Environmental Science 204

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Environmental Science 204

• Population

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ImPaCT(Ehrlich Holdren)
Human Impact (Im) Population (P) x Consumption
(C) x Technology (T)
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Consumption
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American Consumption
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Technologythe wildcard
Cons
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Technologythe wildcard
Pros
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Population
the number of individuals that occupy a defined
area at a given time
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ImPaCT(Ehrlich Holdren)
Human Impact (Im) Population (P) x Consumption
(C) x Technology (T)
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Why We Live in Interesting Times

• Pre 2000 A.D.
• More youth than elderly
• More rural than urban

• Post 2010 A.D.
• More elderly than youth
• More urban than rural

• People alive 1950-2050 A.D. have seen
• Highest growth rate (2.1/year)
• Population double during their lifetime

More people have lived in the last 100 years,
than in all of human history before 1900!
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How do we measure population?

• Total Number
• Growth Rate
• Population Density
• Population Composition

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Population growth since you were born
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How do we measure population?

• Total Number
• Growth Rate
• Population Density
• Population Composition

1.1
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Keep in Mind
2.1 of 3 billion (1960) 63 million/yr
1.2 of 6 billion (1999) 72 million/yr
Still adding a lot of people!
Would need growth rate of 0.9 today to return to
1960 numbers
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Growth - by number
Now about 73 million/yr
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How do we measure population?

• Total Number
• Growth Rate
• Population Density
• Population Composition

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Doubling Time
Doubling time 70/growth rate ()
For example,
King County growth rate 1.5
King County doubling time 70/1.5 47 years
Therfore, by 2050 King County will require 2x
water,food,living space,schools,roads,etc.!
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How do we measure population?

• Total Number
• Growth Rate
• Population Density
• Population Composition

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How do we measure population?

• Total Number
• Growth Rate
• Population Density
• Population Composition

Age, Gender, Income
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Age PyramidChina, 1990
Post-reproductive
Reproductive
Pre-reproductive
Population in thousands
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Age PyramidChina, 1990(Interpretation)
Great Step Famine
Baby Boom
1 Child Policy
Baby Boom Echo
Population in thousands
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Predicting the Future from Age Pyramids
Increasing
Stable
Decreasing
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Population MomentumCongo
World Age Pyramids
http//www.census.gov/ipc/www/idbpyr.html
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US Age Pyramids
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What controls growth?
Local Population Change (natality
immigration) (mortality emigration)
World Population
natality mortality
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Natality
Crude Birthrate births per 1000 people per unit
time Total Fertility Rate number of children
born to average woman
(Replacement Fertility Rate 2.1)
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Mortality
Crude Deathrate deaths per 1000 people per unit
time Life Expectancy average age of death Life
Span maximum age of death
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What is the Future of the Human Population?
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How do Populations Grow?
A pattern of growth that varies, and may even
temporarily decrease, but grows over time, such
as 1, 3, 7, 5, 11, 10, 15.

• Random
• Arithmetic
• Exponential

Time
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How do Populations Grow?
A pattern of growth that increases at a constant
amount per unit time, such as 1, 2, 3, 4, 5, 6, 7.

• Random
• Arithmetic
• Exponential

Time
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How do Populations Grow?
A pattern of growth that increases at a
increasing amount per unit time, such as 2, 4,
8,16, 32, 64, 128.

• Random
• Arithmetic
• Exponential

Time
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Human Population is
exponential.
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What Happens Next?

• Random
• Arithmetic
• Exponential
• Malthusian Growth
• Logistic Growth

Thomas Malthus
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What Happens Next?
J-Curve

• Random
• Arithmetic
• Exponential
• Malthusian Growth
• Logistic Growth

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What Happens Next?
S-Curve

• Random
• Arithmetic
• Exponential
• Malthusian Growth
• Logistic Growth

Growth rate slows as population approaches
carrying capacity.
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Environmental Resistance
Any environmental factor that reduces population
growth (density dependant).
Examples Disease Predator-Prey
Relationships Stress Competition
Note There are also density-independent
factors. -mostly random events (fire, natural
disaster, climate)
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What isour fate?
J-Curve
What is the carrying capacity?
S-Curve
UN Prediction (2000)
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Demographic Transition
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ChallengesAhead
Without AIDS
With AIDS