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Social Systems of Primates
Part I: Introduction: what are primates? Part II: Laws of social behaviour
Competition and conflict regulation Cooperation and relationships
Part III: Socioecology of females Costs and benefits of group living Socioecological Paradigm
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Part I: Introduction: what are primates?
a rather unspecialized (primitive), small to medium-sized mammal
with rather mobile digits with nails (rather than claws) ( arboreal)
with an emphasis on vision relative to smell with forward-pointing eyes, stabilized by the
postorbital bar ( visual predators) with larger than average brain size for its body size which lives longer than average for its body size With a tendency to live in permanent, mixed-sex
groups
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The Primate Syndrome What is a primate?
a rather unspecialized (primitive), small to medium-sized mammal
with rather mobile digits with nails (rather than claws) ( arboreal)
with an emphasis on vision relative to smell with forward-pointing eyes, stabilized by the
postorbital bar ( visual predators) with larger than average brain size for its body size which lives longer than average for its body size With a tendency to live in permanent, mixed-sex
groups
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Primate diversityAfrica Madagascar Americas Asia
N species 79 68 132 78
N genera 21 15 19 16
N families 4 6 5 5
N spp+ subsp
174 70 200 183
% (semi-) terrestrial
35.4 3.0 0.0 20.3
From CI Orlando workshop 2000; Oates (2005)
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Why not study primates?
1. Large animals that live at low densities and live long lives:
Small data sets, even after long study2. Primates are difficult and expensive to keep
in captivity3. Difficult to do experiments on primates,
even if they only involve social manipulations (ethical considerations)
Field data are often correlative In captivity, simple experiments are possible
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Why study primates nonetheless?1. Spectacular social diversity:
Great opportunity to do comparisons to test explanatory frameworks for primate (and human) behavior
2. Social complexity unmatched among mammals Especially social relationships and behavioral dynamics
in them3. Easy to observe in detail:
Most are diurnal, visually oriented, can be habituated to observers
4. Humans are primates as well! Phylogeny matters for understanding a species behavior
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Humans are a great ape, split off from African great apes ca 6-8 Mya
14 8 6.5 2
Human
Jeffry Oonk
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Primate specializations: hands and brains
Features of hands (and feet) grasping hands sensitive finger tips flat nails on fingers & toes opposable big toe (except us)
galago
rhesus macaque
chimpanzee
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Primates are brainy mammals
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Variation in relative brain size among primates
MacLeod 2004
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Hypothesized selective advantages of greater cognitive abilities
Social strategizing (Machiavellian intelligence)
Spatio-temporal distribution of resources (spatial memory, mental maps)
Acquiring hidden or protected foods: extraction, processing (Technical intelligence)
Arboreal clambering
Byrne & Whiten 1988
Milton 1988
Parker & Gibson 1977; Byrne 1997
Povinelli & Cant 1995
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A very popular idea: Machiavellian intelligence
Barrett, Henzi & Dunbar 2003
But:Uncertainty about best scaling method (body size effect)Is group size best proxy for social complexity?
apes monkeys prosimians
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Difficulties with the Machiavellian intelligence hypothesis
Some major contrasts in intelligence are not explainedSocial complexity in great apes not greater than in many monkeys
versus
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Other difficulties with the social strategizing hypothesis
Some major contrasts in intelligence are not explainedWhy are some lemurs not just as smart as monkeys?
versus
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Other difficulties cannot distinguish between the benefits
whenever cognitive abilities are domain-general
Impossible to disentangle selective agent
selects forimproves ability to deal withsocial
challenges
improvedcognitive skills
spatio-temporal food distr.
