Nonhuman Primate Behavior Chapter 9

Anthropocentrism Anthropocentric - Viewing nonhuman animals in terms of human motives, and experience and capabilities Emphasizing the importance of humans over everything else

What is Behavior? Anything organisms do that involves action and response to internal or external stimuli The response of an individual or group to its environment May or may not be deliberate Not necessarily the result of conscious decision making The underlying principles of behavioral evolution lie in the interactions between a number of environmental and physiological variables

Behavioral Ecology Focus on the relationship between behaviors, natural environment, and biological traits of the species Based on the assumption that animals, plants, and microorganisms evolved together Behaviors have evolved through the operation of natural selection: Some behaviors are influenced by genes and are subject to natural selection the same way physical characteristics are

The Evolution of Behavior Behavior as phenotype Behavioral phenotypes that increase fitness pass on genes at a faster rate Genes do not code for specific behaviors (aggression, cooperation, etc.) Genetics Species vary in their limits and potentials for learning and behavioral flexibility Natural selection acts on genetic factors shaped by the ecological setting of past and present

Why Be Social? Group living exposes animals to competition with other group members, so why not live alone? Costs of competition are offset by the benefits of predator defense provided by associating with others Group living evolved as an adaptive response to a number of ecological variables

Social Bonding Primate groups are usually based on relationships between females (female bonded kin groups) The types of groups that primates form include Monogamous pairs Polyandrous groups One-male groups Multi-male groups Fission-fusion groups

Why Primates Form Groups There are two main hypotheses: Resource-defense model Focus on the notion that a group of animals can better defend resources Species that rely on foods distributed in clumps tend to be more protective of resources Predation model Emphasizes the risk that primates face from predators Primates in larger groups will have a better chance to detect predators and potentially defend themselves

Resources Leaves Insects Fruits and nuts Abundant, dense, and support large groups of animals Insects Widely scattered, causing animals to feed on them alone or in small groups of two or three Fruits and nuts Occur in clumps and are most efficiently exploited by smaller groups of animals Large groups break up into smaller subunits to feed

Predation Primates are vulnerable to many predators Snakes, birds of prey, leopards, wild dogs, lions, other primates, etc. Where predation pressure is high, large communities are advantageous These may be multi-male, multi-female groups or congregations of one-male groups

Group Size Several factors determine the size of a particular primate group. These include whether the primate is: Nocturnal or diurnal Arboreal or terrestrial Type of diet Benefits in terms of energy (calories) obtained from food versus costs (energy expended) of obtaining and digesting

Other Factors that Influence Social Structure Body Size Larger animals require fewer calories and therefore consume larger amounts of lower quality foods Larger animals are better able to retain heat and their overall energy requirements are less Relationships with Non-predatory Species Many primate species associate with other primate and non-primate species for various reasons, including predator avoidance

Other Factors that Influence Social Structure (cont’d) Dispersal Members of one sex leave the group in which they were born when they become sexually mature Individuals who leave find mates outside their natal group Life Histories Developmental stages that typify members of a species and influence reproductive rates Examples: length of gestation, time between pregnancies, period of infant dependency, age of sexual maturity, and life expectancy

Dominance Dominance hierarchies – Primate organization that imposes order and establishes parameters of individual behavior Higher-ranking animals have greater access to preferred food items and mating partners than lower ranking individuals. Dominance hierarchies are sometimes called “pecking orders” Learned May change over the animal’s life Factors that influence dominance: Sex Age Aggression Time in the group Motivation Mother’s position

Aggression Intragroup Aggression Intergroup Aggression Lead to group disruption Frequently develops out of competition for resources Often resolved through submission Dominant individuals may keep subordinates from food Intergroup Aggression Home range – permanent association with a territory Core area – are within the home range which contains the highest concentration of predictable resources Where the group is most frequently found Territory - portion of the home range defended against intrusion

Primate Cultural Behavior Cultural behavior is learned Passed from generation to generation through observation and instruction Nonhuman primate infants Observe their mothers and others Learn about food items, appropriate behaviors, and how to use and modify objects

Examples of Cultural Behavior Japanese macaques and sweet potato washing Orangutan nest building Gorilla depth testing Chimpanzee termite fishing, leaf sponges, hunting “spears,” nut cracking