Section 16-3
The Process of Speciation
16-3 The Process of Speciation
 Speciation
 The Formation of New Species
 Species
 A Group of Organisms That Breed With One
Another And Produce Fertile Offspring
 Individuals In The Same Species Share A Common
Gene Pool
Isolating Mechanisms
Key Concept:
As New Species Evolve,
Populations Become More
Reproductively Isolated
From Each Other
Isolating Mechanisms
Reproductive Isolation
 When Members Of Two Populations
Cannot Interbreed And Produce
Fertile Offspring

The Populations Have Separate Gene
Pools
Reproductive Isolation
Can Occur Through:
1. Behavioral Isolation
2. Geographic Isolation
3. Temporal Isolation
Behavioral Isolation
Two or More Populations Are Capable of
Interbreeding But Don’t Due To:
 Behavior Differences e.g.
Different Courtship Rituals
 Other Types of Behavior

Courtship Songs
 Courtship Behavior
 Sleep/Wake Cycles, etc.

Behavioral
Isolation
Populations May Share
Eastern
Meadowlark
Western
Meadowlark
Overlapping Territories
Each Species Has
Separate Mating Song
Geographic Isolation
Populations Are Separated By
Geographic Barriers e.g.
Rivers
Mountains
Bodies of Water
Deserts
Geographic Isolation
 Grand Canyon Squirrels
 Colorado River Formation Of
The Grand Canyon Separated
Populations Of Abert Squirrels
About 10,000 Years Ago.
 Separate species – The Kaibab
Squirrel Developed
Kaibab
Abert
Temporal Isolation
Two Or More Species Reproduce
At Separate Times
 Three species of Orchids Each
Release Pollen On Different Days
 Frogs in same pond breed in
different months
Testing Natural Selection In Nature
 Galapagos Finches
 Darwin’s Radiation Theory
Proven By Peter & Rosemary
Grant of Princeton
University
 Required


Variation
Beak Size Must Change
Fitness
Testing Natural Selection In Nature
Grants Realized Darwin’s
Hypothesis Relied On Two
Testable Assumptions:
1. Inheritable Variation Must Be
Present In Current Population
2. Variations Must Produce Enough
Differences In Fitness That
Natural Selection Will Occur
Variation
On A Single Island Grant’s Mapped:
Populations
Breeding Success
Wing, Leg, Beak Length
Beak Depth & Color
Feather Colors
Bird Mass
They Verified Genetic Variation
Natural Selection
The Grant's studied finches on Daphne Major, a
small island (800 sq. yd)
In 1977 island had only 2mm of rain instead of
normal 130mm...
The drought resulted in a loss of 84% of
medium ground finch population.
Most died of starvation!
Rapid Evolution
They Were Able To Document
Several Incidences of Rapid
Evolution On Daphne Major
Over Several Decades
Speciation In Darwin’s Finches
Key Concept
Speciation In The Galapagos Finches
Occurred By Founding Of A New
Population, Geographic Isolation,
Changes In The New Populations Gene
Pool, Reproductive Isolation, And
Ecological Competition
Speciation In Darwin’s Finches
Speciation In Darwin’s Finches
Speciation In Darwin’s Finches
Speciation In Darwin’s Finches
A & B Don’t Mate
Speciation In Darwin’s Finches
Speciation In Darwin’s Finches