AEC 360  Ecology

Lecture 8:  Evolutionary ecology
 

I.  Overview
    A.  Definition: 
 
 

    B.  History
        1.  Linnaeus 1700's taxonomy and hierarchical classification of species
        2.  Cuvier (1801) demonstrates that extinction has occurred
        3.  Transitional forms: Species are not static, but change through time
        4.  Hutton and Lyell describe long-term geological change


        5.  Species are related, not independent:  Homologies

        6.  Propagation of varieties of domesticated species


II.  The Theory of Evolution by Natural Selection (Darwin): case study with the medium ground finch

    A.  Individuals within species are variable
 
 

    B.  Some of these variations are passed on to offspring
 
 

    C.  In every generation, more offspring are produced than can survive
 
 

    D.  Survival and reproduction are not random:  those with most favorable variations are naturally selected



    E. Evolution in finches has continued 



    F. Color mismatch in snowshoe hares as temperature warms 


IV.  The modern synthesis
    A.  The Theory of Evolution by Natural Selection restated:

            -- As a result of mutation and independent assortment of alleles, individuals within populations are variable for nearly all traits
            -- Genetic variations are passed on to offspring independent of other genes
            -- In most generations, more offspring are produced than can survive
            -- Survival and reproduction are not random:  individuals with alleles that best adapt them to their environment survive and reproduce


    B.  It is important to recognize that Natural Selection:
        1.  acts on individuals, but consequences are for populations
        2.  acts on phenotypes, but changes are of genotypes
        3.  is backward looking, not forward looking
        4.  is not random, but also not progressive


V.  Examples: Scale insects and cyanide
            -- important current issues in pest control
 

VI.  A detailed example of the pepper moth
    A.  History of Kettlewell's studies
            1. Differences in fitness between light (typical) and dark (melanic) forms
            2.  Inherited trait controlled by a single dominant gene
            3.  Conducted mark-recapture studies and estimated relative fitness

 

    B.  What caused selection for color in pepper moths?


         

VII.  Attributes of selection

    A.  The strength of selection
        1.  Heritability describes the quantitative relationship in a trait between parents and their offspring
 
 

    B.  Selection may be:
        1.  Stabilizing,  example with human babies



        2.  Directional, example with cliff swallows



        3.  Disruptive, example of disruptive selection in African finches
 
 
 

    C.  Selection may favor heterozygotes 



 

    D.  Selection may depend on the frequency of alleles or genotypes


        1.  Example of scale-eating fish

            -Bites scales off other fish
            -Mouth is directed at side it bites
            -If fish with mouths on one side are more abundant, prey become wary on that side
            -Rare phenotypes perform better