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Population Dynamics and Growth. Exponential Growth. ideal habitat -maximum reproduction -unlimited resources. Population size ( N ). Increase often followed by crash. Time ( t ). Reindeer on an Alaskan island. 2,000. 1,500. Number of reindeer. 1,000. 500. 1910. 1920. 1930. 1940.

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Population Dynamics and Growth


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exponential growth
Exponential Growth
  • ideal habitat
  • -maximum reproduction
  • -unlimited resources

Population size (N)

Increase often

followed by

crash

Time (t)

slide3

Reindeer on an Alaskan island

2,000

1,500

Number of reindeer

1,000

500

1910

1920

1930

1940

1950

Year

moose and wolves on isle royale
Moose and wolves on Isle Royale

5,000

Moose population

Wolf population

4,000

3,000

Number of moose

100

90

80

2,000

70

60

Number of wolves

50

40

1,000

30

20

500

10

0

1900

1910

1930

1950

1970

1990

2000

Year

1999

logistic growth
Logistic Growth

Carrying capacity

-accelerating, decelerating

K

-growth slows as

population size approaches

carrying capacity

Population size (N)

-number that environment

can support indefinitely

Time (t)

Carrying capacity set by limiting factor

sheep in tasmania
Sheep in Tasmania

2.0

1.5

Number of sheep (millions)

1.0

.5

1800

1825

1850

1875

1900

1925

Year

human population growth exponential or logistic8
Human population growth-exponential or logistic?

-appears exponential

-history may suggest logistic

-periods of rapid growth

followed by stability

human population growth exponential or logistic9
Human population growth-exponential or logistic?

Cultural evolution

-tool-making revolution

-agricultural revolution

-industrial (technological) revolution

carrying capacity for humans
Carrying capacity for humans

Set by:

-famine

-disease

-warfare

Will these become more common as

population approaches carrying capacity?

population demographics
Population Demographics
  • What affects human population size

and growth rate?

Birth rate and death rate

Migration rate

Fertility rate

Age structure

Average marriage age

factors affecting human population size
Factors Affecting Human Population Size

Population

Change

=

(Births + Immigration) – (Deaths + Emigration)

  • Population change equation
  • Zero population growth (ZPG)
  • Birth rate (number/1000 people/year)
  • Death rate (number/1000 people/year)
birth and death rates
Birth and death rates
  • U.S. - 16 and 9 (7 or 0.7%)
  • Rwanda - 52 and 18 (34 or 3.4%)
  • World - 26 and 9 (17 or 1.7%)

32

30

28

26

24

Births per thousand population

22

20

18

End of World War II

16

Demographic

transition

Depression

Baby boom

Baby bust

Echo baby boom

14

0

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

Year

factors affecting death rate
Factors Affecting Death Rate

Infant deaths

per 1,000 live births

<10

<10-35

<36-70

<71-100

<100+

Data not

available

  • Life expectancy
  • Infant mortality rate (IMR)
rate of natural increase
Rate of Natural Increase

Rate of natural increase = crude birth rate–crude death rate

Developing Countries

Developed Countries

50

50

Crude

birth rate

40

40

Rate of

natural increase

Rate of

natural

increase

Rate per 1,000 people

© 2004 Brooks/Cole – Thomson Learning

30

30

Crude

birth rate

Crude

death rate

20

20

Crude

death rate

10

10

0

0

1800

2000

1775

1850

1900

1950

2050

1800

2000

1775

1850

1900

1950

2050

Year

natural rate of increase
Natural Rate of Increase

Annual world

population growth

<1%

1-1.9%

2-2.9%

3+%

Data not

available

1% - triple in 100 years

2% - 7X in 100 years

migration rates
Migration Rates
  • Affect regional populations
  • e.g., United States
  • Net gain of 4/1000 people/year
  • Add to 7 from BR - DR = 11 (1.1%)
fertility rates
Fertility Rates
  • Average number of children born to a

woman during her childbearing

years (ages 15-44)

  • Replacement level fertility rates

for ZPG

  • Total fertility rates
fertility rates19
Fertility Rates
  • Replacement level fertility rates

for ZPG

- developed countries - 2.1/woman

- developing countries - 2.5

- total world - 2.3-2.4

fertility rates20
Fertility Rates
  • Total fertility rates

- developed countries - 1.9 (U.S. 1.8)

