Transcript Chapter 17: Evolution of Populations

Chapter 17:
Evolution of Populations
Section 17-3:
The Process of Speciation
Isolating Mechanisms
• Natural selection and genetic drift alone to not
create new species
• Speciation is the formation of new species
• Reproductive isolation occurs when a
population splits into 2 groups, and the two
populations can no longer interbreed
• Different species
Isolating Mechanisms
• Behavioral isolation occurs when two
populations that are capable of interbreeding
develop differences in courtship rituals or other
behaviors
• Geographic isolation occurs when two
populations are separated by geographic barriers
• Temporal isolation occurs when two or more
species reproduce at different times
Testing Natural Selection in Nature
• Darwin proposed that Galapagos finches
descended from common ancestor, with natural
selection shaping beaks as they adapted to
different food sources
Testing Natural Selection in Nature
• The Grants measured and recorded beak lengths
• Documented directional selection as
environmental conditions changed
Speciation in Darwin’s Finches
• How founder effect and natural selection lead to
reproductive isolation
• Current hypothesis is speciation in Darwin’s
finches occurred by founding of new
population geographic isolation, changes
in the new population’s gene pool,
behavioral isolation, and ecological
competition
Founders Arrive
• Few finches from South
America arrived in Galapagos
• Founder effect
Geographic Isolation
• Island environment different
from mainland
• Island finch population
evolved into new species
• Some crossed to new island
• Usually don’t fly over water
Changes in Gene Pools
• Populations on each island
adapt to local environments
• Distinct populations form with
distinct phenotypes
Behavioral Isolation
• If you bring populations back
together, they will probably
not breed
• Mating preference
• Now have reproductive
isolation – two distinct species
Competition and Continued Evolution
• Competition requires finches
to develop different
adaptations, different levels of
fitness
• More specialized birds have
less competition
• New species develop