Great Ideas in Science: Lecture 14 – Ecosystems Professor Robert Hazen UNIV 301 All living systems live in ecosystems of many interacting organisms

Great Ideas in Science:Great Ideas in Science:Lecture 14 – EcosystemsLecture 14 – Ecosystems

Professor Robert HazenProfessor Robert Hazen

UNIV 301UNIV 301

All living systems live in All living systems live in ecosystems of many interacting ecosystems of many interacting

organisms.organisms.

Three Definitions of EvolutionThree Definitions of Evolution

1.1. Evolution as Change:Evolution as Change: Life on Life on Earth has changed over timeEarth has changed over time

2.2. Common descent:Common descent: All living All living things on Earth descended things on Earth descended from a common ancestor.from a common ancestor.

3.3. Natural selection:Natural selection: The process The process by which life evolved is by which life evolved is Darwinian natural selectionDarwinian natural selection

First Definition of Evolution: First Definition of Evolution: Change Over TimeChange Over Time

Observational evidence overwhelmingly Observational evidence overwhelmingly supports the theory that life originated supports the theory that life originated on Earth billions of years ago as a single on Earth billions of years ago as a single cell, and has been changing ever since.cell, and has been changing ever since.

FossilsFossils

Molecular BiologyMolecular Biology

Cellular biologyCellular biology

GeneticsGenetics

Comparative anatomyComparative anatomy

Observations of nature and of breedingObservations of nature and of breeding

Extinct AnimalsExtinct Animals

TRILOBITESTRILOBITES

If you accept observational evidence, then the unambiguous conclusion is

that life has changed over time.

Three Related TermsThree Related Terms

1.1. CreationismCreationism

2.2. Young Earth CreationismYoung Earth Creationism

3.3. Scientific CreationismScientific Creationism

1. Creationism1. Creationism

Creationists believe that God Creationists believe that God created the universe and life.created the universe and life.

Many creationists accept the Many creationists accept the BibleBible’’s creation story as a s creation story as a metaphor; they rely on metaphor; they rely on empirical evidence (Psalm 19).empirical evidence (Psalm 19).

Many scientists are also Many scientists are also creationists in this sense.creationists in this sense.

2. Young Earth Creationism2. Young Earth Creationism Young-Earth creationists believe in a Young-Earth creationists believe in a

literal reading of Genesis.literal reading of Genesis.• Earth is about 10,000 years old.Earth is about 10,000 years old.• Geology features caused by NoahGeology features caused by Noah’’s Flood.s Flood.• All species created in modern form.All species created in modern form.• Minor evolutionary changes only.Minor evolutionary changes only.

For many young-Earth creationists, For many young-Earth creationists, the findings of science are irrelevant the findings of science are irrelevant at best, and possibly dangerous and at best, and possibly dangerous and subversive.subversive.

3. Scientific Creationism3. Scientific Creationism Scientific creationists search for Scientific creationists search for

empirical evidence that supports the empirical evidence that supports the tenets of young-Earth creationism.tenets of young-Earth creationism.

SC is not science, because its basic SC is not science, because its basic tenets are not subject to change tenets are not subject to change based on empirical evidence.based on empirical evidence.

Even if its tenets conformed to Even if its tenets conformed to observational evidence, observational evidence, ““scientificscientific”” creationism would not be science.creationism would not be science.

Should creationism be taught in the Should creationism be taught in the science classroom?science classroom?

Second Definition of Second Definition of Evolution: Common DescentEvolution: Common Descent

Common descent means that all Common descent means that all living things descended from the living things descended from the first living cell.first living cell.

Tree diagrams reveal ancestral Tree diagrams reveal ancestral relationships.relationships.

Second Definition of Second Definition of Evolution: Common DescentEvolution: Common Descent

Common descent means that all Common descent means that all living things descended from the living things descended from the first living cell.first living cell.

Tree diagrams reveal ancestral Tree diagrams reveal ancestral relationships.relationships.

The search for fossil The search for fossil intermediates supports common intermediates supports common descent.descent.