- developing countries - 3.8

(Rwanda-8.5, Kenya-8.0)

- total world - 3.4

fertility rates21
Fertility Rates

Births per woman

< 2

4-4.9

2-2.9

5+

No

Data

3-3.9

fertility rates22
Fertility Rates
  • Time lag to ZPG

- about 3 generations (~70 years)

required to achieve ZPG once

replacement level fertility rates

are reached

population age structure
Population Age Structure

Male

Female

Rapid Growth

Guatemala

Nigeria

Saudi Arabia

Slow Growth

United States

Australia

Canada

Zero Growth

Spain

Austria

Greece

Negative Growth

Germany

Bulgaria

Sweden

Ages 0-14

Ages 15-44

Ages 45-85+

average marriage age
Average Marriage Age
  • or age at birth of first child
  • Higher marriage age leads to reduced

reproductive period, which leads to

lower fertility rates

average marriage age25
Average Marriage Age
  • Current U.S. marriage age - 24 (F)
  • Reduces 30-year reproductive period (15-44)

to 21-year reproductive period (24-44)

- 30% reduction

  • Reduces 15-year prime reproductive period

(15-29) to a 6-year prime reproductive period

(24-29) - 60% reduction

  • Expectation: >25 needed to affect fertility rate
current needs for large families
Current Needs for Large Families
  • Increased income
  • High infant mortality
  • Support for elderly
  • Few opportunities for women outside

the home

  • Family planning unavailable
can population growth be slowed
Can population growth be slowed?
  • Family planning
  • Economic development
family planning
Family Planning
  • Goal: help people have only as many

children as they want, when they

want them

family planning29
Family Planning
  • Contraceptive methods

- pills, devices, abortion

(1 in 5 pregnancies terminated by abortion

in world, 1 in 3 in U.S.)

family planning30
Family Planning
  • Economic incentives, disincentives

- direct incentives for contraceptive use, etc.

- delayed incentives

- old-age pensions

- health insurance

- free education for small families

- penalties

- extra taxes, reduce/withhold benefits for

too many children

family planning31
Family Planning
  • Increased women’s rights

- jobs

- education

- shown to lead to lower fertility rates

economic development
Economic Development
  • Goal: encourage people to want

fewer children

  • Stimulating economy influences

demographics

- demographic transition model

- reduction in birth rate is ultimate

goal

the demographic transition
The Demographic Transition

Stage 1

Preindustrial

Stage 2

Transitional

Stage 3

Industrial

Stage 4

Postindustrial

High

80

70

60

Birth rate

50

Birth rate and death rate

(number per 1,000 per year)

Relative population size

40

30

Death rate

20

10

Total population

Low

0

Low

growth rate

Increasing Growth

growth rate

Very high

growth rate

Decreasing

growth rate

Low

growth rate

Zero

growth rate

Negative

growth rate

Time

case study slowing population growth in china 1 3 billion people
Case Study: Slowing Population Growth in China (1.3 billion people)

Generally positive results: begun in 1972

  • Economic incentives
  • Free medical care
  • Preferential treatment
  • Intrusive and coercive
  • Locally administered
china s program the details birth rate cut in half
China’s Program: The Details -birth rate cut in half
  • Encourage later marriage (24-28 F, 26-30 M)
  • Family planning decentralized
  • Pledge benefits, penalties
  • Mandatory sterilization for >2 children)
  • Free contraceptives (IUD), sterilization

abortion

  • 83% participation, fertility rate 5.7 to 1.7
case study slowing population growth in india 1 1 billion people
Case Study: Slowing Population Growth in India (1.1 billion people)

Generally disappointing results:

  • Poor planning (centralized)
  • Bureaucratic inefficiency
  • Low status of women

(desire for male child)

  • Extreme poverty
  • Lack of support
india s program the details no effect
India’s Program: The Details -no effect
  • Only 20% participation
  • Majority rural, illiterate (high fertility rate,

high infant mortality)

  • 36% of population <15 years of age
  • Mid-1970s - voluntary sterilization!
  • 1978 raised minimum marriage age
  • Education to rural areas via satellite
cutting global population growth
Cutting Global Population Growth
  • Family planning
  • Reduce poverty
  • Elevate the status of women