AEC 360  Ecology

Lecture 12:  Dispersal and migration

I.  Definitions
    Dispersal -- movement of individuals away  from the place of birth
    Migration movement of individuals  between one place and another

II.  Dispersal
    A.  Why disperse?
        1.  Colonize new sites
        2.  Gets an individual away from its parents
        3.  Cost of dispersal: may end up in an unsuitable environment, die

    B.  Dispersal in plants
            1.  plant seeds are dispersed by wind, water, animals, or explosion

            2.  plants may put energy into helping their seeds survive the process of dispersal, with cost to parents but adaptation may increase survival

    B.  Dispersal in wild Chilies
        1.  If fruits are meant to be consumed and dispersed by animals, why do they also produce chemical compounds to deter consumption:  Why are chilies hot?

        2.  Two hypotheses to explain why chilies are hot:
            a.  General deterrence predicts that capsaicin is:   1) Not selective 2) Not related to the quality of the seed disperser

            b. Directed deterrence predicts that effects of capsaicin are 1) Selective 2) Directed at seed predators and low quality dispersers

        3.  Evidence
             a.  Is the deterrence in peppers selective?

                    --  Who consumes chiles?

                    --  Who is deterred by capsaicin?

            b.  How is the deterrence in peppers directed?
                    --  Seed viability

                    --  Seed dispersal

        4.  Effects of fungus on chili seeds 

        5.  Red cockaded woodpecker
                -females disperse, but males may stay as helpers to raise subsequent generations
                -helpers inherit nesting sites, creating nesting cavities is time-intensive (~2 yrs)
                -males disperse more if:
                    -they are small
                    -they have lots of male siblings
                    -their natal territory is low quality
                    -area has other nesting sites


III.  Migration
    A.  Allows animals to tolerate seasonally unsuitable conditions

    B.  Examples of long-distance migration

    C.  How do animals migrate:  Monarch butterflies
        1.  Phases of monarch migration

        2.  How do monarchs find their way?
            --  Time-compensated sun compass
            -- Wind direction
            -- Geographical features
            -- Magnetic compass orientation?

            (Note: Other animals may use memory to guide their way)