14.1 The origin of species is the source of biological diversity

14.1 The origin of species is the source of biological diversity
Speciation is the emergence of new 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 3.6 billion years ago Student Misconceptions and Concerns 1. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 14.1 How speciation increases diversity.

14.2 There are several ways to define a species
Taxonomy is the branch of biology that names and classifies species and groups them into broader categories Carolus Linnaeus developed the binomial system of naming organisms using physical characteristics to distinguish over 11,000 species Similarities between some species and variation within species can make defining species difficult Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

The biological species concept defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring Reproductive isolation prevents gene flow and maintains separate species Members of different species do not usually mate with each other. If members of one species do mate with members of another species, the offspring will probably not be fertile. Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

The morphological species concept classifies organisms based on observable phenotypic traits It can be applied to asexual organisms, fossils, and in cases when we donít know about possible interbreeding There is some subjectivity in deciding which traits to use Point out that this is the concept actually used by most field biologists, who recognize their species by morphological traits. Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

The ecological species concept defines a species by its ecological role or niche Consider the cichlids, which are similar in appearance but feed at different depths in the lake Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

The phylogenetic species concept defines a species as a set of organisms representing a specific evolutionary lineage Morphological or DNA similarities or differences can be used to define a species Defining the amount of difference required to distinguish separate species is a problem Students may find the large number of species concepts puzzling. It is important to discuss the strengths and limitations of each species concept. Clarify for students that (1) a particular species concept may or may not be appropriate in considering whether a specific set of populations represents different species, and (2) a specific set of populations may or may not be considered separate species, depending on the species concept that is used. Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 14.2A Similarity between the eastern spotted skunk (top) and western spotted skunk (bottom).

Figure 14.2B Diversity within one species.

14.3 Reproductive barriers keep species separate
Reproductive barriers serve to isolate a species gene pool and prevent interbreeding Reproductive barriers are categorized as prezygotic or postzygotic, depending on whether they function before or after zygotes form Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

Table 14.3 Reproductive Barriers between Species.

Prezygotic Barriers Prezygotic barriers prevent mating or fertilization between species In temporal isolation, two species breed at different times (seasons, times of day, years) In habitat isolation, two species live in the same general area but not in the same kind of place Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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 Copyright © 2009 Pearson Education, Inc.

Figure 14.3A Habitat isolation: Two closely related species of garter snake reproductively isolated because one lives on land (left) and the other lives mainly in water (right).

Figure 14.3B Habitat isolation: Courtship ritual in blue-footed boobies as a behavioral barrier between species.

Prezygotic Barriers In behavioral isolation, there is little or no sexual attraction between species, due to specific behaviors 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 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 14.3C Mechanical isolation: Because these snails' shells spiral in opposite directions, their genital openings (indicated by arrows) cannot be aligned and mating cannot occur.

Figure 14.3D Gametic isolation: Gametes of these red and purple urchins are unable to fuse because proteins on the surface of the eggs and sperm cannot bind to one another.

Postzygotic Barriers Postzygotic barriers operate after hybrid zygotes are 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 The process of speciation depends on whether reproductive barriers prevent gene flow between populations Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 14.3E Reduced hybrid fertility: A horse (above left) and a donkey (above right) may produce a hybrid, sterile offspring, a mule.

If two related species live in the same area, would natural selection favor the evolution of prezygotic or postzygotic reproductive isolating mechanisms? Prezygotic reproductive isolating mechanisms are much less costly than postzygotic reproductive isolating mechanisms, which lead to provisioning and (in some species) care of an offspring that is an evolutionary dead end. Student Misconceptions and Concerns 1. 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 grouping exists. Could such grouping represent shared ancestry? Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

MECHANISMS OF SPECIATION
MECHANISMS OF SPECIATION Copyright © 2009 Pearson Education, Inc.

14.4 In allopatric speciation, geographic isolation leads to speciation
In allopatric speciation, populations of the same species are geographically separated, separating their gene pools Changes in the allele frequencies of each population may be caused by natural selection, genetic drift, and mutation, unaffected by gene flow from other populations 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. 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. Copyright © 2009 Pearson Education, Inc.

Gene flow between populations is initially prevented by a geographic barrier The Grand Canyon and Colorado River separate two species of antelope squirrels 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. 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. Copyright © 2009 Pearson Education, Inc.

A. harrisi A. leucurus South North
Figure 14.4 Allopatric speciation of geographically isolated antelope squirrels. Ask students for other examples of suitable barriers, then make the point that the size and nature of the barrier vary from species to species. South North

Likelihood of allopatric speciation increases when a population is small and isolated A small population may have a different gene pool due to the founder effect Genetic drift and natural selection may have a greater effect in a small population in a new habitat Explain to your students that species do not evolve—or arise—because of need. Biological diversity exists and the environment selects. Evolution is not deliberate. It is reactive. Species do not decide or plan to change. 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. 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. Copyright © 2009 Pearson Education, Inc.

