1. The human population and the environment Chapter 4
AP Environmental
The human population and the environment
Chapter 4

2. Population Dynamics Population: Species: Population dynamics
A group of individuals of the same species living in the same area of interbreeding and sharing genetic information.
Species:
All individuals that are capable of interbreeding.
Made up of populations
Population dynamics
The general study of population changes.

3. Population Dynamics Formula to represent population change:
Human population is usually presented as a crude rate which is a given number per 1000.
Example: If the crude death rate is 9 then that represents 9 out of every 1000 people died in that given time frame. Expressed as a percentage this would equal 0.9%.
Crude growth = crude birth rate – crude death rate ( g = b-d) and represents a net change in the population
P1 = number of individuals at a given time
P2 = number of individuals at a later time
P2 = P1 + (B – D) + (I – E)

4. Population Dynamics
Growth rates can be determined using a series of equations that factor in the number of births or deaths in a population with a known population size (N).
birth rate (b)= B/N
death rate (d) = D/N
Growth rate (g) = (B-D)/N

5. Age Structure Population age structure:
The proportion of the population in each age class
Affects current and future birth rates, death rates and growth rates
Has an impact on the environment
Has complications for current and future social and economic status.

6. Age Structure

7. History of Human Population
Hunters and gatherers
The world’s population was probably less than a few million
Early, pre-industrial agriculture
Allowed a much greater density of people
The first major increase in human population
Machine age
Industrial revolution led to rapid increase in human population
The Modern era
Rate of population has slowed in wealthy nations but continues to increase rapidly in poorer, less developed nations.

8. Population Changes
Exponential growth represents a constant net rate of increase.
The rate of net increase for the human population in the graph has exceeded the exponential rate
Factors like a decline in death rate have caused the growth in the net rate of increase

9. Where do you see population trends increasing? Why?
Population Changes
Where do you see population trends increasing? Why?

10. Population Changes

11. Exponential growth and doubling time
The current growth rate for the human population falls between 1-2% so doubling time is expected to be between years.
*Remember: doubling time = 70/R
No population can sustain exponential growth rate indefinitely because of resource constraints within the environment

12. Logistic Growth The logistic growth curve Logistic carrying capacity
“S” shaped curve that is generated by the logistic growth equation.
A small population grows rapidly
But the growth rate slows down
The population eventually reaches a constant size.
Logistic carrying capacity
The population size at which births equal deaths and there is no net change in population
*There is very little evidence that animal populations actually follow true logistic growth patterns

13. Logistic Growth

14. Growth Factors
Total Fertility Rate (TFR) is a major factor in the growth or maintenance of a population over time.
Total fertility refers to the average number of children that could be born to a woman if she follows the normal rates of fertility and survives from birth through her reproductive years.
In populations an important figure in fertility is called Replacement Level Fertility.
Replacement level fertility means that a woman produces enough children to maintain the current population levels

15. Growth Factors
Fertility rates are generally higher in developing countries because of a need for labor and caregivers within the household, a lack of education in birth control, and cultural beliefs
Worldwide fertility rates are dropping due to higher levels of urbanization, especially in developing countries
If fertility rates were to drop below replacement levels then the population could stabilize

16. 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 a decline in population growth.
Stage I: Decline in death rate
Stage II: High growth rate
Stage III: Birth rate drops toward the death rate, leading to low or zero growth rate

18. Demographic Transition

19. Demographic Transition

20. Effects of the Human Population
The total impact of the human population on the environment is:
the average impact of an individual multiplied by the total number of individuals
For individuals, the impact is determined by the amount of the environment that is considered necessary to support a particular lifestyle. This is also called an ecological footprint.
T = P x I

21. Effects of the Human Population
Human carrying capacity
The number of people that can live on Earth at the same time?
To determine:
Extrapolate from past growth
The “Packing Problem” approach
Considers how many people might be packed onto Earth, not taking into sufficient account the need for lands and oceans to provide food, water, energy, construction materials, and scenic beauty and the need to maintain biological diversity

22. Nature’s effect on Humans
Acute or epidemic disease
Appears rapidly in the population,
Affects a comparatively large percentage of it,
Declines then almost disappears, only to reappear later
Chronic disease
Is always present in a population
Typically occurs in a relatively small but relatively constant presentation of the population
Examples include heart disease, cancer, and stroke

24. Nature’s effect on Humans
Maximum lifetime:
The genetically determined maximum possible age to which an individual of a species can live
Life expectancy:
The average number of years an individual can expect to live given the individual’s present age

25. Nature’s effect on Humans
Short-term factors
Those that affect a population during the year in which they become limiting
Intermediate-term factors
Those whose effects are apparent after one year but before ten years
Long-term factors
Those whose effects are not apparent for ten years
Some factors fit into more than one category

26. Population Solutions: Zero Population Growth
Delay the age of first childbearing by women
Birth control
Biological and Social
Breast-feeding, which can delay resumption of ovulation
Abstinence
Induction of sterility with natural agents
Contraceptive devices
National Programs to Reduce Birth Rates
Formal family planning programs to
explain the problems arising from rapid population growth
Describe the benefits to individuals of reduced population growth.