Population Dynamics and Growth. Exponential Growth Time (t) Population size (N) -ideal habitat...
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Population Dynamics and GrowthPopulation Dynamics and Growth
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Exponential GrowthExponential Growth
Time (t)
Po
pu
lati
on
siz
e (N
)
-ideal habitat-maximum reproduction-unlimited resources
Increase oftenfollowed bycrash
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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
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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
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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
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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
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Human population growth-exponential or logistic?Human population growth-exponential or logistic?
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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
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Human population growth-exponential or logistic?Human population growth-exponential or logistic?
Cultural evolution
-tool-making revolution
-agricultural revolution
-industrial (technological) revolution
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Carrying capacity for humansCarrying capacity for humans
Set by:
-famine-disease-warfare
Will these become more common aspopulation approaches carrying capacity?
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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
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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)
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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%)
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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)
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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
roo
ks/Co
le – Th
om
son
Learn
ing
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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
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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%)
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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
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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
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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
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Births per woman
< 2
2-2.9
3-3.9
4-4.9
5+
NoData
Fertility RatesFertility Rates
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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
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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
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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
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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
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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
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Can population growth be slowed?Can population growth be slowed?
Family planningFamily planning
Economic developmentEconomic development
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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
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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.)
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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
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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
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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
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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
er p
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
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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
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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
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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
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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
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Cutting Global Population GrowthCutting Global Population Growth
Family planningFamily planning
Reduce povertyReduce poverty
Elevate the status of womenElevate the status of women