Sections 5-2 & 5-4Sections 5-2 & 5-4

Evolution and BiodiversityEvolution and Biodiversity

What is Evolution?

Core Case StudyCore Case StudyEarth: The Just-Right, Adaptable PlanetEarth: The Just-Right, Adaptable Planet

Oxygen LevelOxygen LevelOn earth, oxygen comprises 21 On earth, oxygen comprises 21 percent of the atmosphere. If oxygen percent of the atmosphere. If oxygen were 25% fires would erupt were 25% fires would erupt spontaneously, if it were 15%, human spontaneously, if it were 15%, human beings would suffocate.beings would suffocate.

Water Vapor Levels. Water Vapor Levels. If water vapor If water vapor levels in the atmosphere were greater levels in the atmosphere were greater than they are now, a runaway than they are now, a runaway greenhouse effect would cause greenhouse effect would cause temperatures to rise too high for temperatures to rise too high for human life. If they were less, an human life. If they were less, an insufficient greenhouse effect would insufficient greenhouse effect would make the earth to cold to support make the earth to cold to support human life. human life.

Figure 4-1Figure 4-1

Biological Biological EvolutionEvolution

Proposes Proposes theories about theories about development of development of the variety of the variety of species we find species we find on the earth on the earth today.today.

Figure 4-2Figure 4-2

How Do We Know Which Organisms How Do We Know Which Organisms Lived in the Past?Lived in the Past?

Our knowledge about Our knowledge about past life comes from past life comes from

• FossilsFossils• chemical analysischemical analysis• cores drilled out of cores drilled out of

buried ice, buried ice, • DNA analysis.DNA analysis.

Figure 4-4Figure 4-4

EVOLUTION, NATURAL SELECTION, EVOLUTION, NATURAL SELECTION, AND ADAPTATIONAND ADAPTATION

Biological evolution Biological evolution by natural selection involves the by natural selection involves the change in a population’s genetic makeup through change in a population’s genetic makeup through successive generations.successive generations.

Natural selectionNatural selection: a difference in reproductive success : a difference in reproductive success of certain traits due to organisms’ interactions with of certain traits due to organisms’ interactions with their environment.their environment.

Ex. Ex.

AdaptationAdaptation: an organism’s characteristics or traits that : an organism’s characteristics or traits that allow it to survive and reproduce in an environment.allow it to survive and reproduce in an environment.

Natural Selection and AdaptationNatural Selection and Adaptation Three conditions are necessary for biological Three conditions are necessary for biological

evolution:evolution: Genetic variability Genetic variability Traits must be heritableTraits must be heritable Trait must lead to Trait must lead to differential reproductiondifferential reproduction. .

An adaptive trait is any heritable trait that An adaptive trait is any heritable trait that enables an organism to survive through enables an organism to survive through natural selection and reproduce better under natural selection and reproduce better under prevailing environmental conditions.prevailing environmental conditions.

Natural Selection Natural Selection

Limits on Adaptation through Limits on Adaptation through Natural SelectionNatural Selection

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

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

Common Myths about Evolution Common Myths about Evolution through Natural Selectionthrough Natural Selection

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

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

GEOLOGIC PROCESSES, CLIMATE CHANGE, GEOLOGIC PROCESSES, CLIMATE CHANGE, CATASTROPHES, AND EVOLUTIONCATASTROPHES, AND EVOLUTION

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

influence climate.influence climate. The movement of continents have allowed The movement of continents have allowed

species to move.species to move.

Climate Change and Natural Climate Change and Natural SelectionSelection

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

Figure 4-6Figure 4-6

Catastrophes and Natural SelectionCatastrophes and Natural Selection

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

SPECIATIONSPECIATION

Speciation: Theoretically, a new species can Speciation: Theoretically, a new species can arise when members of a population become arise when members of a population become isolated for a long period of time.isolated for a long period of time. Genetic makeup changes prevent them from Genetic makeup changes prevent them from

producing fertile offspring with the original producing fertile offspring with the original population if reunited.population if reunited.

Geographic IsolationGeographic Isolation

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

Figure 4-10Figure 4-10

Evolutionary DivergenceEvolutionary Divergence

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

Figure 4-9Figure 4-9

Coevolution: A Biological Arms RaceCoevolution: A Biological Arms Race

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

species.species. Or plants and pollinatorsOr plants and pollinators

Extinction: Lights OutExtinction: Lights Out

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

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

Figure 4-11Figure 4-11

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

Definition of BiodiversityDefinition of Biodiversity

BiodiversityBiodiversity is the is the

variation of life formsvariation of life forms

within a given ecosystem, within a given ecosystem,

biome, biome,

or on the entire Earth.or on the entire Earth.

From Wikipedia: http://en.wikipedia.org/wiki/BiodiversityFrom Wikipedia: http://en.wikipedia.org/wiki/Biodiversity

Effects of Humans on BiodiversityEffects of Humans on Biodiversity

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

Figure 4-13Figure 4-13

HUMAN IMPACTS ON TERRESTRIAL HUMAN IMPACTS ON TERRESTRIAL BIODIVERSITYBIODIVERSITY

We have depleted We have depleted and degraded some and degraded some of the earth’s of the earth’s biodiversity and these biodiversity and these threats are expected threats are expected to increase.to increase.

Figure 10-2Figure 10-2

Fig. 10-2, p. 192

Alteration of natural chemicalcycles and energy flows

Indirect Effects

Loss ofBiodiversity

Climatechange

Human PopulationSize and resource use

Human Activities

Agriculture, industry, economicproduction and consumption, recreation

Changes in number anddistribution of species

Pollution of air, water,and soil

Degradation and destructionof natural ecosystems

Direct Effects

H I P P O + CH I P P O + C H-Habitat Loss-destruction, degradation H-Habitat Loss-destruction, degradation

and fragmentation and fragmentation I-Invasive Species I-Invasive Species P-Population of humans increasingP-Population of humans increasing P-Pollution P-Pollution O-OverharvestingO-Overharvesting + C- Climate Change+ C- Climate Change

Why Should We Care About Biodiversity?Why Should We Care About Biodiversity?

Use ValueUse Value: For the : For the usefulness in terms of usefulness in terms of economic and economic and ecological services.ecological services.

Nonuse ValueNonuse Value: : existence, aesthetics, existence, aesthetics, bequest for future bequest for future generations.generations.

The Value of BiodiversityThe Value of Biodiversity

Figure 10-3Figure 10-3