Evolution and Biodiversity

Chapter 4

Chapter Overview Questions• How do scientists account for the

development of life on earth?

• What is biological evolution by natural selection, and how can it account for the current diversity of organisms on the earth?

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

Chapter Overview Questions (cont’d)

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

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

Video: Creation vs. Evolution

• From ABC News, Environmental Science in the Headlines, 2005 DVD.

Videos\creation_evolution.flv -

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?

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

Figure 4-4Figure 4-4

What is Evolution?

• Biological Evolution: change in a population’s genetic makeup (gene pool) through successive generations.– Populations, NOT individuals, evolve by becoming

genetically different

• Microevolution: small genetic changes that occur in a population

• Macroevolution: long-term, large-scale evolutionary changes through which new species are formed and other species are lost

Facts about Evolution through Natural Selection

• Evolution through natural selection is about the most descendants.– Organisms do not develop certain traits

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

GEOLOGIC PROCESSES, CLIMATE CHANGE, CATASTROPHES, AND

EVOLUTION

• 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.– The locations of continents and oceanic basins

influence climate.– The movement of continents have allowed

species to move.

Video: Continental Drift

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Climate Change and Natural Selection

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

Figure 4-6Figure 4-6

Catastrophes and Natural Selection

• 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.

Microevolution

• Gene pool

• Alleles

• Mutations

• Natural selection

What are three types of natural selection?

• Directional natural selection: changing environmental conditions cause individuals with traits at one end of the normal range become more common than midrange forms. – Example: evolution of genetic resistance to

pesticides among insects and to antibiotics among disease-carrying bacteria

Second type of natural selection

• Stabilizing natural selection: tends to eliminate individuals on both ends of the genetic spectrum and favor individuals with an average genetic makeup.– Occurs when an environment changes little,

and most members of the population are well adapted to that environment

Third type of natural selection

• Diversifying natural selection: occurs when environmental conditions favor individuals at both extremes of the genetic spectrum and eliminate or sharply reduce number of individuals with normal genetic traits.– A population is split into two groups.

Animation: Stabilizing Selection

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Animation: Diversifying Selection

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Animation: Moth Populations

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Animation: Adaptive Trait

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Hybridization and Gene Swapping: Other Ways to

Exchange Genes• New species can arise through hybridization.

– Occurs when individuals to two distinct species crossbreed to produce a fertile offspring.

• Some species (mostly microorganisms) can exchange genes without sexual reproduction.– Horizontal gene transfer

What is Coevolution?

• Coevolution is used to describe cases where two (or more) species reciprocally affect each other’s evolution. So for example, an evolutionary change in the morphology of a plant, might affect the morphology of an herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore...and so on.

Ecological Niches and Adaptation

• Ecological niche: species functional role in an ecosystem.– Involves range of tolerance for various physical and

chemical conditions (water availability, for example)– Types and amounts of resources it uses, such as

food or nutrients– How it interacts with other living and nonliving

components of the ecosystem– The role it plays in the energy flow and matter cycling

in the ecosystem

How is the niche different from a habitat?

• The niche is like a species’ occupation, whereas the habitat is like its address

• The niche represents the adaptations or adaptive traits that its members have acquired through evolution

What is the difference between a species’ fundamental niche and its realized niche?

• The fundamental niche is the full potential range of conditions and resources it could use if there were no competition from other species

• The realized niche is the part of the fundamental niche in a community or ecosystem that the species actually occupies

Generalist vs. Specialist Species

• Generalist species: have broad niches– Can live in many different places– Eat a variety of foods– Tolerate a wide range of environmental conditions

• Rats, mice, white-tailed deer, cockroaches, flies

• Specialist species: have narrow niches– Live in only one type of habitat– Use only one or a few types of food– Tolerate only a narrow range of climatic and other environmental

conditions– Makes them more prone to extinction when conditions change

• Tiger salamander, red-cockaded woodpeckers, spotted owls

Generalist and Specialist Species: Broad and Narrow Niches

• Generalist species tolerate a wide range of conditions.

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

Figure 4-7Figure 4-7

Specialized Feeding Niches

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

Figure 4-8Figure 4-8

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

What limits adaptation?

• A change in environmental conditions • Reproductive capacity.

– Quickly reproducing populations adapt in a short time– Slowly reproducing populations take a long time to

adapt through natural selection

• Most of the population has to die or become sterile so individuals with the desirable trait could predominate and pass the trait on.

Different species of bowerbird construct elaborate bowers and decorate them with different colors in order to woo females. The Satin bowerbird (left) builds a channel between upright sticks, and decorates with bright blue objects, while the MacGregor’s Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal. Evolutionary changes in mating rituals, such as bower construction, can contribute to speciation.

http://evolution.berkeley.edu/evolibrary/article/_0_0/evo_44

Speciation, Extinction, and Biodiversity

• Speciation: when two species arise from one.– Geographic isolation: groups of the same

population of a species become physically separate for long periods

• Part of the population migrates • Population separated by a physical barrier• Population separated by volcanic eruption or

earthquake• A few individuals are carried to a new location by

wind or water

Speciation

• Reproductive isolation: mutation and natural selection operate independently in two geographically isolated populations and change the gene pools in different ways (called divergent evolution).

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

Extinction: Lights Out

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

The golden toad of Costa Rica’s The golden toad of Costa Rica’s Monteverde cloud forest has Monteverde cloud forest has become extinct. Reason?become extinct. Reason?

Figure 4-11Figure 4-11

How do species become extinct?

• Extinction is the second process affecting the number and types of species on the earth

• When environmental conditions change, a species must– Evolve, or become better adapted– Move to a more favorable environment, if

possible– Cease to exist (become extinct)

Fig. 4-12, p. 93

Tertiary

Bar width represents relative number of living speciesEra Period

Species and families experiencing

mass extinction

Millions 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

Pal

eozo

icM

eso

zoic

Cen

ozo

ic

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

Earth’s long-term patterns of speciation and extinction

• Affected by:– Large-scale movements of the continents– Gradual climate changes caused by

continental drift and slight shifts in the earth’s orbit around the sun

– Rapid climate change caused by catastrophic events (such as large volcanic eruptions, huge meteorites and asteroids crashing into earth)

Types of Extinction

• Background extinction

• Mass extinction

• Mass depletion

• Adaptive radiations

Effects of Humans on Biodiversity

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

Figure 4-13Figure 4-13

How do speciation and extinction affect biodiversity

• Speciation minus extinction equals biodiversity• Mass extinction and mass depletions temporarily

reduce biodiversity• Also create evolutionary opportunities• Much evidence indicates that humans have

become a major force in premature extinction of species– During the 20th century, extinction rates increased by

100-1000 times the natural background rate

GENETIC ENGINEERING AND THE FUTURE OF EVOLUTION

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

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

Figure 4-15Figure 4-15

Genetic Engineering: Genetically Modified Organisms (GMO)

• GMOs use recombinant DNA – genes or portions

of genes from different organisms.

Figure 4-14Figure 4-14

Animation: Transgenic Plants

• From ABC News, Biology in the Headlines, 2005 DVD.

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THE FUTURE OF EVOLUTION

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

aging, organ defects.

• Genetic engineering can help improve human condition, but results are not always predictable.– Do not know where the new gene will be located

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

Controversy Over Genetic Engineering

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

• Should genetic engineering and development be regulated?

• What are the long-term environmental consequences?