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Plant Ecology - Chapter 6
Outcomes of Natural Selection
Phenotypic Variation
Natural selection
acts on phenotypic
variation, selecting
against traits that
are poorly adapted
to the existing
environment
Phenotypic Variation
For natural selection
to act, phenotypic
variation must be
heritable (have a
genetic basis), and
must produce
fitness differences
Phenotypic Variation
Directional selection
Stabilizing selection
Disruptive selection
Genotype-Environment
Interactions
Differences among
individuals with
different genotypes
may depend on the
environment
Different
expressions
3 Patterns of Adaptation
1) Different phenotypes
specialize in different
environments
2) Phenotypic plasticity
to match environments
3) Single phenotype for
all environments passable
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
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
Decreasing Variation
Natural selection reduce genetic variation
Genetic drift - change in
gene frequencies do to
random sampling
effects - small
populations most
affected
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
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
Speciation
Allopatric, parapatric,
sympatric
Common to both plants
and animals
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