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