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Chapter 4

Evolution and Biodiversity

Chapter Overview Questions Ø How do scientists account for the

development of life on earth? Ø What is biological evolution by natural

selection, and how can it account for the current diversity of organisms on the earth?

Ø How can geologic processes, climate change and catastrophes affect biological evolution?

Ø What is an ecological niche, and how does it help a population adapt to changing the environmental conditions?

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Chapter Overview Questions (cont’d)

Ø How do extinction of species and formation of new species affect biodiversity?

Ø What is the future of evolution, and what role should humans play in this future?

Ø How did we become such a powerful species in a short time?

Core Case Study Earth: The Just-Right, Adaptable

Planet Ø During the 3.7 billion

years since life arose, the average surface temperature of the earth has remained within the range of 10-20oC.

Figure 4-1

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ORIGINS OF LIFE

Ø 1 billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change.

Figure 4-2

Biological Evolution

Ø This has led to the variety of species we find on the earth today.

Figure 4-2

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Fig. 4-3, p. 84

Modern humans (Homo sapiens sapiens) appear about 2 seconds before midnight

Recorded human history begins about 1/4 second before midnight

Origin of life (3.6-3.8 billion years ago)

Age of mammals

Age of reptiles

Insects and amphibians invade the land

First fossil record of animals

Plants begin invading land Evolution and

expansion of life

How Do We Know Which Organisms Lived in the Past?

Ø Our knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis.

Figure 4-4

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EVOLUTION, NATURAL SELECTION, AND ADAPTATION

Ø Biological evolution by natural selection involves the change in a population’s genetic makeup through successive generations. l  genetic variability l  Mutations: random changes in the structure or

number of DNA molecules in a cell that can be inherited by offspring.

Natural Selection and Adaptation: Leaving More Offspring With

Beneficial Traits Ø Three conditions are necessary for biological

evolution: l  Genetic variability, traits must be heritable, trait

must lead to differential reproduction. Ø An adaptive trait is any heritable trait that

enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions.

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Coevolution: A Biological Arms Race

Ø  Interacting species can engage in a back and forth genetic contest in which each gains a temporary genetic advantage over the other. l  This often happens between predators and prey

species.

Hybridization and Gene Swapping: other Ways to Exchange Genes

Ø New species can arise through hybridization. l  Occurs when individuals to two distinct species

crossbreed to produce an fertile offspring. Ø Some species (mostly microorganisms) can

exchange genes without sexual reproduction. l  Horizontal gene transfer

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Limits on Adaptation through Natural Selection

Ø A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce. l  Humans have a relatively slow generation time

(decades) and output (# of young) versus some other species.

Common Myths about Evolution through Natural Selection

Ø Evolution through natural selection is about the most descendants. l  Organisms do not develop certain traits because

they need them. l  There is no such thing as genetic perfection.

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GEOLOGIC PROCESSES, CLIMATE CHANGE, CATASTROPHES, AND

EVOLUTION

Ø The movement of solid (tectonic) plates making up the earth’s surface, volcanic eruptions, and earthquakes can wipe out existing species and help form new ones. l  The locations of continents and oceanic basins

influence climate. l  The movement of continents have allowed

species to move.

Fig. 4-5, p. 88

135 million years ago

Present 65 million years ago

225 million years ago

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Climate Change and Natural Selection

Ø Changes in climate throughout the earth’s history have shifted where plants and animals can live.

Figure 4-6

Catastrophes and Natural Selection

Ø Asteroids and meteorites hitting the earth and upheavals of the earth from geologic processes have wiped out large numbers of species and created evolutionary opportunities by natural selection of new species.

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ECOLOGICAL NICHES AND ADAPTATION

Ø Each species in an ecosystem has a specific role or way of life. l  Fundamental niche: the full potential range of

physical, chemical, and biological conditions and resources a species could theoretically use.

l  Realized niche: to survive and avoid competition, a species usually occupies only part of its fundamental niche.

Generalist and Specialist Species: Broad and Narrow Niches

Ø Generalist species tolerate a wide range of conditions.

Ø Specialist species can only tolerate a narrow range of conditions.

Figure 4-7

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SPOTLIGHT Cockroaches: Nature’s Ultimate

Survivors Ø 350 million years old Ø 3,500 different species Ø Ultimate generalist

l  Can eat almost anything. l  Can live and breed almost

anywhere. l  Can withstand massive

radiation. Figure 4-A

Specialized Feeding Niches

Ø Resource partitioning reduces competition and allows sharing of limited resources.

Figure 4-8

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Evolutionary Divergence

Ø Each species has a beak specialized to take advantage of certain types of food resource.

Figure 4-9

SPECIATION, EXTINCTION, AND BIODIVERSITY

Ø Speciation: A new species can arise when member of a population become isolated for a long period of time. l  Genetic makeup changes, preventing them from

producing fertile offspring with the original population if reunited.

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Geographic Isolation

Ø …can lead to reproductive isolation, divergence of gene pools and speciation.

Figure 4-10

Extinction: Lights Out

Ø Extinction occurs when the population cannot adapt to changing environmental conditions.

Ø The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate.

Figure 4-11

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Fig. 4-12, p. 93

Tertiary

Bar width represents relative number of living species Era Period

Species and families experiencing

mass extinction Millions of years ago

Ordovician: 50% of animal families, including many trilobites.

Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.

500

345

Cambrian

Ordovician

Silurian

Devonian

Extinction

Extinction

Pale

ozoi

c M

esoz

oic

Cen

ozoi

c

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. Carboniferous

Permian

Current extinction crisis caused by human activities. Many species are expected to become extinct within the next 50–100 years. Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks.

Extinction

Extinction

Triassic

Jurassic

Cretaceous

250

180

65 Extinction

Extinction Quaternary Today

Effects of Humans on Biodiversity

Ø The scientific consensus is that human activities are decreasing the earth’s biodiversity.

Figure 4-13

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GENETIC ENGINEERING AND THE FUTURE OF EVOLUTION

Ø We have used artificial selection to change the genetic characteristics of populations with similar genes through selective breeding.

Ø We have used genetic engineering to transfer genes from one species to another.

Figure 4-15

Genetic Engineering: Genetically Modified Organisms (GMO)

Ø GMOs use recombinant DNA l  genes or portions

of genes from different organisms.

Figure 4-14

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How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living In the Environment.

Ø Should we legalize the production of human clones if a reasonably safe technology for doing so becomes available? l  a. No. Human cloning will lead to widespread

human rights abuses and further overpopulation. l  b. Yes. People would benefit with longer and

healthier lives.

THE FUTURE OF EVOLUTION

Ø Biologists are learning to rebuild organisms from their cell components and to clone organisms. l  Cloning has lead to high miscarriage rates, rapid

aging, organ defects. Ø Genetic engineering can help improve human

condition, but results are not always predictable. l  Do not know where the new gene will be located

in the DNA molecule’s structure and how that will affect the organism.

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Controversy Over Genetic Engineering

Ø There are a number of privacy, ethical, legal and environmental issues.

Ø Should genetic engineering and development be regulated?

Ø What are the long-term environmental consequences?

Case Study: How Did We Become Such a Powerful

Species so Quickly? Ø We lack:

l  strength, speed, agility. l  weapons (claws, fangs), protection (shell). l  poor hearing and vision.

Ø We have thrived as a species because of our: l  opposable thumbs, ability to walk upright,

complex brains (problem solving).