How do new species arise?
-- Speciation -• Species: group of organisms that can
interbreed and produce fertile offspring
• Speciation: the process by which genetically
distinct species arise.
Speciation: Formation of new species
• As adaptations and differences accumulate,
the organisms become so different that they
cannot interbreed (reproduce) anymore
Speciation:
Formation of New Species
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If a population becomes separated, or a group of
individuals becomes isolated, they may change over
time.
They may change so much that they cannot
interbreed anymore with the members of the
original population. Reproductive Isolation.
Reproductive Isolation is the first step towards the
formation of a new species
What influences reproductive isolation:
1. Geographic Isolation (Allopatric Speciation)
2. Behavioral Isolation (Sympatric Speciation)
3. Temporal Isolation (Sympatric Speciaton)
1. Geographic Isolation
• A physical barrier separates (splits) the original
population
• As time passes, the environment may selects
for different traits and the 2 populations become
genetically different AND can’t reproduce
• Barriers: Rivers, mountains, bodies of water
Kaibab and Abert Squirrels
Kaibab
Abert
- The Kaibab squirrel
(Sciurus aberti
kaibabensis) became
geographically
isolated from the
common ancestor
about 10,000 years
ago.
- Its closest relative is
the Abert squirrel
(Sciurus aberti aberti)
- They live in opposite
sides of the Grand
Canyon
Wrasses: Original population split up when the
isthmus of Panama was formed
- 2 species now, one on each side of Central America
2. Temporal Isolation
(Time of Reproduction)
• Groups of individuals reproduce at different
times. The genes of the 2 groups do not mix.
• It is happening now with some of the migratory
birds that decide not to migrate.
• The birds that do not migrate start mating
before the migratory ones come back.
• Eventually they might become different enough
that they may not recognize each other.
Robins usually migrate south to warmer climates.
Some are not migrating. They reproduce before
the migrating individuals return.
3. Behavioral Isolation
(Reproductive Behavior changes)
• If 2 populations have different
courtship behaviors, they will not
be able to interbreed
• Different songs (birds) or mating
calls (frogs)
• Different scents (smells)
• A simple mutation can cause a change
Types of Speciation
• Allopatric – the evolution of geographically
isolated populations into distinct species.
• Sympatric - the process through which new
species evolve from a single ancestral species
while inhabiting the same geographic region