Population Dynamics and GrowthPopulation Dynamics and Growth

Exponential GrowthExponential Growth

Time (t)

Po

pu

lati

on

siz

e (N

)

-ideal habitat-maximum reproduction-unlimited resources

Increase oftenfollowed bycrash

2,000

1,500

Nu

mb

er o

f re

ind

eer

1910 1920 1930 1940 1950

Year

1,000

500

Reindeer on an Alaskan island

5,000

4,000

3,000

2,000

1,000

500

Nu

mb

er o

f m

oo

se

100

90

80

70

60

50

40

30

20

10

01900 1910 1930 1950 1970 1990 2000

1999Year

Nu

mb

er of w

olves

Moose population

Wolf population

Moose and wolves on Isle RoyaleMoose and wolves on Isle Royale

Logistic GrowthLogistic Growth

Time (t)

Po

pu

lati

on

siz

e (N

)

K-accelerating, decelerating Carrying capacity

-growth slows aspopulation size approachescarrying capacity

-number that environmentcan support indefinitely

Carrying capacity set by limiting factor

2.0

1.5

1.0

.5

Nu

mb

er o

f sh

eep

(m

illio

ns)

1800 1825 1850 1875 1900 1925

Year

Sheep in TasmaniaSheep in Tasmania

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

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

-appears exponential

-history may suggest logistic

-periods of rapid growth followed by stability

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

Cultural evolution

-tool-making revolution

-agricultural revolution

-industrial (technological) revolution

Carrying capacity for humansCarrying capacity for humans

Set by:

-famine-disease-warfare

Will these become more common aspopulation approaches carrying capacity?

Population DemographicsPopulation Demographics

What affects human population size and growth rate?

What affects human population size and growth rate?

1) Birth rate and death rate2) Migration rate3) Fertility rate4) Age structure5) Average marriage age

1) Birth rate and death rate2) Migration rate3) Fertility rate4) Age structure5) Average marriage age

Factors Affecting Human Population SizeFactors Affecting Human Population Size

Population change equationPopulation change equation

Zero population growth (ZPG)Zero population growth (ZPG)

Birth rate (number/1000 people/year)Birth rate (number/1000 people/year)

Death rate (number/1000 people/year)Death rate (number/1000 people/year)

PopulationChange

PopulationChange == (Births + Immigration) – (Deaths + Emigration)(Births + Immigration) – (Deaths + Emigration)

Birth and death ratesBirth and death rates

U.S. - 16 and 9 (7 or 0.7%) U.S. - 16 and 9 (7 or 0.7%)

Rwanda - 52 and 18 (34 or 3.4%) Rwanda - 52 and 18 (34 or 3.4%)

32

30

2826242220181614

0

Bir

ths

pe

r th

ou

sa

nd

po

pu

lati

on

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

Demographictransition

Depression

End of World War II

Baby boom Baby bust Echo baby boom

World - 26 and 9 (17 or 1.7%) World - 26 and 9 (17 or 1.7%)

Infant deathsper 1,000 live births

<10<10-35<36-70<71-100<100+Data notavailable

Factors Affecting Death RateFactors Affecting Death Rate

Life expectancy Life expectancy Infant mortality rate (IMR) Infant mortality rate (IMR)

Rate of Natural IncreaseRate of Natural Increase

Developed Countries50

40

30

20

10

017751800 1850 1900 1950 2000 2050

Rate ofnatural increase

Crudebirth rate

Crudedeath rate

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

Developing Countries50

40

30

20

10

017751800 1850 1900 1950 2000 2050

Rat

e p

er 1

,000

peo

ple Crude

birth rate

Rate ofnaturalincreaseCrude

death rate

Year

© 2004 B

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Natural Rate of IncreaseNatural Rate of Increase

<1%

1-1.9%

2-2.9%

3+%Data notavailable

Annual worldpopulation growth

1% - triple in 100 years2% - 7X in 100 years

Migration RatesMigration Rates

Affect regional populations Affect regional populations

e.g., United States e.g., United States

Net gain of 4/1000 people/year Net gain of 4/1000 people/year

Add to 7 from BR - DR = 11 (1.1%) Add to 7 from BR - DR = 11 (1.1%)

Fertility RatesFertility Rates

Average number of children born to a woman during her childbearing years (ages 15-44)

Average number of children born to a woman during her childbearing years (ages 15-44)

Replacement level fertility rates for ZPG

Replacement level fertility rates for ZPG

Total fertility ratesTotal fertility rates

Fertility RatesFertility Rates

Replacement level fertility rates for ZPG

- developed countries - 2.1/woman - developing countries - 2.5 - total world - 2.3-2.4

Replacement level fertility rates for ZPG

- developed countries - 2.1/woman - developing countries - 2.5 - total world - 2.3-2.4

Fertility RatesFertility Rates

Total fertility rates

- developed countries – 1.6 (U.S. 2.2) - developing countries – 2.9 (older values:Rwanda-8.5, Kenya-8.0) - total world – 2.7

Total fertility rates

- developed countries – 1.6 (U.S. 2.2) - developing countries – 2.9 (older values:Rwanda-8.5, Kenya-8.0) - total world – 2.7

Births per woman

< 2

2-2.9

3-3.9

4-4.9

5+

NoData

Fertility RatesFertility Rates

Fertility RatesFertility Rates

Time lag to ZPG

- about 3 generations (~70 years) required to achieve ZPG once replacement level fertility rates are reached

Time lag to ZPG

- about 3 generations (~70 years) required to achieve ZPG once replacement level fertility rates are reached

