unit 4, part 2: the human population and the environment
TRANSCRIPT
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Unit 4, Part 2: 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
• Demographics 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 - What if no one is having babies? What if 70% of the population is under age 30? (true in several countries)
– Impact on the environment - do older people have as large an impact as young people?
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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 (Japan?)– 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
• Human pop growth is now appr. 1.2%
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History of Human Population Growth
• 1. Early period of hunter and gathers - the total population was < a few million (>10,000 yrs ago)
• 2. Rise of agriculture- allowed for increase in population density and increased human population
• 3. Industrial revolution - improvements in health and food supply led to rapid inc in population
• 4. Today - the rate of growth is 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 >6.6 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 @ 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 (Ti) of the human population on environment = average individual impact x total # of individuals or …
• Ti = P x I
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Population and Technology
• Modern technology increases the use of resources and enables us to effect the environment in new ways.– E.g. CFCs, automobiles
– Therefore we see that although technology lowers birth rates and decreases death rates, it increases the the average environmental impact per person
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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.
– “distribution-problem” - largely it’s a matter of where people are and how many there are in that area
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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….. Leading to – Stage V
• Decision that might need to be made– Stop research on diseases of old age?– Reduce birth rate?– Wait for Malthus’ projections to come true?– Disallow “certain” people from having babies?
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Human Death Rates
• Acute or epidemic diseases - appear rapidly and affect a large numbers before declining.
• Chronic disease- always present in a pop, typically occurring in small as result of long environmental exposure. (Smoking: lung cancer)
• Emerging diseases could effect both industrial and less developed nations because of long range rapid transportation– SARS– West Nile Virus– Epidemic flu (or Pandemic - H1N1 - Swine flu)
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Longevity and Its Effect on Population Growth
• Maximum lifetime- maximum possible age to which an individual of a species can live.
• Life expectancy- the average # of years an individual can expect to live.– Higher in developed nation - due to availability of
sanitation and technology
– Japan highest, 82 years
– Developing nations - Botswana, Lesotho and Swaziland lowest, 35 years; notice the dramatic differential!
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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– ONLY Zero population growth will allow for a
“sustainable” future.
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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– Wide range of approaches
• Information• Accesses to birth control• Rewards and penalties - Canadian system example
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What will our future look like?
New York City Billings, Montana