Anthropology Mini Essays

Lecture #11—Primate Behavior I— Behavioral Ecology and Social


Today’s Questions

• What is behavioral ecology? What two main questions does it answer?

• What is the primate adaptation?

• Why do primates live in groups?

• What are the various types of primate mating systems?

Why Study Primate Behavior?

• Behavior Evolved

– Behavioral Ecology—the study of behavior as an adaptation to the environment

• Physical Environment

• Social Environment

– Answers Two Main Questions

• How do ecological factors influence primate behavior?

• How do these ecological factors explain differences between species?

The Primate Adaptation

• The Primate Adaption is primarily SOCIAL

– Primate social behavior evolved in response to the ecological problems primates experience

• Primates live in groups • Benefits

– Feeding efficiency and defense of resources

– Access to mates

– Predator defense


Why live in groups?

Feeding Efficiency and Resource Defense

Feeding Competition

Access to Mates

Mating Competition

Predator Defense

Attracting Predators

Diet, Predation, and Group Size

• Tend to find larger groups when:

– Resources are defensible

– Predation pressure is high

Social Organization and Mating Systems

• Type and size of group is influenced by: – Resource competition – Activity patterns – Habitat, predators

• Mating systems has implications for: – Group size – Territoriality – Sexual dimorphism – Transfer

• Exogamy—one or both sexes leave the group they were born into at sexual maturity

• Inbreeding avoidance

Social/Mating Systems



• Males solitary, large home ranges that overlap several females

• Females and dependent offspring, sometimes two females travel together (sisters or mother-daughter)

• Dramatic sexual dimorphism • Females show behavioral indicators of fertility

(presenting to males) • Males compete for access to females’ territories, direct

and indirect competition – Solitary but polygynous—1 male defends mating access to

more than one female

• Both sexes disperse at sexual maturity

Solitary Orangutans and Nocturnal Lemurs


• Adult bonded pair and their dependent offspring—juveniles and infants, early adolescents

• Individuals are solitary for a time before finding a partner, both sexes work to prevent neighboring same-sex conspecifics from mating with their partner

• No size sexual dimorphism • Females show behavioral indicators of fertility • Both sexes disperse at sexual maturity, usually

pushed out of the group by same-sex parent

Pair-Bonded Gibbons, Siamangs, Titi Monkeys


• One adult female, >1 adult male, dependent offspring of various ages

• Callitrichids—Marmosets and Tamarins – Twinning common, males invest heavily in offspring,

do most of the carrying while mothers forage (high energetic cost to twins) • Adaptation to high predation pressure

– Not very sexually dimorphic

– Females show behavioral indicators of fertility (presenting to males)

Polyandry Marmosets and Tamarins


• One adult male, >1 adult female, dependent offspring of various ages, and all-male bands or solitary males

• High degree of sexual dimorphism—males compete to become associated with a group of females or to recruit new females

– Females show behavioral indicators of fertility (presenting to males)



• Permanent aggregation of multiple adults of both sexes, offspring of various ages

• Sometimes associated with female sexual swellings—advertise fertility to attract males

– Competition between males for access to females—can be aggressive, direct competition but also indirect (consortships—one male convinces a female to go off with him for a few hours or days; often friends)


• Females mate with multiple males – Paternity obfuscation—infanticide avoidance, paternal


• Females exert a high degree of choice – because females invest so much more heavily in offspring

in general, females want to maximize their returns from mating

– sexual receptivity signals • swellings (physiological) • specific behaviors—presentations • mate choice—females will only mate with preferred males

• Male transfer, females stay in natal group—strong bonds within and between matrilines



• Multimale/multifemale groups where the larger community splits into smaller daily foraging parties

– Bonobos and chimpanzees

– Males compete for access to females directly and indirectly

• Sperm competition

• Females transfer, males stay


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