FossilsFossils Fossils prove that life on Earth has Fossils prove that life on Earth has

changed over time; most extinct.changed over time; most extinct. Fossils demonstrate that these Fossils demonstrate that these

changes are gradual and changes are gradual and progressive (simple to complex)progressive (simple to complex)

All known fossils fit All known fossils fit

into a pattern into a pattern

of continuous of continuous

evolutionevolution..

Geological TimeGeological Time

FossilsFossils

StrataStrataYounger = higherYounger = higher

Gradual EvolutionGradual Evolution

Objections to Common DescentObjections to Common Descent ““Darwinists rarely mention the whale Darwinists rarely mention the whale

because it presents them with one of because it presents them with one of their most insoluble problems. They their most insoluble problems. They believe that somehow a whale must believe that somehow a whale must have evolved from an ordinary land-have evolved from an ordinary land-dwelling animal, which took to the sea dwelling animal, which took to the sea and lost its legs. … A land mammal and lost its legs. … A land mammal that was in the process of becoming a that was in the process of becoming a whale would fall between two stools – whale would fall between two stools – it would not be fitted for life on land it would not be fitted for life on land or sea, and would have no hope of or sea, and would have no hope of survival.survival.””

Alan Haywood, 1985Alan Haywood, 1985

Whale EvolutionWhale Evolution

AmbulocetusAmbulocetus


AmbulocetusAmbulocetus


RodhocetusRodhocetus


BasilosaurusBasilosaurus


The power of the theory of evolution by natural selection is its predictive power. If we see a gap in the fossil record, then we can predict what kind of rock and what age of rock to search, and we can make a good guess as to what kind of fossil we’re likely to find.

From DNA to ProteinFrom DNA to Protein1.1. Transcription: Use DNA to make mRNA Transcription: Use DNA to make mRNA

2.2. Attach mRNA to ribosomeAttach mRNA to ribosome

3.3. Translation: RNA to amino acidsTranslation: RNA to amino acids

4.4. Fold amino acids into proteinFold amino acids into protein

The Genetic The Genetic CodeCode

The Cell Theory, 1839The Cell Theory, 1839 All living things are composed of cellsAll living things are composed of cells The cell is the fundamental unit of lifeThe cell is the fundamental unit of life All cells arise from previous cellsAll cells arise from previous cells

CONCLUSIONS:CONCLUSIONS:

Observational evidence Observational evidence

overwhelmingly supports the overwhelmingly supports the

hypothesis of common hypothesis of common

descent for all known life descent for all known life

forms, living and fossil, on forms, living and fossil, on

Earth.Earth.

Third Definition of Evolution: Third Definition of Evolution: Natural Selection (Darwin)Natural Selection (Darwin)

•Populations exhibit variation.Populations exhibit variation.

•More individuals are born than More individuals are born than will survive.will survive.

•The most fit individuals are more The most fit individuals are more likely to reproduce.likely to reproduce.

Charles Darwin (1809-1882)Charles Darwin (1809-1882)

Charles Darwin:Charles Darwin:The Beagle at GalapagosThe Beagle at Galapagos

MicroevolutionMicroevolution

Phacops trilobites: Almost unchanged from 440 to 370 million years!

MicroevolutionMicroevolution

Unanswered Questions Unanswered Questions about Evolutionabout Evolution

How does macroevolution occur?How does macroevolution occur?

Why are some species static?Why are some species static?

What is the rate of evolution?What is the rate of evolution?

What is the rate of extinction?What is the rate of extinction?

What causes mass extinctions?What causes mass extinctions?

MacroevolutionMacroevolution

How did such an amazing diversity of trilobites arise?

Eye EvolutionEye EvolutionEye EvolutionEye Evolution

“To suppose that the eye, with all its inimitable

contrivances for adjusting the focus to different

distances, for admitting different amounts of light,

and for the correction of spherical and chromatic

aberration, could have been formed by natural

selection, seems, I freely confess, absurd in the

highest possible degree …”

Charles Darwin, On the Origin of Species


Selection rules for model eye evolution:Selection rules for model eye evolution:

1. Vary curvature, aperture, and central 1. Vary curvature, aperture, and central refractive index randomly by refractive index randomly by 1%.1%.

