NATURAL SELECTION - a case study    by   Peter & Rosemary Grant

        medium ground finch of Galapagos Islands off Ecuador   [Darwin's Finches*]

        medium ground finch lives on seeds, cracks them open via force of beak
        the Grant's studied finches on Daphne Major, an small island (800 sq. yd)

        in 1977 island had only 2mm of rain instead of normal 130mm...
                drought (also in 2003) resulted in a loss of 84% of medium ground finch population
                most died of starvation,
                        seeds of Tribulus cistoides, primary food source --> were hard to open   
                        unless birds had large, deep beaks, [the survivors had deeper beaks]

        Natural Selection lead to increase in average beak depth of survivors (graph of data*)
        Offspring of survivors in subsequent years had beaks 0.5mm deeper.
       
This type of evolutionary change is known as character displacement.
   
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      2005, Charles Mallery, Department of Biology, University of Miami, Coral Gables, FL 33124               Last Update - 04 Sep 2008