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Where did we (primates) come from?

Ancient tree shrew (similar to strepsirhines) 

Becomes social

diurnal, highly social (monkeys apes)

What is a group?

A # of animals which remain together in or separate from a larger unit and mostly interact with each other

territory

(defended piece of land)

home range

portion of land where one mostly lives/spends most of time in 

5 General types of social groups

1. Solitary 

2. Pair-bonded (gibbons) 

3. Multi male, one female

4. One male, multi female 

5. Multi male multi female

groups can be _______ members

2-1000

Solitary group examples

1. Aye-ayes, tarsiers

Paired primates examples

1. Owl monkeys

paired primates purpose

related to parental care, infanticide avoidance 

Multi male, one female

example

Pygmy marmoset

Multi male, one female purpose

1. Related to twinning and paternal care, Deals with pressure of raising multiple offspring at one time 

One male, multi female

Gorillas -> silverback typically the single breeding male

Multi male multi female

1. Fission-fusion organization (chimps + humans)

2. Fission into small subgroups -> fuse into large subgroups

Grouping is based on _______

a combo of food availability

1st level

Multi-level societies

Multi-level societies ex

gelada, hamadryas baboons

1st level

• Reproductive units: 1-12 females and their kids, 3-4 males

• All-male units: 2-15 males

2nd level

Bands

2nd level components

2-27 repro units, several all-male

2.5th level

Herds

2.5th level components

60 units from diff bands, only together a short time

final level

communities

final level components

1-4 bands with overlapping home ranges

pressures that all organisms face - avoiding

predation, aggression, disease

pressures that all organisms face - finding

food, mates

Dilution effect:

safety increases, safety in numbers Communal care of offspring

Benefits of Group living 

1. Deter, detect, dilute predators

2. Split offspring care

3. Access and control of territory

Costs of group living

1. Social stress

2. Competition for resources

3. Disease

Sociality is favored when

• Predation pressure is high

• Group defense is beneficial

Group size is constrained when:

• High resource competition

• Disease

The socioecological model:

Females are the core of the model -> female primates typically raise kids

Female behaviors are affected by resources

they go where the resources are 

Dispersed vs clumped resources

• Leads to different levels of competition 

• Dispersed: scramble competitions -> low within-group competition

The size of the resource determines

how many females can monopolize it

When between-group competition is HIGH:

1. Larger group will outcompete smaller groups.

2. Cooperate to defend territory

3. Females will stay in their natal groups (female philopatric)

When within-group competition is LOW:

1. Tolerant

2. Egalitarian

1. Egalitarian:

1. Prosocial behaviors are directed towards kin and non-kin

1. Tolerant

1. Less strict hierarchies, more tolerance of subordinates

Limiting resource for male reproductive success

access to females