Chapter 7

Primate Behavior

Chapter Outline The Evolution of Behavior Why Be Social? Primate Social Behavior Reproduction and Reproductive Behaviors Mothers, Fathers, and Infants Primate Cultural Behavior Language The Primate Continuum

Behavior 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.

Behavioral Ecology 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 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 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

Larger animals require fewer calories per unit of weight than smaller animals.

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.

Factors That Influence Social Structure Distribution of Resources

Leaves can be abundant will support large groups of animals.

Fruits and nuts occur in clumps. These can most efficiently be 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.

Factors That Influence Social Structure 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 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 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 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 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 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 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.

Primate Social Behavior: Dominance Many primate societies are organized into

dominance hierarchies. These impose a certain degree of order by

establishing parameters of individual behavior. Higher-ranking animals have greater access to

preferred food items and mating partners than lower ranking individuals.

Dominance hierarchies are sometimes called “pecking orders.”

Factors that Influence Dominance Status

Sex Age Aggression Time in the group Intelligence Motivation Mother’s social position

Primate Social Behavior: Communication 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.

Primate Social Behavior: Aggression 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 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.

Primate Social Behavior Affiliative Behaviors 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.

Patterns of Reproduction 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.

Reproductive Strategies 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.

Sexual Selection 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 Strategy? 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 The basic social unit among all primates is the

female and her infants. Except in species in which monogamy or

polyandry occur, males do not participate in rearing offspring.

Monkeys raised without a mother were not able to form lasting affectional ties.

The mother-infant relationship is often maintained throughout life.

Primate Cultural Behavior Cultural behavior is learned; it’s 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.

Language Nonhuman animals haven’t been

considered capable of communicating about external events, objects, or other animals.

It has been assumed that nonhuman animals use a closed system of communication, where vocalizations don’t include references to specific external phenomena.

Language These views have been challenged:

Vervet monkeys use specific vocalizations to refer to particular categories of predators, such as snakes, birds of prey, and leopards.

Other studies have demonstrated that numerous nonhuman primates produce distinct calls that have specific references.

The Primate Continuum Human brains are larger than primate brains,

but the neurological processes are functionally the same.

That humans are part of an evolutionary continuum is the basis for animal research, yet we cage nonhuman primates without regard for their needs.

Nonhuman primates should be maintained in social groups and introduced to habitat enrichment programs.

Quick Quiz

1. 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 Dominance hierarchies result in

dominant individuals having priority access to food.

2. 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.

3. Vervet monkey communicationa) is used to support the theory that

primate vocalizations do not include external events or objects.

b) is limited to scent marking and an occasional bark.

c) includes specific sounds for different categories of predators (air, tree or ground).

d) is sophisticated with regard to food.

Answer: c Vervet monkey communication includes

specific sounds for different categories of predators (air, tree or ground).

4. In a group's territory there is usually a _________________ area where the highest concentration of resources can be found.

Answer: core In a group's territory there is usually a

core area where the highest concentration of resources can be found.