Transcript Lecture 14 – Ecosystems

Great Ideas in Science:
Lecture 14 – Ecosystems
Professor Robert Hazen
UNIV 301
All living systems live in ecosystems
of many interacting organisms.
Three Definitions of Evolution
1.
2.
3.
Evolution as Change: Life on
Earth has changed over time
Common descent: All living
things on Earth descended
from a common ancestor.
Natural selection: The process
by which life evolved is
Darwinian natural selection
First Definition of Evolution:
Change Over Time
Observational evidence overwhelmingly
supports the theory that life originated
on Earth billions of years ago as a single
cell, and has been changing ever since.
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Fossils
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Molecular Biology
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Cellular biology
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Genetics
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Comparative anatomy
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Observations of nature and of breeding
Extinct Animals
TRILOBITES
If you accept observational evidence,
then the unambiguous conclusion is
that life has changed over time.
Three Related Terms
1.
2.
Creationism
Young Earth Creationism
3.
Scientific Creationism
1. Creationism



Creationists believe that God
created the universe and life.
Many creationists accept the
Bible’s creation story as a
metaphor; they rely on
empirical evidence (Psalm 19).
Many scientists are also
creationists in this sense.
2. Young Earth Creationism

Young-Earth creationists believe in a
literal reading of Genesis.
•
•
•
•

Earth is about 10,000 years old.
Geology features caused by Noah’s Flood.
All species created in modern form.
Minor evolutionary changes only.
For many young-Earth creationists,
the findings of science are irrelevant
at best, and possibly dangerous and
subversive.
3. Scientific Creationism

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Scientific creationists search for
empirical evidence that supports the
tenets of young-Earth creationism.
SC is not science, because its basic
tenets are not subject to change
based on empirical evidence.
Even if its tenets conformed to
observational evidence, “scientific”
creationism would not be science.
Should creationism be taught in the
science classroom?
Second Definition of
Evolution: Common Descent


Common descent means that all
living things descended from the
first living cell.
Tree diagrams reveal ancestral
relationships.
Second Definition of
Evolution: Common Descent



Common descent means that all
living things descended from the
first living cell.
Tree diagrams reveal ancestral
relationships.
The search for fossil intermediates
supports common descent.
Fossils



Fossils prove that life on Earth has
changed over time; most extinct.
Fossils demonstrate that these
changes are gradual and
progressive (simple to complex)
All known fossils fit
into a pattern
of continuous
evolution.
Geological Time
Fossils
Strata
Younger = higher
Gradual Evolution
Objections to Common Descent
“Darwinists rarely mention the whale
because it presents them with one of
their most insoluble problems. They
believe that somehow a whale must
have evolved from an ordinary landdwelling animal, which took to the sea
and lost its legs. … A land mammal
that was in the process of becoming a
whale would fall between two stools –
it would not be fitted for life on land
or sea, and would have no hope of
survival.”
Alan Haywood, 1985
Whale Evolution
Ambulocetus
Whale Evolution
Ambulocetus
Whale Evolution
Rodhocetus
Whale Evolution
Basilosaurus
Whale Evolution
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 Protein
1.
2.
3.
4.
Transcription: Use DNA to make mRNA
Attach mRNA to ribosome
Translation: RNA to amino acids
Fold amino acids into protein
The Genetic
Code
The Cell Theory, 1839
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All living things are composed of cells
The cell is the fundamental unit of life
All cells arise from previous cells
CONCLUSIONS:
Observational evidence
overwhelmingly supports the
hypothesis of common descent
for all known life forms, living
and fossil, on Earth.
Third Definition of Evolution:
Natural Selection (Darwin)
• Populations exhibit variation.
• More individuals are born than
will survive.
• The most fit individuals are more
likely to reproduce.
Charles Darwin (1809-1882)
Charles Darwin:
The Beagle at Galapagos
Microevolution
Phacops trilobites: Almost unchanged from 440 to 370 million years!
Microevolution
Unanswered Questions
about Evolution

