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Patterns of Evolution. SBI3U0. Patterns of Evolution. We have learned: Evolution occurs in slow steps Mutations Genetic Drift and Natural Selection Changing allele frequencies Accumulation of mutations and natural selection often leads to speciation

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patterns of evolution1
Patterns of Evolution
  • We have learned:
    • Evolution occurs in slow steps
      • Mutations
      • Genetic Drift and Natural Selection
      • Changing allele frequencies
    • Accumulation of mutations and natural selection often leads to speciation
  • What patterns do we see in this speciation?
    • Do species always evolve to be drastically different from one another?
adaptive radiation
Adaptive Radiation
  • Adaptive radiation occurs when one species evolves into several different species
    • This usually happens relatively quickly
    • The new species usually fill empty ecological niches
  • What forces these new species to form?
    • Usually the introduction of new resources that aren’t being used by other species
  • A prime example is the many species of finches Darwin observed in the Galapagos islands
    • Aptly named Darwin’s finches as a group
darwin s finches
Darwin’s Finches
  • On mainland South America the finch species feed mainly on seeds
    • Other food sources (insects, fruits, plants, etc...) are mainly consumed by other species
  • The finch population is strictly limited by stabilizing selection
    • Smaller finches must compete with other species for smaller seeds
    • Larger finches must compete with other species for larger/harder seeds
darwin s finches1
Darwin’s Finches
  • When the ancestor of the current finch species traveled over to the Galapagos islands there was little competition for food
  • This allowed the finches who were naturally larger or smaller to exploit different food sources from the bulk of the finch population
    • Thus there was a niche for those birds
    • As they passed down their genes, the populations of birds exploiting alternative food sources grew
    • This lead to the eventual sympatric speciation of these birds
divergent evolution
Divergent Evolution
  • Every ecosystem has a wide range of niches and roles
    • Eg: every ecosystem has producers, consumers, decomposers, and scavengers
    • Among these groups are several different specialized species
  • One species can eventually evolve into several different species that fill different niches and roles
    • This is called divergent evolution
divergent evolution rodents
Divergent Evolution - Rodents

Squirrel, Deer mouse, flying squirrel, porcupine, beaver

divergent evolution marsupials
Divergent Evolution - Marsupials

Kangaroo, Koala, Wallaby,Wombat, Possum

divergent evolution marsupials1
Divergent Evolution - Marsupials

Tasmanian Devil, Diprotodon, Bandicoot, Thylacine

convergent evolution
Convergent Evolution
  • Convergent Evolution
    • When two species evolve to occupy the similar niches
    • This is most obvious when you compare species from different ecosystems
  • If two separate species are placed under similar selective pressures they tend to evolve similar structures
convergent evolution1
Convergent Evolution

Cacti – Americas Euphorbia – Africa

convergent evolution2
Convergent Evolution

Sharks – Mostly Deep Sea Dolphins – Shallow water (continental shelves)

  • In many instances organisms evolve traits alongside one another
    • This is called coevolution
  • Two organisms can place selective pressures on each other
    • This forces them to evolve together
    • They often become more and more dependant on one another
    • Referred to as an “evolutionary arms race”
    • Most common in species with symbiotic relationships

Hawk Moth Madagascar Long-spurred Orchid

30 cm tongue 30 cm spur (with nectar)

patterns of evolution2
Patterns of Evolution

Brazil nut Agouti

  • Pg 345 #1-7