Understanding Primate Sociality & Reproductive Patterns
- Prosimii (sub-order)
- retain ancestral sensory traits (e.g. nose, b/w vision, ears)
- many species with adaptations (derived traits) to specific ecological niches
- example: Aye Aye
- example: Galago
- example: Ring-tailed Lemur (video)
- Adaptive radiation / speciation of Lemurs on Madagascar
- Anthropoidea (suborder)
- group that includes New World Monkeys, Old World Monkeys, Apes and Humans
- common traits include color vision, loss of acute senses of smell & hearing, and relatively larger brains
Monkeys vs Apes:
- apes have larger bodies and relatively larger brains (and prolonged period of infant dependence means single births are spaced at long intervals)
- apes lack tails
- apes have mobile, rotary shoulder joint which allows them to brachiate and hang from their arms (monkeys are quadrupeds that jump and run along the tops of branches or on the ground)
- apes have wider torso and shorter, stiffer lumbar region
- Gibbons & Siamangs ("lesser apes" or Hylobatidae family) : small bodied brachiators, fruit eaters, defend small territories in canopy of SE Asian rainforest, mate for life in pair bonds, show little sexual dimorphism
- Orangutans ("Great Ape" or Pongidae family: 1 species Pongo pygmaeus) : large, sexually dimorphic "4-handed" brachiators, fruit eaters (but will eat some leaves, bark etc), females live in small, solitary territories in SE Asian rainforest, monitored by dominant male which can physically dominate females... less dominant males cruise for mating opportunities
- Gorillas (Pongidae family: 1 species Gorilla gorilla, with regional subspecies in different parts of Africa) : largest primate, sexually dimorphic, terrestrial in tropical forest habitats, knuckle-walkers, vegetarian (mountain gorillas eat terrestrial herbaceous vegetation exclusively, lowland gorillas also eat fruit when they can get it), live together in harems of females and infants with resident silver back dominant male
- Chimpanzees (Pongidae family: 2 species Pan paniscus or "bonobo", and Pan troglodytes or "common chimpanzee" which has three regional subspecies) medium-sized ape, and much less dimorphic that other Pongidae, terrestrial in a range of habitats, including tropical forest, woodlands and grassland savannas, knuckle-walkers, omnivores, live in large communities where females often transfer from natal group and tend to have separate ranges, and males stay in territory where they were born and cooperate to patrol entire territory (to monitor females and defend against male interlopers)
- what strategies do the different apes use to compete for mates, and/or food?
- in what ways do their habitats constrain or influence their social organization?
- all these apes have large brains... what selective advantages might "intelligence" have for them and how do they use their intelligence in their native habitat?
Primate Life History Patterns
Relatively large brain size slows maturation of primates, extends the length of their reproductive cycle and gives them longer lives than other mammals. This puts a premium on learning as a key to survival and reproductive success, in addition to biological adaptation. Single births are the norm, and primate parents can improve their offspring's chance of survival through socio-behavioral investment.
Sociobiological Principles important for understanding Primate Social Organization
Strategies for reproductive success: avoiding predation, finding food, getting mates
Why do primates behave altruistically? The difference between Darwinian Fitness (personal reproductive success) and Inclusive Fitness -- also known as Kin selection -- favoring the reproductive success of yourself and your close kin.What are the advantages and disadvantages of group life, from a sociobiological perspective? (cooperation vs competition)
There is a great diversity of monkey species. There are three articles in your A105 reader that describe interesting traits of monkeys. "Junk Food Monkeys" describes some of the physiological traits we have in common with baboons. And then two articles focus on the complex social organization of monkeys, describing their mating strategies and social ranking behavior.
We will focus on understanding the social organization and mating structure of baboons in order to understand how primatologists study such issues.
Old World Monkey Case Study: Savanna Baboons: multi-male (male transfer) multi-female (Female bonded), ranked societies. Female reproductive cycle means females mate only once every two years. (they are only sexually receptive when they are in estrus). High social rank (dominance status) does not guarantee reproductive success... but altruistic behavior and "special relationships" can be an effective strategy. highly sexually dimorphic in body size and morphology
- troop life: multi-male, multi-female pattern
- behavioral advantages (e.g. predator avoidance)
- behavioral disadvantages (e.g. competition for food & mates)
- alternative explanations/theories of primate grouping behavior discussed in textbook
- different patterns of male and female investment in offspring
- the potential lifetime fitness differs between females (limited by their reporductive capacity... maximum = 10-15 offspring in a lifetime) and males (limited by sperm counts and access to females...)
- maternal lineages are stable core of troop
- promiscuous mating: paternity uncertain
- males transfer out of natal troop
- male Darwinian Fitness challenge: how to compete for access to mates?
- "Be big and bold": sexual selection can lead to sexual dimorphism (e.g. canines, body size)... the strength of this selection pressure depends upon social structure of primate society
- "Nice guys can finish first" : female mate choice of affiliative, or less-aggressive males may aid their reproductive success
For primatologists to understand the behavior of primates in nature, long-term field studies are necessary that use systematic techniques to record behavior. Assignment 2 is designed to give you some experience in these types of observations... studying the human primate!
Interested in Primates? Here are some additional links to check out:
Jane Goodall Institute
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Last updated: 11 February 2000
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