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Anthro 101:Human Biological Evolution lecture on Primate Ecology. Rebecca Frank, LAVC F2010
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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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