BIO 360  Ecology

Lecture 11: Social behavior

I.  Types of social behaviors and their consequences
        A.  Social behaviors can be organized by their consequences for donors and recipients
        1.  Selfishness benefits the donor, but not the recipient
            -- Territoriality is common in mobile animals
            --  Dominance behavior is common when territories are impractical
            --  Tragedy of the Commons is an example of a selfish behavior that is manifest in human interactions

        2.  Cooperation is a behavior that benefits both the donor and the recipient
            --  Social groups, like schools or flocks
            --  Group defense
            --  Cooperating has both benefits and costs -- there are tradeoffs 
                Benefits: less time looking for predators or food
                Costs: more rapid exploitation of food 

        3.  Altruism is a behavior that benefits the recipient but not the donor (see below)

        4.  Spitefulness benefits neither the donor nor the recipient, and cannot be favored by natural selection

II.  Why would altruism evolve?  Kin Selection
    A.  Differential reproduction among lineages of closely related individuals based on genetic variation in social behavior

    B.  Inclusive fitness:   contribution of behavior to own reproductive success plus contribution of behavior to relatives reproductive success

    C.  Coefficient of relatedness:  the likelihood that two individuals share copies of any particular gene

        1.  Trace all paths of descent
        2.  Multiply relatedness from direct lines
        3.  Add relatedness from independent lines

    D.  The case of social insects
        1.  Adults live together
        2.  Overlapping generations
        3.  Cooperation in nest building and brood care
        4.  Reproductive dominance

        5.  Relatedness in haplodiploid organisms
            -- sisters are more related than mothers and offspring; fathers are not related to sons 

    E.  The case of meercats:  altruism or cooperation?
        1.  Only stand guard when they are full
        2.  Guard whether related or unrelated
        3.  Stand guard close to their burrow
        4.  Are not killed by predators when guarding
        5.  When fed (hard boiled eggs!) they were more likely to guard
        6.  A selfish behavior!

III.  Can altruism evolve where individuals are unrelated? 

    A.  Generally, the answer is no selfishness and cooperation are the evolutionary rule!

    B.  Game theory:  the outcomes of interactions given the behavior of another individual

   D.  Do we find altruism in nature, or human societies?

        1.  Yes, but only when behaviors are repeated

        2.  Reciprocal altruism: altruism now in expectation of altruism by other in the future

        3.  In repeated interactions, reputation, forgiveness, and punishment make altruism possible in evolution