Env Lec 6

• Malthusian Theory


  The theory that the human population problem is caused by rapid population growth outpacing the growth of food production
• Thomas Malthus eloquently stated the human population problem almost 200 years ago
• Malthus foresaw that the pressure of rapid human population growth will lead to problems
• Malthus's theory


  Based on population dynamics and its relationship with the availability of resources
• Malthus proposed the principle that human populations grow exponentially while food production grows at an arithmetic rate
• Malthus urged controls on population growth to avoid a catastrophe where humans would have no resources to survive on
• Malthus said the development of mankind was severely limited by the pressure that population growth exerted on the availability of food
• From the perspective of modern science, Malthus's statements simply point out that in a finite world nothing can grow or expand forever, not even the population of the smartest species ever to live on Earth
• Critics of Malthus


  Point out that his predictions have yet to come true, and that technology has provided a way out allowing us to live at greater densities
• Supporters of Malthus


  Remind critics of the limits of a finite world, and that Malthus must be correct about the final outcome of unchecked growth, even if he was wrong about the timing
• Some people believe Earth can support many more people than it does now, but in the long run there must be an upper limit
• The basic issue is how to achieve a constant world population, or at least halt the increase in population, in a way most beneficial to most people
• Population


  A group of individuals of the same species living in the same area or interbreeding and sharing genetic information
• Population dynamics


  The study of population changes over time and factors which affect the changes
• Demography


  The statistical study of human populations
• Five key properties of any population

  • Abundance (size of a population)
  • Birth rate
  • Death rate
  • Growth rate (difference between birth and death rates)
  • Age structure
• Changes in abundance depend on growth rate
• Growth rate = difference between birth rate and death rate
• Rates are expressed as number per 1,000, not percentage
• Crude birth rate


  Number of births per 1,000 individuals per year, called "crude" because population age structure is not taken into account
• Crude death rate


  Number of deaths per 1,000 individuals per year
• Crude growth rate


  Net number added per 1,000 individuals per year, also equal to the crude birth rate minus crude death rate
• Population is not distributed uniformly around the world, with some areas supporting large populations and others being very sparsely populated
• Population patterns and rates of growth change over time, with tremendous disparities around the world between a relatively small, old, and wealthy population with high consumption rates per capita, and a very large, young, and poor population with relatively low consumption rates per capita
• Population density

  Measurement of the number of people in an area, calculated by dividing the number of people by area and usually shown as the number of people per square kilometer
• Factors of high population density


  • Low and flat large land area
  • Access to water
  • Resources
  • Temperate climate- suitable to grow crops
  • Political stability
  • Good economic condition
  • Good facilities- hospitals, schools etc.
• Factors of low population density

  • High mountainous land, island etc
  • Dry, desert and arid climate
  • Few resources
  • Lack of political and social stability
  • Limited economic opportunities
  • Lack of services
• One or a few factors don't determine density, a complex combination of many factors influence density significantly
• The world's population grew from 1 billion in 1804 to 6 billion in 1999, with the time between each billion increasing from 123 years to just 12 years
• Three Revolutions that led to historical population growth

  • Agricultural Revolution (8000 BC): Domestication of Plants and Animals
  • Industrial Revolution (1750 AD): Agricultural mechanization, transport, sanitation, health
  • Medical Revolution (1900 AD): Elimination of many historical causes of death
• Hunter and Gatherer Societies (before 9000 BC)


  • Population between 250,000 to 2 million
  • Population density: 1 person/ 130-260 Km2
  • Rate of growth: 0.00011% per year
• Early, Pre-industrial, Agricultural Societies (9000 BC - 1600 AD)


  • Population grew from about 100 million in 1 AD to 500 million in 1600 AD
  • Population density: 1-2 person/ Km2
  • Rate of growth: 0.03% per year
• The Machine Age (Industrial Societies) (1600 AD - 1960 AD)


  • Population grew from 500 million in 1600 AD to 3 billion in 1960 AD
  • Population growth rate was 0.1% per year
• The Modern Era (1960 AD - present)


  • Population grew from 3 billion in 1960 AD to 6.7 billion in 2007 AD
  • Population growth rate reached 2% in the mid-20th century and has declined slightly to 1.4%
  • Use of technology has altered nature and caused significant environmental damage
• Calculating Change in Population

  1. P2 = P1 + (B - D) + (I - E)

  2. Where P1 = number of individuals at time 1, P2 = number at time 2, B = births, D = deaths, I = immigrants, E = emigrants

  3. Growth rate g = (B - D)/N or g = G/N
• Exponential growth


  Population growth at a rate proportional to the size of the population
• Exponential growth leads to a doubling time, where the population doubles in a fixed period
• Use of technology has altered much of the nature in a number of ways and caused significant damage to the environment: increased air pollution, water pollution, waste production, soil depletion and degradation, groundwater depletion, habitat destruction and degradation, biodiversity depletion
• Calculating Change in Population

  1. P2 = P1 + (B - D) + (I - E)

  2. where P1 = number of individuals in a population at time 1, P2 = number of individuals in that population at some later time 2, B = number of births in the period from time 1 to time 2, D = number of deaths from time 1 to time 2, I = number entering as immigrants, E = number leaving as emigrants

  3. The growth rate of a population is then g = (B - D)/N or g = G/N
• Exponential Growth


  • Population that grows at a rate proportional to the size of the population
  • Growth that increases at a consistent rate
  • Annual growth rate is a constant percentage of the population
  • A constant rate of growth applied to a continuously growing base over a period of time