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  • 1. Speciation The Process of Evolution
  • 2. Speciation
    • Formation of a new species
    • Species :
      • a population that can breed freely and produce fertile offspring
    • Speciation often occurs when part of the population is isolated from another part
      • Selective pressures of the environment in one area may be different from pressures in another area
  • 3. What is a Species?
    • Definition :
    • Morphospecies - based on appearance
    • Biologic species - a population that can breed freely and produce fertile offspring
    • The largest unit of population in which gene flow is possible
    • Limitations:
      • doesn’t work for asexual organisms
      • extinct life forms
      • populations that are geographically isolated - sometimes call subspecies
    • No clear answer; idea is arbitrary
  • 4. Patterns of Speciation
    • Fossil record shows 2 patterns:
    • Anagenesis ( phyletic evolution)
      • the transformation of an unbranched lineage of organisms, sometimes creating an organism different enough to be a new species
    • Cladogenesis
      • branching evolution; budding of one or more new species from a parent species that continues to exist.
  • 5. Anagenesis vs. Cladogenesis
  • 6. Causes of Speciation
    • Speciation often occurs when part of the population is isolated from another part
    • Geographic Isolation
      • most common
      • a physical barrier develops (changing course of a river; separation of an island)
      • Selective pressures in one area are different from pressures in another area
    • Reproductive Isolation
      • another form of isolation
  • 7. Isolation
  • 8. Geographic Isolation
    • Biogeography of Speciation
    • Classified according to geographic relationship between new and old species
    • Sympatric
      • population becomes reproductively isolated in the midst of the parent population
      • ranges of new and old species overlap.
    • Allopatric
      • species are physically separated
      • more likely in small populations
    • Adaptive radiation is allopatric :
      • emergence of numerous species from a common ancestor that spreads to several new environments.
  • 9. Allopatric vs. Sympatric
  • 10. Allopatric Barriers
  • 11. Geographic Isolation
  • 12. Reproductive Isolation
    • Example: organisms breed at different times
    • Reproductive barriers are of 2 types:
    • Prezygotic
      • before the formation of fertilized eggs
      • impedes mating or fertilization
    • Postzygotic
      • after
  • 13. Reproductive Isolation
  • 14. Prezygotic Isolation
    • Impedes mating or fertilization
    • Habitat isolation
      • not geographically separated, but occupy different niches within an area, e.g. trees versus ground
    • Temporal isolation
      • breed at different times
    • Behavioral isolation
      • don’t produce appropriate courtship signals
    • Mechanical isolation
      • anatomically incompatible
    • Gametic isolation
      • mating occurs but gametes rarely fuse to form zygotes
  • 15. Behavioral Isolation: Courtship Barrier
  • 16. Postzygotic Barriers
    • Hybrid inviability
      • offspring don’t make it
    • Hybrid sterility
      • e.g. mules
    • Hybrid breakdown
      • F 2 are sterile or weak
  • 17. Introgression
    • Alleles pass a reproductive barrier when a fertile hybrid mates with a parent species
    • Increases variation
    • Rare
      • 2 species remain distinct
  • 18. Post Speciation Evolution
    • Divergent Evolution
      • Process by which related organisms become less alike
      • occurs after speciation
      • at first 2 new species are very similar, but over time become more & more different.
    • Adaptive radiation is a special type of divergent evolution
      • Many new species from a single parent species
  • 19. Adaptive Radiation
  • 20. Timing of Evolution
    • Most scientists accept natural selection as the process of evolution
    • The timing is controversial
    • Gradualism
      • the traditional view
      • a slow, steady accumulation of changes, leads to new species
    • Punctuated Equilibrium
      • long periods of inactivity followed by big jumps
    • Fossil record provides evidence that the pace of evolution varies
      • The same evidence is used to support different ideas
      • Could be some of both
  • 21. Gradualism vs. Punctuated Equilibrium