I. I.Population Dynamics - History A. A.Thomas Malthus (1766-1834) English parson Became concerned...

I. Population Dynamics - History

A. Thomas Malthus (1766-1834)• English parson• Became concerned that unrestricted population

growth would cause demand to exceed availability of resources

• Predicted widespread poverty and famine• Global population < 1 billion

• Malthusians - People who forecast disaster due to overpopulation

• Many of Malthus’ predictions did not occur• Agricultural improvements (did not foresee)• Birth control (rejected on moral grounds)PopClock


B. Demographic Transition• Theory developed to explain human population dynamics

in response to economic development• Cohen – Four Stages

1) High birth & death rates (nearly equal but variable) Growth rate low

2) Death rate falls and becomes less variable, birth rate still high Growth rate rises, population increases. Mortality transition

3) Birth rate drops, death rate remains low or declines, growth rate slows, population increases. Fertility transition

4) Low birth & death rates (nearly equal, not variable), growth rate low or negative, population larger than before (1)

• This process has occurred in many developed nations• United States, Canada, Japan, Western Europe

• Mortality and fertility transitions typically due to greater affluence, improved health care, changing social expectations, etc.


B. Demographic Transition• In recent years death rates in many developing

nations have decreased• Status of the social and economic changes that will

supposedly lead to stable populations is unclear• Some neo-Malthusians pessimistic that transition to

lower birth rates and stable populations will occur• Garrett Hardin - “Lifeboat Ethics”

• Barry Commoner - Anti-Malthusian• Main cause of environmental degradation is

inappropriate use of technology, not simple population growth

• Ecologically sound development more important than population control

II. Population Dynamics - Theory

A. Background• Understanding human population dynamics

requires understanding population theory• Earth is a closed system (no immigration/emigration)

• Population size is dynamic equilibrium between• Biotic potential• Environmental resistance

• Two basic growth models• Density-independent (exponential) growth• Density-dependent (logistic) growth


B. Density-Independent Growth• Population growth with unlimited resources• In nature, usually occurs rarely and briefly• Limited by maximum reproduction rate for a

species• Inversely related to generation time• Ex - Higher for mouse than human


B. Density-Independent Growth• Not sustainable indefinitely in the real world

• Assumes/Requires unlimited resources

• Increasing population density limits ability of individuals to acquire resources

• Density affects/limits population growth rate

C. Density-Dependent Growth• Based on idea that a given environment only

can support a limited number of individuals• Carrying capacity

• Population growth described by logistic growth model

• Environmental resistance increases as population size increases

III. Population Dynamics - Trends

A. Demographics• Global population reached 6 billion in Oct 1999• Most population growth currently taking place in

developing nations• Developing nations contain 80% of global population• Percentage of global population growth in developing

nations• 1950 – 85%• Today – 99%


B. Total Fertility Rate (TFR)• TFR = Fecundity• 2.0 = Replacement level fertility• Global TFR

• 1950 – 5.0• 2007 – 2.60 (48% decrease)

• Africa – 4.73 (Mali – 7.38, Niger – 7.37)• Asia – 2.41 (India – 2.81, China – 1.75)• N America – 2.26 (Canada – 1.61, Mexico – 2.39,

USA – 2.09)• Europe – 1.45 (Lithuania – 1.21, Italy – 1.29,

Spain – 1.29)

Source: U.S. Census Bureau


C. Infant Mortality Rate (IMR)• Global IMR

• 1950 – 156 deaths per 1000 births (15.6%)• 2007 – 44.0 deaths per 1000 births (4.40%)

• 72% decrease• Europe – 0.76%• Africa – 8.03%



D. Birth and Death Rates• 1950

• Birth rate – 37 per 1000 people per year• Death rate – 20 per 1000 people per year

• Growth = 17 per 1000 people per year = 1.7%

• 2007• Birth rate – 20.2 per 1000 people per year• Death rate – 8.4 per 1000 people per year

• Growth = 11.8 per 1000 people per year = 1.18%

• Developed nations – 0.22% (0.06 B-D + 0.16 I)• Developing nations – 1.38% (1.43 B-D – 0.05 E)



E. Age and Life Expectancy• Median Age

• World – 28.0 years• Developed nations – 39.2 years

• Europe – 39.8 years• N. America – 32.0 years

• Developing nations – 25.8 years• Africa – 19.3 years

• Life Expectancy• 1950 – 46 years• 2007 – 65.7 years

• Africa – 51.9 years (Swaziland – 32.2 years)• Europe – 74.8 years (Andorra – 83.5 years)• N. America – 75.9 years (USA – 78.0 years)



F. Population Projections - UN1. Low Variant (TFR 1.35 by 2050)

• 2050 – 7.68 billion• 2150 – 3.2 billion

2. Medium Variant (TFR 1.85 by 2050)• 2050 – 9.08 billion• 2150 – 9.7 billion

3. High Variant (TFR 2.35 by 2050)• 2050 – 10.65 billion• 2150 – 24.8 billion

4. Constant Variant (TFR = 2.59)• 2050 – 11.66 billion• 2150 – 51.2 billion

United Nations Population Division

IV. Population – Environmental Effects

• Ehrlich – “Earth can support a larger population of cooperative, far-sighted, vegetarian pacifist saints than of competitive, myopic, meat-eating, war-making typical human beings. All else being equal, Earth can hold more people if they have relatively equal access to the requisites of a decent life than if the few are able to monopolize resources and the many must largely do without. The problems of population, social and economic inequity, and environmental deterioration are thus completely intertwined.”


• Not all humans impact the environment equally

• Industrialized nations currently house 22% of the world’s population but consume

• 60% of food• 70% of energy• 75% of metals• 85% of wood• Generate 75% of CO2 emissions


B. I = PAT (Ehrlich and Holdren)• I = Environmental Impact of nation• P = Population• A = Affluence (reflects consumption)• T = Technology (reflected in pollution)

• Ex – Changes in CFC emissions related to technology, not population

• Developments in technology historically not directed toward environmental preservation

I. I.Population Dynamics - History A. A.Thomas Malthus (1766-1834) English parson Became concerned...

Documents

Transcript of I. I.Population Dynamics - History A. A.Thomas Malthus (1766-1834) English parson Became concerned...