How does macroevolution occur?
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Why are some species static?
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What is the rate of evolution?
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What is the rate of extinction?
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What causes mass extinctions?
Macroevolution
How did such an amazing diversity of trilobites arise?
Eye 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
Eye Evolution
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).
Selection rules for model eye evolution:
1. Vary curvature, aperture, and central
refractive index randomly by 1%.
2. If visual acuity (spatial resolution)
increases, then retain that variation.
Eye Evolution
This evolutionary sequence is
continuously driven by selection.
What is the Rate of
Evolution?
Punctuated Equilibria (a)
versus Gradualism (b)
Mass Extinctions
Mass Extinctions and the
Rate of Evolution
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Rate of extinction
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Mass extinctions
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Mechanisms
• 10%-20% extinct in
5-6 million years
• 30%-90% extinct
• At least 5 episodes
• Asteroids
• volcanoes
Mass Extinctions
Evidence from the Fossil Record
Mass Extinctions
Evidence from Iridium
Mass Extinctions
Evidence from Foraminifera
What Causes Mass Extinctions?
Human Activities
What Causes Mass Extinctions?
Human Activities
Ecology and Ecosystems
Ecology: The study of
natural living systems
Ecosystems: Consist of
biotic and abiotic
components
Community: All organisms
in an ecosystem
• Producers
• Consumers
• Decomposers
Ecosystems
Key Idea: Living things live in
ecosystems of many interdependent
organisms
1. Ecosystems consist of both living
and nonliving parts
2. Energy flows through
3. Matter is recycled
4. Every organism occupies an
ecological niche (two species
cannot occupy same niche)
5. Stable ecosystems achieve balance
among populations
6. Ecosystems can be disrupted
Every Ecosystem Consists of
Both Living and Nonliving Parts
Abiotic: The chemical and physical
environment
Biotic: All living organisms that
form the ecological community
Energy Flows
Through Ecosystems

Food Web
• Interactions of organisms

Trophic Levels
•
•
•
•
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Photosynthetic plants
Herbivores
Carnivores
Decomposers
Most energy is lost as heat
• 10% is transferred from one
level to the next.
Matter is Recycled by
Ecosystems
Carbon: Atoms continuously cycle
Stable Ecosystems Achieve a
Balance Among Their Populations
Homeostasis is a balance among
populations.
Resources are always limited.
While we observe some variation
in populations, overall they are
relatively constant.
Law of Unintended Consequences
Changing one part of a complex
system may cause unintended
changes in other parts of the system
Nile perch
Peter’s mountain mallow
Three Environmental Problems
Acid Rain
2. Ozone Hole
Greenhouse Effect
1.
3.
These are very different
problems, though all arise from
human activities that change
composition of the atmosphere.
1. Acid Rain and
Urban Air Pollution
1. Acid Rain and
Urban Air Pollution
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Burning introduces chemicals
• Nitrogen oxides
• Sulfur compounds
• Hydrocarbons
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Consequences
• Air pollution
• Acid rain
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Reduce emissions
• Power plants
• Vehicles
2. The Ozone Problem
Ozone
• Molecule of 3
oxygen atoms
• Absorbs
ultraviolet
radiation
The Ozone Layer
• Concentration in
stratosphere
• Detected with
aircraft
2. The Ozone Problem
The concentration of
ozone is reduced
yearly over Antarctica
This problem has been
linked to release of
chlorofluorocarbons
(CFCs)
One solution is to reduce
emissions of CFCs
3. The Greenhouse Effect
Atmosphere traps heat like
a greenhouse
One consequence is global
warming, or climate
change
Three main points
CO2 is a greenhouse gas
Burning fossil fuels increases
CO2
Average global temperature
has significantly increased:
1990s was the warmest
decade until the 2000s,
which was even warmer.
3. Greenhouse Effect
Debates About Global
Climate Change
Are increased CO2 levels
responsible for these
temperature increase?
To what extent do the
world’s oceans exchange
CO2 with the atmosphere?
To what extent does
solar energy output
vary over time?
Changing Ocean Currents?
Gulf stream & N Atlantic current
Debates About Global
Climate Change
What impact might global
warming have?
Melting ice caps
Rising ocean levels
Warming of Northern
Hemisphere
Debates About Global
Climate Change
What impact might global
warming have?
Melting ice caps
Rising ocean levels
Warming of Northern
Hemisphere
Ecological impacts
Debates About Global
Climate Change
What impact might global
warming have?
Melting ice caps
Rising ocean levels
Warming of Northern
Hemisphere
Ecological impacts
Meteorological impacts
Debates About Global
Climate Change
What impact might global
warming have?
Melting ice caps
Rising ocean levels
Warming of Northern
Hemisphere
Ecological impacts
Meteorological impacts
Possible international
solutions?
A final thought…
Most environmental problems
are tied to some extent to the
growth of human population.
• Today ~ 6 billion
• 2050 ~ 9 billion
• 2100 ???
How many people can
Earth sustain?
Estimates vary widely from 3
to 30 billion people
It depends on your definition
of “sustain.”
All experts agree that a
population of greater than
30 billion is a unsustainable.