Download Ch 16 SpeciesOrigin

Ch.16 The Origin of Species
• What Is a Species?
• How Do New Species Form?
– allopatric and sympatric speciation
• How Is Reproductive Isolation Between
Species Maintained?
• What Causes Extinction?
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Copyright © 2005 Pearson Prentice Hall, Inc.
What Is a Species?
• Biologists Need a Clear Definition of
Species
• Species Are Groups of Interbreeding
Populations
• Appearance Can Be Misleading
– Members of a species may differ in
appearance
(F16.1 p. 303)
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Copyright © 2005 Pearson Prentice Hall, Inc.
How Do New Species Form?
• Models of allopatric and sympatric
speciation
(F16.2 p. 304)
• Allopatric Speciation
(F16.3 p. 305)
– By Geographic Separation of a Population
• Sympatric Speciation
(F16.4 p. 305)
– By Ecological Isolation of a Population
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Allopatric
Sympatric
original population
original population
geographical isolation
ecological isolation
genetic divergence
genetic divergence
reproductive isolation
reproductive isolation
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Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
How Do New Species Form?
• Changes in Chromosome Number Can
Lead to Sympatric Speciation
– Speciation by polyploidy
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(F16.5 p. 306)
Case 1: Selffertilization
meiosis
Case 2: Breeds with
normal diploid parent
fertilization
meiosis
viable, diploid gametes
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meiosis fails;
no viable gametes
How Do New Species Form?
• Change Over Time Within a Species
Can Cause Apparent “Speciation” in the
Fossil Record
– Interpreting an evolutionary tree (F16.6 p. 307)
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time
present
past
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Inc.
change
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in form
How Do New Species Form?
• Under Some Conditions, Many New
Species May Arise
– Adaptive radiation
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(F16.7 p. 308)
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Copyright © 2005 Pearson Prentice Hall, Inc.
Maintaining Reproductive Isolation
Between Species
(T16.1,p. 310)
• Premating Isolating Mechanisms Prevent
Mating Between Species
– Members of Different Species May Be Prevented
from Meeting
– Different Species May Occupy Different Habitats
• Ecological isolation
(F16.8 p. 309)
– Different Species May Breed at Different Times
• Temporal isolation
(F16.9 p. 309)
– Different Species May Have Different Courtship
Rituals
– Species’ Differing Sexual Organs May Foil Mating
Attempts
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Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Maintaining Reproductive Isolation
Between Species (T16.1,p. 310)
• Postmating Isolating Mechanisms Limit
Hybrid Offspring
– One Species’ Sperm May Fail To Fertilize
Another Species’ Eggs
– Hybrid Offspring May Survive Poorly
– Hybrid Offspring May Be Infertile
• Mechanisms of Reproductive Isolation
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Copyright © 2005 Pearson Prentice Hall, Inc.
What Causes Extinction?
• Localized Distribution & Overspecialization Make
Species Vulnerable in Changing Environments
– Very localized distribution can endanger a species
(F16.10 p. 311)
– Extreme specialization places species at risk
(F16.11 p. 311)
– Ethiopian wolves
(FE16.1 p. 312)
– Interactions with Other Organisms May Drive a
Species to Extinction
– Habitat Change and Destruction Are the Leading
Causes of Extinction
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.