1. Chapter 4: The Human Population and the Environment

2. Basic Concepts of Population Dynamics
A population is a group of individuals of the same species living in the same area.
A species is all individuals that are capable of interbreeding.
A species is made up of populations.

3. Basic Concepts of Population Dynamics
Five key properties of any population
Abundance
Birth rates
Death rates
Growth rates
Age structure

4. Basic Concepts of Population Dynamics
Demography is the statistical study of human populations.
The general study of population changes is called population dynamics.
How rapidly a pop changes depends on GR
Growth rate = birth rate – death rate

5. Age Structure The proportion of the population at each age.
Implication for current and future social and economic conditions
Impact on the environment

6. Age Structure Four general types
Pyramid- population w/ many young and high death rate (short average lifetime)
Inverted pyramid- top heavy
Column- birth rate and death rate are low and a high % of pop is elderly
Column w/ a bulge- event in the past caused a high birth or death rate for some age group

7. Age Structure

8. Kinds of Population Growth
Exponential Growth
A pop increasing by a constant percentage per unit time.
Human pop growth peaked at 2.1%
Now at 1.2%

9. History of Human Population Growth
1. Early period of hunter and gathers- total pop < a few million
2. Rise of agriculture- allowed for increase in pop density and inc in human pop
3. Industrial revolution- improvements in health and food supply led to rapid inc in pop
4. Today- rate of growth slow in industrialized nations but high in less developed nations

10. Human Population Growth

12. Human Population Growth

13. Present Human Population Rates of Growth
Current world population >6.6 billion
With annual growth rate of 1.2%
At this rate 84 million people added to Earth in 1 year
Correlation between poverty and population growth
Positive feedback

14. Present Human Population Rates of Growth
Current US growth rate 0.6%

15. Projecting Future Population Growth
Doubling time (time required for a pop to double in size) is very sensitive to growth rate
It changes quickly as g.r. changes
US w/ a g.r. of 0.6% has a doubling time of 117 yrs
Nicaragua w/ a g.r. of 2.7%, d.t. = 26 yrs
Northern Europe w/ a g.r. of 0.2%, d.t. = 350 yrs

17. Logistic Growth Curve S shaped curve
Increase exponentially only temporarily
Then growth rate would decline
Reach an upper pop logistic carrying capacity (g.r. = 0)

19. Logistic Growth Curve
Little evidence that animal populations actually follow this growth curve
Involves assumptions
Constant environment
Constant carrying capacity
Homogeneous population
Unlikely if death rate continue to decrease

20. Demographic Transition
Three stage pattern of change in birth rates and death rates
Occurred during the process of industrial and economic development of Western nations
Leads to decline in pop growth rate

21. Demographic Transition
Stage 1
Nonindustrial country
Birth rate and death rate high, growth rate low
Stage 2
Period of high growth rate
W/ industrialization death rate declines but birth rate stays high

22. Demographic Transition
Stage 3
Birth rate drops toward death rate
Growth rate decreases
Will take place if parents come to believe that having a small family is to their benefit.

26. Population and Technology
Impact that all humans pose on the environment is a result of two factors
Number of people
Impact of each person on the environment
Total impact of the human pop on enviro = average impact of an ind x total # of ind
T = P x I

27. Population and Technology
Modern technology increases the use of resources and enables us to effect the enviro in new ways.
E.g. CFCs, automobiles
Population x technology reveals irony (T=P x I)
Improving standard of living increases P
Countering the benefits of declining I

28. Human Carrying Capacity
How many people can live on Earth at the same time?
Answer depends on the quality of life people desire and are willing to accept.
Estimates vary based on assumptions made.
“packing-problem”
Deep ecology

29. Quality of life
If people of the world were to live at the same level as those in US
High resource use
Carrying capacity would be low
If people of the world were to live at the same level as those in Bangladesh
Poverty and heavy drain on biodiversity
Carrying capacity would be much higher

30. Potential Effects of Medical Advances on Demographic Transition
Second decline in death rate
Leads to Stage IV
A second stable state would arise if birth rate then falls
Stage V
Decision needs to be made
Stop research on diseases of old age
Reduce birth rate
Or do neither and wait for Malthus’ projections

32. Human Death Rates
Acute or epidemic disease- appears rapidly in pop, affects a large % and then declines.
Chronic disease- always present in a pop, typically occurring in small %
Emerging diseases could effect both industrial and less developed nations
SARS
West Nile Virus
Epidemic flu

34. Longevity and Its Effect on Population Growtrh
Maximum lifetime- maximum possible age to which an ind of a species can live.
Life expectancy- the average # of years an ind can expect to live.
Higher in developed nation
Japan highest, 82 years
Botswana, Lesotho and Swaziland lowest, 35 years

35. Each age class within a population has its own life expectancy.

36. Limiting Factors
Human populations will eventually be limited by some factor or combo of factors
Short-term - affect pop during the year in which they become limiting
Intermediate-term - effects are apparent after 1 yr but before 10yrs.
Long-term – effects are not apparent for 10yrs

37. How Can We Achieve Zero Population Growth?
Simplest and one of the most effective is to delay the age of 1st childbearing by women.

38. How Can We Achieve Zero Population Growth?
Birth Control
Breast-feeding can delay resumption of ovulation
Family planning methods from abstinence to induction of sterility w/ natural agents

39. National Programs to Reduce Birth Rates
The choice of population control methods is an issue that involves social, moral and religious beliefs
Vary from country to country
Wide range of approaches
Information
Accesses to birth control
Rewards and penalties