Bio5C 6.1-6.2

CATCH UP 8:20

  • fitness - reproductive success

  • evolution - change in allele frequency over time

NATURAL SELECTION

  • selection - process of differential survival and reproduction that determines which traits are adaptive

  • selection…

    • results from struggle to survive

      • individuals who survive were “selected” by environment

    • improves adaptedness - the match between organism and environment

    • acts on phenotype

      • whole organism must survive - not just “well adapted” parts

      • ex. white rabbits can hide from predators in snow. does not mean they can literally just sit in snow their whole life, they must eat, get rid of bodily waste, and escape if detected.

    • acts on genotype only as it influences the phenotype

  • selection pressure - intensity of selection process

    • at HIGH selection pressure, having the wrong trait = instant death (ex. being the wrong color an standing out to predators, birth defects, etc.)

    • at LOW selection pressure, variation is not a big deal and does not result in instant death (ex. a flower being pink instead of yellow - a bee will find the flower no matter the color)

  • traits that improve survival and reproduction are “selected for”

  • traits that reduce survival and reproduction are “selected against”

  • POLLEV: evolution is not the same thing as adaptation

    • adaptation - process that improves fitness in response to natural selection (mutation, drift, gene flow change allele frequency without resulting in adaptation)

  • the adaptation process

    • 1) selection on phenotypes

    • 2) alleles from fit individuals become more common in next generation

    • 3) proliferation of adaptive traits

  • not all phenotypes are adaptive traits

    • adaptations are heritable traits that improve fitness

    • ex. of adaptations (things to be inherited by offspring)

      • colorful flowers

      • heat sensing organ (snakes)

      • long bill (hummingbirds)

      • water storage in leaves and stems

    • ex. of non-adaptive traits (things not inherited by offspring)

      • mollusk shells (they fluctuate in response to predation pressure/amount of fish around)

      • learning a skill

      • altered growth (trees) in extreme environments

    • if the phenotypic change is not heritable, it is not an adaptive trait

      • birds that open milk bottles pass on the ability to learn, but not the ability to open milk bottles specifically

ARTIFICIAL SELECTION

  • artificial selection - when humans are the main selective agent, not the environment

  • human selection is artificial because phenotypes would be lost quickly if human selection stopped

  • 3 outcomes of selection

    • directional selection for or against a phenotype that rapidly changes phenotype distribution; new phenotype distribution is shifted to one end

    • disruptive -

    • stabilizing