Ages 0-14Ages 0-14 Ages 15-44Ages 15-44 Ages 45-85+Ages 45-85+

Rapid GrowthGuatemala

NigeriaSaudi Arabia

Rapid GrowthGuatemala

NigeriaSaudi Arabia

Slow GrowthUnited States

AustraliaCanada

Slow GrowthUnited States

AustraliaCanada

MaleMale FemaleFemale

Zero GrowthSpainAustriaGreece

Zero GrowthSpainAustriaGreece

Negative GrowthGermanyBulgariaSweden

Negative GrowthGermanyBulgariaSweden

Population Age StructurePopulation Age Structure

Average Marriage AgeAverage Marriage Age

or age at birth of first childor age at birth of first child

Higher marriage age leads to reduced reproductive period, which leads to lower fertility rates

Higher marriage age leads to reduced reproductive period, which leads to lower fertility rates

Average Marriage AgeAverage Marriage Age

Current U.S. marriage age - 24 (F)Current U.S. marriage age - 24 (F)

Reduces 30-year reproductive period (15-44) to 21-year reproductive period (24-44)

- 30% reduction

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

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 Expectation: >25 needed to affect fertility rate

Current Needs for Large FamiliesCurrent Needs for Large Families

Increased incomeIncreased income

High infant mortalityHigh infant mortality

Support for elderlySupport for elderly

Few opportunities for women outside the home

Few opportunities for women outside the home

Family planning unavailableFamily planning unavailable

Can population growth be slowed?Can population growth be slowed?

Family planningFamily planning

Economic developmentEconomic development

Family PlanningFamily Planning

Goal: help people have only as many children as they want, when they want them

Goal: help people have only as many children as they want, when they want them

Family PlanningFamily Planning

Contraceptive methods

- pills, devices, abortion(1 in 5 pregnancies terminated by abortion

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

Contraceptive methods

- pills, devices, abortion(1 in 5 pregnancies terminated by abortion

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

Family PlanningFamily 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

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 PlanningFamily Planning

Increased women’s rights- jobs- education

- shown to lead to lower fertility rates

Increased women’s rights- jobs- education

- shown to lead to lower fertility rates

Economic DevelopmentEconomic Development

Goal: encourage people to wantfewer children

Goal: encourage people to wantfewer children

Stimulating economy influencesdemographics- demographic transition model- reduction in birth rate is ultimate goal

Stimulating economy influencesdemographics- demographic transition model- reduction in birth rate is ultimate goal

The Demographic TransitionThe Demographic Transition

LowLow

HighHigh

Rel

ativ

e p

op

ula

tio

n s

ize

Rel

ativ

e p

op

ula

tio

n s

ize

Bir

th r

ate

and

dea

th r

ate

(nu

mb

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er 1

,000

per

yea

r)B

irth

rat

e an

d d

eath

rat

e(n

um

ber

per

1,0

00 p

er y

ear) 8080

7070

6060

5050

4040

3030

2020

1010

00

Stage 1Preindustrial

Stage 1Preindustrial

Stage 2Transitional

Stage 2Transitional

Stage 3IndustrialStage 3

IndustrialStage 4

PostindustrialStage 4

Postindustrial

Lowgrowth rate

Lowgrowth rate

Increasing Growthgrowth rate

Increasing Growthgrowth rate

Very highgrowth rateVery high

growth rateDecreasinggrowth rateDecreasinggrowth rate

Lowgrowth rate

Lowgrowth rate

Zerogrowth rate

Zerogrowth rate

Negativegrowth rate

Negativegrowth rate

Birth rate

Total population

Death rate

TimeTime

Case Study: Slowing Population Growth in China (1.3 billion people)Case Study: Slowing Population Growth in China (1.3 billion people)

Economic incentivesEconomic incentivesFree medical careFree medical carePreferential treatmentPreferential treatmentIntrusive and coerciveIntrusive and coerciveLocally administeredLocally administered

Generally positive results: begun in 1972Generally positive results: begun in 1972

China’s Program: The Details -birth rate cut in halfChina’s Program: The Details -birth rate cut in half

Encourage later marriage (24-28 F, 26-30 M) Encourage later marriage (24-28 F, 26-30 M)

Family planning decentralized Family planning decentralized

Pledge benefits, penalties Pledge benefits, penalties

Mandatory sterilization for >2 children Mandatory sterilization for >2 children

Free contraceptives (IUD), sterilizationabortion

Free contraceptives (IUD), sterilizationabortion

83% participation, fertility rate 5.7 to 1.7 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)

Poor planning (centralized)Poor planning (centralized)Bureaucratic inefficiencyBureaucratic inefficiencyLow status of women

(desire for male child)

Low status of women(desire for male child)

Extreme povertyExtreme poverty

Lack of supportLack of support

Generally disappointing results:begun in 1950sGenerally disappointing results:begun in 1950s

India’s Program: The Details -no effectIndia’s Program: The Details -no effect

Only 20% participation Only 20% participation Majority rural, illiterate (high fertility rate,

high infant mortality)

Majority rural, illiterate (high fertility rate,high infant mortality)

36% of population <15 years of age 36% of population <15 years of age

Mid-1970s - voluntary sterilization! Mid-1970s - voluntary sterilization!

1978 raised minimum marriage age 1978 raised minimum marriage age

Education to rural areas via satellite Education to rural areas via satellite

Cutting Global Population GrowthCutting Global Population Growth

Family planningFamily planning

Reduce povertyReduce poverty

Elevate the status of womenElevate the status of women