1. Chapter 14
The Origin of Species

2. Introduction Many species of cormorants around the world can fly.
Many species of cormorants around the world can fly.
Cormorants on the Galápagos Islands cannot fly.
How did these flightless cormorants get to the Galápagos Islands?
Why are these flightless cormorants found nowhere else in the world?
© 2012 Pearson Education, Inc. 2

3. Mechanisms of Speciation
Figure 14.0_1
Chapter 14: Big Ideas
Figure 14.0_1 Chapter 14: Big Ideas
Defining Species
Mechanisms of Speciation 3

4. Figure 14.0_2
Figure 14.0_2 Flightless cormorant 4

5. Introduction
An ancestral cormorant species is thought to have flown from the Americas to the Galápagos Islands more than 3 million years ago.
Terrestrial mammals could not make the trip over the wide distance, and no predatory mammals naturally occur on these islands today.
Without predators, the environment of these cormorants favored birds with smaller wings, perhaps channeling resources to the production of offspring.
© 2012 Pearson Education, Inc. 5

6. DEFINING SPECIES
© 2012 Pearson Education, Inc. 6

7. 14.1 The origin of species is the source of biological diversity
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.
Every time speciation occurs, the diversity of life increases.
The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.
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.
© 2012 Pearson Education, Inc. 7

8. Figure 14.1
Figure 14.1 Great cormorant (Phalacrocorax carbo) drying its broad wings 8

9. 14.2 There are several ways to define a species
The word species is from the Latin for “kind” or “appearance.”
Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions.
How similar are members of the same species?
What keeps one species distinct from others?
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. 9

10. 14.2 There are several ways to define 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.
Therefore, members of a species are similar because they reproduce with each other.
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. 10

11. 14.2 There are several ways to define a species
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. 11

12. Figure 14.2A
Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right) 12

13. Figure 14.2A_1
Figure 14.2A_1 Similarity between two species: the eastern meadowlark (part 1) 13

14. Figure 14.2A_2
Figure 14.2A_2 Similarity between two species: the western meadowlark (part 2) 14

15. Figure 14.2B
Figure 14.2B Diversity within one species 15

16. 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.
© 2012 Pearson Education, Inc. 16

17. Grizzly bear Polar bear Hybrid “grolar” bear Figure 14.2C
Figure 14.2C Hybridization between two species of bears
Hybrid “grolar” bear 17

18. Figure 14.2C_1
Grizzly bear
Figure 14.2C_1 Hybridization between two species of bears (part 1) 18

19. Figure 14.2C_2
Polar bear
Figure 14.2C_2 Hybridization between two species of bears (part 2) 19

20. Hybrid “grolar” bear Figure 14.2C_3
Figure 14.2C_3 Hybridization between two species of bears (part 3) 20

21. 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. 21

22. 14.2 There are several ways to define a species
The ecological species concept
defines a species by its ecological role or niche and
focuses on unique adaptations to particular roles in a biological community.
For example, two species may be similar in appearance but distinguishable based on
what they eat or
where they live.
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. 22

23. 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.
© 2012 Pearson Education, Inc. 23

24. 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.
© 2012 Pearson Education, Inc. 24

25. 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 25

26. 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
© 2012 Pearson Education, Inc. 26

27. Figure 14.3B
Figure 14.3B Habitat isolation 27

28. Figure 14.3B_1
Figure 14.3B_1 Habitat isolation (part 1) 28

29. Figure 14.3B_2
Figure 14.3B_2 Habitat isolation (part 2) 29

30. Figure 14.3C
Figure 14.3C Temporal isolation 30

31. Figure 14.3C_1
Figure 14.3C_1 Temporal isolation: The eastern spotted skunk (part 1) 31

32. Figure 14.3C_2
Figure 14.3C_2 Temporal isolation: The western spotted skunk (part 2) 32

33. 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. 33

34. Figure 14.3D
Figure 14.3D Behavioral Isolation 34

35. Figure 14.3E
Figure 14.3E Mechanical isolation 35

36. Figure 14.3F
Figure 14.3F Gametic isolation 36

37. 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.
© 2012 Pearson Education, Inc. 37

38. Horse Donkey Mule Figure 14.3G Figure 14.3G Reduced hybrid fertility38

39. Figure 14.3G_1
Figure 14.3G_1 Reduced hybrid fertility: horse (part 1)
Horse 39

40. Figure 14.3G_2
Figure 14.3G_2 Reduced hybrid fertility: donkey (part 2)
Donkey 40

41. Figure 14.3G_3
Figure 14.3G_3 Reduced hybrid fertility: hybrid mule (part 3)
Mule 41

42. MECHANISMS OF SPECIATION
MECHANISMS OF SPECIATION
© 2012 Pearson Education, Inc. 42

43. 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.
© 2012 Pearson Education, Inc. 43

