Anthropology Mini Essays

Lecture #11 — Primate Behavior I — Behavioral Ecology and Social Structure Today’s Questions • What is behavioral ecology? What two main questions does it answer? • What is the primate adaptation? • Why do primates live in groups? • What are the various types of primate mating systems? Why Study Primate Behavior? • Behavior Evolved – Behavioral Ecology — the study of behavior as an adaptation to the environment • Physical Environment • Social Environment – Answers Two Main Questions • How do ecological factors influence primate behavior? • How do these ecological factors explain differences between species? The Primate Adaptation • The Primate Adaption is primarily SOCIAL – Primate social behavior evolved in response to the ecological problems primates experience • Primates live in groups • Benefits – Feeding efficiency and defense of resources – Access to mates – Predator defense • Costs – COMPETITION Why live in groups? Feeding Efficiency and Resource Defense Feeding Competition Access to Mates Mating Competition Predator Defense Attracting Predators Diet, Predation, and Group Size • Tend to find larger groups when: – Resources are defensible – Predation pressure is high Social Organization and Mating Systems • Type and size of group is influenced by: – Resource competition – Activity patterns – Habitat, predators • Mating systems has implications for: – Group size – Territoriality – Sexual dimorphism – Transfer • Exogamy — one or both sexes leave the group they were born into at sexual maturity • Inbreeding avoidance Social/Mating Systems PAIR -BONDED SOLITARY Solitary/ Polygynous • Males solitary, large home ranges that overlap several females • Females and dependent offspring, sometimes two females travel together (sisters or mother -daughter) • Dramatic sexual dimorphism • Females show behavioral indicators of fertility (presenting to males) • Males compete for access to females’ territories, direct and indirect competition – Solitary but polygynous — 1 male defends mating access to more than one female • Both sexes disperse at sexual maturity Solitary Orangutans and Nocturnal Lemurs Pair - Bonded • Adult bonded pair and their dependent offspring — juveniles and infants, early adolescents • Individuals are solitary for a time before finding a partner, both sexes work to prevent neighboring same -sex conspecifics from mating with their partner • No size sexual dimorphism • Females show behavioral indicators of fertility • Both sexes disperse at sexual maturity, usually pushed out of the group by same -sex parent Pair - Bonded Gibbons, Siamangs , Titi Monkeys Polyandry • One adult female, >1 adult male, dependent offspring of various ages • Callitrichids — Marmosets and Tamarins – Twinning common, males invest heavily in offspring, do most of the carrying while mothers forage (high energetic cost to twins) • Adaptation to high predation pressure – Not very sexually dimorphic – Females show behavioral indicators of fertility (presenting to males) Polyandry Marmosets and Tamarins Uni - Male/ Polygynous • One adult male, >1 adult female, dependent offspring of various ages, and all -male bands or solitary males • High degree of sexual dimorphism — males compete to become associated with a group of females or to recruit new females – Females show behavioral indicators of fertility (presenting to males) Uni - Male Multimale - Multifemale /Promiscuous • Permanent aggregation of multiple adults of both sexes, offspring of various ages • Sometimes associated with female sexual swellings — advertise fertility to attract males – Competition between males for access to females — can be aggressive, direct competition but also indirect ( consortships — one male convinces a female to go off with him for a few hours or days; often friends) Multimale - Multifemale /Promiscuous • Females mate with multiple males – Paternity obfuscation — infanticide avoidance, paternal investment • Females exert a high degree of choice – because females invest so much more heavily in offspring in general, females want to maximize their returns from mating – sexual receptivity signals • swellings (physiological) • specific behaviors — presentations • mate choice — females will only mate with preferred males • Male transfer, females stay in natal group — strong bonds within and between matrilines Multimale - Multifemale /Promiscuous Fission - Fusion • Multimale / multifemale groups where the larger community splits into smaller daily foraging parties – Bonobos and chimpanzees – Males compete for access to females directly and indirectly • Sperm competition • Females transfer, males stay Fission - Fusion