BIOS 5445: Human Ecology
Dr. Stephen Malcolm, Department of Biological Sciences
•  Lecture 4. Population
ecology:
–  Lecture summary:
•  Population growth:
–  Growth curves.
–  Rates of increase.
•  Mortality & survivorship.
•  Age structure.
•  Population regulation:
–  Abiotic factors.
–  Biotic factors.
Custer s Last Stand (1943) by Thomas Hart Benton,
The Albrecht-Kemper Museum of Art
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 1
2. Population growth:
•  Biotic potential:
–  Species characteristic.
–  Capacity to reproduce at a given rate:
•  Balance between birth rate (natality) & death rate (mortality).
•  Environmental resistance:
–  Collective abiotic and biotic forces that reduce biotic
potential.
–  Variation results in population change.
•  Terms introduced by Royal Chapman (1928).
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 2
3. Population growth - growth curves:
•  Sigmoidal growth
curve:
–  S-shaped (Fig. 4-1)
of yeast cells in
culture:
•  Pearl (1928).
–  Generated by
changes in growth
rate:
•  Fig. 4-2.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 3
4. Population growth - growth curves:
•  Carrying capacity:
–  Asymptote of the sigmoidal growth curve.
–  Births = deaths.
–  Maximum that the environment can support.
–  Can be increased or decreased:
•  For yeast if toxic wastes are removed the
population grows larger.
•  If wastes accumulate population shrinks.
•  Temperature, nutrients, space will all affect the
carrying capacity.
•  Dynamic equilibrium.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 4
5. Population growth - growth curves:
•  J-shaped curve - periods of rapid, exponential growth:
–  Fig. 4-3 thrips on roses in Australia (Davidson & Andrewartha, 1948).
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 5
6. Population growth - growth curves:
•  Rates of increase:
–  Intrinsic rate of natural increase (r):
•  Measured under optimal conditions.
•  Represents the reproductive potential
•  Inverse relationship between r and generation
time, body size and environmental benignness.
•  Stable population r = 0.
–  Net reproductive rate (R):
•  Number of female offspring that replace each
female of the previous generation.
•  Stable population R = 1.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 6
7. Mortality and survivorship - survivorship
curves:
•  E.S. Deevey Jr.
(1947).
•  Pearl (1928):
–  3 types of
survivorship
curve (Fig. 4-4).
•  Type 1 - late
loss (humans).
•  Type 2 constant loss.
•  Type 3 - early
loss.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 7
8. Mortality and survivorship - survivorship
variation:
•  Changes in life expectancy at birth in the
United States:
Date
White males
White
females
1850
38.3
40.5
n/a
n/a
1900
48.3
51.1
32.5
35.0
1950
66.3
72.0
58.9
62.7
1990
72.7
79.4
67.0
75.2
Dr. S. Malcolm
Nonwhite
males
Nonwhite
females
BIOS 5445: Human Ecology
Lecture 4: Slide - 8
9. Age structure:
•  3 major age groups (Bodenheimer, 1958):
–  Prereproductive, Reproductive, Postreproductive
•  Influence 3 types of populations:
–  (a) Expanding, (b) Stable, (c) Diminishing.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 9
10. Population regulation - abiotic factors:
•  Nutrients:
–  Sodium in soil can limit populations of meadow
voles through adrenocortical responses to crowding
(stress hormones).
•  Physical factors/weather:
–  Sunlight, temperature, moisture.
–  Drought/flooding - direct and indirect impacts.
–  Storms, hurricanes, tornadoes, blizzards etc.
•  Food:
–  Amount and availability - famine cycles.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 10
11. Population regulation - biotic factors:
•  Horizontal processes within trophic
levels:
–  Competition.
–  Mutualism.
•  Vertical processes between trophic
levels:
–  Herbivory.
–  Parasitism (micro- & macro-parasites).
–  Predation.
–  Mutualism.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 11
12. Predation:
•  Cycle dynamics of
Paramecium (prey),
and Didinium
(predator) in
homogenous
environments without
reintroductions (a)
and with
reintroductions (b) of
prey and predator.
–  Gause (1934).
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 12
13. Interspecific competition:
•  Competition for
limited
resources
leads to:
–  Competitive
exclusion:
•  Fig. 4-7.
–  Coexistence
through
character
displacement:
•  Niche
differentiation.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 13
14. Intraspecific competition and densitydependent self-regulation:
•  Malthus (1798) and Nicholson (1957)
argued that human and animal
populations are regulated by densitydependent factors that either increase
mortality or decrease natality as
density increases (Fig. 4-8).
•  Others argue that density-independent,
abiotic interactions and interspecific
processes are more important in
population regulation.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 14
Figure 4-2. Growth rate and growth
curve of yeast cells.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 15
Figure 4-8. Growth curve of the blowfly showing regular
fluctuations caused by self-adjustment (Nicholson, 1955).
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 4: Slide - 16
17. References:
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Begon, M., J.L. Harper & C.R. Townsend. 1996. Ecology. 3rd edition. Blackwell Science, Oxford,
1068 pp.
Bodenheimer, F.S. 1958. Animal ecology today. Monographiae Biologicae 6, 276 pp.
Chapman, R.N. 1928. The quantitative analysis of environmental factors. Ecology 9(2): 111-122.
Davidson, J., and H.G. Andrewartha. 1948. Annual trends in a natural population of Thrips
imaginis (Thysanoptera). Journal of Animal Ecology 17(2): 193-199.
Davidson, J., and H.G. Andrewartha. 1948. The influence of rainfall, evaporation and
atmospheric temperature on fluctuations in the size of a natural population of Thrips
imaginis (Thysanoptera). Journal of Animal Ecology 17(2): 200-222.
Deevey,Jr. E.S. 1947. Life tables for natural populations of animals. The Quarterly Review of
Biology 22(4): 283-314.
Gause, G.F. 1934. Experimental analysis of Vito Volterra’s mathematical theory of the struggle
for existence. Science 79(2036): 16-17.
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.
Nicholson, A.J. 1957. The self-adjustment of populations to change. Cold Spring Harb. Symp.
Quant. Biol. 22: 153-173.
Pearl, R. 1928. The rate of living. Being an account of some experimental studies on the biology
of life duration. University of London Press, London.
Dr. S. Malcolm
BIOS 5445: Human Ecology
Lecture 6: Slide - 17