SCI 112: Introduction to Environmental Science
LECTURE NOTES - POPULATION GROWTH

Cunningham & Cunningham (2011) - chapters 3 & 4

updated January 2013

 

THEORETICAL METHODS TO MEASURE POPULATIONS

a) Population Growth (p. 63-64, fig 3.18)
    * measure population at various times to count
       a) determine area or location of study (ideal to have a lab)
       b) determine initial population size
       c) count all individuals at set times
       d) analyze with graph to observe changes in population size
    * good if can do under controlled conditions
        - get ideal growth
        - can then compare to real world
    * problems if:
        - hard to count numbers
       - slow population growth

b) Survivorship (p. 65-66 + fig 3.21)
    * follow individuals through life and determine age at death
        a) determine age span of species
        b) count all born in a short period of time
        c) follow through life till last dies, record age when each dies
        d) graph data to see shape of graph
    * typical to have 4 types
        (a) few deaths at young age, many live to old age (ex. humans)
        (b) equal chance of death at any age (ex. birds)
        (c) some deaths at young age, many live to old age (ex rabbits)
        (d) most die at young age, the few that survive live long time (ex. oak trees, insects)
    * good for study of populations which you can follow deaths
    * problem if long life span

c) Age Structure distribution (p. 87 + fig 4.9)
    * age all individuals at a set time
       a) define your area
       b) categorize the species into about 10 age groups
       c) count all individuals by age
       d) graph by age group and compare to other groups
    * great if only a short period of time
    * problem if hard to age individuals
    * three types seen for human populations (as categorized by country)
         rapid growth (triangular) – youngest age groups most common
         slow growth (rectangular) – relatively even numbers, young to middle age
         no growth/decline (diamond) – middle most common, young of small numbers

 


HUMAN POPULATION GROWTH HISTORY (pp. 78-79 + fig 4.3)

Beginnings of documented human population growth about 8,000 years ago|
Three areas where cities developed first
       Middle East (Mesopotamia)
       Mexico and central America
       southern China
All these areas developed as a result of domestication of animals and agriculture

From 500 BC to 1600 world population growth very little if any
Growth due to:
       expansion to new areas
       development of agricultural systems
Decreases due to:
       disease & plague (black death - bubonic plague)
       wars
       starvation (including those due to natural disasters)

Major change in humans starting about 1700: Industrial Revolution
       Development of a mechanized method to produce products
       The result was more production for less work
The process greatly affected human population growth
       reduced death rate, then later birth rates
       process appears to be by country

 f7-03_human_population_

 

DEMOGRAPHY (pp. 81-89)
    = statistical study of a population and its influence on social and environmental conditions
    Why study? – to make social, political and resources decisions

Human population in 2010 estimated at 7 billion!
two countries now (as of 2009) have over 1 billion persons (table 4.2, p. 81)
      China - 1.34 billion
      India - 1.17 billion
     USA - 308 million

To study growth rate, one needs information on (pp. 84-85):
1) Births - Number of births (fertility)
       Birth Rate = number per 1000 individuals
2) Deaths - Number of deaths (mortality)
       Death Rate = number per 1000 individuals
Use this to calculate the Overall Growth Rate:
       birth rate – death rate

Natural populations at optimum will have exponential growth
For humans is expressed as either:
        1) a proportion: 15 per 1,000
        2) a percentage: 1.5%
Human average for planet = 1.2%
        data is commonly collected by country:
                     USA: 0.6%        China: 1.6%      India: 1.9%       Iraq: 2.8%
        Africa with highest percentages (2-3+ %)
        South America & Asia with 1-2%
        North America Australia & Europe up to 1%

Another method of study is life expectancy
    average estimated life span at time of birth
    historically humans lived to about 35
    in last 100 years the life expectancy has more than doubled in some countries

 

DEMOGRAPHIC TRANSITION (pp. 89-91)
= process of population change with a transition from an agricultural to industrialized  way of life

* Several stages to the process:
1) Preindustrial (= pre-modern)
       much work is done by hand, low productivity
       poor health care, medical, and sanitary situations
       high birth rate, high death rate
       population numbers remain relatively constant
       Ex: Amerindians of South America
2) Industrializing (= Urbanizing)
       new machinery introduced, increased productivity
       health care, medical, and sanitation improves
       death rate decreases, birth rate remains high
       population numbers jump upward
       Ex.: India, China
3) Industrial (= mature)
       society values shift to monetary, not human resources
       health care, medical, and sanitation good
       death rate low, birth rate decreases
       population numbers stabilize
       Ex.: USA
4) Postindustrial (= developed)
       most of society relates to money, not human resources
       health care, medical, and sanitation good
       birth rate continues to decrease
       population numbers decline
       Ex.: Sweden & some other European countries

Graphical representation of changes (fig 4.13, p. 90)

 

f7-14_theoretical_birth

With the transition, population numbers increase!
    how much of the world has gone through the transition?
    how much population growth will there be in the near future?

USA & Europe went thru demographic transition by 1930
    Much of remainder of world in process now
    big problem due to a large % of world population
    several countries trying to limit natural process

Mechanisms to stop population growth with demographic transition:
    1) go through process quickly
    2) develop and advertise family planning programs
        common in India & China
        birth control
    3) create tax incentives and laws to limit family size
        increased taxes for more than 2 children
        get women into work force

 

UNIQUE HUMAN FEATURES RELATED TO POPULATION GROWTH

1) Population density NOT related to density of resources
    densely populated countries have a smaller resource base
    we have developed cities (urbanization)
        in 1970 37% of humans lived in a city (10,000 +); 2005 about 50%

2) Life expectancy has changed significantly
    among highest of world in USA - 77 years (male = 76, female =81)
    very low in Burundi – 40 years (fig 4.8)
    highly tied to a country’s GNP (economic well being)

3) Immigration makes the story more complex
    immigration usually occurs into more-developed regions (such as the USA)
    the migration changes the demographics of each country

4) Fertility rates vary greatly between countries for social reasons (pp. 88-89)
    undeveloped countries still have a high social value on children
    developed countries place more value on money

5) The role of women in society varies greatly (p. 91)
    complain in USA of < 50% of work force being female;
       some countries with essential no women in control
   educational levels different
    Why should we care?
        fertility rate tied to women
       educated women with lower fertility
       lower fertility means slowed population growth

 


WHAT CAN YOU DO TO HELP LIMIT POPULATION GROWTH?

1) have fewer children and support those who think the same
    if you wish to have children around - why not adopt?
    if your wish them to be genetically yours - how about 1, or at most 2?’

2) advocate family planning
    use contraceptives and advertise their use
    this helps prevent unwanted pregnancies & reduces abortions

3) buy locally grown produce, or grow your own -
    many foreign countries are killing themselves by exporting
    also use less energy to transport food

4) support and mandate equal opportunities for women
    women in work force are less likely to have children
    educated women are less likely to have children

5) advocate positive thinking and respect for all life
    help support a life of dignity for all

6) help foster children in developing countries
    food, sanitary water, and an EDUCATION
    want the communities to become self-sufficient