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Time Line
• 1.8 MYBP Beginning of Pleistocene
• 1.7 MYBP Ancestral mammoth arrives in
America
• ~ 0.2 MYBP Modern humans evolve in Africa
• ~ 0.015 MYBP Modern humans arrive in
America
• 0.01 MYBP 135 spp. extinct, last glacial retreat
Dispersal of Humans
Nature 7 Dec. 2000 p. 653.
Climate Change in Pleistocene
Humans arrive
in Australia
Humans arrive
in America
Australia
• Colonized ~ 50,000
years ago.
• No global warming at
this time.
• Offers a natural
experiment to compare
human predation and
climate change.
Genyornis
Gifford Miller, 1999
Genyornis (1999 Research!)
Miller et al., 1999. Science 283: 205-208
Summary (but 8 years ago!)
• “From consideration of all of these stories
for different continents there does not
appear to any one factor responsible for the
late Pleistocene extinctions . . . What is
likely is that the primary lethal effect was
the combination of these factors, acting in a
synergistic manner on a fauna
unaccustomed to so many disruptions at
once.” Burney 1993.
My Opinion
• Human Hunting
– Almost certainly
– More work needed on early social structure
• Humans as Disease Vectors
– Intriguing
• Predator-Prey Theory
– Not an issue in America or Australia
– Relevant to Africa
• Climate Change
– Probably a factor in America
Are we on the verge of a
MASS EXTINCTION?
Review: Deterministic Threats
• Change in physical environment
– climate change
– habitat destruction
– pollution
• Change in biotic environment
– Competition
– Predation (including disease and human hunting)
– Mutualism
Current Extinction Methods of
Humans
• Overkill (Stellar’s sea cow)
• Introduced species
– predators, disease, competitors
• Habitat destruction
• Global climate change
• Warfare
The Last Stellar’s Sea Cow, 1768
Whales Hunted to Near Extinction
• 1800’s - A record three
year cruise killed <
100 whales.
• 1933 - ~30,000 whales
killed, 2.5 million
barrels of whale oil.
• 1967 - ~60,000 whales
killed, 1.5 million
barrels of oil
Introduced Predators
Domestic animals
become feral predators
Brown tree snake
(Guam rail)
Tibbles eats all
Stephan Island
Wrens (1894)
W.B. Espeut introduces
mongooses onto Jamaica (1872)
Bird Extinctions in Eastern N.A.
The Heath Hen: Multiple Causes
Nature Conservancy magazine
July/August 1998 p. 8-9
Disease
New Scientist 5 August 2000 p.35. Article by Debora MacKenzie
Humans and Disease
http://www.sciencemag.org/cgi/content/full/287/5452/443
Lyme Disease
Deforestation
• 110,000 km2 per year, 20 hectares per
minute (A. Sommer, 1976)
• 55 km2 per year (an area the size of WV),
10 hectares per minute (P. and A. Ehrlich
• 150,000 km2 per year, 25 hectares per
minute, one football field every second (N.
Myers 1989).
Deforestation