Transcript Chapter 6: Primate Ecology

Chapter 6: Primate Ecology
•Survival
–Getting enough to eat
•Types of food and metabolic needs
•Territories and Ranges
–Avoid being eaten
•Predation
•Sociality
–Types of social groups
–Sexual composition
–Dominance Hierarchies
Getting Enough to Eat
• Larger animals
need more food
overall
• Smaller animals
need
proportionally
more calories.
Nutrients and Toxins
•Primates have diverse diets
•Different primates eat different combinations of foods
•Need a good source of protein and a good source of
carbohydrates (sugars)
Body Size and Diet are Related
Different Diets have Different
Adaptive Problems
Eating, Traveling & Resting
Territories vs. Ranges
Territories are not overlapping,
boundaries are defended
Ranges are overlapping,
not exclusive
Predation
• Smaller primate more likely to be victims of predators
– Higher predation may lead to larger primates and a shift in food
• Effects choice of where you live
• Different defense mechanisms
– Shelters
– Activity patterns
– Warning calls
• Form of cooperation
• Multi species cooperation
• Different calls for different predators
Sociality
•
Why be social?
– Two reasons (Alexander)
1. To avoid predation
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Safety in numbers (tend to form large groups)
Harder to feed everyone
2. Common resources capture
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Social hunters (tend to be small)
• Diminishing return problem
Collective defense of territory or competition with other
groups
• Balance of power
Types of Primate Social Groups
Solitary: Orangutans
Polygyny one-male: Gorillas
Monogamous: Gibbons
Polygyny multimale: Chimps
Polyandrous: Tamarinds
Resource Competition and
Dispersal Patterns
• Resources are patchy and limited
– Greater competition and dominance hierarchies
• Within group competition greater than between group
– Females will form kin based coalitions
– Females will form dominance hierarchies
– Female philopatry – Matrilocal
• Between group competition > within group competition
– Females will be more egalitarian
– Females will still favor kin and be philopatric
• Both within and between group competition is strong
– Combination of the previous two contexts
• Females favor kin groups – philopatric
• Females more egalitarian
• When resources are dispersed you get scramble
competition
– Females have little motivation to form dominance hierarchies
– Females have little reason to form coalitions or be philopatric
• Rare?
• Where are the males?
– Males go where the unrelated females are.
– If females are philopatric then males must leave their natal group
to avoid inbreeding depression.
– The more females in a group the more they become a
defendable (patchy) reproductive resource for males
• The more females in a group the harder for one male to
monopolize them, especially if they have asynchronous estrus.
How do Chimps and Humans Fit in all of this?
• Not very well!
– Male philopatry – Patrilocal (even Bonobos)
– The socioecological models presented in you book
would lead you to believe that Chimps and our
common ancestor live in a scramble competition
context, but they don’t, and they are territorial.
– Other possibilities?
• Wrangham and Madson argue that
– Chimps and Human males will be territorial if resources are
defendable (patchy) and important to females
– If resources are not defendable, males will fight over females
Cost of Grouping Hypothesis
(Wrangham)
• Males have an advantage in the cost of grouping
– Males can forage farther for the same energy costs
(more efficient) because they are caring babies or the
extra weight of pregnancy (women paying a higher
cost for reproduction)
– You can put more males in a given area (fixed amount
of food) than you can put females
– Because of the lower cost of grouping men form
larger groups than males.
– They use there larger coalitions to compete with other
groups of males, but also to dominate females.
What about Bonobos?
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Bonobos don’t compete with gorillas for food
More food to eat
The cost of grouping goes down for males and females
Females are not longer disadvantaged in terms of the
cost of grouping
• Females are better at forming coalitions (through sex)
despite male philopatry (Patrilocallity)
• Females dominate Males