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<strong>Social</strong> <strong>Systems</strong> of Primates<br />

• Part I: Introduction: what are primates?<br />

• Part II: Laws of social behaviour<br />

– Competition and conflict regulation<br />

– Cooperation and relationships<br />

• Part III: Socioecology of females<br />

– Costs and benefits of group living<br />

– Socioecological Paradigm<br />

1


Part I: Introduction: what are<br />

primates?<br />

– a rather unspecialized (‘primitive’), small to mediumsized<br />

mammal<br />

– with rather mobile digits with nails (rather than claws)<br />

( arboreal)<br />

– with an emphasis on vision relative to smell<br />

– with forward-pointing eyes, stabilized by the<br />

postorbital bar ( visual predators)<br />

– with larger than average brain size for its body size<br />

– which lives longer than average for its body size<br />

– With a tendency to live in permanent, mixed-sex<br />

groups<br />

2


The Primate Syndrome<br />

• What is a primate?<br />

– a rather unspecialized (‘primitive’), small to mediumsized<br />

mammal<br />

– with rather mobile digits with nails (rather than claws)<br />

( arboreal)<br />

– with an emphasis on vision relative to smell<br />

– with forward-pointing eyes, stabilized by the<br />

postorbital bar ( visual predators)<br />

– with larger than average brain size for its body size<br />

– which lives longer than average for its body size<br />

– With a tendency to live in permanent, mixed-sex<br />

groups<br />

3


Primate diversity<br />

Africa Madagascar Americas Asia<br />

N species 79 68 132 78<br />

N genera 21 15 19 16<br />

N families 4 6 5 5<br />

N spp+<br />

subsp<br />

% (semi-)<br />

terrestrial<br />

174 70 200 183<br />

35.4 3.0 0.0 20.3<br />

From CI Orlando workshop 2000; Oates (2005)


Why not study primates?<br />

1. Large animals that live at low densities and<br />

live long lives:<br />

• Small data sets, even after long study<br />

2. Primates are difficult and expensive to keep<br />

in captivity<br />

3. Difficult to do experiments on primates,<br />

even if they only involve social<br />

manipulations (ethical considerations)<br />

• Field data are often correlative<br />

• In captivity, simple experiments are possible<br />

5


Why study primates nonetheless?<br />

1. Spectacular social diversity:<br />

• Great opportunity to do comparisons to test explanatory<br />

frameworks for primate (and human) behavior<br />

2. <strong>Social</strong> complexity unmatched among mammals<br />

• Especially social relationships and behavioral dynamics<br />

in them<br />

3. Easy to observe in detail:<br />

• Most are diurnal, visually oriented, can be habituated to<br />

observers<br />

4. Humans are primates as well!<br />

• Phylogeny matters for understanding a species’ behavior<br />

6


Humans are a great ape, split off from<br />

African great apes ca 6-8 Mya<br />

14 8 6.5 2<br />

Human<br />

Jeffry Oonk<br />

7


Primate specializations: hands and brains<br />

Features of hands (and feet)<br />

– grasping hands<br />

– sensitive finger tips<br />

– flat nails on fingers & toes<br />

– opposable big toe (except us)<br />

chimpanzee<br />

rhesus macaque<br />

galago<br />

8


Primates are brainy mammals<br />

9


Variation in relative brain size among<br />

MacLeod 2004<br />

primates<br />

10


Hypothesized selective advantages<br />

of greater cognitive abilities<br />

• <strong>Social</strong> strategizing (“Machiavellian<br />

intelligence”)<br />

• Spatio-temporal distribution of<br />

resources (spatial memory, mental<br />

maps)<br />

• Acquiring hidden or protected foods:<br />

extraction, processing (“Technical<br />

intelligence”)<br />

• Arboreal clambering<br />

Byrne & Whiten 1988<br />

Milton 1988<br />

Parker & Gibson 1977;<br />

Byrne 1997<br />

Povinelli & Cant 1995<br />

11


A very popular idea:<br />

Machiavellian intelligence<br />

apes monkeys prosimians<br />

Barrett, Henzi & Dunbar 2003<br />

But:<br />

Uncertainty about best<br />

scaling method (body<br />

size effect)<br />

Is group size best proxy<br />

for social complexity?<br />

12


Difficulties with the<br />

Machiavellian intelligence hypothesis<br />

Some major contrasts in intelligence are not explained<br />

<strong>Social</strong> complexity in great apes not greater than in many monkeys<br />

