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Chapter 4.2

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Transcript

  • 1. Human Population Chapter 4.2
  • 2. World Population
    • Census is taken every 10 years
    • Demography = the study of human population size, density and distribution, movement and its birth and death rates
  • 3. Human population growth
    • Human population growth is different from bacteria population growth in that we can consciously change our environment
      • ex: we eradicated smallpox
      • ex: developed methods for producing more food
      • ex: infant mortality rate has decreased
      • ex: technological developments improved water quality
    • Result = live longer and produce more offspring that live long enough to produce more offspring
  • 4. Calculating growth rate
    • Determined by many factors: births, deaths, immigration, emigration
      • Birthrate : number of live births per 1000 population in a given year
      • Death rate : number of deaths per 1000 population in a give year
      • Immigration: movement of individuals into a population
      • Emigration: movement out of a populations
  • 5. Calculating growth rate cont.
    • Formula: (version 1)
    • (Birth rate + Immigration rate) – (Death rate + Emigration rate) = Population Growth Rate
    • Formula: (version 2… used often because immigration and emigration rates are not accurate)
    • Birth rate – Death rate = Population Growth Rate (PGR)
  • 6. Calculating growth rate cont.
    • If birthrate of a population = death rate of a population  then PGR = 0
      • Population is changing, but it is stable
    • If PGR > 0, more individuals are entering the population than leaving
      • Population is growing
    • If PGR < 0, more individuals are leaving than entering
      • Populations might start decreasing
  • 7. The effect of a positive growth rate
    • If PGR = 1.7% in 1995 and then PGR = 1.3% in 2001
      • The world is populating, but just at a slower rate
    • Unless GROWTH RATE BECOMES NEGATIVE, the population continues to grow (just not rapidly)
  • 8. Doubling time
    • Doubling time : the time needed to double in size
    • It depends on current population and growth rate
      • slow or negative growth rate  it will take a long time
      • often called a “developed country”
    • If there is a rapid doubling time  often referred to as a “developing country”
    • Formula:
    • Doubling time (in years) = 70 / annual percent growth rate
  • 9. Age structure
    • The proportion of the population that are in different age levels
    • Age structure graph tells you
      • how many males and females there are in a population
      • how many people there are at each age level
    • Rapidly growing countries have a wide base because a large percentage of the population is made up of children and teenagers
    • A stable population has a fairly equal percentage of people in each age category
  • 10. Ecology and growth
    • Needs differ throughout the world
    • Some = concerned w/ basic needs. Others = concerned about maintaining healthy conditions
    • Resources that humans depend on daily
      • uncontaminated drinking water (and for agriculture)
      • adequate sewage facilities
      • ability to provide food
  • 11. Ecology and growth cont.
    • Resources needed for life (struggling to survive)
      • food
      • water
      • (both can become scarce)
    • Other problems = where to properly dispose of waste
    • These conditions can lead to stress on current resources and contribute to spread of disease

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