Population Dynamics and Growth Population size N Exponential

Population Dynamics and Growth

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

Reindeer on an Alaskan island Number of reindeer 2, 000 1, 500 1, 000 500 1910 1920 1930 Year 1940 1950

Moose and wolves on Isle Royale 5, 000 Moose population Wolf population 3, 000 100 90 80 2, 000 70 60 1, 000 50 40 500 20 1900 1910 30 1950 Year 1970 1990 2000 1999 10 0 Number of wolves Number of moose 4, 000

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

Sheep in Tasmania Number of sheep (millions) 2. 0 1. 5 1. 0 . 5 1800 1825 1850 1875 Year 1900 1925

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

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

Birth and death rates Ø U. S. - 16 and 9 (7 or 0. 7%) Ø Rwanda - 52 and 18 (34 or 3. 4%) Births per thousand population Ø World - 26 and 9 (17 or 1. 7%) 32 30 28 26 24 22 20 18 16 14 0 1910 End of World War II Demographic transition 1920 Depression 1930 1940 Baby boom 1950 1960 Year Baby bust 1970 Echo baby boom 1980 1990 2000 2010

Factors Affecting Death Rate Ø Life expectancy Ø Infant mortality rate (IMR) Infant deaths per 1, 000 live births <10 -35 <36 -70 <71 -100 <100+ Data not available

Rate of Natural Increase Rate of natural increase = crude birth rate–crude death rate 40 Rate per 1, 000 people 50 Rate of natural increase 30 Crude birth rate 20 Crude death rate 10 0 17751800 1850 1900 1950 50 Developing Countries Crude birth rate 40 30 Crude death rate 20 Rate of natural increase 10 2000 2050 0 17751800 1850 1900 1950 Year 2000 © 2004 Brooks/Cole – Thomson Learning Developed Countries 2050

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% - 7 X in 100 years

Migration Rates Ø Affect regional populations Ø e. g. , United States Ø Net gain of 4/1000 people/year Ø Add to 7 from BR - DR = 11 (1. 1%)

Fertility Rates Ø Average number of children born to a woman during her childbearing years (ages 15 -44) Ø Replacement level fertility rates for ZPG Ø Total fertility rates

Fertility Rates Ø Replacement level fertility rates for ZPG - developed countries - 2. 1/woman - developing countries - 2. 5 - total world - 2. 3 -2. 4

Fertility Rates Ø 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

Fertility Rates Births per woman <2 4 -4. 9 2 -2. 9 5+ 3 -3. 9 No Data

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

Population Age Structure Male Female Rapid Growth Guatemala Nigeria Saudi Arabia Ages 0 -14 Slow Growth United States Australia Canada Ages 15 -44 Zero Growth Spain Austria Greece Negative Growth Germany Bulgaria Sweden Ages 45 -85+

Average Marriage Age Ø or age at birth of first child Ø Higher marriage leads to reduced reproductive period, which leads to lower fertility rates

Average Marriage Age Ø Current U. S. marriage - 24 (F) Ø Reduces 30 -year reproductive period (15 -44) to 21 -year reproductive period (24 -44) - 30% reduction Ø Reduces 15 -year prime reproductive period (15 -29) to a 6 -year prime reproductive period (24 -29) - 60% reduction Ø Expectation: >25 needed to affect fertility rate

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

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

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

Family Planning Ø Contraceptive methods - pills, devices, abortion (1 in 5 pregnancies terminated by abortion in world, 1 in 3 in U. S. )

Family Planning Ø 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 Ø Increased women’s rights - jobs - education - shown to lead to lower fertility rates

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

The Demographic Transition Stage 2 Transitional Stage 3 Industrial Stage 4 Postindustrial High 80 70 Relative population size Birth rate and death rate (number per 1, 000 per year) Stage 1 Preindustrial 60 50 Birth rate 40 30 Death rate 20 10 0 Total population Low Increasing Growth Very high Decreasing Low Zero growth rate growth rate Time Low Negative growth rate

Case Study: Slowing Population Growth in China (1. 3 billion people) Generally positive results: begun in 1972 Ø Economic incentives Ø Free medical care Ø Preferential treatment Ø Intrusive and coercive Ø Locally administered

China’s Program: The Details birth rate cut in half Ø Encourage later marriage (24 -28 F, 26 -30 M) Ø Family planning decentralized Ø Pledge benefits, penalties Ø Mandatory sterilization for >2 children Ø Free contraceptives (IUD), sterilization abortion Ø 83% participation, fertility rate 5. 7 to 1. 7

Case Study: Slowing Population Growth in India (1. 1 billion people) Generally disappointing results: begun in 1950 s Ø Poor planning (centralized) Ø Bureaucratic inefficiency Ø Low status of women (desire for male child) Ø Extreme poverty Ø Lack of support

India’s Program: The Details no effect Ø Only 20% participation Ø Majority rural, illiterate (high fertility rate, high infant mortality) Ø 36% of population <15 years of age Ø Mid-1970 s - voluntary sterilization! Ø 1978 raised minimum marriage Ø Education to rural areas via satellite

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