Anthro 101: Human Biological Evolution

Lecture 10: Primate Ecology

Office Drop-in Hours AHS 308 Tutoring Lab Hours AHS 232T 5:30 - 6:30 M & T 1 - 4Th 11:15 - 12:15, 1:15 - 3:15 Student ID requiredF 12 - 1:30by appointment

Attendance survey

• List three primate characteristics that differentiate primates from other mammals.

• Write your name on the other side of the card.

Zoo Project - any questions?

• Friday Oct. 15th & Saturday Oct. 16th @ 9:45• Due Oct. 21st - 3rd Exam Oct. 21st

• Exam 2 Extra Credit - fix your mistakes and show me or Kirsten - Due Oct. 21st

• Optional Fieldtrip - any interest?• Natural History Museum - Age of Mammals• Sun. Nov. 7th or Sat. Nov. 20th or Sun. Nov. 21st• $6.50 admission, free parking, near USC

Why do primates live in groups?

• Advantages of group life

• Costs of group life

• Why do primates live in so many kinds of groups?

• Balancing costs & benefits

• Socioecology

Behavioral Ecology• The study of the evolution of behavior

• emphasizing the role of ecological factors as agents of natural selection

• Resources (diet), predators, climate, “conspecifics,” etc.

• How do these factors affect behavior?

• In primates, focus especially on the influence of these on social organization

• Socioecology: the study of how social structure and organization are influenced by organisms' environment

1. Why do primates live in groups?

• Most mammals are solitary

• Many prosimians solitary

• Why are diurnal primates

social?

Major benefits of group life• Protection versus

predators• Better access to

resources• Access to potential mates

Large cats prey on primates

lion

leopard

jaguar

cheetah

tiger

Large primates can defend themselves against big cats, but many small ones can’t

Raptors prey on primates

Martial eagle

Harpy eagle

Hawk eagle

Crocodiles can take primates

A variety of snakes prey on primates

python

Primates prey on other primates

Chimps hunt red colobus monkeys

Baboons prey on vervets

Humans and domestic dogs kill primates

Dog with langur infant

Hunter with gorilla head

Predation is rarely observed, but can sometimes be inferred

leopard paw print

drag marks

baboon jaw & hair

Indirect evidence of predation

• Wound observed • Healthy animals disappear

overnight

Oryx, back wound

Juvenile, scalp wound

For diurnal primates, sociality is an effective anti-predator strategy

1. Detection

2. Dilution

3. Defense

Detection: In larger groups, there are more eyes to watch out for predators

Dilution: In groups, any particular individual less likely to be caught by predator

Imagine chance of being caught = 1/n, where n = group size

risk = 1/2

risk = 1/12

Defense: Many strategies for diurnal primates

• Sleep in trees, cliffs• Defensive weaponry • Large body size • Vigilance• Alarm calls• Mobbing• Interspecific associations

Two or more species may associate to reduce predator risk: Interspecific Associations - 3D’s

Diana monkey Red colobus

Ground predators Eagles

Nocturnal primates use different strategies

• Hide during day• Park infants while feeding• Solitary• Quiet• Cryptic

Sociality also has costs 1. Competition

2. Contagion

3. Cuckoldry

4. Inbreeding

5. Cannibalism

6. Infanticide

2. Natural selection shapes social organization to balance the costs & benefits of group living

• Socioecology = study of how ecological forces shape the size and structure of social groups

Solitary (but differentiated social relationships)

OrangutanLoris

• each individual lives alone, occasionally meet up for mating

• may chose to neighbour with kin, meet more often

Monogamous (territorial pairs + offspring)

Titi monkeys

Gibbons

Mountain gorillas

Black and white colobus

One-male, Multi-female groups (polygyny)

Pygmy marmoset

marmoset

Callitrichids

One-female, two-male groups (Polyandry)

Ring-tailed lemurs

Savanna baboons

Multi-male, multi-female groups

Spider monkeys

Chimpanzees

Communities (fission-fusion social organization)

Socioecology: Competition for food is particularly important for females• Nutrition affects:

• Ability to conceive• Viability of pregnancy• Lactation

• Male reproduction is more influenced by access to females than by nutrition

Food, competition, and social behavior are thought to be linked

Dominance Relationships

Competitive Regime

Distribution of food

Value of Alliances

Female Relationships

DispersalPatterns

The distribution of food affects they type of competition

Clumped, valuable patches Dispersed, low value patches

The distribution of food affects the nature of competition

• Dispersed --> scramble competition • Food is distributed evenly• Food items not worth fighting over• Scramble to get enough food• no direct competition

• Clumped --> contest competition• Resources are scarce & valuable• Resources are worth fighting over• Contest access to particular resources

Contest competition can produce dominance relationships

• A & B want same piece of food FIGHT• Bigger, stronger, more experienced one will win• When one consistently defeats other = dominance

relationship• If A always beats B & C• And B always beats C

= dominance hierarchy

Food, competition, and social behavior are thought to be linked

DominanceHierarchy

Contest Competition

Distribution of food

Value of Alliances

Female Relationships

DispersalPatterns

If dominance rank affects access to resources,

• Females will strive for high rank• Females may benefit from help in their fights

• Alliances useful

If females come to rely on alliances…

• Will develop relationships with allies• associate with certain females• groom certain females

• May prefer kin as allies• Kin share genes = kin selection• Inclusive fitness

• Will remain with allies/kin • Females will be philopatric• Males will disperse to prevent

inbreeding

Alliances can also affect structure of dominance relationships

• A beats B• A helps A’ beat B• A’ can beat B• A and A’ will outrank B

• Dominance hierarchy will have female relatives next to each other in rank

Monkey B

Monkey A

Monkey A’

Food, competition, and social behavior are thought to be linked

Dominance Hierarchy

Contest Competition

Distribution of food

AlliancesValuable

Close Bonds

Female Philopatry

Eg: baboons & capuchins

If dominance does not affect access to resources, then…

Unstablehierarchy

ScrambleDistribution

of food Weak bonds

Male/femaledispersal

No alliances

Eg: gorillas & langur monkeys

What about males?

• There are differences between sexes in what matters most

for fitness:

• Female fitness depends on access to resources

• Male fitness depends on access to females

• Social organization depends on:

• Distribution of resources (for females)

• Distribution of females (for males)

Social organization is driven by sex differences. Why?

What about males?

• Male fitness depends mainly on access to females• Males don’t benefit much from alliances - can’t

share mating opportunities very well• So, males go where females are

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Number of Females

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