Session 14: Social Organization
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Primate behavior, organization, mating patterns.
1. Key Concepts:
2. Terms & Definitions:
- Anisogamy
- Different sized gametes.
3. Social Organization and Complexity:
The "why" questions of behavior: how can we separate these questions, especially as related to social organization. What’s the difference between them? For example, A and D are very closely related, but A is phylogenetic, or what’s already happened, while D is what’s happening now.
- Evolutionary cause underlying a behavior.
- Developmental or ontogenetic cause underlying behavior.
- Proximate stimulus eliciting the behavior.
- Functional, or fitness related, impact of the behavior.
4. Why Social organization?
Evolution, sex, and social organization:
Differences between sexes will impact and structure society.
- Sex differences in reproduction:
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- anisogamy and parental investment.
- physiological differences and dimorphism.
- investment patterns.
- anisogamy and parental investment.
- Sexual selection.
- Phylogenetic and ecological constraints on sex differences.
OSR (operational sex ratio):
OSR is expressed and limited by energetic constraints. The higher the OSR, the lower the competition for females. One male – multi females organization results in one male constantly observing while females groom, etc. Adult male has very low internal interaction. The operational sex ratio and demography of groups has a huge impact on the way groups are structured.
- Expected number of reproductively active males to females.
- Prediction of expected level of competition.
- Assumptions of females as limiting sex.
Mating patterns:
We assume, in evaluating mating patterns, that females map to resources and males map to females. Why would a female want to be social? Mating patterns (and resulting social structure) are a compromise between male and female strategies constrained by external and internal variables. Mating patterns, broadly labeled as polygamous, polygynous, polyandrous, and to a lesser extent behaviorally monogamous, really exist in more subtle variations:
- single male groups and mating.
- age graded groups and mating.
- multi male/ multi female groups.
- consortships.
- extra pair copulations (EPCs).
- seasonal breeding.
Grouping types (Demographic labels) of extant primates
- multifemale/multimale--The group consists of >1 adult female and >1 adult male and immatures. Variants:
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- cohesive group.
- fission-fusion.
- community.
- Unimale/mutlifemale--A cohesive group consists of one adult male and greater than one adult female and young.
- Unifemale/multimale--A cohesive group consists of one adult female and greater than one adult male and young.
- Two-adult group--A cohesive group consisting of one adult female, one adult male and immatures.
- Dispersed sociality--Individual primates with individual ranges that overlap extensively. Interactions between individuals within the overlapping ranges can be frequent or infrequent, vocal and/or visual, and/or tactile. Occasionally multi-individual subgroups may form.
Why live in groups:
Group living has demonstrated costs and benefits. The general model of food competition or foraging is the most often cited explanation for group living. Additional hypotheses supporting the evolution of group living include response to predation pressure, assistance rearing offspring, and infanticide avoidance.
Notes from the field: Variable social organization and primate evolution
Examples of intraspecific variation in grouping patterns
| Species |
Group composition |
Study |
|---|---|---|
| Propithecus diadema edwardsi | Unimale/mutlifemale= 9 groups Unifemale/multimale=11 groups Two-adult group=12 groups |
Pochron and Wright, 2003 |
| Semnopithecus entellus | Unimale/multifemale= 27 groups Multifemale/multimale=229 groups all male=4 groups |
Treves and Chapman, 1996 |
| Hylobates lar | Two-adult group= 3 groups Unifemale/multimale= 1 group |
Brockelman, et al., 1998 |
| Gorilla gorilla berengei | 7 groups observed Unimale/Multifemale= 41.1% of observation time Multimale/multifemale=36.8% of observation time allmale=22.1% of observation time |
Robbins, 1995 |
| Saguinus mystax | Two adult group= 27 groups Unimale/multifemale= 30 groups Unifemale/multimale= 52 groups Multifemale/Multimale= 163 groups |
Sussman and Garber, 1987 |
5. Social Organization- What is it?
Social organization is emergent property stemming from the combining of the following broad elements. Why a female would be social is ultimately irrelevant, due to the phylogenetic role. It is more important to identify social organization “rules” because these emerge from multiple levels of understanding and behaviors (mating system, social constraints, etc). The group is just a snapshot.
- Mating patterns.
- Grouping patterns.
- Social structure.
- Ecological constraints.
- Move away from a reductionist perspective.
- The group as a dynamic social entity.
Social organization emerges from the conflux of its constituent components
Emergence is an important part of social reality.
Interconnections between the individual, the group and the population
Sociality is adaptive. What is the social mind? Learning in respect to being aware of the other members of the group. Cueing individuals for interactions with other individuals; being perceptive to other individuals' reactions/expectations. These constraints are especially important to address in research design.
5. Additional Material:
Required Reading:Primates in Perspective. 2007. C.J. Campbell, A. Fuentes, K.C. MacKinnon, M. Panger, S.K. Bearder. Oxford University Press.
Chapter 37: Social Organization: Social Systems and the Complexities in Understanding the Evolution of Primate Behavior - Fuentes
