BIOS 5445: Human Ecology
Dr. Stephen Malcolm, Department of Biological Sciences
•  Lecture 5. The Human
Population:
–  Lecture summary:
•
•
•
•
•
•
Early warnings.
Population growth.
Age structure.
Mortality & survivorship.
Demographic transition.
Carrying capacity & food.
Tertullian of Carthage (André Thevet 1584,
Special Collections Library, University of Michigan)
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 1
2. Early warnings:
•  Tertullian of Carthage (c160-225), Christian
writer in North Africa:
–  c200: We are burdensome to the world, the
resources are scarcely adequate to us; and our
needs straighten us and complaints are everywhere
while already nature does not sustain us.
•  Thomas Robert Malthus (1766-1834),
English economist:
–  1798: An Essay on the Principle of
Population as It Affects the Future
Improvement of Society.
•  I said that population, when unchecked,
increased in a geometrical ratio, and
subsistence for man in an arithmetical ratio.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 2
3. Population growth curve:
•  Sigmoidal growth
curve:
–  If population growth of
organisms is commonly sigmoidal, does this
describe human
population growth?
–  Are human
populations regulated?
•  By famine, disease,
pestilence, warfare,
infanticide,
contraception,
celibacy?
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 3
4. Global population growth:
•  Appears to be a J-shaped curve (exponential) (Fig. 5-1):
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 4
5. Global population growth:
•  When will population growth slow to births =
deaths at a carrying capacity ?
–  2110 at 1990 rate to give 10.5 billion
–  2040 if natality decreased to give 8 billion
–  2130 at higher growth rate to give 14 billion.
•  Changes in increase rates:
–  0-1 billion
–  1-2 billion
–  2-3 billion
–  3-4 billion
–  4-5 billion
–  5-6 billion
Dr. S. Malcolm
1800
1930
1960
1975
1987
1999
>100,000 years
130 years
30 years
15 years
12 years
12 years (stable rate?)
BIOS 5445: Human Ecology
Lecture 5: Slide - 5
6. Change in annual rates of growth:
•  Doubling time:
–  = 69.3/% growth rate (roughly 70/% increase).
–  e.g. for 2% growth doubling time = 69.3/2 = 34.7 y
•  Nt = NoRt or 2No = NoRt or ln2 (0.693) = Rt
•  Doubling t = ln2/R
–  Global growth rate peaked in 1965 at almost 2%
(Table 5-1) with a doubling time of 35 years.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 6
7. Regional population growth:
•  Projected growth much higher in developing
regions (Fig. 5-2) than developed:
–  Developing - Africa, South Asia, Latin America.
–  Developed - Europe, North America, former USSR.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 7
8. Regional population growth:
•  United Nations predict 8.16 billion people by
2025 mostly in developing regions.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 8
9. Regional demography (Table 5-3):
•  Density and growth rate appear to be inversely
related.
•  Growth rate and per capita GNP may be
positively correlated.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 9
10. Regional age structure in 1990 (UN medium
projection from estimated 1988 population):
Developed
(high median age)
Postreproductive
Reproductive
Prereproductive
Undeveloped
(low median age)
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 10
11. Natality & Mortality:
•  Numbers/1000/y
•  Decrease in mortality
rates most significant
- especially in
developing countries
(Fig. 5-4).
•  Widening gap
generates the faster
population increase
in developing
countries of Fig. 5-2.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 11
12. Changes in life expectancy:
•  Estimated life span at
birth:
–  1980 = 61y (72dev, 57u).
–  1990 = 64y (74dev, 61u).
–  1995 = 76y (US):
•
•
•
•
33 in 1620 (pilgrims).
47 in 1900.
60 in 1930.
71 in 1971.
•  Life expectancy varies
by gender & ethnicity.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 12
13. Mortality in the USA (Fig. 5-6):
Baby
boom
Flu
pandemic
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 13
14. Global mortality - declines in infant
mortality (no. deaths <1y/1,000):
<
27
Dr. S. Malcolm
15
BIOS 5445: Human Ecology
Lecture 5: Slide - 14
15. Natality in the USA - shifts in births (Fig. 5-7):
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 15
16. Global
natality:
Steady decrease
with time:
Family planning
& reduced need
for large families
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 16
17. Factors that
affect natality:
•  Biological factors:
–  Nutrition & health
–  Length of reproductive
period
–  Length of lactation.
•  Cultural factors:
–  E.g. Samoans (Fig. 5-8).
–  Abortion, infanticide,
promiscuity, marriage,
divorce, taboos,
morality, religion, birth
control, migration etc.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 17
18. Lack clutch size - how many children?
•  (a) prediction based on offspring fitness trade-off.
•  (b) inclusion of cost of reproduction and maximum net benefit.
–  as cost of reproduction increases, so clutch size decreases.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 18
19. The demographic transition:
births
deaths
Fig 13.5 from Bush, M.B. 1997. Ecology of a Changing Planet. Prentice Hall.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 19
20. Implications of population growth:
•  Age-structure shift to more older people:
–  China:
•
•
•
•
4.9% elderly (over 65) in 1982
5.9% in 1990
7.0% in 2000
13.0% in 2025
= 50 million
= 66 million
•  Feeding people:
–  Starvation and malnutrition:
•  World Bank estimated >700 million people in 1986 or 13% of
the world lacked enough food for an active healthy life.
•  In 1990s 950 million people were chronically malnourished.
–  Food production.
•  Agricultural output increases at about 2% per year - not
enough to feed everyone.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 20
21. Earth s carrying capacity:
•  Maximum number of people the Earth can support:
–  United nations Food and Agriculture Organization projections.
–  Capacity of the land:
•  Arable & grazing land equals about half the total land surface (Table 5-6).
•  179% increase in croplands from 1950 to 1990 (1.5 x 109 ha).
•  1 ha land supports 3 people = 4.5 bilion, but about half arable is in use.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 5: Slide - 21
22. References:
•  Begon, M., J.L. Harper & C.R. Townsend. 1996. Ecology. 3rd edition.
Blackwell Science, Oxford, 1068 pp.
•  Bush, M.B. 1997. Ecology of a Changing Planet. Prentice Hall.
•  Kormondy, E.J., & D.E. Brown. 1998. Fundamentals of human
ecology. Prentice Hall. 503 pp.
•  Malthus, T. 1798. An essay on the principle of population. London.
•  Stiling, P. 2002. Ecology. Theories and applications. 4th edition.
Prentice Hall, Upper Saddle River, NJ, 403 pp.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 6: Slide - 22