Lecture4_NatlSel_2009 - Change in Readings! Evolutionary...

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Evolutionary processes: Natural selection S. Hedtke BIO 370 9/8/09 Change in Readings! SWITCH reading for Thurs. 9/10 and Tuesday 9/15 (doing genetic drift on Tuesday) Evolutionary forces ->> change in genetic variation within populations • Mutation -> the source of all variation • Natural selection -> often reduces variation • Gene flow -> moves variation from population to population • Genetic drift -> decreases variation due to random chance Darwin’s postulates: natural selection 1. Individuals within a species are variable. 2. Some of these variations are passed on to offspring. 3. In every generation, more offspring are produced than can survive. 4. The survival and reproduction of individuals is not random: the individuals who survive and go on to reproduce are those with the most favorable variations. Exponential Growth
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Exponential Growth Logistic Growth carrying capacity carrying capacity Logistic Growth 1. Initial exponential growth 2. Decline in growth rate 3. Zero growth rate at carrying capacity 4. Decline in growth rate is due to: - resource limitations - direct and indirect competition Observation : Organisms produce more offspring than can survive ! direct and indirect competition for resources to survive and reproduce ! differential reproduction Differential Survival : A A A B B B t ime 1 time 2 A A A B B B X X Differential Survival : A A A B B B Differential Reproduction: time 1 time 2 A A A B B B A A A B B B A A A B B B A A B B B B B B B X X
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Differential Survival : A A A B B B Differential Reproduction : Differential Survival Reproduction : time 1 time 2 A A A B B B A A A B B B A A A B B B A A A B B B A A B B B B B B B A A A B B B A A B B B B B B B X X X X X Differential Survival Reproduction : A A A B B B A A A B B B A A B B B B B B B X X X Conditions for Natural Selection : 1. Reproduction 2. Heredity 3. Variation in heritable traits
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Lecture4_NatlSel_2009 - Change in Readings! Evolutionary...

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