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What causes extinction?

What causes extinction?. Old explanations: Maladaptation - organisms evolved poorly-adapted features Racial senescence - species became “weak over time” Discuss the likelihood of these explanations with your table. Adaptation, not maladaptation. No mechanism for maladaptation

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What causes extinction?

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  1. What causes extinction? • Old explanations: • Maladaptation - organisms evolved poorly-adapted features • Racial senescence - species became “weak over time” • Discuss the likelihood of these explanations with your table

  2. Adaptation, not maladaptation • No mechanism for maladaptation • Natural selection increases, not decreases, fitness • Species aren’t organisms - no programmed “species death” and no mechanism for “weak genes”

  3. Is everyone equally vulnerable to extinction? • Generalists v. specialists • Relationship between extinction and speciation rates • Organisms that speciate readily also tend to have short species duration - high speciation and high extinction rates go together • Talk at your table about what would cause high speciation rates

  4. Examples • High extinction and speciation: • Mammals (E=0.71/my, S=0.93/my) • Also trilobites, ammonites, graptolites • Low extinction and speciation • Clams (E=0.09/my, S=0.15/my) • Nautiloids

  5. Mass Extinction Causes • Coincidence: lots of organisms happened to die at the same time. Can be ruled out statistically. • Need to be especially cautious if the species that go extinct are unstable groups • More persuasive if stable groups also suffer extinction

  6. Mass Extinction Causes • Coincidence • Physical causes: • changes in climate • Salinity • living space: reduction in continental shelf space due to plate motions or regression

  7. Mass Extinction Causes • Coincidence • Physical causes • Biological causes: competition, predation

  8. Mass Extinction Causes • Coincidence • Physical causes • Biological causes • Catastrophe: impact, volcanoes

  9. Permo-Triassic extinction • Coincidence?: Over 90% of life dies, so definitely real

  10. Permo-Triassic extinction • Coincidence? No • Physical: Continental configuration and regression • Reduced continental shelf space • Glaciation • Severe climate

  11. Permo-Triassic extinction • Coincidence? No • Physical: • Continental configuration and regression • Biological: Appearance of biological “bulldozers”: • Shallow burrowers • Earlier life was immobile bottom dwellers (brachiopods, bryozoans, crinoids, etc.)

  12. Permo-Triassic extinction • Coincidence? No • Physical: Continental configuration and regression • Biological: Appearance of biological “bulldozers” • Catastrophe: • Impact? Probably not • Lack of tektites, shocked quartz • Some iridium, but not enough

  13. Permo-Triassic extinction • Coincidence: No • Physical: Continental configuration and regression • Biological: Appearance of biological “bulldozers” • Catastrophe: • Impact? Probably not • Volcanoes (Methane hydrates)

  14. Flood Basalt effects • Increased carbon dioxide and global warming • Acid rain from sulphur • Release of methane hydrates from ocean floor

  15. Testing the volcanic hypothesis • For volcanic hypothesis to be credible: • Eruptions must predate the extinction • Extinctions must not be instantaneous • Expect to see pulses of extinction as disaster intensifies

  16. Permian • Sooo… • It’s complicated - plenty of instability: physical, biological and disaster • Insufficient evidence yet to point to a single cause

  17. Cretaceous-Tertiary Extinction • Coincidence:85% species extinction, so it’s real • No big physical changes - many small continents with lots of shelf space, mild climate • No big biological changes preceding the extinction, no big change in ecological structure of the oceans after the extinction • That only leaves catastrophe

  18. K/T Catastrophe • Impact hypothesis • Volcanic hypothesis

  19. Impact scenario • Asteroid about 10 km (6 mi.) struck, probably in Yucatan at Chicxulub

  20. Impact scenario • Asteroid about 10 km (6 mi.) struck, probably in Yucatan at Chicxulub • Immediate heat shock and wildfires near impact site

  21. Impact scenario • Asteroid about 10 km (6 mi.) struck, probably in Yucatan at Chicxulub • Immediate heat shock and wildfires near impact site • Particulates of gypsum (Ca2SO4) cause acid rain, killing plankton

  22. Impact scenario • Asteroid about 10 km (6 mi.) struck, probably in Yucatan at Chicxulub • Immediate heat shock and wildfires near impact site • Particulates of gypsum (Ca2SO4) cause acid rain, killing plankton • Particulates create clouds, block sun, killing plants

  23. Impact scenario • Asteroid about 10 km (6 mi.) struck, probably in Yucatan at Chicxulub • Immediate heat shock and wildfires near impact site • Particulates of gypsum (Ca2SO4) cause acid rain, killing plankton • Particulates create clouds, block sun, killing plants • Temperature drops, killing organisms with no tolerance for cold

  24. Evidence • Crater at Chicxulub

  25. Evidence • Crater at Chicxulub • Iridium spike Asteroids have higher iridium abundance than Earth’s crust. Iridium of Earth is mostly in the mantle and core.

  26. Evidence • Crater at Chicxulub • Iridium spike • Shocked quartz Two directions of lamellae typical of impacts

  27. Evidence • Crater at Chicxulub • Iridium spike • Shocked quartz • Tektites Glass globules from melting of surface and striking object

  28. Evidence • Crater at Chicxulub • Iridium spike • Shocked quartz • Tektites • Soot Carbon in boundary clay from wildfires

  29. Evidence • Crater at Chicxulub • Iridium spike • Shocked quartz • Tektites • Soot • C-13 indicates catastrophic extinction

  30. Who dies? Planktonic orgs. Ocean surface ecosystem Orgs. with poor thermoregulation Who lives? Biological effects: predictions

  31. Who dies? Planktonic orgs. Ocean surface ecosystem Orgs. with poor thermoregulation Who lives? Bottom dwellers who eat dead things Orgs. with dormancy capability Biological effects: predictions

  32. Who actually dies? Planktonic forams Marine reptiles Ammonites Dinosaurs Birds Non-flowering plants Marsupials Biological effects

  33. Who actually lives? Bottom communities: clams, snails, crustaceans, etc. Placental mammals Angiosperms Amphibians Turtles Insects Biological effects

  34. Volcanic hypothesis • Huge volcanic eruption produces climatic change, acid rain • Volcanoes bring up iridium • BUT: • Problems demonstrating that the eruption is the right age • Basaltic eruptions usually produce little ash, so little climate change

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