I. Population Dynamics - History

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

• Per-capita growth rate (r)• r = b - d (per-capita birth rate - death rate)• r > 0 population growing• r < 0 population shrinking• r = 0 ZPG

II. Population Dynamics - Theory

A. Background• Instantaneous growth rate of a population may

be represented by dN/dt = rN• dN/dt - Change in population size over time• r - Per-capita growth rate• N - Population size

• Two basic growth models• Density-independent growth• Density-dependent growth

II. Population Dynamics - Theory

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

a species (rmax)• rmax inversely related to generation time

• Ex - Higher for mouse than human• Population growth rate described by

• dN/dt = rmaxN• Exponential growth

II. Population Dynamics - Theory

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

II. Population Dynamics - Theory

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

can support a limited number of individuals• Carrying capacity (K)

• Population growth described by logistic growth model

• dN/dt = rmaxN (1-N/K)• Environmental resistance (N/K) increases as N

increases

III. Population Dynamics - Trends

A. Demographics• Global population reached 6 billion in Oct 1999

and 7 billion in Oct 2011• 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%

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UN Population Division

III. Population Dynamics - Trends

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

• 1950 – 5.0• 2010 – 2.45 (51% decrease)

• Africa – 4.37 (Niger – 7.19, Somalia – 6.40)• Asia – 2.18 (India – 2.73, China – 1.64)• N America – 2.04 (Canada – 1.65, Mexico – 2.41,

USA – 2.07)• Europe – 1.59 (Bosnia – 1.18, Germany – 1.36)• PRB Map

Source: UN Population Division

UN Population DivisionRoberts 2011

III. Population Dynamics - Trends

C. Infant Mortality Rate (IMR)• Global IMR

• 1950 – 156 deaths per 1000 births (15.6%)• 2010 – 43 deaths per 1000 births (4.30%)

• 72.4% decrease• Europe – 0.7%• Africa – 7.50%

Source: UN Population Division

III. Population Dynamics - Trends

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%• 2010

• Birth rate – 19.4 per 1000 people per year• Death rate – 8.3 per 1000 people per year

• Growth = 11.1 per 1000 people per year = 1.11%• Developed nations – 0.23% (0.07 B-D + 0.16 I)• Developing nations – 1.28% (1.33 B-D – 0.05 E)

Source: UN Population Division

III. Population Dynamics - Trends

E. Age and Life Expectancy• Median Age

• World – 29.4 years (2011)• Developed nations – 39.7 years

• Europe – 40.2 years• N. America – 36.9 years

• Developing nations – 26.8 years• Africa – 19.7 years

• Life Expectancy• 1950 – 46 years• 2010 – 68.9 years

• Africa – 56.0 years (Swaziland – 48.7 years)• Europe – 76.1 years (Andorra – 83.5 years)Source: UN Population Division

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III. Population Dynamics - Trends

F. Population Projections - UN1. Low Variant (TFR: 2.45 1.55 by 2100)

• 2050 – 8.1 billion, 2100 – 6.2 billion

2. Medium Variant (TFR: 2.45 2.03)• 2050 – 9.3 billion, 2100 – 10.1 billion

3. High Variant (TFR: 2.45 2.51)• 2050 – 10.6 billion, 2100 – 15.8 billion

4. Constant Variant (TFR = 2.45 4.44)• 2050 – 10.9 billion, 2100 – 26.8 billion

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