Population Dynamics and Growth

Exponential Growth Time (t) Population size (N) -ideal habitat -maximum reproduction -unlimited resources Increase often followed by crash

2,000 1,500 Number of reindeer Year 1, Reindeer on an Alaskan island

5,000 4,000 3,000 2,000 1, Number of moose Year Number of wolves Moose population Wolf population Moose and wolves on Isle Royale

Logistic Growth Time (t) Population size (N) K -accelerating, decelerating Carrying capacity -growth slows as population size approaches carrying capacity -number that environment can support indefinitely Carrying capacity set by limiting factor

Number of sheep (millions) Year Sheep in Tasmania

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? Cultural evolution -tool-making revolution -agricultural revolution -industrial (technological) revolution

Carrying capacity for humans Set by: -famine -disease -warfare Will these become more common as population approaches carrying capacity?

Population Demographics  What affects human population size and growth rate?  What affects human population size and growth rate? 1) Birth rate and death rate 2) Migration rate 3) Fertility rate 4) Age structure 5) Average marriage age 1) Birth rate and death rate 2) Migration rate 3) Fertility rate 4) Age structure 5) Average marriage age

Factors Affecting Human Population Size  Population change equation  Zero population growth (ZPG)  Birth rate (number/1000 people/year)  Death rate (number/1000 people/year) Population Change Population Change = = (Births + Immigration) – (Deaths + Emigration)

Birth and death rates  U.S and 9 (7 or 0.7%)  Rwanda - 52 and 18 (34 or 3.4%) Births per thousand population Year Demographic transition Depression End of World War II Baby boomBaby bustEcho baby boom  World - 26 and 9 (17 or 1.7%)

Infant deaths per 1,000 live births <10 <10-35 <36-70 < <100+ Data not available Factors Affecting Death Rate  Life expectancy  Infant mortality rate (IMR)

Rate of Natural Increase Developed Countries Rate of natural increase Crude birth rate Crude death rate Rate of natural increase = crude birth rate–crude death rate Developing Countries Rate per 1,000 people Crude birth rate Rate of natural increase Crude death rate Year © 2004 Brooks/Cole – Thomson Learning

Natural Rate of Increase <1% 1-1.9% 2-2.9% 3+% Data not available Annual world population growth 1% - triple in 100 years 2% - 7X in 100 years

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  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 rates

Fertility Rates  Replacement level fertility rates for ZPG - developed countries - 2.1/woman - developing countries total world  Replacement level fertility rates for ZPG - developed countries - 2.1/woman - developing countries total world

Fertility 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 < No Data Fertility 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 0-14 Ages Ages Rapid Growth Guatemala Nigeria Saudi Arabia Rapid Growth Guatemala Nigeria Saudi Arabia Slow Growth United States Australia Canada Slow Growth United States Australia Canada Male Female Zero Growth Spain Austria Greece Zero Growth Spain Austria Greece Negative Growth Germany Bulgaria Sweden Negative Growth Germany Bulgaria Sweden Population Age Structure

Average Marriage Age  or 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 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 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

Current Needs for Large Families  Increased income  High infant mortality  Support for elderly  Few opportunities for women outside the home  Few opportunities for women outside the home  Family planning unavailable

Can population growth be slowed?  Family planning  Economic development

Family 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 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 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 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 Development  Goal: encourage people to want fewer children  Goal: encourage people to want fewer children  Stimulating economy influences demographics - demographic transition model - reduction in birth rate is ultimate goal  Stimulating economy influences demographics - demographic transition model - reduction in birth rate is ultimate goal

The Demographic Transition Low High Relative population size Birth rate and death rate (number per 1,000 per year) Birth rate and death rate (number per 1,000 per year) Stage 1 Preindustrial Stage 1 Preindustrial Stage 2 Transitional Stage 2 Transitional Stage 3 Industrial Stage 3 Industrial Stage 4 Postindustrial Stage 4 Postindustrial Low growth rate Low growth rate Increasing Growth growth rate Increasing Growth growth rate Very high growth rate Very high growth rate Decreasing growth rate Decreasing growth rate Low growth rate Low growth rate Zero growth rate Zero growth rate Negative growth rate Negative growth rate Birth rate Total population Death rate Time

Case Study: Slowing Population Growth in China (1.3 billion people)  Economic incentives  Free medical care  Preferential treatment  Intrusive and coercive  Locally administered Generally positive results: begun in 1972

China’s Program: The Details - birth rate cut in half  Encourage later marriage (24-28 F, M)  Family planning decentralized  Pledge benefits, penalties  Mandatory sterilization for >2 children  Free contraceptives (IUD), sterilization abortion  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)  Poor planning (centralized)  Bureaucratic inefficiency  Low status of women (desire for male child)  Low status of women (desire for male child)  Extreme poverty  Lack of support Generally disappointing results: begun in 1950s Generally disappointing results: begun in 1950s

India’s Program: The Details - no effect  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  Mid-1970s - voluntary sterilization!  1978 raised minimum marriage age  Education to rural areas via satellite

Cutting Global Population Growth  Family planning  Reduce poverty  Elevate the status of women