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Extinction Rates in the Cenozoic Era

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23 diapositives · 294 Views · Dec 19, 2019

Explore background extinction rates and factors contributing to the mass extinctions of large mammals in the Cenozoic Era. Study the impact of human activity, climate change, and predator-prey dynamics on biodiversity loss.

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  1. Check updated study questionsand help file on calculating background rates of extinction.Exam Resources Section

  2. Cenozoic Era Epoch Traditional period names Million years ago New period names .01 Holocene (Recent) Quaternary Pleistocene 1.8 Neogene Pliocene 5 Miocene 24 Tertiary Oligocene 37 Paleogene Eocene 58 Paleocene 65 Cretaceous

  3. American Pleistocene Extinctions • 135 species of large mammals went extinct in N. and S. America about 11,000 years ago. • Why? • Climate change • Human mediated

  4. Early Sites in the Americas • Clovis People expand into the Americas • 15,000 years ago • Maybe 20-40,000 years ago http://www.sciam.com/2000/0900issue/0900nemecekbox2.html

  5. Clovis People’sspear and arrowpoints, scrapers

  6. Human Predation • Overkill Hypothesis • Archeological evidence of hunting tools • Arrow points etc. embedded in fossilized bones • Blitzkrieg • Naïve predators or ineffective defenses

  7. New WorldBlitzkrieg?

  8. But . . . Predator-Prey Theory? Predator switches to more common prey Prey Density Prey is maintained at low density Time

  9. Mammoth Hunter . . .or Fish Catcher? http://www.sciam.com/2000/0900issue/0900nemecek.html

  10. Human-Mediated Extinction • Predation • Overkill • Blitzkrieg • Disease • Fire

  11. Human Rats http://www.sciam.com/interview/2001/010201macphee/index.html

  12. Gradual Extinctions?

  13. Climate-Change Hypothesis • ME took place during the last glacial retreat 10 to 11,000 years ago. • Less savanna and grasslands, and more deciduous forests and swamp environments. • Hypothesis: Mega-herbivores went extinct and destabilized communities. The whole pyramid tumbled.

  14. Evidence Against • No large-scale extinctions of mega-vertebrates for previous glacial retreats. • More extinctions expected in areas most affected by climate change • north of N.A. and tropics of S.A

  15. Interaction of Hunting and Climate Change • Mega-herbivores as “ecosystem engineers” • Keystone Herbivore Hypothesis • Domino Extinctions

  16. Keystone Removal of keystone herbivores causes extinction cascade for midsize herbivores and their predators (Domino Effect) Owen-Smith: Keystone Herbivore Hypothesis (1987)

  17. The Chicken and the Egg

  18. Large mammals selected against: Taxa of South American land mammals Large and small species Existing before man’s arrival Extinct 10,000 years ago Large-bodied species Genera: 153 56 54 96%

  19. Pleistocene Survivors - I • Holarctic Distribution • grizzly bear, moose, elk, wolves, musk-oxen • But . . . • llama, tapirs, prong-horn antelope, mountain goat

  20. Pleistocene Survivors - II • Susceptibility to environmental change • Grizzly bears vs. sabre-toothed tigers • Vulnerability to human hunters • Mountain goat vs. woolly mammoth

  21. % Extinctions of Terrestrial Genera ( >44 kg adult)

  22. What About Africa? • Human history? • Climate change? • Equivocal evidence