44. 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.
© 2012 Pearson Education, Inc. 44

45. South rim North rim A. harrisii A. leucurus Figure 14.4A
Figure 14.4A Allopatric speciation of geographically isolated antelope squirrels 45

46. Figure 14.4A_1
A. harrisii
Figure 14.4A_1 Allopatric speciation of geographically isolated antelope squirrels (A. harrisii) 46

47. Figure 14.4A_2
A. leucurus
Figure 14.4A_2 Allopatric speciation of geographically isolated antelope squirrels (A. leucurus) 47

48. 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 48

49. 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.
© 2012 Pearson Education, Inc. 49

50. 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 50

51. 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 51

52. Typical M. lewisii (pink)
Figure 14.5B_1
Typical M. lewisii (pink)
Figure 14.5B_1 Transferring an allele between monkey flowers changes flower color and influences pollinator choice (part 1). 52

53. M. lewisii with red-color allele
Figure 14.5B_2
M. lewisii with red-color allele
Figure 14.5B_2 Transferring an allele between monkey flowers changes flower color and influences pollinator choice (part 2). 53

54. Typical M. cardinalis (red)
Figure 14.5B_3
Figure 14.5B_3 Transferring an allele between monkey flowers changes flower color and influences pollinator choice (part 3).
Typical M. cardinalis (red) 54

55. M. cardinalis with pink-color allele
Figure 14.5B_4
Figure 14.5B_4 Transferring an allele between monkey flowers changes flower color and influences pollinator choice (part 4).
M. cardinalis with pink-color allele 55

56. 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
© 2012 Pearson Education, Inc. 56

57. 14.6 Sympatric speciation takes place without geographic isolation
Many plant species have evolved by polyploidy in which cells have more than two complete sets of chromosomes.
Sympatric speciation can result from polyploidy
within a species (by self-fertilization) or
between two species (by hybridization).
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
© 2012 Pearson Education, Inc. 57

58. Parent species 2n = 6 Tetraploid cells 4n = 12
Figure 14.6A_s1 1
Parent species 2n = 6
Tetraploid cells 4n = 12
Figure 14.6A_s1 Sympatric speciation by polyploidy within a single species (step 1) 58

59. Parent species 2n = 6 Tetraploid cells 4n = 12 Diploid gametes 2n = 6
Figure 14.6A_s2 1 2
Parent species 2n = 6
Tetraploid cells 4n = 12
Figure 14.6A_s2 Sympatric speciation by polyploidy within a single species (step 2)
Diploid gametes 2n = 6 59

60. Viable, fertile tetraploid species 4n = 12
Figure 14.6A_s3 1
Self- fertilization 3 2
Parent species 2n = 6
Tetraploid cells 4n = 12
Viable, fertile tetraploid species 4n = 12
Figure 14.6A_s3 Sympatric speciation by polyploidy within a single species (step 3)
Diploid gametes 2n = 6 60

61. Species A 2n = 4 Gamete n = 2 Gamete n = 3 Species B 2n = 6
Figure 14.6B_s1
Species A 2n = 4
Gamete n = 2
Figure 14.6B_s1 Sympatric speciation producing a hybrid polyploid from two different species (step 1)
Gamete n = 3
Species B 2n = 6 61

62. Chromosomes cannot pair Can reproduce asexually
Figure 14.6B_s2
Chromosomes cannot pair
Species A 2n = 4
Gamete n = 2 1
Sterile hybrid n = 5
Figure 14.6B_s2 Sympatric speciation producing a hybrid polyploid from two different species (step 2)
Can reproduce asexually
Gamete n = 3
Species B 2n = 6 2 62

63. Chromosomes cannot pair
Figure 14.6B_s3
Chromosomes cannot pair
Species A 2n = 4
Gamete n = 2 3 1
Sterile hybrid n = 5
Viable, fertile hybrid species 2n = 10
Figure 14.6B_s3 Sympatric speciation producing a hybrid polyploid from two different species (step 3)
Can reproduce asexually
Gamete n = 3
Species B 2n = 6 2 63

64. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation.
Hybridization between two species accounts for most of these species.
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 abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction.
© 2012 Pearson Education, Inc. 64

65. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Polyploid plants include
cotton,
oats,
potatoes,
bananas,
peanuts,
barley,
plums,
apples,
sugarcane,
coffee, and
bread wheat.
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 abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction.
© 2012 Pearson Education, Inc. 65

66. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Wheat
has been domesticated for at least 10,000 years and
is the most widely cultivated plant in the world.
Bread wheat, Triticum aestivum, is
a polyploid with 42 chromosomes and
the result of hybridization and polyploidy.
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 abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction.
© 2012 Pearson Education, Inc. 66

67. Figure 14.7_3
Figure 14.7_3 The evolution of bread wheat, Triticum aestivum 67

68. Sterile hybrid (14 chromosomes) Sterile hybrid (21 chromosomes)
Figure 14.7 AA  BB
Wild Triticum (14 chromo- somes)
Domesticated Triticum monococcum (14 chromosomes) 1
Hybridization AB
Sterile hybrid (14 chromosomes) 2
Cell division error and self-fertilization
AABB DD
T. turgidum Emmer wheat (28 chromosomes)
Wild T. tauschii (14 chromosomes) 3
Hybridization
ABD
Sterile hybrid (21 chromosomes) 4
Cell division error and self-fertilization
Figure 14.7 The evolution of bread wheat, Triticum aestivum
AABBDD
T. aestivum Bread wheat (42 chromosomes) 68

69. Sterile hybrid (14 chromosomes)
Figure 14.7_1 AA  BB
Wild Triticum (14 chromo- somes)
Domesticated Triticum monococcum (14 chromosomes) 1
Hybridization AB
Sterile hybrid (14 chromosomes)
Figure 14.7_1 The evolution of bread wheat, Triticum aestivum (part 1) 2
Cell division error and self-fertilization
AABB DD
T. turgidum Emmer wheat (28 chromosomes)
Wild T. tauschii (14 chromosomes) 69

70. Sterile hybrid (21 chromosomes)
Figure 14.7_2
AABB DD
T. turgidum Emmer wheat (28 chromosomes)
Wild T. tauschii (14 chromosomes) 3
Hybridization
ABD
Sterile hybrid (21 chromosomes)
Figure 14.7_2 The evolution of bread wheat, Triticum aestivum (part 2) 4
Cell division error and self-fertilization
AABBDD
T. aestivum Bread wheat (42 chromosomes) 70

71. 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.
© 2012 Pearson Education, Inc. 71

72. 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. 72

73. 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. 73

74. 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) 74

75. Cactus-seed-eater (cactus finch)
Figure 14.8_1
Figure 14.8_1 Examples of differences in beak shape and size in Galápagos finches (part 1)
Cactus-seed-eater (cactus finch) 75

76. Tool-using insect-eater (woodpecker finch)
Figure 14.8_2
Figure 14.8_2 Examples of differences in beak shape and size in Galápagos finches (part 2)
Tool-using insect-eater (woodpecker finch) 76

77. Seed-eater (medium ground finch)
Figure 14.8_3
Figure 14.8_3 Examples of differences in beak shape and size in Galápagos finches (part 3)
Seed-eater (medium ground finch) 77

78. 14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches
Peter and Rosemary Grant have worked
for more than three decades,
on medium ground finches, and
on tiny, isolated, uninhabited Daphne Major in the Galápagos Islands.
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 work of the Grants with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving.
© 2012 Pearson Education, Inc. 78

79. 14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches
Medium ground finches and cactus finches occasionally interbreed. Hybrids
have intermediate bill sizes,
survive well during wet years, when there are plenty of soft, small seeds around,
are outcompeted by both parental types during dry years, and
can introduce more genetic variation on which natural selection acts.
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 work of the Grants with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving.
© 2012 Pearson Education, Inc. 79

80. Mean beak size Arrival of new species Larger
Figure 14.9
Arrival of new species
Larger
Large beaks can crack large seeds
Competitor species, G. magnirostris
Mean beak size
Smaller beaked G. fortis can feed on small seeds
Severe drought
Severe drought
Figure 14.9 Changes in mean beak size in the medium ground finch (G. fortis)
Smaller
1975
1980
1985
1990
1995
2000
2005
Year 80

81. 14.10 Hybrid zones provide opportunities to study reproductive isolation
What happens when separated populations of closely related species come back into contact with each other?
Biologists try to answer such questions by studying hybrid zones, regions in which members of different species meet and mate to produce at least some hybrid offspring.
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
Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology.
© 2012 Pearson Education, Inc. 81