feeding challenges
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Characterizing primate life histories
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Important primate featuresFeatures of life history
Small litters Long mother-
infant bond Slow
development Long life span
Features of social life
Almost always in groups Groups tend to be stable
(permanent) Groups contain adults of
both sexes (mixed-sex, or bisexual groups)
Complex social behavior
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Implications of the primate peculiarities
Arboreality slow life history Diurnality large, mobile groups Hands dextrous foraging Relative brain size ecological and social cognition Life history time for learning, group stability, social
relationships Infant carrying nomadism in ranging, risk of infanticide
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Lorises & Galagos
Anthropoids
Primate Primate RadiationsRadiations
Tarsiers
Lemurs
Prosimians
Strepsirrhini
Haplorrhini
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Modern prosimian primates
Nycticebus(Lorisoidea)
Eulemur(Lemuroidea)
Tarsius(Tarsioidea)
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Modern anthropoid primates
New World monkeys
(Ceboidea)Apes
(Hominoidea)
Old World monkeys(Cercopithecoidea)
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Conditions favoring evolution of complex social behavior & social cognition
1. Gregariousness= group living: opportunities for frequent social
interactions 2. Individual recognition (= Stable
groups): allows for social relationships
3. Slow life history: allows establishment of long-term
relationships4. Diurnal activity period:
allows vocal + visual communication, hence differentiation of messages to targets
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The importance of phylogeny
Prosimians versus anthropoids
Old World Primates versus New World Primates
Great apes versus monkeys
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Lorises & Galagos
Anthropoids
Primate Primate RadiationsRadiations
Tarsiers
Lemurs
Prosimians
Strepsirrhini
Haplorrhini
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Shared-Derived Traits of Anthropoids(relative to tarsiers + strepsirhines)
Far more likely to be diurnal And therefore more likely to range widely
Larger body size (except for the extinct lemurs) Always carrying offspring
More nomadic, slower development Greater risk of infanticide
Reduced reliance on olfaction and increased reliance on vision Visual communication creates more opportunities for complex
sociality Larger brain size relative to body size
accompanied by superior cognitive abilities Systematically gregarious in mixed-sex groups
Usually accompanied by sexual dimorphism
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Modes of infant care
Affects:- range use, mobility: central place foraging vs nomadism- reproductive biology, vulnerability to infanticide: male-female association
cache carry
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Activity period and gregariousness in primates
van Schaik, unpubl. N.B. Cathemeral included in diurnal
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Social life of anthropoids
Prosimians not as socially complex as anthropoids
(even if gregarious)
versus
Extensive coalitions only in anthropoids
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Anthropoids: heritage of visual communication- facial expressions
QuickTime and aTIFF (LZW) decompressor
are needed to see this picture.
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Shared-Derived Traits of Old World Primates (relative to Plathyrhines)
More likely to be terrestrial More likely to have large body size, and hence Greater sexual dimorphism in size and weapons
More evidence for sexual harassment and forced matings by males
More systematically trichromatic vision Lower reliance on olfaction (no scent-marking) Longer gut retention time
Better able to digest high-fiber diets
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Ecological contrasts between NW-OW monkeys
New World Monkeys
Old-World Monkeys
Gut Retention Time
Short Long
Home range area per group weight
Larger Smaller
Group sizes Mainly small Often large
Prevalence of pairs
High (incl. coop breeding)
Very low
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Shared-Derived Traits of Great Apes(relative to Old World Monkeys)
Larger body size Less vulnerable to predation (provided in trees) More vulnerable to competition (nutritious foods)
Larger brain size & superior cognitive abilities e.g. mirror self-recognition; theory of mind Far greater tool use abilities
Sociality despite fission-fusion: Male-female association and female sexual activity as much as
ecologically possible Tendency toward social tolerance in most dyads, incl. food sharing,
cooperation among non-relatives Relatively very slow life history, including long periods of
development and learning Nest-building
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Patterns in primate socioecology(mainly based on Clutton-Brock & Harvey 1977a, b)
Body size: Nocturnal species tend to be small (up to ca 1-2 kg), and live in small social
units, as compared to diurnal ones; Insectivores tend to be smaller than frugivores which tend to be smaller than
folivores; Terrestrial species tend to be bigger than arboreal ones; Larger species tend to show increased sexual dimorphism in body size.
Group size: Insectivores are often solitary; frugivorous groups tend to be larger and more
wide-ranging than folivorous ones; Species living in open savanna tend to live in larger groups than forest-living
species; Bigger species tend to live in larger groups; Group size has strong effects on range use: daily travel distance, home range
area.
Population density: Larger animals tend to live at lower densities; Densities of folivores> frugivores > insectivores.