versus<br />

13


Other difficulties with the<br />

social strategizing hypothesis<br />

Some major contrasts in intelligence are not explained<br />

Why are some lemurs not just as smart as monkeys?<br />

versus<br />

14


• whenever<br />

cognitive<br />

abilities are<br />

domaingeneral<br />

• Impossible to<br />

disentangle<br />

selective agent<br />

Other difficulties<br />

cannot distinguish between the benefits<br />

feeding<br />

challenges<br />

social<br />

challenges<br />

spatio-temporal<br />

food distr.<br />

improves selects ability for to deal with<br />

improved<br />

cognitive skills<br />

15


Characterizing primate life histories<br />

16


Important primate features<br />

Features of life history<br />

• Small litters<br />

• Long motherinfant<br />

bond<br />

• Slow<br />

development<br />

• Long life span<br />

Features of social life<br />

• Almost always in groups<br />

• Groups tend to be stable<br />

(permanent)<br />

• Groups contain adults of<br />

both sexes (mixed-sex, or<br />

bisexual groups)<br />

• Complex social behavior<br />

17


Implications of the primate peculiarities<br />

• Arboreality slow life history<br />

• Diurnality large, mobile groups<br />

• Hands dextrous foraging<br />

• Relative brain size ecological and social cognition<br />

• Life history time for learning, group stability, social<br />

relationships<br />

• Infant carrying nomadism in ranging, risk of infanticide<br />

18


Lemurs<br />

Lorises &<br />

Galagos<br />

Tarsiers<br />

Anthropoids<br />

Primate<br />

Radiations<br />

Strepsirrhini<br />

Prosimians<br />

Haplorrhini<br />

19


Modern prosimian primates<br />

Nycticebus<br />

(Lorisoidea)<br />

Eulemur<br />

(Lemuroidea)<br />

Tarsius<br />

(Tarsioidea)<br />

20


Modern anthropoid primates<br />

New World<br />

monkeys<br />

(Ceboidea)<br />

Old World monkeys<br />

(Cercopithecoidea)<br />

Apes<br />

(Hominoidea)<br />

21


Conditions favoring evolution of complex social<br />

behavior & social cognition<br />

1. Gregariousness= group living:<br />

• opportunities for frequent social<br />

interactions<br />

2. Individual recognition (= Stable<br />

groups):<br />

• allows for social relationships<br />

3. Slow life history:<br />

• allows establishment of long-term<br />

relationships<br />

4. Diurnal activity period:<br />

• allows vocal + visual communication,<br />

hence differentiation of messages to<br />

targets<br />

22


The importance of phylogeny<br />

• Prosimians versus anthropoids<br />

• Old World Primates versus New World<br />

Primates<br />

• Great apes versus monkeys<br />

23


Lemurs<br />

Lorises &<br />

Galagos<br />

Tarsiers<br />

Anthropoids<br />

Primate<br />

Radiations<br />

Strepsirrhini<br />

Prosimians<br />

Haplorrhini<br />

24


Shared-Derived Traits of Anthropoids<br />

(relative to tarsiers + strepsirhines)<br />

• Far more likely to be diurnal<br />

– And therefore more likely to range widely<br />

• Larger body size (except for the extinct lemurs)<br />

• Always carrying offspring<br />

– More nomadic, slower development<br />

– Greater risk of infanticide<br />

• Reduced reliance on olfaction and increased reliance on<br />

vision<br />

– Visual communication creates more opportunities for complex<br />

sociality<br />

• Larger brain size relative to body size<br />

– accompanied by superior cognitive abilities<br />

• Systematically gregarious in mixed-sex groups<br />

– Usually accompanied by sexual dimorphism<br />

25


Modes of infant care<br />

cache carry<br />

Affects:<br />

- range use, mobility: central place foraging vs nomadism<br />

- reproductive biology, vulnerability to infanticide: male-female association<br />

26


Activity period and gregariousness<br />

in primates<br />

van Schaik, unpubl. N.B. Cathemeral included in diurnal<br />

27


<strong>Social</strong> life of anthropoids<br />

Prosimians not as socially complex as anthropoids<br />

(even if gregarious)<br />

Extensive coalitions only in<br />

anthropoids<br />

versus<br />

28


Anthropoids:<br />

heritage of visual communication- facial expressions<br />

QuickTime and a<br />

TIFF (LZW) decompressor<br />

are needed to see this picture.<br />

29


Shared-Derived Traits of Old World<br />

Primates (relative to Plathyrhines)<br />

• More likely to be terrestrial<br />

• More likely to have large body size, and hence<br />

• Greater sexual dimorphism in size and weapons<br />

– More evidence for sexual harassment and forced matings by<br />

males<br />

• More systematically trichromatic vision<br />

• Lower reliance on olfaction (no scent-marking)<br />

• Longer gut retention time<br />

– Better able to digest high-fiber diets<br />

30


Ecological contrasts between NW-OW monkeys<br />

New World<br />

Monkeys<br />

Old-World<br />

Monkeys<br />

Gut Retention<br />

Time<br />

Short Long<br />

Home range area Larger<br />

per group weight<br />

Smaller<br />

Group sizes Mainly small Often large<br />

Prevalence of<br />

pairs<br />

High (incl. coop<br />

breeding)<br />

Very low


Shared-Derived Traits of Great Apes<br />

(relative to Old World Monkeys)<br />

• Larger body size<br />

– Less vulnerable to predation (provided in trees)<br />

– More vulnerable to competition (nutritious foods)<br />

• Larger brain size & superior cognitive abilities<br />

– e.g. mirror self-recognition; theory of mind<br />

– Far greater tool use abilities<br />

• <strong>Social</strong>ity despite fission-fusion:<br />

– Male-female association and female sexual activity as much as<br />

ecologically possible<br />

– Tendency toward social tolerance in most dyads, incl. food sharing,<br />

cooperation among non-relatives<br />

• Relatively very slow life history, including long periods of<br />

development and learning<br />

• Nest-building<br />

32


Patterns in primate socioecology<br />

(mainly based on Clutton-Brock & Harvey 1977a, b)<br />

• Body size:<br />

• Nocturnal species tend to be small (up to ca 1-2 kg), and live in small social<br />

units, as compared to diurnal ones;<br />

• Insectivores tend to be smaller than frugivores which tend to be smaller than<br />

folivores;<br />

• Terrestrial species tend to be bigger than arboreal ones;<br />

• Larger species tend to show increased sexual dimorphism in body size.<br />

• Group size:<br />

• Insectivores are often solitary; frugivorous groups tend to be larger and more<br />

wide-ranging than folivorous ones;<br />

• Species living in open savanna tend to live in larger groups than forest-living<br />

species;<br />

• Bigger species tend to live in larger groups;<br />

• Group size has strong effects on range use: daily travel distance, home range<br />

area.<br />

• Population density:<br />

• Larger animals tend to live at lower densities;<br />

• Densities of folivores> frugivores > insectivores.<br />

33


Part II: The Rules of <strong>Social</strong><br />

Behavior<br />

34


<strong>Social</strong> definitions used in this<br />

course<br />

• <strong>Social</strong>ity = involving interactions with known conspecifics (note:<br />

group-living is not required, but individual recognition is)<br />

• <strong>Social</strong> organization = spatial distribution of individuals =<br />

