dr. stephen malcolm, department of biological...

BIOS 5445: Human Ecology Dr. S. Malcolm Week 13: Slide - 1

•  Week 13. Intraspecific competition & conflict:

–  Lecture summary: •  Distribution & abundance. •  Nicholson vs Andrewartha &

Birch. •  Scramble & contest competition. •  Density-dependence &

resources. •  Human populations & stress. •  Correlations: resources & war.

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

Louis XIV (1643-1715) - France produced 9% more cereals per capita in 1700 than in 1789


2. Explaining distribution and abundance - contrasting views:

•  (1) A.J. Nicholson (1954): – Australian. – Density-dependent, biotic interactions

most influence population size. •  (2) H.G. Andrewartha and L.C. Birch (1954):

– Also Australians. – Density-dependent processes:

• Have minor or secondary importance. • Play no part in determining abundance.


3. Andrewartha & Birch:

•  Numbers of animals limited by: –  (1) Shortage of resources. –  (2) Unavailability of these resources in

comparison to dispersal abilities. –  (3) shortage of time when r is positive:

•  Fluctuations caused by weather, predators etc.

•  So they rejected divisions of: – Density-dependent vs density-independent. – Biotic vs physical factors.


4. Nicholson:

•  “Governing reaction induced by density change holds populations in a state of balance in their environments”,

•  “...the mechanism of density governance is almost always intraspecific competition, either amongst animals for a critically important requisite, or amongst natural enemies for which the animals concerned are requisites” – Nicholson (1954).


5. Nicholson - abiotic vs biotic factors:

•  Although he recognized that density-independent factors like rainfall could influence the level at which density-dependent

biotic interactions “governed”, he considered that density-dependent processes play a key role in regulating populations.

•  Based on lab experiments with blowflies (Begon et al., 1996)


6. Two kinds of intraspecific competition after Nicholson:

•  (1) scramble (exploitation): –  interact indirectly via direct resource use:

•  e.g. flies on a cow pat, or plants competing for light, or resource depletion zones.

•  (2) contest (interference): –  interact directly via indirect resource use:

•  e.g. territoriality, or fighting for females, or use of allelochemicals and space as a resource.

•  Figs. 6.1 & 6.2 show both kinds and negative effects of competition in single species populations.


7. Density dependence:

•  Competition increases with density (Fig. 6.14). •  Density dependence can vary with increasing

density (Fig. 6.3): –  density independence –  undercompensating density dependence:

•  Births > deaths. –  exactly compensating density dependence:

•  Births = deaths. –  overcompensating density dependence.

•  Births < deaths.


8. k-values and density dependent mortality:

•  Use of k-values of mortality due to competition can define competition according to the slope b of the relationship of k-values plotted against the logarithm of initial density (before the effects of competition) as in Fig 2.3 (Hassell, 1976): –  b = 0: density independence –  b < 1: undercompensating density dependence –  b = 1: exact density dependent compensation

(contest competition) –  b > 1: overcompensating density dependence –  b = ∞: overcompensating density dependence

(scramble competition) •  k = log density before competition - log density after

competition.


9. Human populations and resources:

•  Correlations between demographic growth and political crisis: –  Goldstone (1991)


10. Political demography of early modern England (Goldstone, 1991, Fig. 3):


11. Political Stress Indicator “psi” (Goldstone, 1991)

•  ψ = fiscal distress x mobility/competition x mass mobilization potential (MMP).

•  Measures for England 1500-1750 (Fig. 4).

•  Mounting crisis and revolution in early seventeenth century


12: Population stress

•  Stress (ψ ) in England, France & Germany 1820-1847: –  Goldstone (1991) –  Figs 12 & 13 –  Quote from Fischer

(1996), pages 179-181


13. Correlation between resource cost and conflict (Fischer, 1996, Fig. 3.01):


14. Correlation between resources, theft and conflict in England 1740-1802 (Fischer, 1996, Fig. 3.14):


15. Twentieth century resource cost and conflict (Fischer, 1996, Fig. 4.16):


16. Population dynamics and political instability in China 200 BCE-1070 CE (Fig. 8.6: Turchin, 2003):

Internal War Index


17. Effects of population density and political instability on population rate of change in China 200 BCE - 430 CE (Fig. 8.7: Turchin, 2003):


18. Picasso’s Guernica painted in 1937 of the Spanish civil war:


Figure 6.1: Intraspecific competition among cave beetles eating cricket eggs (a) scramble, (b) contest.


Figure 6.2: Red deer population size, birth weight and survivorship.


Figure 6.3: Density dependent mortality in flour beetles: 1 = density independent, 2 = undercompensating mortality, 3 = overcompensating mortality


Figure 6.14: Effects of density on growth rate & size in frogs and reindeer.


Figure 2.3 (Hassell, 1976):

(Exploitation) (Interference)


References: •  Andrewartha, H.G., & L.C. Birch. 1954. The distribution and abundance of

animals. University of Chicago Press, Chicago. •  Begon, M., J.L. Harper & C.R. Townsend. 1996. Ecology: Individuals,

Populations and Communities. Blackwell Scientific, Oxford. •  Diamond, J. 1999. Guns, germs, and steel. W.W. Norton & Co, New York.

480 pages. •  Fischer, D.H. 1996. The great wave. Price revolutions and the rhythm of

history. Oxford University Press, Oxford, 536 pages. •  Goldstone, J.A. 1991. Revolution and rebellion in the early modern

world. University of California Press, Berkeley. 608 pages. •  Hanson, V.D. 2001. Carnage and culture. Landmark battles in the

rise of western power. Doubleday, New York. 492 pages. •  Nicholson, A.J. 1954. An outline of the dynamics of animal populations.

Australian Journal of Zoology 2: 9-65. •  Turchin, P. 2003. Historical dynamics. Why states rise and fall.

Princeton University Press, Princeton, 245 pp.

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