Chapter 24 Notes

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Chapter 24 Notes

• The Origin of Species

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The Origin of Species

• There is more to evolution than just explaining
  how adaptations evolve in a population.
• Evolution must also explain macroevolution the
  origin of a new taxonomic group
• Speciation development of a new species

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The Origin of Species

• The fossil record displays two patterns of
  speciation anagenesis and cladogenesis
• Anagenesis the accumulation of changes
  associated with the transformation of one species
  into another
• Cladogenesis the budding of new species from a
  parent species that still exists.

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The Origin of Species
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Concept 24.1

• Species means kind or appearance
• - we distinguish plants and animals by
  differences in appearance

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Concept 24.1

• The biological species concept emphasizes
  reproductive isolation
• - Ernst Mayr (1942)
• Biological species concept defines a species as
  a population whose members have the potential to
  interbreed in nature and produce viable, fertile
  offspring.

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Concept 24.1

• Prezygotic and postzygotic barriers isolate the
  gene pools of biological species
• - any factor that impedes two species from
  producing fertile hybrids contributes to
  reproductive isolation
• - reproductive isolation prevents populations
  form interbreeding even if their ranges overlap

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Concept 24.1

• Prezygotic barriers impede mating between
  species or hinder the fertilization of the ova
• Habitat isolation two species live in different
  habitats low occurrence of interaction

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Concept 24.1

• Behavioral isolation special signals that
  attract mates, along with elaborate behaviors
  unique to a species
• Temporal isolation two species breed at
  different times (day, seasons, years)

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Concept 24.1

• Mechanical isolation anatomically incompatible
• Gametic isolation gametes rarely fuse to form a
  zygote sperm might not be able to travel to the
  ova

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Concept 24.1

• Postzygotic barriers prevent the hybrid zygote
  from developing into a viable, fertile adult
• Reduced Hybrid Viability abort hybrid at some
  embryonic stage

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Concept 24.1

• Reduced hybrid fertility hybrids are completely
  or largely sterile
• - Donkey horse mule
• Hybrid breakdown the first generation of hybrids
  are fertile, but as those mate with one another,
  the offspring of the next generation are sterile

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Concept 24.1

• Evolutionary biologists have proposed several
  alternative concepts of species
• Ecological species concept defines a species in
  terms of its ecological niche, the set of
  environmental resources it uses
• - ex. A parasite may be defined by is
  adaptations to its host

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Concept 24.1

• Pluralistic species concept the factors that are
  most important of the cohesion of individuals as
  a species vary
• Morphological species concept characterize
  species in terms of structural features

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Concept 24.1

• Genealogical species concept defines a species
  as a set of organisms with a unique genetic
  history

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Concept 24.2

• There are two modes of speciation based on how
  gene flow among populations is initially
  interrupted
• Allopatric speciation speciation takes place in
  populations with geographically separate ranges

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Concept 24.2
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Concept 24.2
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Concept 24.2
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Concept 24.2

• Adaptive radiation the speciation of organisms
  through an island chain the islands are far
  apart to permit populations to evolve in
  isolation, but close enough together for the
  occasional dispersion event to occur

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Concept 24.2
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Concept 24.2

• Sympatric speciation speciation takes place in
  geographically overlapping populations
• - chromosomal changes and nonrandom mating
  reduce gene flow

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Concept 24.2
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Concept 24.2

• The punctuated equilibrium model has stimulated
  research on the tempo of speciation
• - paleontologists rarely find gradual
  transitions in fossil forms
• - long periods of stasis (equilibrium)
  punctuated by episodes of speciation

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Concept 24.2