Natural Selection We Can See

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Natural Selection We Can See

• The Case of the Peppered Moth

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• Species become endangered when the population is
  decreased to the point that a stress can affect
  survival.
• Stresses may be natural or human-made.
• Human causes are listed on the next slide.

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H abitat loss I ntroduced Species P ollution P
opulation Growth O ver consumption
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Case of the Peppered Moth

• Peppered moths are a common moth in England.
• There are variations in the coloration of
  peppered moths from silvery white with gray
  speckles to dark gray/black.
• The most common form before 1850 was a mixture of
  white and black called peppered. About 90 of
  the moths found in nature were peppered.

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Case of the Peppered Moth

• There are two alleles for the color of silvery
  moths B for black and b for white. The black
  color is melanin.
• In the laboratory, the moths occur in a ratio of
  1 black2 peppered 1 white.
• BB black, bb white, and Bb peppered.
• The black is the dominant allele causing
  speckling when present.

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Case of the Peppered Moth
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Case of the Peppered Moth

• Peppered moths lived on trees covered by silvery
  lichen.
• During the Industrial Revolution, carbon-fuel
  pollution killed the silvery lichen on urban
  trees.
• Coal soot coated tree trunks causing the trunks
  to become darker.

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Case of the Peppered Moth

• In urban industrial areas, silvery-white peppered
  moths became less common and the dark gray/black
  moths became more common.
• In rural forest regions, the silvery-white
  peppered moth remained the most common type.
• Silvery lichen was still on trees in the rural
  areas.

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Case of the Peppered Moth

• Hypothesis
• Moths that have a camouflage advantage will
  survive and become the most common color type.
• Control natural condition of trees with
  silvery lichen
• Variable carbon soot

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Case of the Peppered Moth

• The next slide shows a tree with silvery lichen.
• Try to find the dark gray peppered moth in the
  next slide.

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Case of the Peppered Moth

• Procedure
• Release the same number of black, peppered,
  and white moths in
• an industrial area where the tree trunks are
  dark and a natural area where the tree trunks
  have silvery lichen.
• 2. Capture and count the surviving moths.
• 3. Compare the populations.

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Case of the Peppered Moth

• Try to find the silvery-white colored peppered
  moth in the next slide.

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Case of the Peppered Moth

• What advantage does camouflage provide the moth?
• Why might the dark-gray variation of peppered
  moth have an advantage in urban areas where tree
  trunks were darkened by coal soot?

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Case of the Peppered Moth
Today, about 90 of the population is light
colored. Why did the population shift back to
pre-Industrial Revolution composition?