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Part II: The Rules of Social Behavior
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Social definitions used in this course
Sociality = involving interactions with known conspecifics (note: group-living is not required, but individual recognition is)
Social organization = spatial distribution of individuals = (composition of the social units) + dispersal mode (which sex)
Social relationship = reflection of the history of interactions between two individuals with respect to their content, quality, and patterning over time, and is a variable that allows us to predict future interactions
Social structure = structure of the social relationships, incl. bonds, of individuals.
Social system = social organization + social structure Social unit = a concrete case of a social system Mating system = N of males, N of females mating in a given
social unit
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Living in Groups
Fundamental problem: beneficial
General benefit from being gregarious Allows specific cooperative endeavors benefiting all
individuals Costly
Living in close proximity increases competition over access to limiting resources
Fundamental conclusion: All group life inevitably involves both competition
and cooperation
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Classifying social interactions by fitness outcome
Recipient
Actor GAIN LOSS
GAINCooperation(mutualism)
Selfish(exploitation, competition)
LOSSService
(altruism)Spite
Virtually all social behavior in animals contains elements of both competition and cooperation
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Competition & Aggression
Competition ensues when there is not enough of a critical resource to satisfy the needs of each individual (= conflict of interest) i.e. increased access to this resource increases fitness
Two possible responses to competition, depending on benefits of excluding others (which is costly): Contest: exclusion from resource possible (also interference
competition) Scramble: exclusion from resource impossible or too
expensive relative to value (also exploitation competition) Successful contest requires aggression
Aggression is instrumental, not pathological
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Dominance
Critical precondition: individual recognition + repeated interactions
Repeated interactions: no escalation needed --displays and signals A is dominant to B if A can predictably provoke submissive
behaviors in B or B will spontaneously signal subordinate status
Cheap and effective way of dealing with conflict of interest (when there is also some overlap in interests!)
Dominance is a feature of a relationship, not of an individual same animal can be dominant to some, subordinate to others
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More on dominance
Dominance in space: territories Dominance is linked to spatial position
Dominance in groups Independent of spatial position or context
How does dominance produce increased fitness? Exclusion from limiting resources Exploitation of subordinates work (e.g. forced grooming, ) Reproductive inhibition (adaptation of subordinate!) Harassment/ killing of subordinates (where no valuable
relationship)
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Dominance hierarchies
Dominance hierarchies are traits of groups Features:
Linearity % of dyads that deviate from linearity (linked to uni-
directionality within dyads) Linearity expected if dyadic dominance is reflection of FA
Steepness Reduction in access to critical resource for each rank down
Degree of correlation with kinship (nepotistic hierarchy)
Relatives cluster together, as a result of coalitions Stability
Especially where co-residing relatives provide mutual support Often upheld by third parties (maintenance of status quo )
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Dominance and nepotism among female primates
Nepotistic: rank inheritance: daughters, once adult, rank directly below mothers.Ranks stableGenerally, higher-ranking matrilines out-reproduce others
Individualistic: no rank inheritance.
Ranks unstable, often reverse age-graded, with youngest mature females
on top.Little variation among
females in lifetime reproductive success
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strictdespotic
dominance style
relaxedtolerant
aggression
interventions in conflicts
de-escalation mechanisms
reconciliation
tolerance of proximity
kin bias in the above variables
respect for possession
Observed features varying in relation to dominance styles
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dom
inan
ce s
tyle
Macaca mulatta SBT subordinate
Macaca fascicularis SBT subordinate
Macaca nemestrina SBT subordinate
Macaca arctoides mock-bite dominant
Macaca sylvanus RM threat dominant
Theropith. gelada RM threat dominant
Macaca silenus none
Macaca tonkeana none
strict
relaxed Preuschoft & van Schaik 2000
Interspecific variation in dominance style
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Conflict Regulation(friends and non-friends alike)
Dyadic, affiliative: Reconciliation Conflict anticipation: prevent escalation
In zoos, often pronounced peak in grooming preceding feeding time Dyadic, agonistic:
Dominance itself! Redirection, aimed disproportionately at kin of the former opponent (Aureli) Retribution (attack former opponent at later moment- not possible in
despotic species) Opportunistic joining of attacks on former opponent (winner support)
Polyadic policing behavior: neutral interventions, supporting fights
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Conflict RegulationReconciliation
Selective (partner-specific) affiliative social contact soon after a conflict (sooner than expected from baseline or matched control observations)
Expected to lead to reduction of anxiety and reoccurrence aggression
Expected only among partners with a valuable relationship
Aureli, de Waal
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Evidence for post-conflict
friendly reunions and for selective
attraction between former
opponents
Aureli et al. 2002
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48Palagi et al. 2006
Bonobo:Conflict
prevention
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Male Policing in pig-tailed macaques
0
0.5
1
1.5
2
2.5
3
Fena
le--
fem
ale
cont
act a
ggre
ssio
n(fr
eq/fe
m/2
0 m
in te
st)
0.5 1 1.5 2 2.5 3 3.5
Removal of adult male
Before During After
Oswald & Erwin 1976
Note:a self-serving explanation is plausible-- only one male per groups, all benefits accrue to him
but why dont others police?
