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Great Ideas in Science: Lecture 14 – Ecosystems: 

Great Ideas in Science: Lecture 14 – Ecosystems Professor Robert Hazen UNIV 301 – December 6, 2006 All living systems live in ecosystems of many interacting organisms.

Three Definitions of Evolution: 

Three Definitions of Evolution 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: 

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. Fossils Molecular Biology Cellular biology Genetics Comparative anatomy Observations of nature and of breeding

Three Related Terms: 

Three Related Terms Creationism Young Earth Creationism Scientific Creationism

1. Creationism: 

1. Creationism Creationists believe that God created the universe and life. Many creationists accept Biblical creation story as metaphorical and thus they rely on empirical evidence. Many scientists are also creationists.

2. Young Earth Creationism : 

2. Young Earth Creationism Young-Earth creationists believe in a literal reading 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: 

3. Scientific Creationism Scientific creationists search for empirical evidence that supports the tenets of young-Earth creationism. SC is not science, because its basic 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: 

Second Definition of Evolution: Common Descent Common descent means that all living things descended from the first living cell. Tree diagrams reveal ancestral relationships. Search for fossil intermediates

Common Descent: 

Common Descent

Objections to Common Descent: 

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 land-dwelling 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: 

Whale Evolution Ambulocetus

Whale Evolution: 

Whale Evolution Basilosaurus

Third Definition of Evolution: Natural Selection: 

Third Definition of Evolution: Natural Selection Natural Selection Populations exhibit variation More individuals born than will survive Most fit more likely to reproduce

Charles Darwin (1809-1882): 

Charles Darwin (1809-1882)

Charles Darwin: The Beagle at Galapagos: 

Charles Darwin: The Beagle at Galapagos

Eye Evolution: 

Eye Evolution 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. 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).

Eye Evolution: 

Eye Evolution This evolutionary sequence is continuously driven by selection.

What is the Rate of Evolution?: 

What is the Rate of Evolution? Punctuated Equilibrium (a) versus Gradualism (b)

Mass Extinctions and the Rate of Evolution: 

Mass Extinctions and the Rate of Evolution Rate of extinction 10%-20% extinct in 5-6 million years Mass extinctions 30%-90% extinct At least 5 episodes Mechanisms Asteroids volcanoes

Mass Extinctions: 

Mass Extinctions Evidence from the Fossil Record

Mass Extinctions: 

Mass Extinctions Evidence from Iridium

Mass Extinctions: 

Mass Extinctions Evidence from Foraminifera

What Causes Mass Extinctions?: 

What Causes Mass Extinctions? Human Activities

What Causes Mass Extinctions?: 

What Causes Mass Extinctions? Human Activities

Ecology and Ecosystems: 

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: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts

Every Ecosystem Consists of Both Living and Nonliving Parts: 

Every Ecosystem Consists of Both Living and Nonliving Parts Abiotic: The chemical and physical environment Biotic: All living organisms that form the ecological community

Ecosystems: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts Energy flows through.

Energy Flows Through Ecosystems: 

Energy Flows Through Ecosystems Food Web Interactions of organisms Trophic Levels Photosynthetic plants Herbivores Carnivores Decomposers Most energy is lost as heat 10% is transferred from one level to the next.

Ecosystems: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts Energy flows through Matter is recycled

Matter is Recycled by Ecosystems: 

Matter is Recycled by Ecosystems Carbon: Atoms continuously cycle

Ecosystems: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts Energy flows through Matter is recycled Every organism occupies an ecological niche (two species cannot occupy same niche)

Ecosystems: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts Energy flows through Matter is recycled Every organism occupies an ecological niche (two species cannot occupy same niche) Stable ecosystems achieve balance among populations

Stable Ecosystems Achieve a Balance Among Their Populations: 

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.

Ecosystems: 

Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms Ecosystems consist of both living and nonliving parts Energy flows through Matter is recycled Every organism occupies an ecological niche (two species cannot occupy same niche) Stable ecosystems achieve balance among populations Ecosystems can be disrupted

Law of Unintended Consequences: 

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: 

Three Environmental Problems Acid Rain Ozone Hole Greenhouse Effect 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 Burning introduces chemicals Nitrogen oxides Sulfur compounds Hydrocarbons Consequences Air pollution Acid rain Reduce emissions Power plants Vehicles

1. Acid Rain and Urban Air Pollution: 

1. Acid Rain and Urban Air Pollution

2. The Ozone Problem: 

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: 

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: 

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

3. Greenhouse Effect: 

3. Greenhouse Effect

Debates About Global Climate Change: 

Debates About Global Climate Change Are increased CO2 levels responsible for 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?

Debates About Global Climate Change: 

Debates About Global Climate Change What impact might global warming have? Rising ocean levels

Changing Ocean Currents?: 

Changing Ocean Currents? Gulf stream & N Atlantic current

Debates About Global Climate Change: 

Debates About Global Climate Change What impact might global warming have? Rising ocean levels Warming of Northern Hemisphere

Debates About Global Climate Change: 

Debates About Global Climate Change What impact might global warming have? Rising ocean levels Warming of Northern Hemisphere Ecological impacts

Debates About Global Climate Change: 

Debates About Global Climate Change What impact might global warming have? Rising ocean levels Warming of Northern Hemisphere Ecological impacts Meteorological impacts

Debates About Global Climate Change: 

Debates About Global Climate Change What impact might global warming have? Rising ocean levels Warming of Northern Hemisphere Ecological impacts Meteorological impacts One possible international solution: The Kyoto accord

A final thought…: 

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?: 

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.

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