Lesson 2: Human Population Growth
Big Question
Why Is Human Population Growth the Underlying Environmental Problem?
The Prophecy of Malthus
“the power of population growth” is “greater than the power of Earth to produce subsistence.”
Lesson 2 / ESRM100 / University of Washington
Basic Concepts of Population Dynamics
• A population is a group of individuals of the same species
living in the same area or interbreeding.
• A species is all individuals that are capable of
interbreeding and is made up of populations.
• Abundance is the size of a population.
• The birth rate is the number of individuals born during a
specified time interval.
• The death rate is the number of individuals who die during
that same time interval.
• The growth rate is the difference between birth rate and
death rate; the net change in the size of the population.
Lesson 2 / ESRM100 / University of Washington
Exponential Growth
• Growth is exponential when it occurs at a constant rate per time period
• Produces a J-shaped growth curve
• The human population has mostly grown exponentially
Lesson 2 / ESRM100 / University of Washington
Major Periods of Human History
• The early period of hunters and gatherers - less than a few million people
• The rise of agriculture - first major increase in the human population
• The Industrial Revolution - improvements in the food supply and health care
led to a rapid population growth
• Today -growth has slowed in industrialized nations but is increasing rapidly in
many less developed nations
Lesson 2 / ESRM100 / University of Washington
The Logistic Growth Curve
• Exponential population growth cannot go on forever;
people would eventually run out of food and space.
• The birth rate should decline and the death rate should
rise, so that the growth rate slows to zero.
• The population should follow a smooth S-shaped curve.
• The population increases exponentially when small, so the
curve rises steeply.
• Then the rate of growth gradually declines, until it reaches
an upper population limit - the logistic carrying capacity.
Lesson 2 / ESRM100 / University of Washington
Is the Logistic Growth Curve Realistic?
• Requires accurate knowledge of the inflection point where growth rate declines.
• Unrealistic assumptions for human populations.
• Death rates do not increase if there are ongoing improvements in health care
and food supplies.
• See the estimated US population at Population Clocks:
http://www.census.gov/main/www/popclock.html
Lesson 2 / ESRM100 / University of Washington
Other Clues to Population Change
Age structure - the proportion of the population in each age group.
Four general types:
• Pyramid
• Column
• Inverted pyramid
• Column with bulge
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Population Change, cont.
• Kenya has pyramid shape with many young people – rapid growth
• United States has column shape – slow growth
• Italy is slightly top-heavy – slow/negative growth
Lesson 2 / ESRM100 / University of Washington
The Demographic Transition
• Stage I - birth and death rates are high until industrialization reduces death
rates
• Stage II - gap between birth and death rates results in high population growth
• Stage III - birth rate drops toward death rate and population growth declines
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The Demographic Transition, cont.
• Some nations are slow to move from stage II to stage III
• Medical advances can affect the demographic transition by decreasing death
rates
Lesson 2 / ESRM100 / University of Washington
Longevity and Its Effect on Population Growth
• The maximum lifetime (longevity) is the
genetically determined maximum possible
age to which an individual can live.
• Life expectancy is the average number of
years an individual can expect to actually
live.
• The human population has grown despite
little or no change in longevity.
Lesson 2 / ESRM100 / University of Washington
Limiting Factors to Population Growth
• Short-term factors: drought, disruption to energy supply, disease
• Intermediate-term factors: desertification, pollutants, disruption to supply of
non-renewable resources
• Long-term factors: Soil erosion, groundwater, climate change
Lesson 2 / ESRM100 / University of Washington
Quality of Life and the Human Carrying
Capacity of the Earth
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•
•
•
What is the human carrying capacity of Earth?
Logistic curve predictions
Packing space
Deep Ecology – moral imperative to preserve the biosphere by limiting human
population
• The higher the quality of life, the lower the Earth’s carrying capacity
Lesson 2 / ESRM100 / University of Washington
How Can We Achieve Zero Population Growth?
• Raise the age of first childbearing
• Social pressures to delay marriage
• Birth control
• Breast feeding
• Family planning
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National Programs to Reduce Birth Rates
• The first country to adopt an official population policy was
India in 1952.
• Many countries now have a family-planning program.
• China has one of the oldest and most effective familyplanning programs:
• encourages couples to have only one child.
• relies on education, family planning control, and a
system of rewards and penalties.
• Should governments force people to limit family size?
Lesson 2 / ESRM100 / University of Washington
How Many People Can Earth Support?
Estimates range from 2.5 billion to 40 billion.
Critical factors are
• Food supply
• Land and soil resources
• Water resources
• Population density
• Technology
Lesson 2 / ESRM100 / University of Washington
Chapter 2: Human Population Growth
Questions? E-mail your TA. [email protected]