(composition of the social units) + dispersal mode (which sex)<br />

• <strong>Social</strong> relationship = reflection of the history of interactions between<br />

two individuals with respect to their content, quality, and patterning over<br />

time, and is a variable that allows us to predict future interactions<br />

• <strong>Social</strong> structure = structure of the social relationships, incl. bonds,<br />

of individuals.<br />

• <strong>Social</strong> system = social organization + social structure<br />

• <strong>Social</strong> unit = a concrete case of a social system<br />

• Mating system = N of males, N of females mating in a given<br />

social unit<br />

35


Living in Groups<br />

• Fundamental problem:<br />

– beneficial<br />

• General benefit from being gregarious<br />

• Allows specific cooperative endeavors benefiting all<br />

individuals<br />

–Costly<br />

• Living in close proximity increases competition over<br />

access to limiting resources<br />

• Fundamental conclusion:<br />

– All group life inevitably involves both competition<br />

and cooperation<br />

36


Classifying social interactions by fitness<br />

Recipient<br />

Actor<br />

GAIN<br />

LOSS<br />

outcome<br />

GAIN LOSS<br />

Cooperation<br />

(mutualism)<br />

Service<br />

(altruism)<br />

Selfish<br />

(exploitation,<br />

competition)<br />

Spite<br />

Virtually all social behavior in animals contains elements of both<br />

competition and cooperation<br />

37


Competition & Aggression<br />

• Competition ensues when there is not enough of a<br />

critical resource to satisfy the needs of each individual<br />

(= conflict of interest)<br />

– i.e. increased access to this resource increases fitness<br />

• Two possible responses to competition, depending on<br />

benefits of excluding others (which is costly):<br />

– Contest: exclusion from resource possible (also interference<br />

competition)<br />

– Scramble: exclusion from resource impossible or too<br />

expensive relative to value (also exploitation competition)<br />

• Successful contest requires aggression<br />

– Aggression is instrumental, not pathological<br />

38


Dominance<br />

• Critical precondition:<br />

– individual recognition + repeated interactions<br />

• Repeated interactions: no escalation needed -displays<br />

and signals<br />

– A is dominant to B if A can predictably provoke submissive<br />

behaviors in B or B will spontaneously signal subordinate<br />

status<br />

– Cheap and effective way of dealing with conflict of interest<br />

(when there is also some overlap in interests!)<br />

• Dominance is a feature of a relationship, not of<br />

an individual<br />

– same animal can be dominant to some, subordinate to others<br />

39


More on dominance<br />

• Dominance in space: territories<br />

– Dominance is linked to spatial position<br />

• Dominance in groups<br />

– Independent of spatial position or context<br />

• How does dominance produce increased<br />

fitness?<br />

– Exclusion from limiting resources<br />

– Exploitation of subordinate’s work (e.g. forced grooming, )<br />

– Reproductive inhibition (adaptation of subordinate!)<br />

– Harassment/ killing of subordinates (where no valuable<br />

relationship)<br />

40


Dominance hierarchies<br />

• Dominance hierarchies are traits of groups<br />

• Features:<br />

– Linearity<br />

• % of dyads that deviate from linearity (linked to unidirectionality<br />

within dyads)<br />

• Linearity expected if dyadic dominance is reflection of FA<br />

– Steepness<br />

• Reduction in access to critical resource for each rank down<br />

– Degree of correlation with kinship (‘nepotistic<br />

hierarchy’)<br />

• Relatives cluster together, as a result of coalitions<br />

– Stability<br />

• Especially where co-residing relatives provide mutual support<br />

• Often upheld by third parties (maintenance of status quo )<br />

41


Dominance and nepotism among<br />

female primates<br />

Nepotistic: rank<br />

inheritance: daughters,<br />

once adult, rank directly<br />

below mothers.<br />

Ranks stable<br />

Generally, higher-ranking<br />

matrilines out-reproduce<br />

others<br />

Individualistic: no rank<br />

inheritance.<br />

Ranks unstable, often<br />

reverse age-graded, with<br />

youngest mature females<br />

on top.<br />

Little variation among<br />

females in lifetime<br />

reproductive success<br />

42


Observed features varying in relation to<br />

dominance styles<br />

strict<br />

“despotic”<br />

aggression<br />

dominance<br />

style<br />

interventions in conflicts<br />

de-escalation mechanisms<br />

reconciliation<br />

tolerance of proximity<br />

kin bias in the above variables<br />

respect for possession<br />

relaxed<br />

“tolerant”<br />

43


Interspecific variation in dominance style<br />

strict<br />

relaxed<br />

dominance style<br />

Macaca mulatta SBT subordinate<br />

Macaca fascicularis SBT subordinate<br />

Macaca nemestrina SBT subordinate<br />

Macaca arctoides mock-bite dominant<br />

Macaca sylvanus RM threat dominant<br />

Theropith. gelada RM threat dominant<br />

Macaca silenus none —<br />

Macaca tonkeana none —<br />

44<br />

Preuschoft & van Schaik 2000


Conflict Regulation<br />

(friends and non-friends alike)<br />

• Dyadic, affiliative:<br />

– Reconciliation<br />

– Conflict anticipation: prevent escalation<br />

• In zoos, often pronounced peak in grooming preceding feeding time<br />

• Dyadic, agonistic:<br />

– Dominance itself!<br />

– Redirection, aimed disproportionately at kin of the former opponent (Aureli)<br />