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The Rules of Social Behavior II
Cooperation in relationships
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Cooperative or altruistic behavior is common in primate groups
Examples:- Coalition formation- Grooming- Food sharing- Communal attacks or defense- Alarm calling or mobbing predator- Cooperative hunting- Communal nursing- Helping breeders rear offspring/ allomothering
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Classifying social interactions by fitness outcome
Recipient
Actor GAIN LOSS
GAINCooperation(mutualism)
Selfish(exploitation, competition)
LOSSService
(altruism)Spite
How can natural selection ever favor service interactions, or even cooperation if it is risky?
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Evolutionary explanations of altruistic interactions among animals
Group selection but free-riders spread within groups much faster than pro-social
groups displace others Kin selection
but does not explain altruism toward non-relatives Reciprocity
Works well for nonhuman primates, especially in the relationshipversion
Also explains exchange of different behaviors, but does not explain group service
Costly signaling Group service enhances reputation of altruist, who gets repaid
later by other group members
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I. Altruism toward kin: Hamiltons rule
Altruism directed (at least on average) toward relatives is favored by natural selection if:
where B = benefit, C = cost, r= relatedness, and i and j are individuals
Bi > Ci B j rij > Ci
Relatedness = probability that two animals share a gene on a locus through descent from a common ancestor Calculating relatedness between two individuals i and j:
ri, j = (0 .5)L
Where: = number of paths between i and j,L = number of steps in a given path
j
i
Here: 1 path, and 2 steps: (0.5)2=0.25
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Coefficients of relatedness and thresholds for altruism
Kin category r
Mother offspring 0.5
Half siblings 0.25
Full siblings 0.5
Aunt niece 0.125 -0.25
Cousins 0.0625-0.125
Grandmother-grandchild
0.2500.250.50.751
Relatedness
Benefit/Cost Ratio
20
40
60
80
100
120
140
bj > 2cibj > 8ci
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Deployment of proximity and
cooperative behavior toward kin in female
macaques
Chapais & Blisle 2004
Note-1: curves steeper for the more risky altruism
Note-2: cooperation requiring competence/skill less likely to be as kin-biased
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Females preferentially interact with kin
Papio cynocephalus
Approach Grunt Groom0
0.1
0.2
0.3
0.4
0.5
0.6
Act
s pe
r hou
r NonkinKin
Silk et al. 1999
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Kin selection: kin recognition
1. Spatial distribution: kin is whoever is encountered in a particular location By parents: inside the nest By offspring: whichever adult is nearby (maternal imprinting)
2. Familiarity rule: kin is whoever has become familiar during early life Easily tested by cross-fostering experiments (humans,
nonhuman primates)3. Phenotype matching: kin is whoever passes matching against innate
template Tested by bringing together relatives that were reared apart Referents for the phenotypic template:
Self (many insects, vertebrates: dedicated (olfactory) systems, incl. MHC)Mother
Rendall 2004
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Primate mothers rely largely on familiarity to recognize kin
Mothers dont recognize own infants right away
Extended mother-infant contact provides cues about other kin (remember switched
babies in hospitals in humans)
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But can primates also recognize paternal kin?
Usually, paternity is uncertain: Pair-bonded species
Extra-pair copulations One-male groups
Incursions from nonresident males, secret matings with outside males
Multi-male groups females mate with many males no long-term pair bonds
But males might use rules of thumb to make pretty good guess about paternity, or do they recognize kin?
