Chapter 7

Primate Behavior

Observing Primates

(a) Rhesus macaques spend much of their time on the ground and are easier to observe than (b) black-and-white colobus.

Terms

Behavior – Anything organisms do that involves action in response to internal or external stimuli.

Free-ranging – Pertaining to non-captive animals living in their natural habitat.

Social Structure – The composition, size, and sex ratio of a group of animals.

Behavioral Ecology - An approach that focuses on the relationship between behaviors, the natural environment, and biological traits of the species.

Factors That Influence Social Structure: Body Size

Larger animals are better able to retain heat and their overall energy requirements are less than for smaller animals.

Factors That Influence Social Structure

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 – The chemical processes within cells that break down nutrients and release energy for the body to use.

Factors That Influence Social Structure

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.

Distribution of Resources

This male mountain gorilla has only to reach out to find something to eat.

Factors That Influence Social Structure

Predation– Primates are vulnerable to many types of predators– Where predation pressure is high, large communities

are advantageous.

Factors That Influence Social Structure

Relationships with Other, Nonpredatory Species

Factors That Influence Social Structure

Dispersal– Members of one

sex leave the group in which they were born when they become sexually mature.

Factors That Influence Social Structure

Life Histories– Life history traits are characteristics or

developmental stages that typify members of a species and influence reproductive rates.

Factors That Influence Social Structure

Factors That Influence Social Structure

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 – Human Activity

Matrilines

Groupings of females who are all descendants of one femaleMatrilines also include dependent male offspring.

Types of Nonhuman Primate Social Groups

One male-multifemale.Multimale-multifemale Monogamous pairPolyandrySolitaryPhilopatric

Sympatric

Living in the same area.

Kibale Forest, Uganda

Primate Social Strategies

Primate Social Behavior: Dominance

Many primate societies are organized into dominance hierarchies. These impose order by establishing parameters of individual behavior.

Breeding and Suppressed Males

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

One young male savanna baboon mounts another as an expression of dominance.

Primate Social Behavior: Communication

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.”

Displays

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

Primate Social Behavior: Aggression

Conflict within a group frequently develops out of competition for resources, including mating partners and food items.

Primate Social Behavior Affiliative Behaviors

Common affiliative behaviors include reconciliation, consolation, and simple amicable interactions between friends and relatives.

Patterns of Reproduction

In most primate societies, sexual behavior is tied to the female’s reproductive cycle.

Reproductive Strategies

Behavioral patterns that contribute to individual reproductive success.

K –selected

Sexual Selection

Infanticide As A Reproductive Strategy?

Hanuman langurs live in groups of one adult male, several females, and offspring.Males without mates form groups and occasionally attack a reproductive male and drive him from his group. Sometimes the new male kills some or all of the group’s infants.

Chacma Baboons

When chacma baboon males migrate into a new group, they “deliberately single out females with young infants and hunt them down”.

Mothers, Fathers and Infants

The basic social unit among primates is the female and her infants.

(a) Sykes monkey. (b) Patas monkey.

Primate mothers with young.

(c) Mongoose lemur. (d) Orangutan. (e) Chimpanzee.

Infant Macaque Clinging to Cloth Mother

Misunderstanding Primates

This unfortunate advertising display is a good example of how humans misunderstand and misrepresent our closest relatives.