Plant Ecology Chapter 6

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Plant Ecology - Chapter 6

• Outcomes of Natural Selection

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Phenotypic Variation

• Natural selection acts on phenotypic variation,
  selecting against traits that are poorly adapted
  to the existing environment

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Phenotypic Variation

• For natural selection to act, phenotypic
  variation must be heritable (have a genetic
  basis), and must produce fitness differences

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Phenotypic Variation

• Directional selection
• Stabilizing selection
• Disruptive selection

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Genotype-Environment Interactions

• Differences among individuals with different
  genotypes may depend on the environment
• Different expressions

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3 Patterns of Adaptation

• 1) Different phenotypes specialize in different
  environments
• 2) Phenotypic plasticity to match environments
• 3) Single phenotype for all environments -
  passable

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Level of Selection

• Natural selection occurs at the level of the
  individual
• Genet or ramet?
• Individual ramets may come and go, but genets can
  exist for long time
• Quaking aspen - 50-60 years vs. 10,000 years

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Increasing Variation

• Mutations - 10 of individuals in most plant
  populations have new mutations each generation
• Migration - spores, pollen, seeds can add new
  variation to populations

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Decreasing Variation

• Natural selection -reduce genetic variation
• Genetic drift - change in gene frequencies do to
  random sampling effects - small populations most
  affected

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Variation Among Populations

• Mutation and genetic drift increase variation
  among populations
• Natural selection can increase or decrease
  variation among populations
• Migration decreases variation among populations

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Ecotypes

• Populations of a species from different habitats,
  that possess genetically based differences in
  appearance, function
• Differences in characteristics retained when all
  grown together in same environment

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Speciation

• Allopatric, parapatric, sympatric
• Common to both plants and animals

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Speciation

• Hybridization - rare, but very frequent in some
  genera - e.g., oaks
• New genetic combinations possibly adapted to
  different environmental conditions than either
  parent species
• Polyploidy - duplication of entire set of
  chromosomes - instant reproductive isolation