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Male rules often lead to recognition of their own infants
Infanticidal males avoid killing own infants
Male baboons are more likely to aid juveniles born after they arrive in group than other juveniles
Male langurs protect infants, but only if they were present when infant was conceived and had mated with mother
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Male baboons protect their own juvenile
offspring more than expected
Buchan et al. 2003
But how do they do it?
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Reciprocal altruism
If altruists take turns giving and receiving benefits, reciprocal altruism can evolve
Reciprocal altruism requires1. Frequent opportunities to interact in future2. Keep track of help given and received3. Must only help if receive help
Primates are good candidates for reciprocal altruism Stable social groups, good memories,
flexible behavior But how to deal with cheating risk?
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Grooming in primates
Original function: Hygiene: removal of dirt and parasites
Associated proximate mechanism: Strong preference for being groomed -
pleasurable experience Derived function:
Use grooming as means to appease dominants, or to pay for receipt of services
But almost exclusively in Old World Primates only
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Trading grooming for aid: experimental confirmation
0
2
4
6
8
10
Prior Grooming No Grooming
Experimental Condition
Dur
atio
n of
Res
pons
e
Seyfarth & Cheney 1984
1. Observe pair grooming1a. Observe same pair without contact2. Play back scream of former groomer to groomee
3. Videotape response
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Market effects on reciprocation and exchanges of services
Back-and-forth of services not necessarily symmetric: should depend on leverageLeverage may vary over time
One major source of variation is demographic: number of potential partners
Example baboon baby-grooming market
Barrett &
Henzi2006
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Cooperation at group-level
Group-level cooperation: Mutualistic (if all share) Problem: free-riding (collective action
problem)
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0
25
50
75
100
% "
freq
uent
"
Single-Male Multi-Male
(n=5)
(n=7)
Presbytis entellusHrdy (1977)
0.00
0.02
0.04
0.06
SM MM
Southeast Asian Presbytisvan Schaik et al. (1992)
* *
B-G
r. en
c. (N
/hr)
0.2
0.4
0.6
0.8
1.0
1.2
B-G
r. en
c. (N
/d)
SM MM
Propithecus verreauxiiRichard (1978)
Propithecus tattersalliMeyers (1993)
0.04
0.06
0.08
0.10
B-G
r. en
c. (N
/hr)
SM MM
Groups with a single male are more likely to engage in escalated between-group encounters
Between-group antagonism
van Schaik 1996
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0.0
25.0
50.0
75.0
100.0
% L
ow R
ange
Ove
rlap
1M, 1F 1M, mF mM, mF
(n=11)
(n=8)
(n=20)
Group composition and range overlap
Groups with a single male and/or a single female are more likely to defend their range against neighboring groups
van Schaik 1996
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Major exception: chimpanzees
Communal hunting Potentially lethal communal
violence between communities patroling & incursions
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Hunting in primates
Many primates eat meat, when they can obtain it e.g. orangutans catch slow
loris
However, hunting (chase or pursuit followed by capture) is extremely rare:Chimpanzees (very common)Capuchin monkeys (common)Bonobos (few cases)
Similarities between chimpanzees and capuchins:Mainly males, often togetherAccompanied by food sharing
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Part III: Socioecology Basic principles
Sex differences in limiting factors Group living Sex differences in dispersal
Female strategies: Females in large groups
Competitive regimes Alliances and bonding patterns
Female strategies in small groups Competition for membership
Females without female associates Territoriality and infanticide avoidance
Male strategies: Female defense polygyny Male alliances & bonding patterns
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Batemans Principle
NB: Species with life-long monogamy tend to have equal variance for the two sexes
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Food limits female reproduction: provisioning and birth rates
Cowlishaw & Dunbar (1999)
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Social strategies predicted Females
Lifetime reproductive success limited by access to shelter or food
Social strategies should serve to improve access to safety or food
Safety best achieved in groups Males
Lifetime reproductive success limited by mating access to females
Social strategies should serve to improve this access
Optimal male strategies depend on female distribution and behavior
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The Socioecological Paradigm
Distribution of +Relationships among
males
length + synchrony of
estrus
IntersexualConflict
male-femaleAssociation + Relationships
Resources Risks
Distribution of +Relationships among
females
(predators, disease)(food, shelter)
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Major primate predatorsRaptors
Harpy Eagle Crowned Hawk-Eagle
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Major primate predatorsFelids
Leopard
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Grouping and predator detection
van Schaik et al. 1983a
Larger groups detect predators at greater distances(same found for 3 other species in same forest)
Macaca fascicularis, Ketambe
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In larger groups, there are more eyes to detect predators
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Predation rate among African forest animals, mainly primates
Negatively correlated with group sizeHigher for terrestrial species than for arboreal onesPositively correlated with group density (encounter rates, search images and specialization by predators?)
