Social behaviour
Biol 455 Mammalogy
March 29, 2005
What is a social group?
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Group of individuals of the same species
organized in a cooperative manner
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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
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Examples of social behaviour
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Alarm calling
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Cooperative rearing of young
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Non-breeder help with lactation and care of young
Coalitions and alliances
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Alarm caller draw predator attention (altruistic)
Cooperate to access resources, need to be
reciprocated
Eusociality
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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
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Benefits of groups
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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
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How social behaviour evolves?
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Group selection: individuals work together
sacrificing personal gain to achieve group
benefits
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Natural selection operating at group-level William 1966, Wilson 1980
Selfish herd
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Each individual try to reduce its chances of
being caught by a predator - Hamilton (1971)
How social behaviour evolves con’t
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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
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How social behaviour evolves con’t
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Reciprocal altruism
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Mutualism
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Individuals cooperate and behave altruistically, if
such act is reciprocated later
Both individuals benefit from relationship with no
apparent cost
Ecological constraints
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Environmental factors restrict the chances of
individuals to breed independently
Could be due to habitat saturation or unpredictable
environment (high cost of reproduction)