82. 14.10 Hybrid zones provide opportunities to study reproductive isolation
Over time in hybrid zones
reinforcement may strengthen barriers to reproduction, such as occurs in flycatchers, or
fusion may reverse the speciation process as gene flow between species increases, as may be occurring among the cichlid species in Lake Victoria.
In stable hybrid zones, a limited number of hybrid offspring continue to be produced.
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
Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology.
© 2012 Pearson Education, Inc. 82

83. Three populations of a species
Figure 14.10A
Newly formed species
Three populations of a species 3
Hybrid zone 1 2 4
Gene flow
Gene flow
Figure 14.10A Formation of a hybrid zone
Hybrid individual
Population
Barrier to gene flow 83

84. Male collared flycatcher
Figure 14.10B
Allopatric populations
Sympatric populations
Male collared flycatcher
Male pied flycatcher
Figure 14.10B Reinforcement of reproductive barriers
Pied flycatcher from allopatric
population
Pied flycatcher from sympatric
population 84

85. Allopatric populations Sympatric populations
Figure 14.10B_1
Allopatric populations
Sympatric populations
Male collared flycatcher
Male pied flycatcher
Figure 14.10B_1 Reinforcement of reproductive barriers (part 1) 85

86. Pied flycatcher from allopatric population
Figure 14.10B_2
Pied flycatcher from allopatric
population
Figure 14.10B_2 Reinforcement of reproductive barriers: Pied flycatcher from allopatric population (part 2) 86

87. Pied flycatcher from sympatric population
Figure 14.10B_3
Pied flycatcher from sympatric
population
Figure 14.10B_3 Reinforcement of reproductive barriers: Pied flycatcher from sympatric population (part 3) 87

88. Pundamilia pundamilia
Figure 14.10C
Pundamilia nyererei
Pundamilia pundamilia
Figure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid water
Hybrid: Pundamilia “turbid water” 88

89. 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
© 2012 Pearson Education, Inc. 89

90. Punctuated pattern Gradual pattern Time Figure 14.11
Figure Two models for the tempo of speciation
Time 90

91. 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. 91

92. 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.
© 2012 Pearson Education, Inc. 92

93. 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.
Explain why polyploidy is important to modern agriculture.
Explain how modern wheat evolved.
Describe the circumstances that led to the adaptive radiation of the Galápagos finches.
© 2012 Pearson Education, Inc. 93

94. You should now be able to
Describe the discoveries made by Peter and Rosemary Grant in their work with Galápagos finches.
Explain how hybrid zones are useful in the study of reproductive isolation.
Compare the gradual model and the punctuated equilibrium model of evolution.
© 2012 Pearson Education, Inc. 94

95. Viable, fertile offspring
Figure 14.UN01
Zygote
Viable, fertile offspring
Gametes
Prezygotic barriers
Postzygotic barriers
• Habitat isolation • Temporal isolation • Behavioral isolation • Mechanical isolation • Gametic isolation
• Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown
Figure 14.UN01 Reviewing the Concepts, 14.3 95

96. Original population a. b. Figure 14.UN02
Figure 14.UN02 Connecting the Concepts, question 1 a. b. 96

97. Species reproductive barriers a few hybrids continue to be produced
Figure 14.UN03
Species
may interbreed in a a.
outcome may be b. c. d.
when
when
when
reproductive barriers
are
are
a few hybrids continue to be produced
Figure 14.UN03 Connecting the Concepts, question 2 e. f.
keeps
and
species separate
speciation is reversed 97

98. Species may interbreed in a a. outcome may be b. c. d.
Figure 14.UN03_1
Species
may interbreed in a a.
outcome may be
Figure 14.UN03_1 Connecting the Concepts, question 2 (part 1) b. c. d. 98

99. reproductive barriers
Figure 14.UN03_2 b. c. d.
when
when
when
reproductive barriers
are
are
a few hybrids continue to be produced e. f.
Figure 14.UN03_2 Connecting the Concepts, question 2 (part 2)
keeps
and
species separate
speciation is reversed 99

100. Reinforcement Fusion Stability Figure 14.10UN
Figure 14.10UN Hybrid zone symbols: Reinforcement, fusion, and stability
Fusion
Stability
100

101. Reinforcement Figure 14.10UN_1
Figure 14.10UN_1 Hybrid zone symbols: Reinforcement (part 1)
Reinforcement
101

102. Figure 14.10UN_2
Figure 14.10UN_2 Hybrid zone symbols: Fusion (part 2)
Fusion
102

103. Figure 14.10UN_3
Figure 14.10UN_3 Hybrid zone symbols: Stability (part 3)
Stability
103