Extinction: past, present, future

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Extinction past, present, future

• Gwen Raitt

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What is Extinction?

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• Extinction is the result of failing to adapt to
  environmental changes (Futuyma 1998). Mechanisms
  of extinction act at the population/metapopulation
  level (Barbault Sastrapradja 1995).

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Populations

• A population is a group of individuals of a given
  species living in a specific geographic area at
  one time.
• Population size and survival depend on
• The availability of resources
• The amount of suitable habitat
• Predation/parasitism
• Disease
• Social interactions

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Mechanisms of Extinction in Single Populations

• Population extinction is certain if, in the long
  term, the mortality rate is higher than the birth
  rate.
• Extinction mechanisms act by affecting the
  mortality and birth rates. The mechanisms may be
  grouped into four categories for single
  populations
• Allee effects
• Demographic uncertainty
• Environmental uncertainty
• Natural catastrophes
• Loss of genetic diversity
• Mechanisms may interact, compounding the effect
  on the population.
• Population size is critical to survival.

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Metapopulations

• A metapopulation is made up of a number of
  spatially separated, extinction-prone local
  populations (or subpopulations) that are linked
  by migration. Other than the classical
  metapopulation, the following types are
  recognized
• Mainland-island metapopulations
• Source-sink metapopulations
• Non-equilibrium metapopulations.
• Metapopulation survival depends on
• Local population survival
• Unoccupied suitable habitat at suitable
  distances
• Sufficient migration for colonization of
  unoccupied habitat to occur.

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Mechanisms of Extinction in Metapopulations

• Extinction of a metapopulation is certain if the
  extinction rate of local populations exceeds the
  rate at which new populations are established.
• Local population extinction mechanisms are those
  of single populations.
• The mechanisms acting at the metapopulation
  level may be grouped into two categories
• Colonization-extinction uncertainty
• Regional uncertainty

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Background Extinction and Extinction Rates

• Extinction is natural (Freeman Herron 1998).
  The normal extinction rate is known as background
  extinction or the background extinction rate
  (Futuyma 1998).
• Background extinction rates are constant within
  clades but vary greatly between clades (Freeman
  Herron 1998).
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Mass Extinctions

• Extinction events were used to demarcate the
  geological time periods (Leakey Levin 1995).
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• Raup Sepkoski (1984) suggest that mass
  extinction events occur periodically (Futuyma
  1998).

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End Ordovician Mass Extinction

• Second largest of the Big Five mass extinctions
  (Futuyma 1998).
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• Possible causes include a drop in temperature and
  a drop in sea level (Futuyma 1998).

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Late Devonian Mass Extinction

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End Permian Mass Extinction

• Biggest of the Big Five mass extinctions
  (Futuyma 1998).
• Marine diversity lost 51 of the families of
  skeletonised invertebrates (Futuyma 1998).
• On land the extinction was less severe, some
  families of amphibians and therapsids were lost,
  some insect orders were lost and the dominant
  plants changed (Futuyma 1998).
• Possible causes include a variable climate, a
  drop in sea level and high volcanic activity
  (Futuyma 1998).

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End Triassic Mass Extinction

• Loss of marine ammonoids and bivalves (Futuyma
  1998).
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End Cretaceous Mass Extinction

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Present Mass Extinction

• There is evidence that the extinctions on New
  Zealand and the Pacific Islands after human
  colonization were ultimately caused by humans
  (Caughley Gunn 1996).
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Human Extinction?

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Conclusions the Future?

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