Chapter 4: The Human Population and the Environment

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Chapter 4 The Human Population and the
Environment
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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.
• A species is all individuals that are capable of
  interbreeding.
• A species is made up of populations.

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Basic Concepts of Population Dynamics

• Five key properties of any population
• Abundance
• Birth rates
• Death rates
• Growth rates
• Age structure

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Basic Concepts of Population Dynamics

• Demography is the statistical study of human
  populations.
• The general study of population changes is called
  population dynamics.
• How rapidly a pop changes depends on GR
• Growth rate birth rate death rate

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Age Structure

• The proportion of the population at each age.
• Implication for current and future social and
  economic conditions
• Impact on the environment

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Age Structure

• Four general types
• Pyramid- population w/ many young and high death
  rate (short average lifetime)
• Inverted pyramid- top heavy
• Column- birth rate and death rate are low and a
  high of pop is elderly
• Column w/ a bulge- event in the past caused a
  high birth or death rate for some age group

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Age Structure
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Kinds of Population Growth

• Exponential Growth
• A pop increasing by a constant percentage per
  unit time.
• Human pop growth peaked at 2.1
• 1965-1970
• Now at 1.2

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History of Human Population Growth

• 1. Early period of hunter and gathers- total pop
  lt a few million
• 2. Rise of agriculture- allowed for increase in
  pop density and inc in human pop
• 3. Industrial revolution- improvements in health
  and food supply led to rapid inc in pop
• 4. Today- rate of growth slow in industrialized
  nations but high in less developed nations

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Human Population Growth
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Human Population Growth
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Present Human Population Rates of Growth

• Current world population gt6.6 billion
• With annual growth rate of 1.2
• At this rate 84 million people added to Earth in
  1 year
• Correlation between poverty and population growth
• Positive feedback

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Present Human Population Rates of Growth
Current US growth rate 0.6
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Projecting Future Population Growth

• Doubling time (time required for a pop to double
  in size) is very sensitive to growth rate
• It changes quickly as g.r. changes
• US w/ a g.r. of 0.6 has a doubling time of 117
  yrs
• Nicaragua w/ a g.r. of 2.7, d.t. 26 yrs
• Northern Europe w/ a g.r. of 0.2, d.t. 350 yrs

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Logistic Growth Curve

• S shaped curve
• Increase exponentially only temporarily
• Then growth rate would decline
• Reach an upper pop limit _at_ logistic carrying
  capacity (g.r. 0)

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Logistic Growth Curve

• Little evidence that animal populations actually
  follow this growth curve
• Involves assumptions
• Constant environment
• Constant carrying capacity
• Homogeneous population
• Unlikely if death rate continue to decrease

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Demographic Transition

• Three stage pattern of change in birth rates and
  death rates
• Occurred during the process of industrial and
  economic development of Western nations
• Leads to decline in pop growth rate

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Demographic Transition

• Stage 1
• Nonindustrial country
• Birth rate and death rate high, growth rate low
• Stage 2
• Period of high growth rate
• W/ industrialization death rate declines but
  birth rate stays high

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Demographic Transition

• Stage 3
• Birth rate drops toward death rate
• Growth rate decreases
• Will take place if parents come to believe that
  having a small family is to their benefit.

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Population and Technology

• Impact that all humans pose on the environment is
  a result of two factors
• Number of people
• Impact of each person on the environment
• Total impact of the human pop on enviro average
  impact of an ind x total of ind
• T P x I

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Population and Technology

• Modern technology increases the use of resources
  and enables us to effect the enviro in new ways.
• E.g. CFCs, automobiles
• Population x technology reveals irony (TP x I)
• Improving standard of living increases P
• Countering the benefits of declining I

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Human Carrying Capacity

• How many people can live on Earth at the same
  time?
• Answer depends on the quality of life people
  desire and are willing to accept.
• Estimates vary based on assumptions made.
• packing-problem
• Deep ecology

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Quality of life

• If people of the world were to live at the same
  level as those in US
• High resource use
• Carrying capacity would be low
• If people of the world were to live at the same
  level as those in Bangladesh
• Poverty and heavy drain on biodiversity
• Carrying capacity would be much higher

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Potential Effects of Medical Advances on
Demographic Transition

• Second decline in death rate
• Leads to Stage IV
• A second stable state would arise if birth rate
  then falls
• Stage V
• Decision needs to be made
• Stop research on diseases of old age
• Reduce birth rate
• Or do neither and wait for Malthus projections

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Human Death Rates

• Acute or epidemic disease- appears rapidly in
  pop, affects a large and then declines.
• Chronic disease- always present in a pop,
  typically occurring in small
• Emerging diseases could effect both industrial
  and less developed nations
• SARS
• West Nile Virus
• Epidemic flu

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Longevity and Its Effect on Population Growtrh

• Maximum lifetime- maximum possible age to which
  an ind of a species can live.
• Life expectancy- the average of years an ind
  can expect to live.
• Higher in developed nation
• Japan highest, 82 years
• Botswana, Lesotho and Swaziland lowest, 35 years

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Each age class within a population has its own
life expectancy.
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Limiting Factors

• Human populations will eventually be limited by
  some factor or combo of factors
• Short-term - affect pop during the year in which
  they become limiting
• Intermediate-term - effects are apparent after 1
  yr but before 10yrs.
• Long-term effects are not apparent for 10yrs

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How Can We Achieve Zero Population Growth?

• Simplest and one of the most effective is to
  delay the age of 1st childbearing by women.

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How Can We Achieve Zero Population Growth?

• Birth Control
• Breast-feeding can delay resumption of ovulation
• Family planning methods from abstinence to
  induction of sterility w/ natural agents

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National Programs to Reduce Birth Rates

• The choice of population control methods is an
  issue that involves social, moral and religious
  beliefs
• Vary from country to country
• Wide range of approaches
• Information
• Accesses to birth control
• Rewards and penalties