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Lecture 21 - Primate Social Structure

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Esteban Parra

ANT203Y5 – BiologicalAnthropology Lecture 21 – January 16, 2014 Primate Social Structure Social Structure - The composition of the social group o Number of individuals  Number of males  Number of females o Age structure o Relatedness of individuals - Dominance interactions - Sexual dimorphism - Behavioral adaptations Models of Primate Behaviour - Early studies focused on ecological descriptions contrasting arboreal and terrestrial primates - Six niches were defined… Six Primate Niches 1) Nocturnal insect eaters 2) Arboreal leaf eaters 3) Arboreal omnivores 4) Semiterrestrial leaf eaters 5) Semiterrestrial omnivores 6) Primates living in arid environments • These categories have been elaborated on over the years Behavioural Ecology - The study of behavior from an ecological and evolutionary perspective o Feeding strategies o Social strategies o Reproductive strategies - Considerations of the cost and benefits to different strategies o e.g., Living in groups is good for noticing predators and defending food resources, but bad in that there are intragroup conflicts. Hierarchies and reconciliation behaviors are means to cope. Some Mating Systems inAction ANT203Y5 – BiologicalAnthropology Lecture 21 – January 16, 2014 Multilevel Troop Structure of the Hamadrya Baboon - At sexual maturity, males leave the unit in which they were born, but stay within the clan. Usually, they become a follower of another unit hearding juvenile or sub-adult females together to form their own new unit. - You have the leader, and several females, and you typically have a follower (a young male who follows the group to see if he can have access to some females to form his own groups) Seasonal and Temporal Changes in Social OrganizationAmong Patas Monkeys - Sometimes you have primarily one form of structures but this may change, depending on who is the alpha male in charge Distribution of Old World Monkey Social Structures - The most common is common is multimale/multifemale Sexual Selection: Darwin’s Picture - Sexual Selection –form of natural selection that is driven my mate choice - Competition will make males stronger and better able to dominate against other males. - Selective choice by females will make flashy traits predominate in males. o Intrasexual selections - competing against each other (males against each other for females) - Darwin’s second book was “The descent of man and selection in relation to sex” published in 1871 Modern Models of Sexual Selection ANT203Y5 – BiologicalAnthropology Lecture 21 – January 16, 2014 1) Males compete with other males 2) Females compete with other females 3) Females select males 4) Males select females 5) After copulation, selection is also acting, in the form of sperm competition and cryptic female choice. Sperm Competition and Testis Size - Agood example among apes: - Humans- 80 kg, testis 20g - Gorillas- 3 times larger - than humans, testis - ½ the size - Chimps-50 kg, testis 60 g Sexual Dimorphism is evidence of sexual selection resulting from competition among males and female preferences in mating partners Body Size Dimorphism and Canine Dimorphism Dominance and Sexual Dimorphism - Strong male dominated societies show moderate to strong sexual dimorphism o Males who are successful are bigger and stronger having competed against other males to secure their status o Whatever component of their success is genetic will be inherited by offspring o In primates, non-genetic components can also be transmitted
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