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Sociobiology and Socioecology

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University of Texas at Austin
ANT 301
Chris Kirk

Sociobiology and Socioecology Blue: Lab notes Wednesday, February 13, 2013 1:59 PM • Sociobiology: Describes the effects of male/female differences in reproductive biology on social behavior. Biological bases for social behavior. o Kin Selection: Hamilton's Rule: Family comes first. You are more willing to help family members other than strangers. o Males and Females: different minimum investment to ensure offspring survival o Everything stemming from the asymmetry in required parental investment by males and females. o Naturalistic Fallacy: If X happens in nature, we should do it too. • Expectations: o Males Mammals: more promiscuous o Female Mammals: More choosy o One result: Male competition for access to females • Q: Aren't there instances in which females reap a benefit from mating with more than one male? o To prevent infanticide o Callitrichids • Female mates with multiple males • Males provide infant care • Still related to reproductive biology (twinning) • Female choosiness is an old idea: o C. Darwin: "The female, with the rarest exceptions is less eager than the male… she is copy and my often be seen endeavoring for a long time to escape." o Formalized as "Bateman's Principle • Angus Bateman: Fruit flies • Provided empirical support for the notion that promiscuity is a good thing • This is usually true in mammals… but it's a generalization. • Another example: Primate females that mate with multiple males partly as a  strategy to avoid infanticide • Investment in Reproduction o Not sex per se. o Flicker (Colaptes auratus) [woodpeckers] • Male: Hammers out nest • Male also does lion's share of incubating and chick guarding (grater parental investment) so… • Females compete for access to males Some females maintain two nests with two male mating partners. Most birds pair-living • Q: Do principle of sociobiology apply to human behavior? o Controversial o E.g. Does Bateman's Rule apply to humans? • A while different course. • Humans more than any other animal rely on LEARNED patterns of behavior in day-to-day life. • Culture modifies and constrains biologically- mediated phenomena • SO: Permanent male/female association in primates may be partly the result of females attempting to avoid male harassment and infanticide • Q: Why be social at all? o True sociality (established relationship and individual recognition) among mammals is rare. o Many mammals solitary or form aggregates • Social Mammals: o Some carnivores o Spotted Hyenas o Lions and big cats o Elephants o Dolphins • For some, benefits are obvious o Cooperative hunting o Cooperative infant care • Q: Why do primates live in groups? o They are definitely costs for group-living… o Costs of sociality: • Competition of food • Competition of mates • Enhanced disease transmission • More conspicuous predators • Predation Defense Model o Carel Van Schaik o Primates live in groups to protect themselves from predators o More eyes and ears o Physical Defense o Dilution effect (probabilities) • Resource Defense Model o Richard Wrangham o Primates live in groups to have better access to food o Large groups can displace small groups at clumped resources like food trees o Solitary: no within group competition for food o But, it may be to your benefit to put up with some within group competition in order to win between group contests o Also: Shared knowledge of where to find food resources o May contribute to foraging efficiency • There is good empirical support for both models o Group size often seems to be determined by balancing costs with the benefits • So: Many primates are social • How primatologists classify social groups: o Female bonded groups • Many primate species live in female-bonded kin groups that remain stable over time • Females stay in their natal (birth) group their entire lives, so that females live with their relatives • Female Philopatry • Philopatry: literally "love of the father land" • Remain in natal group as an adult • In primates, one or both sexes disperses before reaching sexual maturity (Exception: callitrichids) • Key: Inbreeding Avoidance (Avoiding inbreeding depression) • So, in female-bonded primate groups, females o Male bonded groups • Fewer primate species live in male-bonded kin groups • Males stay in their natal (birth) group their entire lives, so that males live with their relatives • Male Philopatry • Female Dispersal • Q: Why are male bonded groups rare?  Males compete more for mates.  Females compete for access to food ----> males compete for access to females  Food can be shared among several females, but most female primates can only be impregnated by one male.  Attempts by individual males to monopolize access to females may prevent formation of male alliances. • Remember: competition between males for access to females can be very intense, and may even result in death. o See box 5.2 on pp 129-130 for more classification schemes. • Social Structure: describes how many adults of each sex are in social groups. Ratio of adult males and females within a social group  Solitary: individuals live alone (Aye-aye, orangutan, mouse lemur)  Offspring can only live with mother until weaning  M & F only come together to mate  Many nocturnal primate species previous thought to be solitary actually live in dispersed social networks: • Individuals sleep in groups and have established relationships • Forage alone ("solitary foragers")  Family: 1 male, 1 female, dependent off spring (Gibbons, Indri, titi monkey)  Dispersed: forage separately, sleep together  Cohesive: feeding, traveling, resting together  Single male/Multi female: (Langur, Gorillas)  1 adult male, 2 or more adult females  Unattached males solitary or form all male bachelor groups  More in danger for infanticide  Multi male/Multi-female (Chimps, Spider monkeys, howler monkeys)  Multiple adults of each sex in social group  Baboons, maccas, bonobos,
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