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Patterns in Evolution

Patterns in Evolution

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Patterns in Evolution

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  1. Patterns in Evolution

  2. Key concept : Evolution occurs in patterns • Evolution through natural selection is not random. • Natural selection can have direction. • The effects of natural selection add up over time.

  3. Convergent Evolution • Defined: evolution toward similar traits in unrelated species due to a similar environment. • Ex: Tuna (fish) and dolphins (mammals). They are an unrelated species living in a similar environment, the ocean. • Faced similar evolutionary pressures.

  4. Divergent Evolution red fox kit fox ancestor Kaibab Squirrel (Grand Canyon) • Defined: Describes evolution toward different traits in closely related species. • Cause: Different environments

  5. Coevolution • Defined: Two or more species evolve in response to changes in each other • Evolutionary paths become connected • Both species receive benefits from the other as a result of adaptations. • Ex: Plants and Insects • Plants: provide insects with nectar • Insect: transfers pollen from one plant to another

  6. Coevolution Continued… • Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race. • Example: Crab vs. Snail & Bacteria vs. Humans

  7. Most bacteria killed Strong Survive Bacterial Resistance Strong Reproduce

  8. Extinction • Defined: The elimination of a species from Earth. • Mass Extinctions: • Cause:Catastrophic events • Ice Age, Meteorites • Destroys many species at global level • Very severe • Rare but much more intense • At least 5 mass extinctions in last 600 million years • Background Extinctions: • Cause:Local changes in environment • Forest fires, habitat destruction. • Affects a few species in a small area • Less severe. • Occur at roughly the same rate as speciation

  9. How Fast Does Evolution Occur? • Gradualism: Slow & steady change of 1 species into another • Small changes continually build over time No exact time frame • Punctuated Equilibrium: Long periods of little change are interrupted by shorter periods of rapid change. • Due to sudden environment change • Ex: Mammal diversity exploded after dinosaur extinction

  10. Gradualism of the Horse

  11. How Fast Does Evolution Occur? To radiate = to s-p-r-e-a-d out • Adaptive radiation: A process of evolution where one species can split into a number of different species. • Ancestral species diversifies into many descendent species • Each adapted to a different environment • Ex: Mammals

  12. Review • How is convergent and divergent evolution different? • What is thought to bring different organisms such as fish and dolphins to have evolved a similar body plan? • What is coevolution? • What does a flower gain from a close relationship with a hummingbird? • What does the hummingbird gain? • How is gradualism and punctuated equilibrium different?