1. Chapter 14
The Origin of Species

2. DEFINING SPECIES
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3. 14.1 The origin of species
Microevolution is the change in the gene pool of a population from one generation to the next.
Speciation is the process by which one species splits into two or more species.
Student Misconceptions and Concerns
Students might not realize that evolutionary change includes both (a) linear events, in which a species changes over time, and (b) branching events, which produce new species and diversity. Some students simply expect that whenever new species evolve, they replace their ancestors.
Teaching Tips
Challenge your students to explain why the field of paleontology has largely been concerned with macroevolution. The broader perspective of evolutionary change studied by paleontologists rarely permits an examination of change within a species.
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4. 14.2 Defining a Species
The biological species concept defines a species as
a group of populations,
whose members have the potential to interbreed in nature, and
produce fertile offspring.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
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5. 14.2 There are several ways to define a species
The biological species concept can be problematic.
Some pairs of clearly distinct species occasionally interbreed and produce hybrids.
For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears.
Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild.
Reproductive isolation cannot usually be determined for extinct organisms known only from fossils.
Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually.
Therefore, alternate species concepts can be useful.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
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6. 14.2 There are several ways to define a species
The morphological species concept
classifies organisms based on observable physical traits and
can be applied to
asexual organisms and
fossils.
However, there is some subjectivity in deciding which traits to use.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
© 2012 Pearson Education, Inc. 6

7. 14.2 There are several ways to define a species
The phylogenetic species concept
defines a species as the smallest group of individuals that shares a common ancestor and thus
forms one branch of the tree of life.
Biologists trace the phylogenetic history of a species by comparing its
morphology or
DNA.
However, defining the amount of difference required to distinguish separate species is a problem.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
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8. 14.2 Reproductive Isolation is Primary Factor in Speciation
Reproductive isolation
prevents members of different species from mating with each other,
prevents gene flow between species, and
maintains separate species.
Therefore, species are distinct from each other because they do not share the same gene pool.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
© 2012 Pearson Education, Inc. 8

9. 14.3 Reproductive barriers keep species separate
Reproductive barriers
serve to isolate the gene pools of species and
prevent interbreeding.
Depending on whether they function before or after zygotes form, reproductive barriers are categorized as
prezygotic or
postzygotic.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.
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10. Individuals of different species Prezygotic Barriers
Figure 14.3A
Individuals of different species
Prezygotic Barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Fertilization
Postzygotic Barriers
Figure 14.3A Reproductive barriers between species
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Viable, fertile offspring 10

11. 14.3 Reproductive barriers keep species separate
Five types of prezygotic barriers prevent mating or fertilization between species.
In habitat isolation, two species live in the same general area but not in the same kind of place.
In temporal isolation, two species breed at different times (seasons, times of day, years).
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.
Video: Blue-footed Boobies Courtship Ritual
Video: Albatross Courtship Ritual
Video: Giraffe Courtship Ritual
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12. 14.3 Reproductive barriers keep species separate
Prezygotic Barriers, continued
In behavioral isolation, there is little or no mate recognition between females and males of different species.
In mechanical isolation, female and male sex organs are not compatible.
In gametic isolation, female and male gametes are not compatible.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.
© 2012 Pearson Education, Inc. 12

13. 14.3 Reproductive barriers keep species separate
Three types of postzygotic barriers operate after hybrid zygotes have formed.
In reduced hybrid viability, most hybrid offspring do not survive.
In reduced hybrid fertility, hybrid offspring are vigorous but sterile.
In hybrid breakdown,
the first-generation hybrids are viable and fertile but
the offspring of the hybrids are feeble or sterile.
Student Misconceptions and Concerns
Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry?
Teaching Tips
Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.
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14. MECHANISMS OF SPECIATION
MECHANISMS OF SPECIATION
KEY: Reproduction between embers of species must become disrupted, leading to establishment of permanent reproductive barriers!
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15. 14.4 In allopatric speciation, geographic isolation leads to speciation
In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools.
Isolated populations will no longer share changes in allele frequencies caused by
natural selection,
genetic drift, and/or
mutation.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation.
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16. 14.4 In allopatric speciation, geographic isolation leads to speciation
Gene flow between populations is initially prevented by a geographic barrier. For example
the Grand Canyon and Colorado River separate two species of antelope squirrels, and
the Isthmus of Panama separates 15 pairs of snapping shrimp.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation.
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17. South rim North rim A. harrisii A. leucurus Figure 14.4A
Figure 14.4A Allopatric speciation of geographically isolated antelope squirrels 17

18. Isthmus of Panama A. formosus A. nuttingi ATLANTIC OCEAN PACIFIC OCEAN
Figure 14.4B
A. formosus
A. nuttingi
ATLANTIC OCEAN
Isthmus of Panama
PACIFIC OCEAN
Figure 14.4B Allopatric speciation in snapping shrimp
A. panamensis
A. millsae 18

19. 14.5 Reproductive barriers can evolve as populations diverge
How do reproductive barriers arise?
Experiments have demonstrated that reproductive barriers can evolve as a by-product of changes in populations as they adapt to different environments.
These studies have included
laboratory studies of fruit flies and
field studies of monkey flowers and their pollinators.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
When discussing Module 14.5, consider referring back to Figure 14.3A. Challenge students to explain how each of the prezygotic barriers might impact the evolution of a new species.
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20. Initial sample of fruit flies
Figure 14.5A
Initial sample of fruit flies
Starch medium
Maltose medium
Mating experiments
Female
Female
Results
Population #1
Population #2
Starch
Maltose
Starch 22 9
Pop#1 18 15
Figure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sources
Male
Male 8 20 12 15
Pop#2
Maltose
Number of matings in experimental groups
Number of matings in starch control groups 20

