Convergent Evolution

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Convergent Evolution
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Convergent Evolution
South American "poison" frogs and ants and their
cousins in Madagascar. Both derive its poison
from a steady diet of ants.
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(No Transcript)
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Shark skeleton is made of _________________
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milkweed
African Milk Tree      
Cactus
fleshy members of the euphorbia and milkweed
families occur mainly in desert regions in Asia
and especially Africa
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Coevolution
Common Garter Snake
Newt
Ants and acacia tree
Heliconia
Hermit hummingbirds
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Adaptive Radiation
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Adaptive Radiation
MAMMALIAN FORELIMBS

• Through natural selection, the form of mammalian
  forelimbs has been modified during the last 65
  million years into many shapes to perform a
  variety of functions.
• By adapting to forest, plains, air, water, and
  underground, mammals have been able to radiate
  (like the sun's rays) into a diversity of
  habitats.
• Studies of comparative anatomy well illustrate
  the "descent with modification" of Darwin and the
  branching out of species from a common ancestor.

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Descendants of a single ancestral plant species
have evolved into many different forms in Hawaii,
collectively called the silversword alliance.
Counterclockwise from above, a vine, mat, shrub,
tree, and the silversword
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Gradualism
If evolution is slow and steady, wed expect to
see the entire transition, from ancestor to
descendent, displayed as transitional forms over
a long period of time in the fossil record.
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Punctuated Equilibrium
1. Stasis A population of mollusks is
experiencing stasis, living, dying, and getting
fossilized every few hundred thousand years.
Little observable evolution seems to be occurring
judging from these fossils.
2. Isolation A drop in sea level forms a lake
and isolates a small number of mollusks from the
rest of the population.
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• Strong selection and rapid change
• The small, isolated population experiences strong
  selection and rapid change because of the novel
  environment and small population size
• The environment in the newly formed lake exerts
  new selection pressures on the isolated mollusks.
  
• The isolated population undergoes rapid
  evolutionary change.

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Reintroduction Sea levels rise, reuniting the
isolated mollusks with their sister lineage

• Expansion and stasis
• The isolated population expands into its past
  range.
• Larger population size and a stable environment
  make evolutionary change less likely.
• The formerly isolated branch of the mollusk
  lineage may out-compete their ancestral
  population, causing it to go extinct

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This process would produce the following pattern
in the fossil record