14.5 In sympatric speciation, speciation takes place without geographic isolation
In sympatric speciation, new species may arise within the same geographic area as a parent species Gene flow between populations may be reduced by factors such as 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 1. 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 Copyright © 2009 Pearson Education, Inc.

14.5 In sympatric speciation, speciation takes place without geographic isolation
Sympatric speciation in animals more commonly occurs through habitat differentiation and sexual selection Remember the cichlids in Lake Victoria! Remind students that speciation events like the ones you are discussing are ongoing and are not limited to the distant past. 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. 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 Copyright © 2009 Pearson Education, Inc.

14.8 Hybrid zones provide opportunities to study reproductive isolation
What happens when isolated populations renew contact? In hybrid zones, members of different species meet and mate to produce 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 1. 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. Copyright © 2009 Pearson Education, Inc.

New species Ancestral species Gene flow
3 Hybrid zone 1 2 4 Gene flow Gene flow Figure 14.8A Formation of a hybrid zone. Four populations are connected by gene flow. A barrier to gene flow separates one population, which has diverged from the other three. Gene flow is reestablished in the hybrid zone. Hybrid Population (five individuals are shown) Barrier to gene flow

Reinforcement Fusion Stability

allopatric population Pied flycatcher from sympatric population
populations Sympatric populations Male collared flycatcher Male pied flycatcher Figure 14.8B Reinforcement of reproductive barriers. Pied flycatcher from allopatric population Pied flycatcher from sympatric population

Allopatric populations Sympatric populations Male collared flycatcher
Figure 14.8B Reinforcement of reproductive barriers. Male pied flycatcher

What may happen in a hybrid zone? Reinforcement: If hybrids are less fit than parent species, natural selection strengthens reproductive barriers Fusion: Weak reproductive barriers between the two species, with considerable gene flow, reverses speciation and two species become one again 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. 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. Copyright © 2009 Pearson Education, Inc.

Stability: Many hybrid zones are stable, continuing to produce hybrids; this allows some gene flow between populations, but each species maintains its own integrity Which of these three outcomes—reinforcement, fusion, or stability—is happening to the Pundamilia species of cichlids in Lake Victoria? The two Pundamilia species are undergoing fusion, with females unable to mate assortively in the murky water. 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. 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. Copyright © 2009 Pearson Education, Inc.

14.9 TALKING ABOUT SCIENCE: Peter and Rosemary Grant study the evolution of Darwin’s finches
Peter and Rosemary Grant have worked on medium ground finches on tiny, isolated, uninhabited Daphne Major in the Galapágos Islands for 35 years Medium ground finches and cactus finches occasionally interbreed Hybrid offspring have intermediate bill sizes and survive well during wet years, when there are plenty of soft, small seeds around During dry years, hybrids are outcompeted by both parental types 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, long-handled) represents a specialization for a particular job or a generalist approach, useful in a variety of applications. Copyright © 2009 Pearson Education, Inc.

Figure 14.9A Rosemary and Peter Grant with mist nets for catching birds.

14.9 TALKING ABOUT SCIENCE: Peter and Rosemary Grant study the evolution of Darwin’s finches
The occasional hybridization between finch species introduces new genes into both populations During drought years, hybrids die out This keeps medium ground finches and cactus finches on separate evolutionary paths 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, long-handled) represents a specialization for a particular job or a generalist approach, useful in a variety of applications. Copyright © 2009 Pearson Education, Inc.

Tool-using insect-eater (woodpecker finch)
Cactus-seed-eater (cactus finch) Figure 14.10A Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet. Tool-using insect-eater (woodpecker finch) Seed-eater (medium ground finch)

14.10 Adaptive radiation may occur when new opportunities arise
In adaptive radiation, many diverse species evolve from a common ancestor Adaptive radiations occur When a few organisms colonize new unexploited areas After a mass extinction Adaptive radiations are linked to new opportunities: lack of competitors, varying habitats and food sources, evolution of new structures Provide examples: Darwin’s finches underwent an adaptive radiation after the ancestral finches colonized the new volcanic islands. The mammals underwent an adaptive radiation after the mass extinctions that ended the Cretaceous Period. 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, long-handled) 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. Copyright © 2009 Pearson Education, Inc.

14.11 Speciation may 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 and rarely took less than 50,000 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 1. 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 Copyright © 2009 Pearson Education, Inc.

Time Figure 14.11A Punctuated equilibrium model.

Figure 14.11B Gradualism model.
Time

Zygote Viable, fertile offspring Gametes Prezygotic barriers • Temporal isolation • Habitat isolation • Behavioral isolation • Mechanical isolation • Gametic isolation Postzygotic barriers • Reduced hybrid viability fertility Hybrid breakdown

Species a. b. c. d. reproductive barriers e. f. a few hybrids
may interbreed in a. outcome may be b. c. d. when when when reproductive barriers are are e. f. a few hybrids continue to be produced keeps and species separate speciation reversed

14.1 The origin of species is the source of biological diversity

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14.1 The origin of species is the source of biological diversity

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