Chapter 5Evolution of Biodiversity

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Earth is home to a tremendous diversity of species

• Ecosystem diversity- the variety of ecosystems within a given region.

• Species diversity- the variety of species in a given ecosystem.

• Genetic diversity- the variety of genes within a given species.

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• Species richness- the number of species in a given area.

• Species evenness- the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals.

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Evolution is the mechanism underlying biodiversity

• Evolution- a change in the genetic composition of a population over time.

• Microevolution- evolution below the species level.

• Macroevolution- Evolution which gives rise to new species or new genera, family, class or phyla.

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Fig. 4-2, p. 84

Variety ofmulticellularorganismsform, firstin the seasand lateron land

Biological Evolution(3.7 billion years)

Chemical Evolution(1 billion years)

Formationof the

earth’searly

crust andatmosphere

Small organic molecules

form inthe seas

Large organic molecules

(biopolymers) form in the seas

First protocells form in the

seas

Single-cell prokaryotes

form in the seas

Single-celleukaryotes

form inthe seas

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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

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Creating Genetic Diversity

• Genes- physical locations on chromosomes within each cell of an organism.

• Genotype- the complete set of genes in an individual.

• Phenotype- the actual set of traits expressed in an individual.

• Mutation- a random change in the genetic code.

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Evolution by artificial and natural selection

• Evolution by artificial selection- when humans determine which individuals breed.

• Evolution by natural selection- the environment determines which individuals are most likely to survive and reproduce.

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Darwin’s theory of evolution by natural selection

• Individuals produce an excess of offspring.

• Not all offspring can survive.

• Individuals differ in their traits.

• Differences in traits can be passed on from parents to offspring.

• Differences in traits are associated with differences in the ability to survive and reproduce.

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Common Myths about Evolution through Natural Selection

ØEvolution 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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Evolution by Random Processes

• Mutation- occur randomly and can add to the genetic variation of a population.

• Genetic drift- change in the genetic composition of a population over time as a result of random mating.

• Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size.

• Founder effect- a change in a population descended from a small number of colonizing individuals.

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Coevolution: A Biological Arms RaceØInteracting 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.

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SPECIATION AND BIODIVERSITY

ØSpeciation: 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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Speciation and extinction determine biodiversity

• Allopatric speciation- when new species are created by geographic or reproductive isolation.

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Fig. 4-9, p. 91

Maui Parrotbill

Fruit and seed eaters Insect and nectar eaters

Kuai Akialaoa

Amakihi

Crested Honeycreeper

Apapane

Akiapolaau

Unknown finch ancestor

Greater Koa-finch

Kona Grosbeak

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Fig. 4-10, p. 92

Different environmentalconditions lead to different selective pressures and evolution into two different species.

SouthernPopulation

Northernpopulation

Adapted to heat through lightweightfur and long ears, legs, and nose, which give off more heat.

Adapted to cold through heavier fur,short ears, short legs,short nose. White furmatches snow for camouflage.

Gray Fox

Arctic Fox

Spreadsnorthward

and southwardand separates

Early foxPopulation

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• Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy, an increase in the number of sets of chromosomes.

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The pace of evolution

A. The rate of environmental changeB. The amount of genetic variation in speciesC.The size of the population involved.D. How fast the species reproduces (generation time)

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Humans?

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Evolution shapes ecological niches and determines species distributions

• Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance.

• Fundamental niche- the ideal conditions for a species.

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Niches

• Realized niche- the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives.

• Niche generalist- species that live under a wide range of conditions.

• Niche specialist- species that live only in specific habitats.

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Fig. 4-7, p. 91

Generalist specieswith a broad niche

Num

ber o

f ind

ivid

uals

Resource use

Specialist specieswith a narrow niche

Nicheseparation

Nichebreadth

Region of niche overlap

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Extinction: Lights Out

ØExtinction occurs when the population cannot adapt to changing environmental conditions.

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

Figure 4-11Monday, May 16, 16

The Fossil Record

• Fossils- remains of organisms that have been preserved in rock. Much of what we know about evolution comes from the fossil record.

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The Five Global Mass Extinctions

• Mass extinction- when large numbers of species went extinct over a relatively short period of time.

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Fig. 4-12, p. 93

Tertiary

Bar width represents relative number of living speciesEra Period

Species and families experiencing

mass extinctionMillions ofyears 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

cM

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 causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.

Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Extinction

Extinction

Triassic

Jurassic

Cretaceous

250

180

65Extinction

ExtinctionQuaternary Today

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The Sixth Mass Extinction

• Scientists feel that we are in our sixth mass extinction, occurring in the last two decades.

• Estimates of extinction rates vary widely, from 2 % to 25% by 2020.

• In contrast to previous mass extinctions, scientists agree that this one is caused by humans.

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ØSome species have characteristics that make them vulnerable to ecological and biological extinction.

SPECIES EXTINCTION

Figure 11-4Monday, May 16, 16

GENETIC ENGINEERING AND THE FUTURE OF EVOLUTION

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

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

Figure 4-15Monday, May 16, 16

Genetic Engineering: Genetically Modified Organisms (GMO)

ØGMOs use recombinant DNA l genes or portions of

genes from different organisms.

Figure 4-14Monday, May 16, 16

THE FUTURE OF EVOLUTION

ØBiologists 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.ØGenetic 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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Case Study:How Did We Become Such a Powerful

Species so Quickly?ØWe lack:

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

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

brains (problem solving).

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