1. Human Population How many people can the Earth sustain?
How big will the world population get? 7

2. Population Dynamics Dynamics of Population Growth
Factors that Increase or Decrease Populations
Factors that Regulate Population Growth

3. Population Dynamics Simple relationship:
The number of individuals in a population changes with time based on the balance between the number of births and numbers of deaths in the population
DN/Dt = birthrate – death rate = rN or
dN/dt = birthrate – death rate = rN
r = growth rate, when r>0, birthrate>death rate
when r<0, birthrate<death rate

4. Exponential growth: Nt = N0ert, where r=growth rate
Only possible under ideal conditions!

5. 5 5

6. J
CS Fig. 6.5
Rapid Growth
Lag 6 6

7. J
CS Fig. 7.3
As observed in movie in lab! 7

8. S
Examples:
Mice, Bacteria in
Petri dish 8

9. CS Fig. 6.6 9

10. Examples of
environmental
factors in an
aquatic environ-
ment that deter-
mine the carrying
capacity 10

11. Many Environmental Factors are related to the
Population density
3: Environmental conditions/ resources deteriorate/ decline
4: Population and population density decrease
1: Population grows when density is low
2: Population density increases

12. Logistic growth
dN/dt =
rN(1-N/K)
where K is the
carrying capacity

13. Finite
amount of
food
available! 13

14. Defining Carrying Capacity
The Carrying Capacity is the“Maximum number of individuals of a population that can be maintained indefinitely by the environmental goods and services that are generated by a given area of the environment”

15. Maximum Number of Individuals
“The Maximum Number of Individuals is determined by the balance between the amount of environmental goods and services that are required by each individual and the quantity of these goods and services that are supplied by the environment.”

16. Given Area
“A given area of the environment is critical to the notion of carrying capacity because the availability of environmental goods and services varies with the type of environment.”

17. Maintained Indefinitely
“Maintained indefinitely refers to the ability of an ecosystem to provide the same quantity and quality of environmental goods and services over time.”

18. Frog requirements
Pond characteristics

19. Limiting factor
For frog population

20. Which pond will
be able to better
recycle the frog’s
waste?

23. Are Humans Different than Bacteria, Moose, and Frogs?
To answer question, need to look at human demography
Are the only two things you can count on Death and Taxes?
No. People will get married, they will have babies.
Demography is the study of statistical data on births, deaths, geographical distributions of populations, growth rates and age structures of populations, etc.

24. CS Fig. 7.6 24

25. 25

26. Low
Birth and
Death rates
High
Birth and
Death rates
Pop
more
evenly
distri-
buted
Most of pop
childbearing
age or
younger
Baby
boomers 26

27. US Population Changes

28. Growing, Stable, and Shrinking Populations
Similar to CS Fig. 7.13
Growing, Stable, and Shrinking Populations

29. Analysis of Population Trends
Which countries’ populations are growing the fastest?
Which are stable or shrinking?
Were the countries with stable or shrinking populations always that way?
No! Clear trend in population growth rates with level of economic development
Trend called the Demographic Transition

30. Similar to CS Fig. 7.17 Low High 30 Phase I Phase II Phase III
Phase IV
High
Similar to
CS Fig. 7.17
Low 30

31. Note
units
for
birth
rates

32. Undeveloped – no transition
Developing – have begun
transition
Developed – completed transition
Births
Per woman 32

34. Similar to
CS Fig. 7.9

35. CS Fig. 7.16
Developed
Developing 35

36. 36

37. CS Fig. 7.14
Projected as more
of world becomes
developed 37

38. Fig. 7.12

39. Life and Death
With increasing health care available to world population, life expectancies will increase
But what controls birthrates?
WOMEN!

40. Total Fertility declines as women’s education increases
CS Fig. 7.19

41. UN population prediction
Based on lowered fertility rates (nearing 3 per woman) they revised their estimates downward
Still high!
3 is still more than 2.1
Declining mortality rates
Population momentum (from young population structure)

42. Fig. 7.20
Long-term UN population projections

43. United Nations
CS p. 139, 9th Ed.

44. Can the Earth sustain 10 to 15 Billion people
Can the Earth sustain 10 to 15 Billion people? OR Can we sustain the Earth with 10 to 15 billion humans on it? OR Can we sustain Earth with 6 billion living an American lifestyle?
Keep this question in mind as we discuss land use, energy use, global warming, pollution, etc.

45. Human Carrying Capacity
“The Maximum Number of Individuals is determined by the balance between the amount of environmental goods and services that are required by each individual and the quantity of these goods and services that are supplied by the environment.”
This balance has changed throughout human history!
Human beginnings (~1-2 million years ago) until ~10,000 years ago, humans like other animals on planet: hunting and gathering
Population less than millions, not billions
~10,000 years ago, humans different from other animals on planet: development of agriculture – manipulation of environment
Population into the many millions
~300 years ago: expanded agriculture and industrialization
Population into the hundreds of millions
~50 years ago: green revolution!
Population into the many billions

46. Human Carrying Capacity
“A given area of the environment is critical to the notion of carrying capacity because the availability of environmental goods and services varies with the type of environment.”
Humans unique from other animals in that they “live” in many environments through trade
Trade has expanded and become more efficient throughout human history

47. Human Carrying Capacity
“Maintained indefinitely refers to the ability of an ecosystem to provide the same quantity and quality of environmental goods and services over time.”
Humans rely on environment not only for subsistence (like frogs), but for goods that give us quality of life
Many resources are being used faster than they are replenished by nature
Humans have found ways to prop up some of these resources, like fisheries and soil fertility, but how indefinite (sustainable) are these methods?

49. The End.
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