– Retribution (attack former opponent at later moment- not possible in<br />

despotic species)<br />

– Opportunistic joining of attacks on former opponent (‘winner support’)<br />

• Polyadic<br />

– ‘policing’ behavior: neutral interventions, supporting fights<br />

45


Conflict Regulation<br />

Reconciliation<br />

• Selective (partner-specific) affiliative social<br />

contact soon after a conflict (sooner than<br />

expected from baseline or matched control<br />

observations)<br />

• Expected to lead to reduction of anxiety<br />

and reoccurrence aggression<br />

• Expected only among partners with a<br />

valuable relationship<br />

Aureli, de Waal<br />

46


Evidence for<br />

post-conflict<br />

friendly<br />

reunions and<br />

for selective<br />

attraction<br />

between former<br />

opponents<br />

Aureli et al. 200247


Bonobo:<br />

Conflict<br />

prevention<br />

Palagi et al. 2006<br />

48


Fenale--female contact aggression<br />

(freq/fem/20 min test)<br />

Male Policing in pig-tailed<br />

3<br />

2.5<br />

2<br />

1.5<br />

1<br />

0.5<br />

0<br />

macaques<br />

Before During After<br />

0.5 1 1.5 2 2.5 3 3.5<br />

Removal of adult male<br />

Note:<br />

a self-serving<br />

explanation is<br />

plausible-- only one<br />

male per groups, all<br />

benefits accrue to him<br />

… but why don’t others<br />

police?<br />

49<br />

Oswald & Erwin 1976


The Rules of <strong>Social</strong> Behavior<br />

II<br />

Cooperation in relationships<br />

50


Cooperative or altruistic behavior is common in<br />

primate groups<br />

Examples:<br />

- Coalition<br />

formation<br />

- Grooming<br />

- Food sharing<br />

- Communal attacks<br />

or defense<br />

- Alarm calling or<br />

mobbing predator<br />

- Cooperative<br />

hunting<br />

- Communal<br />

nursing<br />

- Helping breeders<br />

rear offspring/<br />

allomothering<br />

51


Classifying social interactions by fitness<br />

Recipient<br />

Actor<br />

GAIN<br />

LOSS<br />

outcome<br />

GAIN LOSS<br />

Cooperation<br />

(mutualism)<br />

Service<br />

(altruism)<br />

Selfish<br />

(exploitation,<br />

competition)<br />

Spite<br />

How can natural selection ever favor service interactions,<br />

or even cooperation if it is risky?<br />

52


Evolutionary explanations of altruistic interactions<br />

among animals<br />

• Group selection<br />

– but free-riders spread within groups much faster than pro-social<br />

groups displace others<br />

• Kin selection<br />

– but does not explain altruism toward non-relatives<br />

• Reciprocity<br />

– Works well for nonhuman primates, especially in the relationship<br />

version<br />

– Also explains exchange of different behaviors, but does not<br />

explain group service<br />

• Costly signaling<br />

– Group service enhances reputation of altruist, who gets repaid<br />

later by other group members<br />

53


I. Altruism toward kin:<br />

Hamilton’s rule<br />

Altruism directed (at least on average) toward relatives is<br />

favored by natural selection if:<br />

B i > C i ⇒ B j × r ij > C i<br />

– where B = benefit, C = cost, r= relatedness, and i and j are individuals<br />

• Relatedness = probability that two animals share a gene on a locus through<br />

