1. Chapter 17 – Evolution of Populations
17.3 The Process of Speciation

2. 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.

3. Reproductive  Isolation

4. Reproductive Isolating Mechanisms
What types of isolation lead to the formation of new species? Behavioral Isolation
2. Geographic Isolation
3. Temporal isolation

5. Behavioral Isolation
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!

6. Behavioral Isolation
Species that are behaviorally isolated are likely to have complex mating behaviors, such as elaborate mating rituals

7. Geographic isolation
2. Geographic Isolation - Occurs when two populations are separated by geographic barriers
Examples = Rivers, Mountains, Canyons, and bodies of water.
For example, the Kaibab squirrel is a subspecies of the Abert’s squirrel that formed when a small population became isolated on the north rim of the Grand Canyon. Separate gene pools formed, and genetic changes in one group were not passed on to the other.

8. Geographic Isolation

9. Temporal isolation
Temporal isolation - occurs when two or more species reproduce at different times.
Eastern spotted skunks breed mostly in the later winter months and give birth in late Spring to early Summer.
Western spotted skunks typically breed in September

10. 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.

11. 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.

12. 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!

13. 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.

14. 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!

15. 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

16. 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. 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?