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Speciation. A species is an interbreeding group of organisms When a population is somehow severed from the parent population and over time its gene pool is altered. Allopatric and sympatric. Allopatric speciation. Isolation is the result of a geographic barrier Ex. Galapagos finches

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speciation
Speciation
  • A species is an interbreeding group of organisms
  • When a population is somehow severed from the parent population and over time its gene pool is altered.
  • Allopatric and sympatric
allopatric speciation
Allopatric speciation
  • Isolation is the result of a geographic barrier
  • Ex. Galapagos finches
  • True speciation only occurs if the remaining populations will NOT breed
sympatric speciation
Sympatric speciation
  • No geographic barrier
  • Balanced polymorphisms – insects a certain color with a certain kind of camoflage will mate and isolate themselves from the original population
  • Hybridization – when hybrids are more successful than parental generations
sympatric polyploidy
Sympatric - polyploidy
  • When a sub-population arises in the midst of the parent population
  • Many plant species have accidental polyploidy in meiosis. They produce zygotes with multiple sets of chromosomes.
  • They can no longer reproduce with parental generation.
adaptive radiation
Adaptive Radiation
  • Adaptive radiation – rapid evolution of a variety of species from a single ancestor (ex. Darwin’s finches)
  • Occurs after mass extinctions when 90% of organisms become extinct. Leaves room for others to colonize
what is the tempo of speciation
What is the tempo of speciation?
  • Phyletic gradualism vs. punctuated
  • Punctuated equilibrium model – species most often diverge in spurts of rapid change instead of slow and gradually.
  • Over a few to ten thousand years, genetic drift and natural selection can change small, isolated species
reproductive barriers
Reproductive Barriers
  • Prezygotic barriers – occur before conception
  • Post-zygotic barriers – occurs after conception
pre zygotic barriers
Pre-zygotic Barriers
  • Temporal Isolation – mating or flowering occur at different time of the year/day

Ex. Western spotted skunks breed in fall, while eastern spotted skunks breed in the late winter

  • Habitat Isolation – species living in the same region may occupy different habitats

Ex. Some Garter snakes live in water/some on land

  • Behavioral Isolation-courtshiprituals are very specific

Ex. Birds

  • Mechanical isolation-structuraldifferences in genitalia or flowers prevent copulation or pollen transfer

Ex. Insects and flowers

  • Gametic isolation- male sperm cannot fertilize the egg
post zygotic barriers
Post-zygotic Barriers
  • Hybrid Inviability – hybrid zygotes fail to develop or reach sexual maturity
  • Hybrid Sterility – Hybrid individuals fail to produce young
  • Hybrid breakdown – hybrids have reduced viability with each generation.
patterns of evolution
Patterns of Evolution
  • Divergent evolution – when two isolated population evolve independently (Ex. Brown and polar bears)
  • Convergent Evolution – when two organisms without a common ancestor occupy the same niche, so they have the same characteristics. (ex. Porpoise and penguin)
  • Parallel Evolution – two related species who have made similar evolutionary changes. Ex. Placental and marsupial wolf
  • Co-evolution – predator/prey relationships
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