descent from a common ancestor<br />

• Calculating relatedness between two individuals i and j:<br />

ri, j = (0.5) L ∑<br />

Where:<br />

Σ = number of paths between i and j,<br />

L = number of steps in a given path<br />

i<br />

j<br />

Here:<br />

1 path, and 2 steps:<br />

(0.5) 2 =0.25<br />

54


Coefficients of relatedness and thresholds for<br />

altruism<br />

Kin category r<br />

Mother – offspring 0.5<br />

Half siblings 0.25<br />

Full siblings 0.5<br />

Aunt – niece 0.125 -<br />

0.25<br />

Cousins 0.0625-<br />

0.125<br />

Grandmothergrandchild<br />

0.25<br />

Benefit/Cost<br />

Ratio<br />

140<br />

120<br />

100<br />

80<br />

60<br />

40<br />

20<br />

1<br />

0.75<br />

b j > 2c i<br />

0.5<br />

Relatedness<br />

b j > 8c i<br />

0.25<br />

0<br />

55


Deployment of<br />

proximity and<br />

cooperative behavior<br />

toward kin in female<br />

macaques<br />

Note-1: curves<br />

steeper for the more<br />

risky altruism<br />

Note-2: cooperation<br />

requiring<br />

competence/skill less<br />

likely to be as kinbiased<br />

Chapais & Bélisle 2004<br />

56


Acts per hour<br />

Females preferentially interact with kin<br />

0.6<br />

0.5<br />

0.4<br />

0.3<br />

0.2<br />

0.1<br />

0<br />

Papio cynocephalus<br />

Nonkin<br />

Kin<br />

Approach Grunt Groom<br />

Silk et al. 1999


Kin selection: kin recognition<br />

1. Spatial distribution: kin is whoever is encountered in a particular location<br />

– By parents: inside the nest<br />

– By offspring: whichever adult is nearby (maternal imprinting)<br />

2. Familiarity rule: kin is whoever has become familiar during early life<br />

– Easily tested by cross-fostering experiments (humans,<br />

nonhuman primates)<br />

3. Phenotype matching: kin is whoever passes matching against innate<br />

template<br />

– Tested by bringing together relatives that were reared apart<br />

– Referents for the phenotypic template:<br />

Self (many insects, vertebrates: dedicated (olfactory) systems, incl.<br />

MHC)<br />

Mother<br />

58<br />

Rendall 2004


Primate mothers rely largely on<br />

familiarity to recognize kin<br />

• Mothers don’t<br />

recognize own<br />

infants right away<br />

• Extended motherinfant<br />

contact<br />

provides cues about<br />

other kin<br />

– (remember switched<br />

babies in hospitals in<br />

humans)<br />

59


But can primates also recognize<br />

Usually, paternity is uncertain:<br />

• Pair-bonded species<br />

– Extra-pair copulations<br />

• One-male groups<br />

paternal kin?<br />

– Incursions from nonresident males, secret<br />

matings with outside males<br />

• Multi-male groups<br />

– females mate with many males<br />

– no long-term pair bonds<br />

But males might use “rules of thumb” to make<br />

pretty good guess about paternity, or do they<br />

recognize kin?<br />

60


Male rules often lead to recognition of their own<br />

infants<br />

• Infanticidal males avoid killing own<br />

infants<br />

• Male baboons are more likely to aid<br />

juveniles born after they arrive in<br />

group than other juveniles<br />

• Male langurs protect infants, but only<br />

if they were present when infant was<br />

conceived and had mated with mother<br />

61


Male baboons protect<br />

their own juvenile<br />

offspring more than<br />

expected<br />

But how do they do it?<br />

Buchan et al. 2003<br />

62


Reciprocal altruism<br />

• If altruists take turns giving and<br />

receiving benefits, reciprocal altruism<br />

can evolve<br />

• Reciprocal altruism requires<br />

1. Frequent opportunities to interact in future<br />

2. Keep track of help given and received<br />

3. Must only help if receive help<br />

• Primates are good candidates for<br />

reciprocal altruism<br />

• Stable social groups, good memories,<br />

flexible behavior<br />

• But how to deal with cheating risk?<br />

63


Grooming in primates<br />

• Original function:<br />

– Hygiene: removal of dirt and parasites<br />

• Associated proximate mechanism:<br />

– Strong preference for being groomed -<br />

pleasurable experience<br />

• Derived function:<br />

– Use grooming as means to appease dominants, or<br />

to pay for receipt of services<br />

• But almost exclusively in Old World Primates only<br />

64


Trading grooming for aid:<br />

experimental confirmation<br />

1. Observe pair grooming<br />

1a. Observe same pair without contact<br />

2. Play back scream of former groomer to<br />

groomee<br />

3. Videotape response<br />

Duration of Response<br />

10<br />

8<br />

6<br />

4<br />

2<br />

0<br />

Prior Grooming No Grooming<br />

Experimental Condition<br />

Seyfarth & Cheney 1984


Market effects on reciprocation and<br />

exchanges of services<br />

Back-and-forth of services not necessarily<br />

symmetric: should depend on leverage<br />

Leverage may vary over time<br />

• One major source of variation is<br />

demographic: number of potential partners<br />

Example baboon baby-grooming<br />

market<br />

66<br />

Barrett & Henzi 2006


Cooperation at group-level<br />

• Group-level cooperation:<br />

– Mutualistic (if all share)<br />

– Problem: free-riding (“collective action<br />

problem”)<br />

67


% "frequent"<br />

B-Gr. enc. (N/d)<br />

100<br />

75<br />

50<br />

25<br />

0<br />

1.2<br />

1.0<br />

0.8<br />

0.6<br />

0.4<br />

0.2<br />

Presbytis entellus<br />

Hrdy (1977)<br />

(n=5)<br />

*<br />

(n=7)<br />

Single-Male Multi-Male<br />

Propithecus tattersalli<br />

Meyers (1993)<br />

Between-group antagonism<br />

SM MM<br />

B-Gr. enc. (N/hr)<br />

B-Gr. enc. (N/hr)<br />

0.06<br />

0.04<br />

0.02<br />

0.00<br />

Southeast Asian Presbytis<br />

van Schaik et al. (1992)<br />

0.10<br />

0.08<br />

0.06<br />

0.04<br />

*<br />

SM MM<br />

Propithecus verreauxii<br />

Richard (1978)<br />

SM MM<br />

Groups with a single male<br />

are more likely to engage in<br />

escalated between-group<br />

encounters<br />

van Schaik 1996<br />

68


Group composition and range overlap<br />

% Low Range Overlap<br />

100.0<br />

75.0<br />

50.0<br />

25.0<br />

0.0<br />

van Schaik 1996<br />

(n=11)<br />

(n=8)<br />

(n=20)<br />

1M, 1F 1M, mF mM, mF<br />

Groups with a single male<br />

and/or a single female are<br />

more likely to defend their<br />

range against neighboring<br />

groups<br />

69


Major exception: chimpanzees<br />

• Communal hunting<br />

• Potentially lethal communal<br />

violence between<br />

communities<br />

– patroling & incursions<br />

70


Hunting in<br />

primates<br />

• Many primates eat meat,<br />

when they can obtain it<br />

– e.g. orangutans catch slow<br />

loris<br />

• However, hunting (chase or pursuit followed by capture) is extremely rare:<br />

