Download 17.3 – The Process of Speciation

17.3 – The Process of Speciation
Chapter 17 – Evolution of
Populations
17.3 The Process of Speciation
17.3 – The Process of Speciation
Isolating Mechanisms
Species: A population or group of populations whose
members can interbreed and produce fertile offspring
Speciation - is the formation of a new species. A
species is a population whose members can
interbreed and produce fertile offspring.
When individuals from a population stop
interbreeding, reproductive isolation has occurred.
17.3 – The Process of Speciation
Reproductive  Isolation
17.3 – The Process of Speciation
Reproductive Isolating Mechanisms
• What types of isolation lead to the formation of new species?
1. Behavioral Isolation
2. Geographic Isolation
3. Temporal isolation
17.3 – The Process of Speciation
Behavioral Isolation
1. Behavioral Isolation - Occurs when two populations that
are capable of interbreeding develop differences in
courtship rituals or other behaviors.
Example: these are similar birds whose habitats overlap, but they
will not mate because they use different songs to attract mates!
17.3 – The Process of Speciation
Behavioral Isolation
Species that are behaviorally
isolated are likely to have complex
mating behaviors, such as
elaborate mating rituals
17.3 – The Process of Speciation
Geographic isolation
2. Geographic Isolation - Occurs when two populations are
separated by geographic barriers
Examples = Rivers, Mountains, Canyons, and bodies of
water.
17.3 – The Process of Speciation
Geographic Isolation
17.3 – The Process of Speciation
Temporal isolation
Temporal isolation - occurs when two or more species
reproduce at different times.
17.3 – The Process of Speciation
Speciation in Darwin’s Finches
• Question: How might the founder effect and natural selection
have produced reproductive isolation that led to the
speciation of Galapagos finches?
Answer: Speciation in Galapagos finches happened by:
founding of a new population,
geographic isolation,
changes in the new population’s gene pool,
behavioral isolation,
and ecological competition.
17.3 – The Process of Speciation
1. Founders Arrive
• A long time ago, a few finches
from SOUTH AMERICA arrived
on one of the Galapagos islands.
• Why? (May have been blown off
course by a storm)
• FOUNDER EFFECT:
Allele frequencies of this new
founding finch population was
different from allele frequencies in the original
South American population.
17.3 – The Process of Speciation
2. Geographic Isolation
• Island environment was different than
South America
• Combination of founder effect,
geographic isolation & natural
selection enabled the island finches
to evolve into a NEW SPECIES-Species A
• Then, a few birds from species A moved
to another island.
• The 2 finch populations on the two islands
were now geographically isolated and
no longer shared a common gene pool!
17.3 – The Process of Speciation
3. Changes in Gene Pools
• Over time, populations on each
island ADAPTED to local
environments
• How? Ex. Beak size and seed size,
directional selection
• Over time, natural selection would
have caused that population to
evolve larger beaks, forming a distinct
population, B, with a new phenotype.
17.3 – The Process of Speciation
4. Behavioral Isolation
• If a few birds from the second island
return back to the first
island, will population A reproduce
with population B?
• Probably not! Different courtship
and mate preferences
• So, differences in beak size, combined
with mating behavior, can lead to
reproductive isolation
• Populations are now 2 distinct species!
17.3 – The Process of Speciation
5. Competition & Continued
Evolution
• As these two new species live
together on the first island, they
compete for seeds
• More specialized birds have less
competition for certain seeds &
food!
• Overtime, species evolve in a way
that increases differences
between them! Species B can
evolve into a new Species- C
17.3 – The Process of Speciation
Speciation in Darwin’s Finches
• The combined processes of geographic isolation on
different islands, genetic change, and behavioral isolation
repeated itself over and over across the Galapagos islands
• Over many generations, the process could have produced
the 13 different finch species found there today!
17.3 – The Process of Speciation
Review Questions
• Why did selection increase genetic variation among
finches on different islands?
• How did selection lead to speciation?
• Why did geographic isolation have to occur before
changes happened in the two gene pools?