21. Pollinator choice in typical monkey flowers
Figure 14.5B
Pollinator choice in typical monkey flowers
Pollinator choice after color allele transfer
Typical M. lewisii (pink)
M. lewisii with red-color allele
Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice.
Typical M. cardinalis (red)
M. cardinalis with pink-color allele 21

22. 14.6 Sympatric speciation takes place without geographic isolation
Sympatric speciation occurs when a new species arises within the same geographic area as a parent species.
How can reproductive isolation develop when members of sympatric populations remain in contact with each other?
Gene flow between populations may be reduced by
polyploidy,
habitat differentiation, or
sexual selection.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
The Silvery Salamander, Ambystoma platineum, is a triploid, all-female species living in parts of the U.S. Midwest. It is believed to have formed by the hybridization of two related species thousands of years ago. It is an unusual example of sympatric speciation in animals. A good starting point for learning more about this species is
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23. 14.8 Isolated islands are often showcases of speciation
Most of the species on Earth are thought to have originated by allopatric speciation.
Isolated island chains offer some of the best evidence of this type of speciation.
Multiple speciation events are more likely to occur in island chains that have
physically diverse habitats,
islands far enough apart to permit populations to evolve in isolation, and
islands close enough to each other to allow occasional dispersions between them.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
1. An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.
2. Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration.
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24. 14.8 Isolated islands are often showcases of speciation
The evolution of many diverse species from a common ancestor is adaptive radiation.
The Galápagos Archipelago
is located about 900 km (560 miles) west of Ecuador,
is one of the world’s great showcases of adaptive radiation,
was formed naked from underwater volcanoes,
was colonized gradually from other islands and the South America mainland, and
has many species of plants and animals found nowhere else in the world.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
1. An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.
2. Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration.
© 2012 Pearson Education, Inc. 24

25. 14.8 Isolated islands are often showcases of speciation
The Galápagos islands currently have 14 species of closely related finches, called Darwin’s finches, because Darwin collected them during his around- the-world voyage on the Beagle.
These finches
share many finchlike traits,
differ in their feeding habits and their beaks, specialized for what they eat, and
arose through adaptive radiation.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
Teaching Tips
1. An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.
2. Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration.
© 2012 Pearson Education, Inc. 25

26. Cactus-seed-eater (cactus finch)
Figure 14.8
Cactus-seed-eater (cactus finch)
Tool-using insect-eater (woodpecker finch)
Figure 14.8 Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet
Seed-eater (medium ground finch) 26

27. 14.11 Speciation can occur rapidly or slowly
There are two models for the tempo of speciation.
The punctuated equilibria model draws on the fossil record, where species
change most as they arise from an ancestral species and then
experience relatively little change for the rest of their existence.
Other species appear to have evolved more gradually.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
4. The concept of rarity is likely to be misunderstood when applied to geologic time. Events such as major floods, earthquakes, or asteroid impacts, which might be so rare as to occur every 1,000 years, are actually common in geological terms. Students might not realize that 1,000 such events would be expected to occur over a million years.
Teaching Tips
Have your students think of analogous examples of punctuated equilibrium in our culture. One such example is the switch from vinyl records to compact discs, with the brief transitional form of cassette tapes (which students currently entering college may barely remember). Between the years 1900 and 2000, there were both long periods of stasis (vinyl records) and a relatively short period of transition to CDs and now to digital music files (who knows how long they will last?) Similarly, high-definition television is a new technology replacing more than 50 years’ worth of older technology. Debating the validity of analogies can itself be instructive as students articulate the biological principles and compare them to the analogies.
Animation: Macroevolution
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28. Punctuated pattern Gradual pattern Time Figure 14.11
Figure Two models for the tempo of speciation
Time 28

29. 14.11 Speciation can occur rapidly or slowly
What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)?
In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years.
Overall, the time between speciation events averaged 6.5 million years.
Student Misconceptions and Concerns
1. Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.
2. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).
3. Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error.
4. The concept of rarity is likely to be misunderstood when applied to geologic time. Events such as major floods, earthquakes, or asteroid impacts, which might be so rare as to occur every 1,000 years, are actually common in geological terms. Students might not realize that 1,000 such events would be expected to occur over a million years.
Teaching Tips
Have your students think of analogous examples of punctuated equilibrium in our culture. One such example is the switch from vinyl records to compact discs, with the brief transitional form of cassette tapes (which students currently entering college may barely remember). Between the years 1900 and 2000, there were both long periods of stasis (vinyl records) and a relatively short period of transition to CDs and now to digital music files (who knows how long they will last?) Similarly, high-definition television is a new technology replacing more than 50 years’ worth of older technology. Debating the validity of analogies can itself be instructive as students articulate the biological principles and compare them to the analogies.
© 2012 Pearson Education, Inc. 29

30. You should now be able to
Distinguish between microevolution and speciation.
Compare the definitions, advantages, and disadvantages of the different species concepts.
Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations of closely related species from interbreeding.
Explain how geologic processes can fragment populations and lead to speciation.
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31. You should now be able to
Explain how reproductive barriers might evolve in isolated populations of organisms.
Explain how sympatric speciation can occur, noting examples in plants and animals.
the adaptive radiation of the Galápagos finches.
Compare the gradual model and the punctuated equilibrium model of evolution.
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32. Original population a. b. Figure 14.UN02
Figure 14.UN02 Connecting the Concepts, question 1 a. b. 32