–Chimpanzees (very common)<br />

–Capuchin monkeys (common)<br />

–Bonobos (few cases)<br />

• Similarities between chimpanzees and capuchins:<br />

–Mainly males, often together<br />

–Accompanied by food sharing<br />

71


Part III: Socioecology<br />

• Basic principles<br />

– Sex differences in limiting factors<br />

– Group living<br />

– Sex differences in dispersal<br />

• Female strategies:<br />

– Females in large groups<br />

• Competitive regimes<br />

• Alliances and bonding patterns<br />

– Female strategies in small groups<br />

• Competition for membership<br />

– Females without female associates<br />

• Territoriality and infanticide avoidance<br />

• Male strategies:<br />

– Female defense polygyny<br />

– Male alliances & bonding patterns<br />

72


Bateman’s Principle<br />

NB: Species with life-long monogamy tend to have equal<br />

variance for the two sexes<br />

73


Food limits female reproduction:<br />

provisioning and birth rates<br />

Cowlishaw & Dunbar (1999)<br />

74


<strong>Social</strong> strategies predicted<br />

• Females<br />

– Lifetime reproductive success limited by access to<br />

shelter or food<br />

– <strong>Social</strong> strategies should serve to improve access to<br />

safety or food<br />

– Safety best achieved in groups<br />

• Males<br />

– Lifetime reproductive success limited by mating<br />

access to females<br />

– <strong>Social</strong> strategies should serve to improve this<br />

access<br />

– Optimal male strategies depend on female<br />

distribution and behavior<br />

75


The Socioecological Paradigm<br />

(food, shelter)<br />

length +<br />

synchrony of<br />

estrus<br />

(predators, disease)<br />

Resources Risks<br />

Distribution of +<br />

Relationships among<br />

females<br />

Distribution of +<br />

Relationships among<br />

males<br />

Intersexual<br />

Conflict<br />

male-female<br />

Association +<br />

Relationships<br />

76


Major primate predators<br />

Raptors<br />

Harpy Eagle Crowned Hawk-Eagle<br />

77


Major primate predators<br />

Felids<br />

Leopard<br />

78


Grouping and predator detection<br />

van Schaik et al. 1983a<br />

Macaca fascicularis, Ketambe<br />

Larger groups detect<br />

predators at greater<br />

distances<br />

(same found for 3 other<br />

species in same forest)<br />

79


In larger groups, there are more eyes to<br />

detect predators<br />

80


terrestrial<br />

arboreal<br />

Demographic<br />

evidence for link<br />

between grouping<br />

and predation risk<br />

Shultz et al. 2004<br />

Predation rate among African<br />

forest animals, mainly primates<br />

Negatively correlated with<br />

group size<br />

Higher for terrestrial<br />

species than for arboreal<br />

ones<br />

Positively correlated with<br />

group density (encounter<br />

rates, search images and<br />

specialization by predators?)<br />

81


Comparative evidence for link between<br />

Number Females<br />

group size and predation risk<br />

12<br />

10<br />

Nunn & van Schaik 2000<br />

8<br />

6<br />

4<br />

2<br />

0<br />

Low Medium<br />

High<br />

Predation Risk Levels<br />

Contrasts<br />

82


Between-species association reduces<br />

predation risk<br />

• Associating with another species:<br />

ecologically cheaper than<br />

increasing own group +<br />

different species have different<br />

vigilance patterns<br />

provided range use is compatible<br />

• Absent in Madagascar & Southeast<br />

Asia: no large diurnal raptors!<br />

• Often by species with complementary<br />

anti-predation tactics<br />

Diana monkey Red colobus<br />

Ground<br />

predators<br />

Aerial<br />

predators<br />

83


Feeding and grouping: costs<br />

• Incompatible feeding schedules and<br />

strategies<br />

– Different classes may prefer different food<br />

species or patches<br />

– Different classes may prefer feeding bouts of<br />

different lengths<br />

• Feeding competition<br />

– Depends on numbers of individuals and size/<br />

number of patches<br />

84


Costs of grouping: scramble competition<br />

The ‘pushing forward’ effect,..<br />

…leading to longer daily travel distance in<br />

larger groups<br />

van Schaik et al. 1983<br />

85


Group size effect:<br />

stronger when food is scarce<br />

86<br />

Beehner et al. 2006


Integrating benefits and costs:<br />

optimum group size<br />

87


Competition dissected<br />

• Two kinds:<br />

–Scramble<br />

– Contest<br />

• Two levels:<br />

– Within groups<br />

– Between groups<br />

88


The distribution of food, relative to group size,<br />

affects the nature of competition<br />

• Dispersed, low value resources<br />

generate scramble competition<br />

– Food is distributed evenly<br />

– Food items not worth fighting over<br />

– Scramble to get enough food, no direct<br />

competition<br />

• Clumped, valuable resources<br />

generate contest competition<br />

– Resources are scarce & valuable<br />

– Resources are worth fighting over<br />

– Contest access to particular resources<br />

(assuming animals must stay together)<br />

89


I. Females in groups<br />

basic components of competitive regime<br />

WGC- within-group contest<br />

WGS- within-group scramble WGC + WGS<br />

