranging primates from an ecological and evolutionary
perspective, meaning that they focus on the relationship between behaviours, the natural
environment, and various physiological traits of the species in question.
- Ecological is pertaining to the relationships between organisms and all aspects of their
environment (temperature, predators, non-predators, vegetation, availability of food and water,
types of food, disease organisms, parasites, etc.)
- Behavioural Ecology is the study of the evolution of behaviour, emphasizing the role of
ecological factors as agents of natural selection. Behaviours and behavioural patterns have
been favored because they increase the reproductive ﬁtness off individuals (i.e. they are
adaptive) in speciﬁc environmental contexts.
- It’s based on the underlying assumption that all of the biological components of
ecological systems (animals, plants, and even microorganisms) evolved together.
- Therefore, behaviours are adaptions to environmental circumstances that existed in the
past as much as in the present.
- Behaviours have evolved through the operation of natural selection. If behaviours are
inﬂuenced by genes, then they’re subject to natural selection in the same way physical
- Behaviour constitutes as a phenotype, and individuals whose behavioural phenotypes
increase reproductive ﬁtness will pass on their genes at a faster rate than others.
- Studying complex behaviours from an evolutionary viewpoint doesn’t imply a one gene-one
behaviour relationship, nor does it suggest that behaviours that are inﬂuenced by genes can’t
be modiﬁed through learning.
- The behaviour of insects and other invertebrates is largely under genetic control. Most
behavioural patterns in these species aren’t learned; they’re innate.
- In many vertebrates, especially birds and mammals, the proportion of behaviour thats
due to learning is substantially increased, while the proportion under genetic control is
- This is especially true of primates; and in humans, who are so much a product of
culture, most behaviour is learned.
- At the same time, mammals and birds behaviours are at least partly inﬂuenced by
certain gene products such as hormones.
- Brain cells are directed by the genes within them to produce these chemicals; in this way,
genes can inﬂuence aspects of behaviour.
- Behavioural Genetics is the study of how genes affect behaviour. It’s a relatively new ﬁeld, and
the extent to which genes actually inﬂuence behaviour in humans or other species is unknown.
- Behaviour must be viewed as the product of complex interactions between genetic and
- The limits and potentials for learning and behaviour ﬂexibility vary considerably among
species. These limits and potentials are ultimately set by genetic factors that have been
1 AR103 - Readings pgs. 153-181 Week 3 Notes - Oct. 3, 2011
subjected to natural selection throughout the evolutionary history of every species. This history
has been shaped by the ecological setting not only of living species but also their ancestors.
- Social Structure is the composition, size, and sex ratio of a group of animals. The social
structure of a species is, in part, the result of natural selection in a speciﬁc habitat, an it guides
individual interactions and social relationships.
Some Factors That Inﬂuence Social Structure
▯ Body Size
- As a general rule, larger animals require fewer calories per unit of weight than smaller
animals because they have a smaller ratio of surface area to mass than do smaller
- Since body heat is lost at the surface, they’re able to retain heat more efﬁciently, and
so they require less energy overall.
▯ Basal Metabolic Rate (BMR)
- Metabolism is the chemical processes within cells that break down nutrients and
release energy for the body to use. (When nutrients are broken down into their
component parts, such as amino acids, energy is released and made available for the
cell to use.)
- The BMR concerns metabolism, the rate at which the body uses energy to maintain all
bodily functions while in a resting state. It’s closely correlated with body size, so in
general, smaller animals have a higher BMR than larger ones.
- Smaller primates require an energy rich diet high in protein, fats, and carbohydrates.
While larger primates have a lower BMR and reduced energy requirements relative to
body size, so they can do well with less energy-rich foods, such as leaves.
t e i ▯ D
- Diet, BMR, and Body Size all evolved together. Therefore, when primatologists study
the relationships between diet and behaviour, they consider the beneﬁts in terms of
energy (calories) derived from various food items against the costs (energy expended)
of obtaining and digesting them.
▯ Distribution of Resources
- Various type of foods are distributed in different ways. Depending on the abundance of
a particular food primates with either feed by themselves or groups.
