1. Chapter 7
The Human Population

2. Background Info Earth is ~4.6 billion years old
Modern humans have been on Earth ~200,000 yrs
For most of human history, limiting factors kept population levels low (scarce food, disease, etc)
High human birth and death rates
If we reduce the amount of time life has existed on Earth to one year, from Jan to June all that has existed is bacteria. Animals with heads appeared in Oct and humans appeared on Dec 31st at midnight

3. History of Human Population Growth:
Early period of hunter/gatherers
Total population < a few million
Rise of agriculture
Allowed for increase in population density and increase in human population
Industrial revolution
Improvements in medicine, sanitation and agriculture led to rapid increase in population
Today
Rate of growth slow in industrialized nations but high in less developed nations
Earth’s population has doubled several times since 1600
Industrial
Revolution
begins
Agriculture
begins
Bubonic
plague
Plowing
and
irrigation

4. Factors That Influence Human Population Growth
Demography = study of human populations and their trends
Changes in Population Size
View population as system with inputs and outputs
If inputs > outputs = growth rate is positive
If inputs < outputs = growth rate is negative

5. Global population growth rate = (CBR - CDR) / 10
Crude birth rate (CBR)= the number of births per 1,000 individuals per year
Crude death rate (CDR)= the number of deaths per 1,000 individuals per year
Global population growth rate = (CBR - CDR) / 10
In 2009 there were 20 births per 8 deaths = %?
National population growth rate = (CBR + immigration) - (CDR + emigration) / 10
Doubling time is # of years it takes for population to double = 70 / growth rate (if growth rate remains constant)
“Rule of 70”
Math Behind the Rule of 70
The use of natural logs arises from integrating the basic differential equation for exponential growth: dN/dt = rN, over the period from t=0 to t = the time period in question, where N is the quantity growing and r is the growth rate.

6. Examples of Doubling Time
Nicaragua w/ a growth rate of 2.7%, doubling time = 26 yrs
US w/ a growth rate of 0.6%, doubling time = 117 yrs
Northern Europe w/ a growth rate of 0.2%, doubling time = 350 yrs
“Rule of 70”

7. Fertility
Total fertility rate (TFR) = estimate of the average number of children that each woman in a population will bear
Current TFR for women in US is 2.06
To gauge changes in population size, look at replacement level fertility (RLF) = TFR required to offset the average number of deaths in a population and for the current population size to remain stable
In developed countries RLF is typically 2.1 (one child to replace each parent)
In developing countries RLF is above 2.1
Low levels of industrialization
Income of <$3/day
High mortality among young (TFR needs to be higher than 2.1 to achieve RLF)
Uneducated (especially women)
When TFR = RLF and immigration = emigration, a country’s population is stable (zero population growth)
2 babies per couple (one t replace each person)

8. Projected World Population Growth

9. The 12 Most Populous Countries in the World

10. Life Expectancy
Average number of years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate of that country
Generally higher in countries with better health care
Good predictor of high resource consumption rates and environmental impacts
Often reported in three ways: overall, males, females: In US, ALE is men 75, 78 women

11. Infant and Child Mortality Rates
Determined by access to health care, good nutrition and potable water, and exposure to environmental pollutants
Infant mortality rate = # of deaths under age 1 per 1,000 live births
Child mortality rate = # of deaths under age 5 per 1,000 live births
In 2009, global infant mortality rate 46; Europe was ; U.S. 6.6; Bolivia 50, Liberia 99

12. Aging and Disease
Dependent upon standard of living
Disease is important regulator of human populations
According to World Health Organization (WHO), infectious diseases are the 2nd biggest killer worldwide after heart disease
e.g. HIV, AIDS, malaria and tuberculosis

13. Age Structure
Population growth depends upon number of people of different ages
Age-structure diagram (population pyramids) = displays a population by ages, used to predict future growth

14. Migration
Country with low CBR, but high immigration rate may still experience population growth
U.S. is estimated to grow 44% by 2050
Net migration rate = difference between immigration and emigration per year/per 1,000 people
U.S. gains about 1 million people per year with current population of 300 million = 3.3 per 1,000
Canada = 7 per 1,000 people
Movement of people around the world affects ecological footprint, and humanitarian and health issues (if displaced)
Despite Canada’s 1.6 TFR and US 2.06 TFR, both populations will grow due to immigration

15. Demographic Transition
As a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.

16. Stages of Demographic Transition
Phase 1: Slow population growth because there are high birth rates and high death rates which offset each other.
Phase 2: Rapid population growth because birth rates remain high but death rates decline due to better sanitation, clean drinking water, increased access to food and goods, and access to health care.
Phase 3: Stable population growth as the economy and educational system improves and people have fewer children.
Phase 4: Declining population growth because the relatively high level of affluence and economic develop encourage women to delay having children.

17. Affluence and Fertility

18. Zero Population Growth – can it be achieved?
Possible approaches
Delay age of first child bearing – simplest and most effective
Higher 1st reproduction age = fewer children
In South Asia and Sub-Saharan Africa, 50% of women marry between 15-19; Bangladesh average age is 16; Sri Lanka average age is 25
World Bank estimates that if Sri Lanka model were used, families would average 2.2 fewer children

19. Family Planning
Regulating the number and spacing of offspring through the use of birth control
Increase education of women = increase women’s incomes = decreased birth rates
National programs to reduce birth rates
Information (education)
Increase access to birth control

20. Population Size and Consumption, Impact the Enviroment
Human impact on the environment is a result of several factors:
Number of people
Amount of resources each person uses
Each person has an impact on the environment by eating, drinking, producing waste, consuming products, etc. = “Ecological footprint”

21. Affluence
More affluence = more environmental impact
Gross domestic product (GDP) = the value of all products and services produced in a year in that country.
Made up of consumer spending, investments, government spending, and exports minus imports.
A countries GDP often correlates with its pollution levels.

22. Impact = Population x Affluence x Technology
IPAT Equation
To estimate the impact of human lifestyles on Earth we can use the IPAT equation:
Impact = Population x Affluence x Technology
Modern technology increases the use of resources and enables us to affect the environment in new ways (CFC’s, cars, etc)
(T = P x I) equation reveals irony: Improving standard of living increases P, countering the benefits of declining I
Thai family vs Japanese family

23. Human Carrying Capacity
Background Info
Every 5 days, the global population increases by about 1 million people
In 1798, Thomas Malthus proposed:
Human population grows exponentially, while food supply grows linearly
Humans will eventually exceed food supply
Consequences will be famine, disease, massive human die-off
Malthus –English professor and clergyman

24. How many people can the Earth support?
Limiting Factors
Short Term - affect population immediately (food shortages)
Intermediate Term - affect population for 1-10 years (e.g. desertification, dispersal of pollutants, etc.)
Long Term - effects not apparent until after 10 years (e.g. soil erosion, decline in groundwater supply, climate change)
Earth’s long term carrying capacity
Wood production peaked in 1967
Fish production peaked in 1970
Beef and cereal crop production peaked in 1977

25. Estimation methods
Extrapolation from past growth (assuming populations follow S- curve)
Packing problem approach – how many people can be packed onto the Earth? (50 billion!)
Deep Ecology – sustaining the biosphere (few million people)
Depends on the quality of life people desire and are willing to accept