Shultz et al. 2004
terrestrial
arboreal
Demographic evidence for link between grouping and predation risk
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Comparative evidence for link between group size and predation risk
0
2
4
6
8
10
12
Num
ber F
emal
es
ContrastsHighLow Medium
Predation Risk Levels
Nunn & van Schaik 2000
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Between-species association reduces predation risk
Diana monkey Red colobus
Ground predators
Aerialpredators
Associating with another species:ecologically cheaper than
increasing own group + different species have different
vigilance patternsprovided range use is compatible
Absent in Madagascar & Southeast Asia: no large diurnal raptors!
Often by species with complementary anti-predation tactics
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84
Feeding and grouping: costs
Incompatible feeding schedules and strategies Different classes may prefer different food
species or patches Different classes may prefer feeding bouts of
different lengths Feeding competition
Depends on numbers of individuals and size/ number of patches
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85van Schaik et al. 1983
The pushing forward effect,..
leading to longer daily travel distance in larger groups
Costs of grouping: scramble competition
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86
Group size effect:stronger when food is scarce
Beehner et al. 2006
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87
Integrating benefits and costs:optimum group size
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88
Competition dissected
Two kinds: Scramble Contest
Two levels: Within groups Between groups
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The distribution of food, relative to group size, affects the nature of competition
Dispersed, low value resources generate scramble competition Food is distributed evenly Food items not worth fighting over Scramble to get enough food, no direct
competition
Clumped, valuable resources generate contest competition Resources are scarce & valuable Resources are worth fighting over Contest access to particular resources(assuming animals must stay together)
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90Janson & van Schaik 1988
WGC only
WGC + WGSBGC only
WGS only
WGC- within-group contestWGS- within-group scrambleBGC- between-group contest
a)- dominance effect only (effect of group size on mean gain rate is entirely due to dominance effect)b)- group-size effect only (no dominance effect)c)- only effect is that of group-dominancerelative to other groups
I. Females in groupsbasic components of competitive regime
(c)
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Socioecological model for females:more general cases
van Schaik 1989
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92
The model: main predictions
Strong WG-contest component: female dominance ranks, coalitions, philopatry
Weak WG-contest component: no female bonding, females are willing to disperse-migrate when
conditions are favorable High potential for BG-contest:
incentives for low-rankers granted by high-rankers to ensure their cooperation
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Food, competition, and female social behavior: summary
Dominance Hierarchy
Contest Competition
Distributionof food
AlliancesValuable
CloseBonds
FemalePhilopatry
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94
+
-
+ -Macacamost PapioCercopithecus aethiopsCebusSaimiri sciureusLemur catta
Cercopithecus othersErythrocebus
Papio hamadryas
Saimiri oerstedi
Presbytis thomasi
Papio ursinus p.p.
Eulemur fulvus
BrachytelesAteles paniscus
Gorilla g. beringei
Theropithecus
7
15
Cercocebus atys
Propithecusverreauxi
0
Presbytis entellus?
1?
Testing the model: Decided dominance and coalitions among females
Sterck et al. 1997
decided dominance relations
nepotistic coalitions
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95
+
-
+ -Macacamost PapioCercopithecus aethiopsCebusSaimiri sciureusLemur catta
Cercopithecus others
Erythrocebus
Papio hamadryas
Saimiri oerstedi
Presbytis thomasiP. ursinus p.p.
