Lecture 12 -- Primates: Group Living

Primate carbohydrate sources

Fruit and gums

Primate fat sources

Insect/animal prey, nuts, seeds

Primate protein sources

Insects, animal prey, young leaves

Why are leaves hard to digest

High in fiber — most colobines have enlarged intestines to compensate

Insectivores body size

Tend to be smaller — high energy requirements, need small amounts of high-quality food

Folivores body size

Tend to be larger — can eat large quantities of lower quality food

Why do folivores have smaller home ranges

Leaves are abundant, predictable in space and time

Why do frugivores have larger home ranges

Fruit is less predictable and patchily distributed in space and time

Costs of group living

Greater competition for resources, higher vulnerability to infectious disease

Benefits of group living

Enhanced access to resources, reduced vulnerability to predation

Resource Defense Model

Primates live in groups because groups are more successful defending food resources than lone individuals

3 conditions for joint food defense to be worthwhile

Food is relatively valuable, food sources are clumped in space and time, enough food in patch to meet needs of several individuals

Why does fruit favor group living

Fruit meets all 3 conditions for resource defense — valuable, clumped, sufficient supply

Problem with Resource Defense Model

Doesn't explain why folivores live in large groups since leaves are abundant and easy to access alone

Dominance hierarchy

Ranked system produced by repeated competition — consistent winners and losers emerge

Benefits of dominance hierarchy

High rank = priority access to resources, reduces overall fighting, organizes social interactions

How is rank inherited

Often passed down within family lines

Predator Defense Model

Group living evolved as a defense against predators — grouping reduces individual vulnerability

Evidence for Predator Defense Model

Terrestrial species form larger groups than arboreal, solitary haplorhines are large bodied, juveniles have higher mortality in smaller groups, primates adjust behavior to predation risk

Weakness of Predator Defense Model

Predation is very difficult to observe so hard to establish clear link to group size

Two main reasons primates live in groups

Resource defense and predator defense

Cultural traditions definition

Learned behaviors and practices passed down through generations within a social group

Social learning in primates

Primates learn through observation, imitation, and communication within social groups

Chimpanzee cultural traditions

Tool use for termite fishing, cooperative hunting, distinct vocalizations for different situations

Orangutan cultural traditions

Nest-building techniques passed from mother to offspring, long-term maternal dependence

Capuchin monkey cultural traditions

Tool use for opening nuts, social learning in foraging techniques

Significance of primate cultural traditions

Provides insight into the evolution of human culture