Download SPECIATION •Isolation – Divergent Evolution •Adaptive Radiation

3/4/2013
SPECIATION
SPECIATION
BIOLOGY 11
MECHANISMS OF SPECIATION
•Isolation – Divergent Evolution
• Natural selection modifies populations from
one generation to the next, causing them to
evolve.
• Sometimes evolutionary changes are so
great that some organisms can no longer
interbreed with the original species
• When this happens it is called SPECIATION
ISOLATION
• Speciation begins with the isolation of a part
of the population through migration or a
natural barrier
• Ex. Polar bears / Brown bears
•Adaptive Radiation
•Convergent Evolution
ISOLATION/DIVERGENT
EVOLUTION IN DARWIN’S FINCHES
• When isolated populations evolve
independently it is called divergent
evolution
• If 2 populations remain apart long enough
they will become reproductively isolated
• Now they are 2 separate species –
speciation has occurred
ADAPTIVE RADIATION
• Over time, new species may evolve from one
ancestral species as populations evolve to different
niches
• Multiple branching of a family tree is called
adaptive radiation
• “Adaptive” comes from the fact that one ancestral
species must adapt to occupy a variety of niches
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3/4/2013
ADAPTIVE RADIATION…
ADAPTIVE RADIATION IN FINCHES
• Charles
Darwin
noticed
adaptive
radiation in
the finches on
the
Galapagos
CONVERGENT EVOLUTION
• Different
types of
organisms
with different
ancestors
evolve similar
characteristic
s because
they occupy
similar niches
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