check updated study questions and help file on calculating background rates of extinction. exam...
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Check updated study questionsand help file on calculating
background rates of extinction.Exam Resources Section
Cenozoic EraEpoch
Holocene (Recent)
Pleistocene
Paleocene
.01
1.8
5
24
37
58
65
Millionyears ago
Paleogene
Neogene
New periodnames
Cretaceous
Eocene
Oligocene
Miocene
Pliocene
Quaternary
Tertiary
Traditionalperiodnames
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
http://www.sciam.com/2000/0900issue/0900nemecekbox2.html
Early Sites in the Americas
• Clovis People expand into the Americas
• 15,000 years ago• Maybe 20-40,000
years ago
Clovis People’sspear and arrowpoints, scrapers
Human Predation
• Overkill Hypothesis– Archeological evidence of hunting tools– Arrow points etc. embedded in fossilized bones
• Blitzkrieg– Naïve predators or ineffective defenses
New WorldBlitzkrieg?
But . . . Predator-Prey Theory?P
rey
Den
sity
Time
Predator switches to more common prey
Prey is maintainedat low density
Mammoth Hunter . . .or Fish Catcher?
http://www.sciam.com/2000/0900issue/0900nemecek.html
Human-Mediated Extinction
• Predation– Overkill– Blitzkrieg
• Disease
• Fire
Human Rats
http://www.sciam.com/interview/2001/010201macphee/index.html
Gradual Extinctions?
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.
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
Interaction of Hunting and Climate Change
• Mega-herbivores as “ecosystem engineers”– Keystone Herbivore
Hypothesis
• Domino Extinctions
Keystone
Owen-Smith:KeystoneHerbivoreHypothesis(1987)
Removal of keystone herbivores causes extinction cascade for midsize herbivores and their predators (Domino Effect)
The Chicken and the Egg
Large mammals selected against:
Taxa of South American land mammals
Existingbeforeman’s arrival
Genera: 153 56 54
Extinct10,000years ago
Large-bodiedspecies
96%
Large and small species
Pleistocene Survivors - I
• Holarctic Distribution– grizzly bear, moose, elk, wolves, musk-oxen
• But . . .– llama, tapirs, prong-horn antelope, mountain
goat
Pleistocene Survivors - II
• Susceptibility to environmental change– Grizzly bears vs. sabre-toothed tigers
• Vulnerability to human hunters– Mountain goat vs. woolly mammoth
% Extinctions of Terrestrial Genera ( >44 kg adult)
Extinct Living Total % Extinct
Africa 7 42 49 19.3
N. A. 33 12 45 73.7
S. A. 45 12 57 78.9
Australia 19 3 22 86.4
What About Africa?
• Human history?
• Climate change?
• Equivocal evidence