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 arrivedon one of the Galapagos islands.

• Why? (May have been blown offcourse by a storm)

• FOUNDER EFFECT: Allele frequencies of this newfounding finch population was different from allele frequencies in the originalSouth 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 movedto 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 localenvironments

• 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 firstisland, will population A reproducewith population B?• Probably not! Different courtship and mate preferences• So, differences in beak size, combinedwith 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 lesscompetition 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?