Primatology - group living + sociality

Competition for food, mates, space
Disease transmission
Infanticide

Searching for food
Reduced predation risks - warn with calls, confuse predators with large numbers
Competition with other groups
Mating opportunities
Friendship - social bonding
Social learning opportunities

Uses heuristic approach - aim is to explain all forms of primate social organisations
Models stem from natural history, improved by concepts of:
- Inclusive fitness
- Selfish herd
- Parental investment
Aim is to establish causal relationships between food distribution, predation, mating strategies, social organisations and relationships

Comparative socioecology
Ecological model with predation
Within and between groups food competition determine female social relationships
Competition:
Contest OR scramble
Found there was a network between food distribution, mating, predation and types of relationships that female primates formed

-> linear hierarchies
-> dominance systems
-> philopatry
-> nepotistic relationships (family)
-> skewed resource distribution
-> smaller groups

-> no clear dominance
-> even resource distribution
-> egalitarian relationships
-> dispersal
-> larger groups

Type A - females develop individualistic, egalitarian (equal) dominance hierarchies, no dominance
Type B - females develop nepotistic, despotic (absolute power and authority) dominance hierarchies, some primates rule over others in a group
Type C - philopatric females, egalitarian hierarchies, return to same food sources repeatedly
Type D - nepotistic (favoritism based on kinship), egalitarian hierarchies, 2 groups fighting over same resources

Scramble competition within group (enough resources)

Contest competition within groups
Not enough resources
Decisions about who gets food

High predation pressure + scramble competition within group
High predation pressure + contest competition between groups
(larger groups suffer less from predation than smaller groups)

Low predation pressure + high pop. density + contest competition between groups
Resources given equally within groups

Effect of infanticide

New labels to van Schaik's 1989 model
Added relationships between females and males within groups
Type A = Dispersal-Egalitarian
Type B = Resident-Nepotistic
Type C = Resident-Egalitarian
Type D = Resident-Neoptistic-Tolerant

1991
2 species with similar group sizes and predation risk
1 species = high within-group contest competition:
- Linear dominance hierarchies
- Female philopatry
1 species = low within-group contest competition:
- No dominance hierarchies
- Female dispersal

Scramble competition within group should support large group sizes
BUT observed = relatively small

Patch depletion limits group size expansion
Female reproductive success better in intermediate group sizes
Females disperse to avoid infanticide by males, keeping group sizes low

Species of colobus
Indications of dispersal-egalitarian (type A):
- No female coalitions over food
- Female dispersal
BUT more female-female affiliation than male-female affilitation: indicates resident behaviour
Potentially a response to the risk of infanticide

Ruiter 1986
Capuchins
Small groups = increased time spent vigilant
Small groups = occupy higher strata (reduced predation risk)
Large groups = occupy lower strata

Watts 1990
Females associate with likely father
Females transfer subsequent or simultaneous to infanticide
Females join with infanticidal male in most cases
Group size highly variable within a given year due to female migration

+ Appropriate for explaining primate social systems
- Incosistencies in relating competition, dispersal and social relationships
- Folivore paradox

Biological process where individuals / groups act together

Mutualism:
Different species
Both benefit
Group living:
Same species
Common benefit

Sociality
Anti-predation
Foraging efficiency/hunting success
Thermoregulation
Territorial defence
Parental care and cooperative breeding

Cooperation involves behaviours that come at a cost for the cooperator

Kin selection - Smith 1964
Reciprocal altruism - Trivers 1971
Group selection - Wilson 1975

Behavioural favouring of close genetic relatives
Cooperation with family members
If receiver of altruism shares certain percentage of actor's genotype, the actor also benefits from altruism
Individuals increase their inclusive fitness by being altruistic to their relatives (share genes with)

Cooperating with those who cooperate with the individual
If costs low, benefits high = altruistic alleles can spread by mutually promoting their success
Altruistic acts reciprocated
Form long term social relationships

+ Exchange of commodities
+ Grooming
+ Food sharing
+ Agnositic suppport
- Risk of aggression

Most important way to form friendships
Reduces stress and parasitic load
Subordinates groom dominant
Market commodity (can be exchanged aginst other favours eg. protection/tolerance)
Can be reciprocated

2011
More tolerance over food after reciprocal grooming
More grooming after being tolerant with food resources

Female baboons more social with kin than non-kin have offspring that are more likely to survive (Silk 2009)
Female baboons with stable relationships live longer (Silk 2010)
Subordinate, male chimps more likely to sire if they have strong bonds with the alpha male (Feldblum 2021)

Evidence of passive and active food sharing
Reinforces social bonds
Hunting more common when already have enough food - hunting is a social tool

Acts that have a net loss of evolutionary fitness to the actor but a net gain in fitness to the receiver

Out of selfish interest
Between-group competition

Altruism is a result of selfish motivation
Humans experience sympathy to encourage them to act and alleviate the suffering of others in order to avoid their own suffering

May be many opportunities for altruistic action during actors’ lifetimes
Given actor repeatedly interacts with the same small set of individuals
Pairs of altruists are exposed ‘symmetrically’ to altruistic opportunities (so each actor able to render equal benefits and costs)

o Length of lifetime
o Presence and type of parental care
o Dominance hierarchy structure

If the 3 primary conditions are met and the biological parameters set favourable conditions, reciprocal altruism will evolve as an adaptation in that population

Modification by organisms of the functional relationship between themselves and their environment, through an active change of one of the factors of that environment

Symmetry based = strong mutuality of interactions
Attitudinal based = level of reciprocity based on assessments of recent interactions between individuals (if you are nice, I will be nice)
Calculated = extensive individual score keeping, potential punishment of cheaters

Social intelligence better at explaining sociality in non-human primates
- Primates evolved social-cognitive skills for cooperating and competing with group/community members

Cutural intelligence better at explaining sociality in humans
- Humans also evolved skills for establishing distinct cultural groups, with different physical and symbolic markers

Only species to have a set of social-cognitive skills for participating and exchanging knowledge in cultural groups