Species diversity of major groups of organisms

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Species diversity of major groups of organisms

• Described of species
• Estimated of species
• How are estimates calculated?

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1.65 million described species
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Estimates of Total Species Diversity
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Methods for estimating total species diversity

• Extrapolation from expert estimates and rates of
  species descriptions
• (e.g. Wilson)

• Extrapolation from thorough collection of one
  taxon at one site
• (e.g. Erwin)

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Estimates of total species diversity
extrapolation from expert opinion
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Extrapolation from diversity of one taxon at one
site

• Technique developed by Terry Erwin of Smithsonian
  Institution
• Used canopy fogging technique on Luehea seemannii
  in Panama
• Found 1200 total beetles
• Knew that 162 were specific to Luehea

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Assumptions

• 50,000 tropical tree species, each w/ 162
  host-specialist beetles 8 x 106 beetle species
• Canopy beetles are 40 of all canopy arthropods
  8 x 106 x 2.5 20 x 106 canopy arthopods
• 2x as many canopy as ground arthropod species,
  add another 10 x 106 ground arthropods
• 10 x 106 10 x 106
  30 x 106 total arthopod
  species

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Global species diversity

• We dont know the actual of species
• best guesses vary by an order of magnitude
• Cost of describing species
• Cost of not describing species

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Evolution and Natural Selection

• The generators of biodiversity

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Why is an understanding of evolution critical
for understanding biodiversity?

• All organisms have evolved to present state from
  earliest single-celled living organisms
• Species differentiate from each other via the
  process of evolution by natural selection

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Theory of evolution

• Charles Darwin (1809 -1882)
• Darwin biography
• Trip to South America aboard ship--published
  Voyage of the Beagle
• Returned to England to develop ideas
• Published Origin of Species in 1859

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Darwin proposed the theory of evolution by
natural selection

• Made observations
• Inferred relationships
• Used logic to arrive at conclusion

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Definitions

• Principle of common descent--all living organisms
  descended from common ancestor
• Natural selection-- differential success in
  reproduction
• Fitness--having features that allow survival to
  produce offspring that reproduce
  (context-dependent)
• Adaptation--n. A feature of an organism that
  confers fitness v. the process of acquiring such
  a feature through evolution by natural selection

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Darwinian Logic

• Observations
• Normal levels of fertility lead to exponential
  population increase.
• Most populations normally stable (except for
  seasonal fluctuations).
• Natural resources are limited.

• Inference 1
• Production of more individuals than the
  environment can support leads to a struggle for
  existence among individuals of a population

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Darwins First Conclusion

• Only a fraction of offspring born in each
  generation survive to reproduce.
• The survivors are, by definition, fit.

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Darwinian Logic II.

• Observations
• Individuals in a population vary
• Much variation is heritable.

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Inference 2

• Individuals whose inherited characteristics fit
  them best to their environment are likely to
  leave more offspring than less fit individuals.

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Inference 3

• Unequal ability of individuals to survive and
  reproduce leads to a gradual change in a
  population, with favorable characteristics
  accumulating over the generations.

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Natural Selection

• differential success in reproduction
• contrast to artificial selection, or selective
  breeding of plants and animals to achieve desired
  characteristics
• product of natural selection is adaptation
• Natural selection occurs from the interaction
  between the environment and the inherent
  variability in a population.
• Variations in a population arise by chance, but
  natural selection is not a chance phenomenon
  since environmental factors set definite criteria
  for reproductive success.

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Inference 1
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production of more individuals than the
environment can support leads to a struggle for
existence among individuals of a population
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