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

Transcription

1 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 Lecture 4: Slide - 1

2 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). Lecture 4: Slide - 2

3 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 Lecture 4: Slide - 3

4 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. Lecture 4: Slide - 4

5 5. Population growth - growth curves: J-shaped curve - periods of rapid, exponential growth: Fig. 4-3 thrips on roses in Australia (Davidson & Andrewartha, 1948). Lecture 4: Slide - 5

6 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. Lecture 4: Slide - 6

7 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. Lecture 4: Slide - 7

8 8. Mortality and survivorship - survivorship variation: Changes in life expectancy at birth in the United States: Date White males White females Nonwhite males Nonwhite females n/a n/a Lecture 4: Slide - 8

9 9. Age structure: 3 major age groups (Bodenheimer, 1958): Prereproductive, Reproductive, Postreproductive Influence 3 types of populations: (a) Expanding, (b) Stable, (c) Diminishing. Lecture 4: Slide - 9

10 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. Lecture 4: Slide - 10

11 11. Population regulation - biotic factors: Horizontal processes within trophic levels: Competition. Mutualism. Vertical processes between trophic levels: Herbivory. Parasitism (micro- & macro-parasites). Predation. Mutualism. Lecture 4: Slide - 11

12 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). Lecture 4: Slide - 12

13 13. Interspecific competition: Competition for limited resources leads to: Competitive exclusion: Fig Coexistence through character displacement: Niche differentiation. Lecture 4: Slide - 13

14 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. Lecture 4: Slide - 14

15 Figure 4-2. Growth rate and growth curve of yeast cells. Lecture 4: Slide - 15

16 Figure 4-8. Growth curve of the blowfly showing regular fluctuations caused by self-adjustment (Nicholson, 1955). Lecture 4: Slide - 16

17 17. References: Begon, M., J.L. Harper & C.R. Townsend Ecology. 3 rd edition. Blackwell Science, Oxford, 1068 pp. Bodenheimer, F.S Animal ecology today. Monographiae Biologicae 6, 276 pp. Chapman, R.N The quantitative analysis of environmental factors. Ecology 9(2): Davidson, J., and H.G. Andrewartha Annual trends in a natural population of Thrips imaginis (Thysanoptera). Journal of Animal Ecology 17(2): Davidson, J., and H.G. Andrewartha 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): Deevey,Jr. E.S Life tables for natural populations of animals. The Quarterly Review of Biology 22(4): Gause, G.F Experimental analysis of Vito Volterra s mathematical theory of the struggle for existence. Science 79(2036): Kormondy, E.J., & D.E. Brown Fundamentals of human ecology. Prentice Hall. 503 pp. Malthus, T An essay on the principle of population. London. Nicholson, A.J The self-adjustment of populations to change. Cold Spring Harb. Symp. Quant. Biol. 22: Pearl, R The rate of living. Being an account of some experimental studies on the biology of life duration. University of London Press, London. Lecture 6: Slide - 17