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Natural Selection. I. Necessary Conditions II. Selection in Nature III. Units & Levels of Selection. Necessary Conditions for Evolution by Natural Selection. Variation among individuals Heritability of variation Differential reproduction of variants . Natural Selection.
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Natural Selection I. Necessary Conditions II. Selection in Nature III. Units & Levels of Selection
Necessary Conditions for Evolution by Natural Selection • Variation among individuals • Heritability of variation • Differential reproduction of variants
Natural Selection Phenotypic Selection Genetic Response [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
Mortality Selection Fecundity Selection Phenotypic Selection Nonsexual Selection Sexual Selection [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
Variance Selection Modes of Selection on Continuous Characters Fitness Fitness Fitness Frequency Frequency Frequency Trait Trait Trait Disruptive Selection Directional Selection Stabilizing Selection [Source: Brodie et al. 1995, Trends in Ecology & Evolution 10, 313-318]
Selection Differentials Variance selection Directional selection variance before selection mean before selection variance after selection mean after selection Positive if i > 0 Negative if i < 0 Stabilizing if j < 0 Disruptive if j > 0 [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
Response to Selection where, response to selection selection differential heritability [Source: Falconer 1981, Introduction to Quantitative Genetics, Longman Press]
Selection Coefficients where, relative fitness coefficient of directional selection coefficient of variance selection [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
Advantages of Selection Coefficients • Directly link traits to fitness • Can be used to compare the effects of multiple traits on fitness • Allows on to visualize phenotypic selection
A Definition of Fitness Average lifetime contribution to the breeding population by a phenotype, relative to the contribution of other phenotypes. [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
Empirical Measures of Fitness • Fundamental (Direct) • Estimated Time until Extinction (Forget about it!) • Derived (Indirect) • Growth • Survival • Mating Success • Fecundity [Source: Cooper 1984, Journal of Theoretical Biology 107, 603-629]
Studies Demonstrating Natural Selection in the Wild [Source: Endler 1986, Natural Selection in the Wild, Princeton University Press]
In most cases, directional selection was not very strong. Median β Log (sample size) [Source: Kingsolver et al. 2001, The American Naturalist 157, 245-261]
In most cases, directional selection was not very strong. Frequency Absolute Value of Linear Selection Gradient (β) [Source: Kingsolver et al. 2001, The American Naturalist 157, 245-261]
Strength of selection did not depend strongly on sample size. Median β Log (sample size) [Source: Kingsolver et al. 2001, The American Naturalist 157, 245-261]
Selection differential accord with selection gradients. Selection Differential Linear Gradient (β) [Source: Kingsolver et al. 2001, The American Naturalist 157, 245-261]
Stabilizing and disruptional selection were equally uncommon. Frequency Quadratic Selection Gradient (γ) [Source: Kingsolver et al. 2001, The American Naturalist 157, 245-261]
Bμ is a measure of the strength of selection that is truly independent of the population’s phenotypic variation. [Source: Hereford et al. 2004, Evolution 58, 2133-2143]