Chapter Nine Nonhuman Primate Behavior 2014 The Mc

Why Primates Form Groups • There are two main hypotheses: – the resource-defense model – the predation model • The resource-defense model is based on the idea that a group of animals can defend access to resources, such as fruit trees. • The 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 against predation. © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -2

Kinds of Primate Social Organization • Several factors determine the size of a particular primate group. These include whether the primate is: • nocturnal or diurnal • arboreal or terrestrial • the type of diet • 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 societies © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -3

Case Study: The Gibbon • • Gibbons live in monogamous groups. Grooming is a behavioral pattern common to primates. Play behavior among juveniles is also important. Gibbons are highly territorial. Territorial conflict is expressed mainly through vocalization and display. © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -4

Case Study: The Gelada • Geladas are large, primarily terrestrial monkeys. • The basic social units are the harem and the all-male group. • The smaller units may gather into larger social units that share a home range. • Agonistic behavior is frequently seen. © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -5

Case Study: The Savanna Baboon • Baboons live in a social unit called a troop. – Troops remain within a home range, but the boundaries are not defended. • The adult males are arranged into a dominance hierarchy. – Behaviors associated with this include threat gestures, displacement, presenting, and mounting. • Adult females also form dominance hierarchies, but dominance interactions are not observed as often among females as among males. • Females display a sexual swelling that indicates estrus. • Grooming clusters of females are commonly seen. © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -6

Photos of Baboon Behavior © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved.

Case Study: The Chimpanzee • The chimpanzee spends much time in the trees feeding, resting, and sleeping. • Movement between the trees is done on the ground. • Chimpanzee groups are based on bonds between males. • A chimpanzee community is made by of a continuously changing series of smaller groups, an example of a fission-fusion social organization. • The hunting of meat and use of tools, such as termite sticks, also characterize the chimpanzee. © 2014 The Mc. Graw-Hill Companies, Inc. All rights reserved. 9 -8