2. If visual acuity (spatial resolution) 2. If visual acuity (spatial resolution) increases, then retain that variation.increases, then retain that variation.

D. Nilsson & S. Pelger, “A pessimistic estimate for the time required for an eye to evolve.” Proc. R. Soc. Lond. B 256, 53-58 (1994).


This evolutionary sequence is continuously driven by selection.

What is the Rate of What is the Rate of Evolution?Evolution?

Punctuated Equilibria (a) Punctuated Equilibria (a) versus Gradualism (b) versus Gradualism (b)

Mass ExtinctionsMass Extinctions

Mass Extinctions and the Mass Extinctions and the Rate of EvolutionRate of Evolution

Rate of extinctionRate of extinction• 10%-20% extinct in 5-10%-20% extinct in 5-

6 million years6 million years

Mass extinctionsMass extinctions• 30%-90% extinct 30%-90% extinct • At least 5 episodesAt least 5 episodes

MechanismsMechanisms• AsteroidsAsteroids• volcanoesvolcanoes


Evidence from the Fossil RecordEvidence from the Fossil Record


Evidence from IridiumEvidence from Iridium


Evidence from ForaminiferaEvidence from Foraminifera

What Causes Mass Extinctions?What Causes Mass Extinctions?

Human ActivitiesHuman Activities

What Causes Mass Extinctions?What Causes Mass Extinctions?

Human ActivitiesHuman Activities

Ecology and EcosystemsEcology and Ecosystems

Ecology:Ecology: The study of The study of natural living systemsnatural living systems

Ecosystems:Ecosystems: Consist of Consist of biotic and abiotic biotic and abiotic componentscomponents

Community:Community: All organisms All organisms in an ecosystemin an ecosystem• ProducersProducers• ConsumersConsumers• DecomposersDecomposers

EcosystemsEcosystemsKey Idea: Living things live in Key Idea: Living things live in ecosystems of many interdependent ecosystems of many interdependent organismsorganisms

1.1. Ecosystems consist of both living Ecosystems consist of both living and nonliving partsand nonliving parts

2.2. Energy flows throughEnergy flows through3.3. Matter is recycledMatter is recycled4.4. Every organism occupies an Every organism occupies an

ecological niche (two species ecological niche (two species cannot occupy same niche)cannot occupy same niche)

5.5. Stable ecosystems achieve balance Stable ecosystems achieve balance among populationsamong populations

6.6. Ecosystems can be disruptedEcosystems can be disrupted

Every Ecosystem Consists of Every Ecosystem Consists of Both Living and Nonliving PartsBoth Living and Nonliving Parts

Abiotic: The chemical and physical Abiotic: The chemical and physical environmentenvironment

Biotic: All living organisms that Biotic: All living organisms that form the ecological communityform the ecological community

Energy Flows Energy Flows Through EcosystemsThrough Ecosystems

Food WebFood Web• Interactions of organismsInteractions of organisms

Trophic LevelsTrophic Levels• Photosynthetic plantsPhotosynthetic plants• HerbivoresHerbivores• CarnivoresCarnivores• Decomposers Decomposers

Most energy is lost as heatMost energy is lost as heat• 10% is transferred from one 10% is transferred from one

level to the next.level to the next.

Matter is Recycled by Matter is Recycled by EcosystemsEcosystems

Carbon: Atoms continuously cycleCarbon: Atoms continuously cycle

Stable Ecosystems Achieve a Stable Ecosystems Achieve a Balance Among Their PopulationsBalance Among Their Populations

Homeostasis is a balance among Homeostasis is a balance among populations.populations.

Resources are always limited.Resources are always limited.

While we observe some variation While we observe some variation in populations, overall they are in populations, overall they are relatively constant.relatively constant.

