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Natural Selection

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Title: How does evolution happen? Author: Martin Catherine Last modified by: San Diego City Schools Document presentation format: Custom Other titles – PowerPoint PPT presentation

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Title: Natural Selection


1
Natural SelectionEvolutionary Patterning
2
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3
Natural Selection
  • Natural Selection acts on VARIATIONS
  • Stabilizing Selection conditions favor
    intermediate variants rather than extremes
  • Directional Selection conditions favor
    individuals at one extreme
  • Disruptive Selection conditions favor
    individuals at both extremes

4
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5
Which of these modes represents which type of
selection? What conditions might account for the
observed types of selection among mouse
populations?
6
Sexual Selection Intrasexual vs. Intersexual
Selection
7
  • Intrasexual competition among individual
    within one of the sexes (same sex competes for
    mates of the opposite sex)
  • Ex male-male competition
  • among elk for access to females
  • Intersexual selection between the sexes (mate
    choice)
  • Ex female choice (peahens )
  • for most vibrant showy males
    (peacocks)

8
Evolutionary Patterns
  • Adaptive Radiation common ancestral species
    evolves into many different species as
    populations move into new/ different habitats and
    have adaptations provide a best-fit with
    environment
  • Example Darwins finches certain beak types
    proved more advantageous for procuring food
    within a particular habitat

9
Evolutionary Patterns
  • Divergent Evolution species that were once
    similar to ancestral species become increasingly
    more diversified results in homologous structures

10
Evolutionary Patterns
  • Convergent Evolution unrelated species evolve
    similar traits because they occupy similar
    environments in different parts of the world
  • Similar environmental pressures result in
    analogous structures (Ex aquatic habitat favors
    streamlined body plan and flipper-like
    appendages)

11
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12
Evolutionary Patterns
  • Coevolution evolution of one species affects
    the evolution of another species due to a close
    ecological relationship between the two species
  • Ex mutualism many plants have evolved to
    produce fruits that are consumed by certain
    organisms so that seeds can be dispersed
  • A parasitic relationship is known as
    coevolutionary arms race plants evolve a
    chemical defense against pests and pests in turn
    evolve to resist the defense

13
Rates of Speciation
  • Speciation can occur quickly or slowly
  • Gradualism species originate through a gradual
    change of adaptations over very long periods of
    time many transitional species between ancient
    ancestor and modern-day species
  • Punctuated Equilibrium speciation occurs
    relatively quickly, in rapid bursts, with long
    periods of genetic equilibrium in between
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