Speciation and Extinction

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Speciation and Extinction

• Biogeography
• October 29 - Nov 2

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Speciation and Extinction

• Defining a species
• Morphological definition
• Biological definition
• Subspecies
• Mechanisms of Speciation
• Genetic drift
• Natural selection
• Gene flow
• Types of Speciation
• Allopatric speciation
• Sympatric speciation

• Other Issues
• Convergent evolution
• Parallel evolution
• Coevolution
• Punctuated equilibrium
• Extinction
• Probability of extinction
• Recent extinctions
• Fossil extinctions

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Defining a Species

• Morphologically
• Species are morphologically distinct
• Biologically
• Reproductively isolated (geologically or biol)
• Subspecies
• Populations that are morphologically (and
  therefore presumably) genetically distinct

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Mechanisms of Speciation

• Genetic Drift
• Changes in genetic characteristics of population
  due to pure chance
• Founder Effect
• Natural Selection
• Change in population (genetic/morphological)
  resulting from expression of genetic
  characteristics by individuals in population that
  enhances their survival
• Gene Flow
• Change in genetics of population due to
  introduction of genetic materials from outside
  the population

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Types of Speciation

• Allopatric Speciation
• occurs when pops are geographically isolated so
  gene flow b/w pops cannot occur
• Vicariance events
• Disperal/Founder events
• Peripatric
• Peripheral populations are
• geog. isolated from main
• population and thus genetic
• divergence is accelerated
• (form of Adaptive Radiation)

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Types of Speciation

• Sympatric Speciation
• Speciation occurring within spatially contiguous
  populations
• Parapatric
• evolutionary divergence (speciation) in
  populations that occupy different habitat in the
  same geographic area (sympatric form of adaptive
  radiation)
• Chromosomal changes
• Polyploidy in plants

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Other Issues

• Convergent Evolution
• Unrelated species separated geographically evolve
  similar traits

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Other Issues

• Parallel Evolution
• Descendants of an ancestor now isolated evolve in
  a similar fashion

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Other Issues

• Coevolution
• Mutualistic associations
• Punctuated Equilibrium
• Long periods with no change followed by severe
  environmental changes
• As compared to phyletic gradualism

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Extinction

• The ultimate fate of every species is
  extinction. Brown and Lomolino 2000
• RED QUEEN HYPOTHESIS
• A species must continually evolve in order to
  keep pace with an environment that is perpetually
  changing, because all other species are evolving,
  altering the availability of resources and the
  nature of biotic interactions. Van Valen 1973

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The Probability of Extinction

• Taxon level
• individuals
• subspecies
• species
• more inclusive taxon levels
• trophic cascades

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The Probability of Extinction

• Ecological Groups
• Large body size
• Upper trophic levels
• Highly specialized
• Specifc habitats

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The Probability of Extinction

• Population Size
• Birth rates
• Death rates
• Carrying capacity
• Small populations
• Intrinsic demographic events
• Extrinsic ecological events
• MVP Minimum Viable Population

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The Probability of Extinction
(Quammen 1996 Song of the Dodo, p. 295)
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Recent Extinctions

• Passenger Pigeon
• Barro Colorado Island
• Gray Whale

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Fossil Extinctions

• Mass extinctions
• Permian-Triassic (225 mybp)
• Pleistocene megafauna (10-12K ybp)
• Overkill hypothesis
• Climate hypothesis
• Cretaceous-Tertiary (65 mybp)

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Millenium Ecosystem Assessment 2005