Week 8: Primate Social Behavior

1. Week 8: Primate Social Behavior

2. Sociality • Why be social? • Social living involves costs • Competition for all resources • Intra-group violence (including infanticide) • Disease transmission • What are the benefits? • Two reasons (Alexander) • To avoid predation • Safety in numbers (tend to form large groups) • Harder to feed everyone • Common resources capture • Social hunters (tend to be small) • Diminishing return problem • Collective defense of territory or competition with other groups • Balance of power

3. Types of Primate Social Groups Solitary: Orangutans Polygyny one-male: Gorillas Monogamous: Gibbons Polygyny multimale: Chimps Polyandrous: Tamarinds

5. Brain to Body Weight Across Species

6. Food or Social Interactions?

7. Getting Enough to Eat • Larger animals need more food overall • Smaller animals need proportionally more calories.

8. 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)

9. Body Size and Diet are Related

10. Different Diets have Different Adaptive Problems

11. Eating, Traveling & Resting

12. Territories vs. Ranges Territories are not overlapping, boundaries aredefended Ranges are overlapping, not exclusive

13. 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 (diurnal, nocturnal) • Warning calls • Form of cooperation (Kin selection/Inclusive Fitness • Multi species cooperation (Reciprocal Altruism) • Different calls for different predators

14. 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

15. 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.

16. 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

17. 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.

18. What about Bonobos? • 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

19. Evolution of Culture • Culture is about learning • Cultural behaviors that are not innate • Acquired in a social context • Is culture unique to humans? • NO • Unique to Apes? • NO but rare • Social facilitation vs. Observational learning • Monkeys don’t ape

20. Adaptations for Observational Learning led to: • The ability of innovations to spread through a population without having to evolve new adaptations. • Individuals not having to start from scratch, they could build on the knowledge and skill of others • Cultural explosion • Homo Erectus tools (choppers) were vary useful but did not change. • With Modern Humans there was something equivalent to adaptive radiation with behaviors (tools, art, subsistence practices, etc.,) • New Data indicate that Observational learning has special features • Joint attention • Functional understanding of cause and effect.