- Large groups that feed on fruits, nuts, berries in dispersed trees, and shrubs that
usually occur in clumps can be exploited easily so larger groups break up into subunits
(one male, multi-female groups, or matrilines) to feed.
- Matrilines are groups that consist of a female, her daughters, and their offspring.
Matrilineal groups are common in macaques.
- Species that feed on abundantly distributed resources may also live in one-male
groups, and because food is plentiful, these one-male units are able to join with others
to form large, stable communities.
- Some species that rely on foods distributed in small clumps are protective of
resources, especially if their feeding area is small enough to be defended.
- Some live in small groups composed of a mated pair or a female with one or two
males, and naturally dependent offspring are included.
- Many kinds of foods are only seasonally available (fruits, nuts, seeds, berries). These
primates that rely on seasonal foods must exploit a number of different items and must
also moved about to obtain food throughout the year. This is another factor that tends
to favor smaller feeding groups.
- Depending on a primates size, primates are vulnerable to many types of predators.
2 AR103 - Readings pgs. 153-181 Week 3 Notes - Oct. 3, 2011
- Their responses to predation depend on their body size, social structure, adn the type
- Typically, where predation pressure is high and body size is small, large communities
are advantageous. These may be multi-male or multi-female groups or congregations
of on-male groups.
▯ Relationships with Other, Non-predatory Species
- Many primate species associate with other primate and non-primate species for
various reasons, including predator avoidance. When they do share habitats with other
species, they exploit somewhat different resources.
l a s r e p s i ▯ D
- Inﬂuences social structure and relationships within groups
- In most mammals, members of one sex leave the group in which they were born (natal
group) about the time they reach puberty.
- Male dispersal is the most common pattern in mammals, including primates
- Female dispersal is seen in some colobus species, hamadryas baboons, chimpanzees,
and mountain gorillas.
- In species where the basic social structure is a mated pair, offspring of both sexes
either leave or are driven away by their parents.
- Dispersal may have more than one outcome
- When females leave they join another group, males may do likewise, but some species
frequently live alone for a time, or they may temporarily join an all-male “bachelor”
group until they’re able to establish a group of their own.
- The common result of dispersal is that individuals who leave their natal group usually
ﬁnd mates elsewhere. (leading primatologists to conclude that dispersal is important
because it reduces the risk of interbreeding)
▯ Life Histories
- Life History Traits are characteristics and developmental stages that inﬂuence
reproductive rates. Examples include longevity, age at sexual maturity, and length of
time between births.
- They typify members of a given species and therefore inﬂuence potential
- They have important consequences for many aspects of social life and social
structure, and they can also be critical to species survival.
- Species that live only a few years mature rapidly, reproduce within a year or 2 after
birth, and have short inter-birth intervals. Thus, shorter life histories are advantageous
to species that live in marginal or unpredictable habitats because reproduction can
occur at a relatively rapid rate.
- Longer living species are better suited to stable environmental conditions. The
extended life spans of the great apes in particular, characterized by later sexual
maturation and long inter-birth intervals (3-5 years) means that most females will raise
only 3 or 4 offspring to maturity. This slow rate of reproduction increases the threat of
extinction for all the great apes today.
▯ Activity Patterns
- Most primates are diurnal but some are nocturnal. The nocturnal primates tend to
forage for food alone or in groups of 2 or 3.
▯ Human Activities
- Virtually all nonhuman primate populations are now impacted by human hunting and
forest clearing. These activities severely disrupt and isolate groups, reduce numbers,
reduce resource availability, and eventually can cause extinction.
3 AR103 - Readings pgs. 153-181 Week 3 Notes - Oct. 3, 2011
Why Be Social?
- Groups living exposes animals to competition with other group member for resources, so why
don’t they live alone?
- Competition can lead to injury or even death, plus it’s costly in terms of energy
- The cost of competition are offset by the beneﬁts of predator defense provided by
associating with others.
- Groups composed of several adult males and females are advantageous in areas
where predation pressure is high, particularly in mixed woodlands and on open
savannas. Leopards are the most signiﬁcant predator of terrestrial primates and the
changes escaping a leopard attack are greater for animals that live in groups, where
there are several pairs of eyes looking about.
