1. Demographic inertia
The importance of age structure in determining population growth rate: all individuals are not the same

2. Demographic inertia
The importance of age structure in determining population growth rate: all individuals are not the same
Any individual can be placed into an age class, defined by (for example):
her age
her reproductive potential

3. An example of a “life table”

4. What does a life table tell you?
How long you’ll live (on average)

5. What does a life table tell you?
How long you’ll live (on average)
When reproduction occurs (on average)

6. What does a life table tell you?
How long you’ll live (on average)
When reproduction occurs (on average)
Age structure of the population

7. Why should you care? The “schedule” of births and deaths determines:
the population growth rate, r
the age structure
the “inertia” of population growth

8. Demographic inertia Briefly:
An oft-stated goal of individuals who would like to stabilize the rate of population growth is the achievement of Zero Population Growth (ZPG).

9. Demographic inertia Briefly:
An oft-stated goal of individuals who would like to stabilize the rate of population growth is the achievement of Zero Population Growth (ZPG).
ZPG is usually defined as “net replacement rate”, or 2 children per couple.

10. Demographic inertia Briefly:
An oft-stated goal of individuals who would like to stabilize the rate of population growth is the achievement of Zero Population Growth (ZPG).
ZPG is usually defined as “net replacement rate”, or 2 children per couple.
If ZPG happened tomorrow, how big would the world’s population be when it stopped growing?

11. Demographic inertia If ZPG happened tomorrow…
the world’s population would stop growing when it reached 9.7 billion people (or, 2.8 billion people from now).
WHY?

12. Demographic inertia The key is the population age structure
Click here if you want the gory mathemagical details!

13. The take-home message You Decide
If you want to slow the rate of population growth:
Decrease the birth rate
have fewer children
have them later
Increase the death rate
War
Famine
Pestilence
Disease
You Decide

14. A brief assignment
Since it’s unlikely that the Earth’s population will stabilize below billion (based on current U.N. projections), consider the effect of this doubling of population size on the environmental issue that you’re studying for your semester project.
Be prepared to discuss this effect in class on Thursday.
You should be sure to incorporate these effects into your project web page.