A Multispecies Overkill Simulation

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A Multi-species Overkill Simulation

• The end-Pleistocene Mega-faunal Mass Extinction

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The real question (thesis)

• Whether realistically scaled burst of human
  population growth could have resulted in a
  realistic number of extinctions, and whether such
  a model can correctly predict the extinction and
  survival of particular species on the basis of
  their ecological properties.

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What does the simulation show

• This is a fully mechanistic (human hunting) model
  that is fairly accurate and accounts for
  mega-faunal (greater than 100 kg) extinction in
  North America.
• Without invoking climate change and secondary
  ecological effects

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Bighorn Sheep
http//raysweb.net/wildlife/pages/thumbnailindex.h
tml
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Variables included in the modelOr the Inputs

• Anthropogenic
• Hunting ability
• Growth rate
• Human nutritional needs
• Initial invasion points

• Herbivores
• Population densities
• Body masses
• Competition among prey species in geographic
  ranges
• Food availability
• Energy required

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Model Outputs

• Anthropogenic
• Max pop. density
• Max final pop. density

• Herbivores
• Actually extinct
• Actually surviving
• True fates
• Median extinction age

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Simulation Trials

• 47 trials were run with changing variables
• Trials are broken into 8 categories

• Fast dispersal of prey species (1-16)
• Duration of trial 14,000 years (17)
• No dispersal of prey Species (18-33)
• Varying competition among prey species (34-43)
• Initial invasion point Arizona (44)
• Initial invasion point Florida (45)
• Initial invasion point Connecticut (46)
• Initial population seeded uniformly (47)

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Results of Trial 8Single Best Fit Scenario
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Elk (Cervus elaphus)
http//raysweb.net/wildlife/pages/thumbnailindex.h
tml
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Moose (Alces alces)
http//www.aquatic.uoguelph.ca/mammals/freshwater/
accounts/moose.htm
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Buffalo (Bison bison)
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Complicating factors ignored by the model

• Selective hunting on individual prey species
• Human-induced habitat change
• Possible introduction of pandemic diseases to
  native herbivores by humans
• The possibility that humans actually were present
  at low densities long before the extinction

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Simulations show that anthropogenic caused
extinction is possible

• Ecology and fossil record agree with the model.
• Human caused extinction was plausible and
  unavoidable.

• Model serves as a parable of resource
  exploitation.
• Clear mechanism for an instantaneous ecological
  catastrophe

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Simulation Results are Unambiguous

• Human population growth and hunting invariably
  leads to a major mass extinction