- Predator avoidance is a major factor as to why primates live in groups but not the only one.
Group living evolved as an adaptive response to a number of ecological variables, and it has
served primates well for a very long time.
Primate Social Behaviour
- Because primates solve their major adaptive problems in a social context, we should expect
there to be several behaviours that reinforce the integrity of the group.
- Many primates are organized into dominance hierarchies, which impose a certain degree of
order by establishing parameters of individual behaviour.
- Dominance Hierarchies are systems of social organization wherein individuals within a group
are ranked relative to one another. Higher-ranking animals have greater access to preferred
food items and mating partners than lower-ranking individuals. Dominance hierarchies are
sometimes called “pecking orders.”
- Although aggression is frequently used to increase an individual’s status, dominance usually
serves to reduce the amount of actual physical violence.
- Dominant animals are usually able to exert control simply by making a threatening gesture.
They also are given priority by others, and they usually don’t give way in confrontations.
- Individual rank or status can be measured by access to resources (food, water, and mating
- It’s thought by primatologists that the primary beneﬁt of dominance is the increased
reproductive success of high-ranking animals (but doesn’t mean low-ranking males don’t mate
- High-ranking females have greater access to food than subordinate females, ad since they
obtain more energy for the production and care of offspring they presumably have higher
reproductive success (sometimes infant survival).
- An individual’s position in the hierarchy isn’t permanent and changes throughout life.
- Inﬂuenced by many factors: sex, age, level of aggression, amount of time spent in
group, intelligence, perhaps motivation, and sometimes the mother’s social position.
- In species organized into groups males are generally dominant to females. Within such
groups, males and females have separate hierarchies, although very high-ranking females can
dominate the lowest-ranking males (particularly young males). Although in some species there
are exceptions where females are the dominant sex, or where males and females are
codominant occurring in species that form bonded pairs.
- All primates learn their position in the hierarchy from birth and as an infant.
4 AR103 - Readings pgs. 153-181 Week 3 Notes - Oct. 3, 2011
- Domination and subordination are indicated by gestures and behaviours, this gestural
repertoire is part of every infants learning experience.
- Young primates also acquire rank through play with age peers, and as they spend more time
with play groups their social interactions widen.
- Competition and rough-and-tumble play allow them to learn the strengths and
weaknesses of peers, and they carry this knowledge with them throughout their lives.
- Because of this and early contact with their mothers, as well as subsequent exposure
to peers, young primates are able to negotiate their way through the complex web of
social interactions that make up their daily lives.
- Communication is any act that conveys information, in the form of a message, to another
individual. Frequently, the result of communication is a change in the behaviour of the
recipient. Communication isn’t always deliberate but may instead be the result of involuntary
processes or a secondary consequence of an intentional action.
- Universal among animals and includes scents and unintentional, autonomic responses
and behaviours that convey meaning.
- Autonomic is pertaining to physiological responses not under voluntary control. An example is
blushing in humans. Conveying information regarding emotional states but neither is
deliberate, and communication isn’t intended.
- Such attributes as body posture convey information about an animal’s emotional state.
- Many intentional behaviours serve as communication, in primates it includes: facial
- Among primates and intense stare indicates a mild threat, as well as a quick yawn exposing
the canines, shaking branches, bobbing back and forth.
- Primates also use a variety of behaviours to indicate submission, reassurance, or amicable
- Grooming is picking through fur to remove dirt, parasites, and other materials that may be
present. Social grooming is common among primates and reinforces social relationships.
- A wide variety of facial expressions indicating emotional state is seen in chimpanzees and,
especially bonobos. The play face and fear grin (seen in all primates).
- Primates use a wide assortment of vocalizations for communication. Whether they are
deliberate or not they inform others of possible presence of food or predators.
- Primates also communicate through displays, which are more complicated and frequently
elaborate combinations of behaviours.
- Displays are sequences of repetitious behaviours that serve to communicate emotional
states. Nonhuman primate displays are most frequently associated with reproductive or
agonistic behaviour: examples include chest slapping in gorillas and, in male chimpanzees,
dragging and wavin