social behaviour
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Social behaviour
Biol 455 Mammalogy
March 29, 2005
What is a social group?
Group of individuals of the same species
organized in a cooperative manner
Beyond sexual and parental behaviour
Most social groups are organized
matrilinearlly (mothers, daughters, sisters,
aunts, and nieces)
Male-biased dispersal, male often
unrelated to other adults in group
Examples of social behaviour
Alarm calling
Cooperative rearing of young
Non-breeder help with lactation and care of young
Coalitions and alliances
Alarm caller draw predator attention (altruistic)
Cooperate to access resources, need to be
reciprocated
Eusociality
Reproductive and non-reproductive members help
getting food, defend nest, rear young
Why mammals live in groups?
Relate to two ecological factors: predation
pressure and resource distribution
Cost and benefits of group living
Sociality evolved when benefits of group
living is higher than costs
Benefits of groups
Protection from physical factors - huddling
Protection against predators - “many eyes
hypothesis” or group defense
Finding and obtaining food - cooperation in
hunting
Group defense of resources - maintenance of
territory
Assembling members for locations of mates leks
Division of labor among specialists
Richer learning environment for young
Costs of groups
Increased intraspecific competition for
resources
Increased chance of disease and parasite
transmission
Interference with reproduction
How social behaviour evolves?
Group selection: individuals work together
sacrificing personal gain to achieve group
benefits
Natural selection operating at group-level William 1966, Wilson 1980
Selfish herd
Each individual try to reduce its chances of
being caught by a predator - Hamilton (1971)
How social behaviour evolves con’t
Kin selection
If a gene causes some altruistic behaviour,
the gene’s success depends not on the its
benefit to the individual but itself
b*r> c
Inclusive fitness: reproductive fitness of
individual include the reproductive fitness of
its relatives other than its own offspring
Need to be able to recognize kins
How social behaviour evolves con’t
Reciprocal altruism
Mutualism
Individuals cooperate and behave altruistically, if
such act is reciprocated later
Both individuals benefit from relationship with no
apparent cost
Ecological constraints
Environmental factors restrict the chances of
individuals to breed independently
Could be due to habitat saturation or unpredictable
environment (high cost of reproduction)