Law of Unintended ConsequencesLaw of Unintended ConsequencesChanging one part of a complex Changing one part of a complex system may cause unintended system may cause unintended

changes in other parts of the systemchanges in other parts of the system

Nile perchNile perch

PeterPeter’’s mountain mallows mountain mallow

Three Environmental ProblemsThree Environmental Problems

1.1. Acid Rain Acid Rain

2.2. Ozone HoleOzone Hole

3.3. Greenhouse EffectGreenhouse Effect

These are very different These are very different problems, though all arise from problems, though all arise from human activities that change human activities that change

composition of the atmosphere.composition of the atmosphere.

1. Acid Rain and 1. Acid Rain and Urban Air PollutionUrban Air Pollution

1. Acid Rain and 1. Acid Rain and Urban Air PollutionUrban Air Pollution

Burning introduces chemicalsBurning introduces chemicals• Nitrogen oxidesNitrogen oxides• Sulfur compoundsSulfur compounds• HydrocarbonsHydrocarbons

ConsequencesConsequences• Air pollutionAir pollution• Acid rainAcid rain

Reduce emissionsReduce emissions• Power plantsPower plants• Vehicles Vehicles

2. The Ozone Problem2. The Ozone Problem

OzoneOzone• Molecule of 3 Molecule of 3

oxygen atomsoxygen atoms• Absorbs Absorbs

ultraviolet ultraviolet radiationradiation

The Ozone LayerThe Ozone Layer• Concentration in Concentration in

stratospherestratosphere• Detected with Detected with

aircraftaircraft

2. The Ozone Problem2. The Ozone Problem

The concentration of The concentration of ozone is reduced ozone is reduced yearly over Antarcticayearly over Antarctica

This problem has been This problem has been linked to release of linked to release of chlorofluorocarbons chlorofluorocarbons (CFCs)(CFCs)

One solution is to One solution is to reduce emissions of reduce emissions of CFCsCFCs

3. The Greenhouse Effect3. The Greenhouse Effect

Atmosphere traps heat like Atmosphere traps heat like a greenhouse a greenhouse

One consequence is global One consequence is global warming, or climate warming, or climate changechange

Three main pointsThree main pointsCOCO22 is a greenhouse gas is a greenhouse gasBurning fossil fuels increases Burning fossil fuels increases

COCO22

Average global temperature Average global temperature has significantly increased: has significantly increased: 1990s was the warmest 1990s was the warmest decade until the 2000s, decade until the 2000s, which was even warmer.which was even warmer.

3. Greenhouse Effect3. Greenhouse Effect

Debates About Global Debates About Global Climate ChangeClimate Change

Are increased COAre increased CO22 levels levels responsible for these responsible for these temperature increase?temperature increase?

To what extent do the To what extent do the worldworld’’s oceans exchange s oceans exchange COCO22 with the atmosphere? with the atmosphere?

To what extent does To what extent does

solar energy output solar energy output

vary over time?vary over time?

Changing Ocean Currents?Changing Ocean Currents?Gulf stream & N Atlantic currentGulf stream & N Atlantic current


What impact might global What impact might global warming have?warming have?Melting ice capsMelting ice caps

Rising ocean levelsRising ocean levels

Warming of Northern Warming of Northern HemisphereHemisphere





Ecological impactsEcological impacts






Meteorological impactsMeteorological impacts






Meteorological impactsMeteorological impacts

Possible international Possible international solutions?solutions?

A final thought…A final thought…

Most environmental problems Most environmental problems are tied to some extent to the are tied to some extent to the growth of human population.growth of human population.

• Today ~ 6 billionToday ~ 6 billion

• 2050 ~ 9 billion2050 ~ 9 billion

• 2100 ???2100 ???

How many people canHow many people can Earth sustain? Earth sustain?

Estimates vary widely from 3 Estimates vary widely from 3 to 30 billion peopleto 30 billion people

It depends on your definition It depends on your definition of of ““sustain.sustain.””

All experts agree that a All experts agree that a population of greater than population of greater than 30 billion is a unsustainable.30 billion is a unsustainable.

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Great Ideas in Science: Lecture 14 – Ecosystems Professor Robert Hazen UNIV 301 All living systems live in ecosystems of many interacting organisms