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Biology
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2. 16-3 The Process of Speciation
Photo credit: ©MURRAY, PATTI/Animals Animals Enterprises
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3. 16-3 The Process of Speciation
Speciation is the formation of new species.
Chance
Natural selection
A species is a group of organisms that breed with one another and produce fertile offspring.
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Isolating Mechanisms
Isolating Mechanisms
As new species evolve, populations become reproductively isolated from each other (gene pools must be separated)
When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred.
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Isolating Mechanisms
1. Behavioral Isolation (sympatric) 
Behavioral isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior.
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Isolating Mechanisms
2. Geographic Isolation (allopatric)
Geographic isolation occurs when two populations are separated by geographic barriers such as rivers or mountains.
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Isolating Mechanisms
3. Temporal Isolation (sympatric) 
Temporal isolation occurs when two or more species reproduce at different times.
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8. Testing Natural Selection in Nature
Finches in the Galapagos Islands
Honey Creepers in Hawaii
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9. Testing Natural Selection in Nature
Detailed genetic studies have shown that these finches evolved from a species with a more-or-less general-purpose beak. 
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10. Testing Natural Selection in Nature
Detailed genetic studies have shown that these finches evolved from a species with a more-or-less general-purpose beak. 
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11. Testing Natural Selection in Nature
Peter and Rosemary Grant tested Darwin’s hypothesis, which relied on two testable assumptions:
For beak size and shape to evolve, there must be enough heritable variation in those traits to provide raw material for natural selection.
Differences in beak size and shape must produce differences in fitness, causing natural selection to occur.
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12. Testing Natural Selection in Nature
When food was scarce, individuals with large beaks were more likely to survive.
This graph shows the survival rate of one species of ground-feeding finches, the medium ground finch. 
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16-3
When two species do not reproduce because of differences in mating rituals, the situation is referred to as
temporal isolation.
geographic isolation.
behavioral isolation.
reproductive isolation.
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16-3
The most important factor involved in the evolution of the Kaibab and Abert squirrels of the American Southwest appears to be
temporal isolation.
geographic isolation.
behavioral isolation.
different food sources.
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16-3
One finding of the Grants' research on generations of Galápagos finches was that
natural selection did not occur in the finches.
natural selection can take place often and very rapidly.
beak size had no effect on survival rate of the finches.
natural selection was slow and permanent.
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16-3
All of the following played a role in speciation of Galápagos finches EXCEPT
no changes in the gene pool.
separation of populations.
reproductive isolation.
natural selection.
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16-3
Beak size in the various groups of Galápagos finches changed primarily in response to
climate.
mating preference.
food source.
availability of water.
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18. END OF SECTION