Lesson 2: Human Population Growth

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Lesson 2 Human Population Growth

• Big Question
• Why Is Human Population Growth the Underlying
  Environmental Problem?

2
The Prophecy of Malthus

• the power of population growth is greater than
  the power of Earth to produce subsistence.

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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.

4
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

5
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

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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.

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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.ht
  ml

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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

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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

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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.

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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

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Quality of Life and the Human Carrying Capacity
of the Earth

• 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
  Earths carrying capacity

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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
  family-planning 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?

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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

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Chapter 2 Human Population Growth

• Questions? E-mail your TA. eschelp_at_u.washington.ed
  u