Eulemur fulvus
Brachyteles
Gorilla g. beringeiPan
Theropithecus
7 2
110
Colobusbadius
decided dominance/ coalitions
Testing the model:Philopatry and female bonding
femalephilopatry
Sterck et al. 1997
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96
Testing the model:two squirrel monkeys
Mitchell, Boinski & van Schaik 1991
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97
Explaining tolerant female social structure in primate groups
Original model: increased BGC requires restraint on part of top females Sulawesi macaques
Variant: communal predator defense No evidence
New alternative: communal defense against coercive males No good tests yet
Non-adaptive alternative: multiple stable solutions, arbitrary ?
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Special case: Small groupsexample Thomas Langurs
anatomical adaptation to folivory small groups:
no strong scramble (group size) effects; no strong contest (dominance) effects
single adult male females disperse, and most groups have gradual beginning and
end (groups last ca 6.5 years)
infanticide common (12% of infants born) sneak attacks by extra-group males after loss of male
Sterck 1995; Steenbeek 1999
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99
Group Tenure Phases: significant differences
EARLY MIDDLE LATE
stable
other mm attracted: m actively herds ff in mate defense
ff test new male: seek out extra-group mm, delay reproduction until m proves effective
m gives up mate defense; hidesfrom other groups, may move range
ff with infants often harassed by extra-group mm, avoid them, less alone, rest lower in canopy
infant mortality twice rate of middle phase
Steenbeek 2000
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Understanding Thomas langur social organization
Female rules to minimize infanticide risk:
1 Attach to strong new male, and begin to reproduce when he effectively wards off other males
2 Stay with male until he becomes ineffective protector3 Attach to next male when without dependent infant
and:4 Keep groups small (minimizes risk of violent takeovers by extra-
group males)
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101
Group size and infanticide risk in Thomas langurs
0
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-
102
Group size and infanticide risk in Red Howlers
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103
Female social relationships: Integrating ecological and social drivers
Infanticide risk
Female(s) associated with male
Female gregariousness
Females share protector male(s)
Larger groups(WGS, WGC, BGC)
Social relationships
Predation risk
Infanticide limits Ecology limits
Small group
Social relationships
(competition over membership)
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104
Females without female associates: low predation risk and high vulnerability to competition
Near-solitary, no territories (+ no permanent association with a single male) Daughters stay in/near natal area (philopatric)
e.g. orangutans
Daughters emigrate from natal area (dispersal) e.g. chimpanzees
Solitary and territorial (+ range shared with a male) Bonded with male: associated pairs
e.g. gibbons
Not-bonded with male: dispersed pairs e.g. dwarf lemur
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105Pusey et al 1997
Females (semi-)solitary:competition, but no alliances
Chimpanzees(Gombe)
Females philopatric
Females disperse
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106
Origins of pair-living in primatesO
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107
Evolutionary pathways to pairs(as reconstructed from phylogenetic tree)
To:
From:
DispersedPairs
AssociatedPairs
Solitaryforagers 4 1
Bisexualgroups 0 12
(Fisher exact test: P = 0.0021)van Schaik & Kappeler 2003
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108
Evolution of obligate pairs
Reconstruction of historical transitions:
Conditions favoring transitions:
Ancestral State(not pairs)
Facultative Pairs
Conditions that produce failed polygyny (e.g. low productivity)
Obligate Pairs
Conditions that produce pairs (almost) all the time, usually because one or both have preference for pairs (e.g. minimizing takeover risk!)
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109
Small platyrhines: males and older immatures as helpers
Males invest in offspring Carry infants Share food with infants
Males guard females vsrivals
Closely bonded to mate
marmosettamarin Dusky titi monkeys
Notes:Cooperative breeding: caring males and older immatures not parentsNo risk of infanticide by males
-
110
Gibbons and siamangs form pair bonds and defend territories
Sing duets in territorial displays Females have priority of access
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111
Dispersal patterns potential for kin support
Dispersal: Traditional explanation: response to local density or aggression (not
usually supported) Current explanation: avoidance of inbreeding (passive through
dispersal + active through refusal to mate ) Reduces risk of expressing deleterious mutations Reduces homozygosity, and thus increases developmental stability
Almost always clear sex difference in tendency toward philopatry: Birds: males Mammals: females Explanation: Kin Support Principle
Which sex of offspring can be helped most by parents? Birds: males defend territory and sons can inherit or move next door Mammals: mothers have range and daughters can inherit or move next door
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112
0
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number of females in group
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C. aethiops
Papio spp
M. sylvanus
M. fuscata
other spp. (6)
Male natal dispersal and female group size
P< 0.001
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113
Where male philopatry?1. Difficult to take over a group or a territory, and son may
inherit territory Territory: e.g. gibbons, callitrichids Group: e.g. gorillas
2. Males form large alliance that collectively defends a large range
e.g. chimpanzees
Notes: in case 1, female philopatry is opportunistic, because
male philopatry is opportunistic (inbreeding avoidance!) in case 2, females are forced to become the dispersing
sex (inbreeding avoidance!)
