Ecology Notes

Population Dynamics [Notes]


In 1990, the population of the world had reached 5.3 billion people. In 1998 this population was now 6.06 billion. In 2003, it was 6.3 billion and as of 6/23/04 it was 6.44 billion. This population was unequally divided between the 33 more developed countries (MDC'S), also known as developed and the 150 less developed countries (LDC's), also known as developing countries.
Population growth for the planet is related to only two factors:
Population increase (or decrease) equals net birth rate minus net death rate.
In 1990, the birth rate for the world was 27 live births/1000 persons. The death rate was 9 deaths/1000. This represents a growth rate of 1.8% (27-9)/10 = 18/10 = 1.8. Comparable 1996 rates are a little better with a growth rate of 1.55%. In 2003 the growth rate was 1.26%.
This represents an increase:
1981 1985 1991 19942003
per day 205,000 221,000 260,000 245,500216,000
per week 1,400,000 1,550,000 1,800,000 1,723,0001,512,000
per year 72,800,000 80,600,000 93,600,000 89,596,00078,624,000

Until very recently, population increase has been more the result of a DECREASE IN DEATH RATE than in changes in other factors. Prior to 1940, the birth rate only slightly exceeded the the death rate. Major changes came about with three events:
introduction of
introduction of Streptomycin
and development of DDT


  • I. Births minus Deaths (Factors Affecting Birth Rates)
  • 1. TOTAL FERTILITY RATE (TFR) - An estimate of the average number of children women have during their reproductive years (15-44 in U.S.; 12-49 in LDC's); computed as live births /1000 for women in this age bracket
    2003 average TFR worldwide 2.8
    average TFR (LCD's) 3.1
    average TFR (MDC's) 1.5
  • 2. Average levels of education and affluence (especially female members)
  • 3. Importance of children as part of family labor force.
  • Certain societal signals or attitudes are often at work:
    Stop at Two - ZPG - result 2.1 average
    A boy for you and a girl for me - U.S. ideal - result 3.0
    An heir and a spare - survival in LDC - result 3-5 average
  • 4. Urbanization
  • 5. High cost of raising an educating children - average middle class cost of raising child to age 17 in U.S.- $240,000
  • 6. Educational and employment opportunities for women
  • 7. Infant mortality rates (see also #3)
  • 8. Average marriage age - older brides tend to have fewer children
  • 9. Availability of private and public pension systems
  • 10. Availability of reliable methods of birth control and easy access to information
  • 11. Religious beliefs, traditions, and cultural norms that influence the number of children couples want to have

  • II. Births minus Deaths (Factors Affecting Death rates)
  • 1. Nutrition related to increased food production and food distribution
  • 2. Availability of improved sanitation and water supplies leading to improved personal hygiene and
    leading to a reduced incidence and spread of infectious disease organisms
  • 3. Improvements in medical and public health technology, including antibiotics, immunization, and

  • III. Migration - affects population size for country or region
    (births + immigration) - (deaths + emigration) = population change rate

    1. Doubling Time - only a small percentage change in population growth rate will cause the base number of people to double more rapidly; computed as 70/annual growth rate percentage; current growth rate is 1.26%; this means it will take 55.56 years to double the population if conditions do not change (70/1.26)
    2. Age Structure Diagram or Age Distribution - number or percentage of women of childbearing age and especially the number in the prime reproductive years of 20-29; the shape of the age structure diagram is a key as to whether the population might expand, decline or stay the same.
    METHODS FOR CONTROLLING HUMAN POPULATION GROWTH "The overriding problem in our day is learning to set limits." Garrett Hardin
    Controlling birth rates is the key to controlling the size and growth rate of the human population.
    Demographic Transition - a change in perception as to how many is enough (societal and cultural pressures); Economic development through industrialization will eventually lead to both falling birth rates and falling death rates thus slowing a country's population growth; this transition goes through several stages of development
    Voluntary approaches to limiting the spacing and numbers of children desired; information and contraceptives available to aid this approach; to accept family planning usually requires: an assured food supply together with basic health services; literacy; employment; increase women's rights Family Planning and Birth Control are related but not synonymous
    Examples of Efforts at Human Population Control
    China and India - two approaches - two different results ---------------------------------------------------------------
    Justification of Control and Implication of Lack of Control

    State of the Environment is a function of:
    number of people x rate of resource utilization (consumption) x level of technological sophistication (with associated environmental impact such as energy utilization