BIOS 5445: Human Ecology - Western Michigan University

BIOS 5445: Human Ecology Dr. S. Malcolm Lecture 5: Slide - 1

•  Lecture 5. The Human Population:

–  Lecture summary: •  Early warnings. •  Population growth. •  Age structure. •  Mortality & survivorship. •  Demographic transition. •  Carrying capacity & food.

BIOS 5445: Human Ecology Dr. Stephen Malcolm, Department of Biological Sciences

Tertullian of Carthage (André Thevet 1584, Special Collections Library, University of Michigan)


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.”


3. Population growth curve:

•  Sigmoidal growth curve: –  If population growth of

organisms is common-ly sigmoidal, does this describe human population growth?

–  Are human populations regulated?

•  By famine, disease, pestilence, warfare, infanticide, contraception, celibacy?


4. Global population growth:

•  Appears to be a J-shaped curve (exponential) (Fig. 5-1):


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 1800 >100,000 years –  1-2 billion 1930 130 years –  2-3 billion 1960 30 years –  3-4 billion 1975 15 years –  4-5 billion 1987 12 years –  5-6 billion 1999 12 years (stable rate?)


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.


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.


8. Regional population growth:

•  United Nations predict 8.16 billion people by 2025 mostly in developing regions.


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.


10. Regional age structure in 1990 (UN medium projection from estimated 1988 population):

Developed (high median age)

Undeveloped (low median age)

Pre- reproductive

Reproductive

Post- reproductive


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.


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.


13. Mortality in the USA (Fig. 5-6):

Flu pandemic

Baby boom


14. Global mortality - declines in infant mortality (no. deaths <1y/1,000):

<

27 15


15. Natality in the USA - shifts in births (Fig. 5-7):


16. Global natality:

Steady decrease with time: Family planning & reduced need for large families


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.


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.


19. The demographic transition:

births

deaths

Fig 13.5 from Bush, M.B. 1997. Ecology of a Changing Planet. Prentice Hall.


20. Implications of population growth:

•  Age-structure shift to more older people: –  China:

•  4.9% elderly (over 65) in 1982 = 50 million •  5.9% in 1990 = 66 million •  7.0% in 2000 •  13.0% in 2025

•  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.


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.


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.

BIOS 5445: Human Ecology - Western Michigan University

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