Social Systems of PrimatesPart I: Introduction: what are primates? The Primate SyndromePrimate diversityWhy not study primates?Why study primates nonetheless?Humans are a great ape, split off from African great apes ca 6-8 MyaPrimate specializations: hands and brainsPrimates are brainy mammalsVariation in relative brain size among primatesHypothesized selective advantages of greater cognitive abilitiesA very popular idea: Machiavellian intelligenceOther difficulties cannot distinguish between the benefitsCharacterizing primate life historiesImportant primate features Implications of the primate peculiaritiesModern prosimian primatesModern anthropoid primatesConditions favoring evolution of complex social behavior & social cognitionThe importance of phylogenyShared-Derived Traits of Anthropoids (relative to tarsiers + strepsirhines)Modes of infant careActivity period and gregariousness in primatesAnthropoids: heritage of visual communication- facial expressionsShared-Derived Traits of Old World Primates (relative to Plathyrhines)Ecological contrasts between NW-OW monkeysShared-Derived Traits of Great Apes(relative to Old World Monkeys)Patterns in primate socioecology(mainly based on Clutton-Brock & Harvey 1977a, b)Part II: The Rules of Social Behavior Social definitions used in this courseLiving in GroupsClassifying social interactions by fitness outcomeCompetition & AggressionDominanceMore on dominanceDominance hierarchiesDominance and nepotism among female primatesConflict Regulation(friends and non-friends alike)Conflict RegulationReconciliationEvidence for post-conflict friendly reunions and for selective attraction between former opponentsMale Policing in pig-tailed macaquesThe Rules of Social Behavior II Cooperation in relationshipsCooperative or altruistic behavior is common in primate groups Classifying social interactions by fitness outcomeEvolutionary explanations of altruistic interactions among animalsI. Altruism toward kin: Hamiltons ruleCoefficients of relatedness and thresholds for altruismDeployment of proximity and cooperative behavior toward kin in female macaquesFemales preferentially interact with kinKin selection: kin recognitionPrimate mothers rely largely on familiarity to recognize kin But can primates also recognize paternal kin?Male rules often lead to recognition of their own infantsMale baboons protect their own juvenile offspring more than expectedReciprocal altruismGrooming in primatesTrading grooming for aid: experimental confirmation Market effects on reciprocation and exchanges of servicesCooperation at group-levelMajor exception: chimpanzeesHunting in primatesPart III: SocioecologyBatemans PrincipleFood limits female reproduction: provisioning and birth ratesSocial strategies predictedThe Socioecological ParadigmMajor primate predatorsMajor primate predatorsGrouping and predator detectionIn larger groups, there are more eyes to detect predatorsComparative evidence for link between group size and predation riskBetween-species association reduces predation riskFeeding and grouping: costsCosts of grouping: scramble competitionGroup size effect:stronger when food is scarceIntegrating benefits and costs:optimum group sizeCompetition dissectedThe distribution of food, relative to group size, affects the nature of competitionI. Females in groupsbasic components of competitive regimeSocioecological model for females:more general casesThe model: main predictionsFood, competition, and female social behavior: summaryTesting the model:two squirrel monkeysExplaining tolerant female social structure in primate groupsSpecial case: Small groupsexample Thomas LangursGroup Tenure Phases: significant differencesUnderstanding Thomas langur social organizationGroup size and infanticide risk in Red HowlersFemales without female associates: low predation risk and high vulnerability to competitionFemales (semi-)solitary:competition, but no alliancesOrigins of pair-living in primatesSmall platyrhines: males and older immatures as helpersGibbons and siamangs form pair bonds and defend territoriesDispersal patterns potential for kin supportWhere male philopatry?