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Population Dynamics

Population Dynamics. - the study of how populations change in size, density and age distribution. Populations in Nature. Population Density Most populations clump together: for resources, for protection, for mating, for effective hunting Population Growth =

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Population Dynamics

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  1. Population Dynamics - the study of how populations change in size, density and age distribution

  2. Populations in Nature • Population Density • Most populations clump together: for resources, for protection, for mating, for effective hunting • Population Growth = • (births + immigration) – (deaths + emmigration)

  3. R-selected species and Exponential Growth • R = intrinsic rate of increase = biotic potential • Each individual has maximum number of offspring • Population is well below available resources • Reproductive (life-history strategies) • Reproduce early in life span • Reproduce many offspring • Provide minimum care for offspring • Exponential Growth

  4. K-selected species and Logistic Growth • K = carrying capacity= environmental resistance • Maximum population an ecosystem can sustainably support • Population at or near available resources • Reproductive (life-history strategies) • Reproduce late in life span • Reproduce few offspring • Provide a lot of care for offspring • Logistic Growth

  5. Limiting Factors • Resources limit population growth • Density dependent limiting factors • Density-independent limiting factors

  6. History of the Human Population • Hunter Gatherer Societies (5 m.y.a. – 8,000 b.c.) • Food, water, shelter, etc.were limiting factors • Total population less than a few million • Rise of Agriculture (8,000 b.c. – 1800 a.d.) • Ability to store food improved lifespan • First major increase in population • Industrial Revolution (1800 – present) • Rapid population increase due to sanitation, medicine, and transportation technologies

  7. Changes in Population • Change in population = (births + immigration) – (deaths + emigration) • Age structure diagrams (population pyramids) Predict future population growth

  8. Survivorship Curves

  9. What factors determine fertility rate? • Fertility Rate = number of children a woman has • Total fertility rate • What determines fertility rate? • Cost of raising children and how early they begin work • Availability of private & public pension (retirement) • Urbanization: access to medical care, contraceptives education, and employment for women • Culture, religion, including average age of marriage • Availability of legal abortions

  10. What factors affect mortality rates? • Mortality rate = number of deaths • Indicators of quality of life: • Life expectancy • Infant mortality • What determines mortality rate? • Nutrition • Medical advances • Improved sanitation and safe water

  11. Demographic Transition • Stage 1: Pre-Industrial Age • High birth rate, high death rate • Stage 2: Agricultural/Industrial Age • Death rate declines: improved sanitation, nutrition • Stage 3: Industrial Age • Birth rate declines: social changes • Stage 4: Post-Industrial Age • Low birth rate, low death rate

  12. The Classic Stages of Demographic Transition Note: Natural increase is produced from the excess of births over deaths.

  13. Challenges of Population Growth • Infrastructure: public water, sewer, power plants, power lines, roads, schools, etc. • Clean water • Resource shortages (fuel, wood) • Agriculture can deplete soil • Urban sprawl: traffic, habitat destruction

  14. Population Structures by Age and Sex, 2005 Millions Less Developed Regions More Developed Regions Age 80+ 75-79 70-74 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 15-19 10-14 5-9 0-4 Male Female Male Female Source: United Nations, World Population Prospects: The 2004 Revision, 2005.

  15. World Population Growth Through History 12 11 2100 10 9 Modern Age Old 8 Iron Middle Bronze Stone Age New Stone Age Ages Age Age 7 Future 6 2000 Billions 5 4 1975 3 1950 2 1900 1 1800 Black Death — The Plague 2000 1+ million 7000 6000 5000 3000 1000 A.D. 4000 A.D. A.D. A.D. A.D. A.D. years B.C. B.C. B.C. B.C. B.C. B.C. B.C. 1 1000 2000 3000 4000 5000 Source: Population Reference Bureau; and United Nations, World Population Projections to 2100 (1998).

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