Quaternary Events/Extinctions of the Past
Where have all the Megafauna gone.....?
I. The Facts: once there were megafauna..now there are none
Extinctions occurred
Humans came to North America
Climate changed
II. The Explanations
Overkill (P.A. Martin)
Climate- Evolution
Other Alternatives (a compromise?)
III. Conclusions
Extinctions happen everyday
Will we ever know..
do we care ????
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Megafaunal Extinction
Megafauna: > 44kg (100 lbs)
mostly large grazers, browsers and carnivores
Some examples:
mammoths giant beaver
mastodons giant capybara
sloths camels
sabertooth tigers
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Extinctions occurred without replacement !!!!!!!!!!!!!
Explanations:
Pleistocene Overkill
Human occupation of N. America directly caused extinction of larger
mammals
1) with a gradual destruction of fauna over thousands
of years
2) suddenly in as little as 100 years
Nature of human impact classified as 3 types:
BLITZKRIEG Effect: rapid deployment of human populations w/ big game hunting= rapid demise of big game
INNOVATION Effect: long established human populations adopt new hunting technologies and erase fauna stressed by climate
ATTRITION Effect: extinction takes place relatively slowly
after a long history of human activity b/c loss of habitat and competition for resources
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Climatic Change:
Climatic change theory
1. Extinctions occurred with an episode of climatic change
2. Magnitude of change are correlated with the magnitude of extinctions
3. Mechanisms identified that link climatic change with extinctions given
with type of change extinctions would be the expected result
Many combined reasons for extinction based on climate changes
Increased Seasonality
Decrease plant diversity
Increased anti herbivory mechanisms
Restricted resources
Gestation/Breeding and Birth (Kiltie)
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Increased Seasonality
Axelrod (1967) argues early interglacials were more equitable that the
early holocene/. and it is this loss of equitability that caused extinction
Decrease plant diversity
Gunthrie argues changing seasonal regimes at the end of the Pleistocene
led to an increasingly homogeneous plant community with decreased quality and quantity of
plant resources available
Anti-herbivory mechanisms
Plants may have evolved with increase anti-herbivory mechanisms
Restricted resources led to decreased faunal diversity, body size and
led to
extinction
Gestation/Breeding and Birth (Kiltie)
Shifting birthing and breeding to accommodate drastic climatic
changes isn't feasible for megafauna in short time spans, having offspring
during a cold season or delaying mating may comprise a populations viability
Plaid vs. Stripes
Plaids: mongastrics:
mammoths, horses, camels
Stripes: ruminants:
antelopes, sheep, bison
in Conclusion.............................
It seems to me that it is a combination of factors.
Populations could have been stressed to the breaking point due to climatic
changes and the consequent changes in plant life , gestation and fertility.
Then humans came along and were the final straw.
It seems implausible to rule out one over the other, when we have evidence of
the two occurring simultaneously.