BGC- between-group contest<br />

WGC only<br />

a)- dominance effect only (effect of group<br />

size on mean gain rate is entirely due to<br />

dominance effect)<br />

b)- group-size effect only (no dominance<br />

effect)<br />

c)- only effect is that of group-dominance<br />

relative to other groups<br />

WGS only<br />

BGC only<br />

(c)<br />

90<br />

Janson & van Schaik 1988


van Schaik 1989<br />

Socioecological model for females:<br />

more general cases<br />

91


The model: main predictions<br />

• Strong WG-contest component:<br />

– female dominance ranks, coalitions, philopatry<br />

• Weak WG-contest component:<br />

– no female bonding,<br />

– females are willing to disperse-migrate when<br />

conditions are favorable<br />

• High potential for BG-contest:<br />

– incentives for low-rankers granted by highrankers<br />

to ensure their cooperation<br />

92


Food, competition, and<br />

female social behavior: summary<br />

Distribution<br />

of food<br />

Contest<br />

Competition<br />

Dominance<br />

Hierarchy<br />

Alliances<br />

Valuable<br />

Close<br />

Bonds<br />

Female<br />

Philopatry<br />

93


Testing the model: Decided dominance and<br />

coalitions among females<br />

nepotistic<br />

coalitions<br />

Sterck et al. 1997<br />

+<br />

-<br />

decided dominance relations<br />

+ -<br />

Macaca Theropithecus<br />

most Papio<br />

Cercopithecus aethiops<br />

Cebus<br />

Saimiri sciureus<br />

Lemur catta<br />

Presbytis entellus?<br />

7<br />

1?<br />

0<br />

Eulemur fulvus Propithecus<br />

Saimiri oerstedi verreauxi<br />

Brachyteles<br />

Ateles paniscus<br />

Cercopithecus others<br />

Erythrocebus<br />

Cercocebus atys<br />

Papio ursinus p.p.<br />

Papio hamadryas<br />

Presbytis thomasi<br />

Gorilla g. beringei 15<br />

94


female<br />

philopatry<br />

Sterck et al. 1997<br />

Testing the model:<br />

Philopatry and female bonding<br />

+<br />

-<br />

decided dominance/ coalitions<br />

+ -<br />

Macaca Theropithecus<br />

most Papio<br />

Cercopithecus aethiops<br />

Cebus<br />

Saimiri sciureus<br />

Lemur catta<br />

Cercopithecus others<br />

Erythrocebus<br />

7 2<br />

0<br />

Eulemur fulvus<br />

Saimiri oerstedi<br />

Brachyteles<br />

Papio hamadryas<br />

P. ursinus p.p.<br />

Presbytis thomasi<br />

Gorilla g. beringei<br />

Pan<br />

Colobus<br />

badius<br />

11<br />

95


Testing the model:<br />

two squirrel monkeys<br />

Mitchell, Boinski & van Schaik 1991<br />

96


Explaining tolerant female social<br />

structure in primate groups<br />

• Original model: increased BGC requires restraint<br />

on part of top females<br />

– Sulawesi macaques<br />

• Variant: communal predator defense<br />

– No evidence<br />

• New alternative: communal defense against<br />

coercive males<br />

– No good tests yet<br />

• Non-adaptive alternative: multiple stable<br />

solutions, arbitrary<br />

–?<br />

97


Special case: Small groups<br />

example Thomas’ Langurs<br />

• anatomical adaptation to folivory<br />

• small groups:<br />

– no strong scramble (group size) effects;<br />

– no strong contest (dominance) effects<br />

• single adult male<br />

• females disperse, and most groups have gradual beginning and<br />

end (groups last ca 6.5 years)<br />

• infanticide common (12% of infants born)<br />

– sneak attacks by extra-group males<br />

– after loss of male<br />

Sterck 1995; Steenbeek 1999<br />

98


Group Tenure Phases:<br />

significant differences<br />

EARLY MIDDLE LATE<br />

other mm attracted: m<br />

actively herds ff in mate<br />

defense<br />

ff test new male: seek out<br />

extra-group mm, delay<br />

reproduction until m proves<br />

effective<br />

Steenbeek 2000<br />

stable<br />

m gives up mate defense; “hides”<br />

from other groups, may move<br />

range<br />

ff with infants often harassed by<br />

extra-group mm, avoid them, less<br />

alone, rest lower in canopy<br />

infant mortality twice rate of<br />

middle phase<br />

99


Understanding Thomas’ langur social<br />

organization<br />

Female rules to minimize infanticide risk:<br />

1 Attach to strong new male, and begin to reproduce when he<br />

effectively wards off other males<br />

2 Stay with male until he becomes ineffective protector<br />

3 Attach to next male when without dependent infant<br />

and:<br />

4 Keep groups small (minimizes risk of violent takeovers by extragroup<br />

males)<br />

100


Group size and infanticide risk<br />

Take-over rate per group year<br />

Steenbeek & van Schaik 2001<br />

in Thomas’ langurs<br />

0.6<br />

0.5<br />

0.4<br />

0.3<br />

0.2<br />

0.1<br />

0<br />

mean group<br />

size<br />

1 2 3 4 5 6<br />

Female group size<br />

101


Group size and infanticide risk<br />

in Red Howlers<br />

102


Female social relationships:<br />

Integrating ecological and social drivers<br />

Infanticide risk<br />

Female(s) associated<br />

with male<br />

Predation risk<br />

Females share<br />

protector male(s)<br />

Female<br />

gregariousness<br />

Infanticide limits Ecology limits<br />

Small group<br />

(competition over<br />

membership)<br />

<strong>Social</strong><br />

relationships<br />

Larger groups<br />

(WGS, WGC, BGC)<br />

