Week 8: Primate Social Behavior

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) 1.To avoid predation Safety in numbers (tend to form large groups) Harder to feed everyone 2.Common resources capture 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 Monogamous: Gibbons Polyandrous: Tamarinds Polygyny one-male: Gorillas Polygyny multimale: Chimps

Brain to Body Weight Across Species

Food or Social Interactions?

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

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? 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

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

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.