<strong>Social</strong><br />

relationships<br />

103


Females without female associates:<br />

low predation risk and high vulnerability to competition<br />

• Near-solitary, no territories (+ no permanent<br />

association with a single male)<br />

– Daughters stay in/near natal area (philopatric)<br />

• e.g. orangutans<br />

– Daughters emigrate from natal area (dispersal)<br />

• e.g. chimpanzees<br />

• Solitary and territorial (+ range shared with a male)<br />

– Bonded with male: associated pairs<br />

• e.g. gibbons<br />

– Not-bonded with male: dispersed pairs<br />

• e.g. dwarf lemur<br />

104


Pusey et al 1997<br />

Females (semi-)solitary:<br />

competition, but no alliances<br />

Chimpanzees<br />

(Gombe)<br />

Females ±<br />

philopatric<br />

Females<br />

disperse<br />

105


Origins of pair-living in primates<br />

Otolemur<br />

Galagoides zanzibaricus<br />

Galagoides<br />

Galago<br />

Euoticus<br />

Nycticebus<br />

Loris<br />

Perodicticus<br />

Arctocebus<br />

Phaner<br />

Cheirogaleus<br />

Cheirog. medius<br />

Mirza<br />

Microcebus<br />

Allocebus<br />

Avahi<br />

Indri<br />

Propithecus<br />

Hapalemur<br />

Eulemur<br />

Eulemur rubriventer<br />

Varecia<br />

Lemur<br />

Lepilemur<br />

Daubentonia<br />

Tarsius spectrum<br />

Tarsius pumilus<br />

Tarsius banc. e.a.<br />

Cebuella<br />

Callithrix<br />

Callimico<br />

Leontopithecus<br />

Saguinus<br />

Aotus<br />

Saimiri<br />

Cebus<br />

Callicebus<br />

Pithecia<br />

Chiropotes<br />

Cacajao<br />

Alouatta<br />

Lagothrix<br />

Ateles<br />

Brachyteles<br />

Presbytis<br />

Presbytis potenz.<br />

Semnopithecus<br />

Trachypithecus<br />

Nasalis<br />

Simias<br />

Pygathrix<br />

Rhinopithecus<br />

Colobus<br />

Procolobus<br />

Cercopithecus<br />

Chlorocebus<br />

Erythrocebus<br />

Miopithecus<br />

Allenopithecus<br />

Macaca<br />

Cercocebus<br />

Mandrillus<br />

Lophocebus<br />

Theropithecus<br />

Papio<br />

Hylobates<br />

Pongo<br />

Gorilla<br />

Pan paniscus<br />

Pan trogl.<br />

Pairs<br />

ordered<br />

other<br />

Variable pairs<br />

uniform pairs<br />

106


Evolutionary pathways to pairs<br />

(as reconstructed from phylogenetic tree)<br />

From:<br />

van Schaik & Kappeler 2003<br />

To:<br />

Dispersed<br />

Pairs<br />

Associated<br />

Pairs<br />

Solitary<br />

foragers 4 1<br />

Bisexual<br />

groups 0 12<br />

(Fisher exact test: P = 0.0021)<br />

107


Evolution of obligate pairs<br />

Reconstruction of<br />

historical transitions:<br />

Ancestral State<br />

(not pairs)<br />

Facultative Pairs<br />

Obligate Pairs<br />

Conditions favoring<br />

transitions:<br />

Conditions that produce “failed<br />

polygyny” (e.g. low<br />

productivity)<br />

Conditions that produce<br />

pairs (almost) all the time,<br />

usually because one or both<br />

have preference for pairs<br />

(e.g. minimizing takeover<br />

risk!)<br />

108


Small platyrhines:<br />

males and older immatures as helpers<br />

• Males invest in<br />

offspring<br />

– Carry infants<br />

– Share food with infants<br />

• Males guard females vs<br />

rivals<br />

• Closely bonded to mate<br />

Notes:<br />

Cooperative breeding: caring males<br />

and older immatures not parents<br />

No risk of infanticide by males<br />

tamarin Dusky titi monkeys<br />

109<br />

marmoset


Gibbons and siamangs form pair bonds<br />

and defend territories<br />

Sing duets in territorial displays Females have priority of access<br />

110


• Dispersal:<br />

Dispersal patterns<br />

potential for kin support<br />

– Traditional explanation: response to local density or aggression (not<br />

usually supported)<br />

– Current explanation: avoidance of inbreeding (passive through<br />

dispersal + active through refusal to mate )<br />

• Reduces risk of expressing deleterious mutations<br />

• Reduces homozygosity, and thus increases developmental stability<br />

• Almost always clear sex difference in tendency toward<br />

philopatry:<br />

– Birds: males ⇔ Mammals: females<br />

– Explanation: Kin Support Principle<br />

• Which sex of offspring can be helped most by parents?<br />

– Birds: males defend territory and sons can inherit or move next door<br />

– Mammals: mothers have range and daughters can inherit or move next door<br />

111


Male natal dispersal and female group size<br />

% natal males emigrating<br />

100<br />

75<br />

50<br />

25<br />

0<br />

0 20 40 60 80<br />

number of females in group<br />

P< 0.001<br />

M. fuscata<br />

M. sylvanus<br />

Papio spp<br />

C. aethiops<br />

S. entellus<br />

other spp. (6)<br />

112


Where male philopatry?<br />

1. Difficult to take over a group or a territory, and son may<br />

inherit territory<br />

– Territory: e.g. gibbons, callitrichids<br />

– Group: e.g. gorillas<br />

2. Males form ‘large alliance’ that collectively defends a<br />

large range<br />

Notes:<br />

– e.g. chimpanzees<br />

• in case 1, female philopatry is opportunistic, because<br />

male philopatry is opportunistic (inbreeding avoidance!)<br />

• in case 2, females are forced to become the dispersing<br />

sex (inbreeding avoidance!)<br />

113

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