In-class Activity 10 HUMAN POPULATION EXPLOSION Group _____________________________ ________________ __________________ __________________1. Complete this growth model: ∆N/∆t = (births + immigration) – (deaths + emigration) Are the second parts of ( ) important for projecting world or regional growth? Regional (The world doesn’t have migration- to/from outer space!)2. It took 10000s of years to reach 1 billion by 1800; then only 130,33,15,11, and 12 years to add each succeeding billion. Plot the data. Label axes. Time on X, Population Size on Y; get classic J-shaped, exponential curve.3. Figure 1. What is on the Y-left axis? Annual increment Summarize its pattern. Slow change from 1750-1900, then rapid rise till 1980-90, followed by (projected) rapid decline. What is on the Y-right axis? Population Size Summarize its pattern. Very slow change from 1750-1900; then rapid accelerating increase until about 1990 (inflection point of logistic curve), followed by continuing to increase but at a slightly lower rate (second half of S-curve is beginning = decelerating phase). How do the two variables relate? The annual increment drives the changes in population size. Why does population size increase if annual population increment is decreasing? The absolute size of annual increment is decreasing, but it is still a positive number. What type of growth curve is represented? Partial sigmoid logistic curve. What is causing the change in slope of population size after 2000? The annual increment is declining after 2000, thus causing the rate of change of population size to become smaller and lessening the slope.4. Figure 2. What is on the Y-axis? Total fertility = # children (male + female) per woman Draw a horizontal line at 2XRo for a stable population size. = 2.1 What is 2XRo in most developed regions? below 2.1 worldwide 2.6 The range in 2X Ro among countries? 1.3 Japan/Europe; to 7 in Africa5. Figure 3. What is on the Y axis? Life Expectancy of Birth (yr) Summarize the trend. It increases steadily from 1950-2050, but is higher for more than less developed regions. The slope is greater for less than more developed regions. How does this trend affect population size? With ever increasing life spans, the death rate of the existing population is not declining as rapidly. Hence population size stays higher than if life expectancy were a constant value.6. Figure 4. What two variables are on the Y-axis? Birth rate Death rate Complete this table. Rough estimates only.Stage 1 Stage 2 Stage 3 Stage 4 2006 (see text)Birth rate 5 5 5 - - 1 1 2.1 Death rate 5 5 - - 1 1 1 0.9“r” 0 0 to 4 4 to 0 0 1.1Pop Stable Increasingat fasterrateIncreasingat slowerrate Stable Increasing 7. What is meant by ‘demographic transition? Declines in first death rate, then birth rate that gradually result in a lower value of r (birth-death. Which drops first, B or D? Death rate What is a consequence of this asynchrony in change of the two rates? First, as only death rate declines, a population explosion occurs because b>>>d. Then birth rate drops. When b =d, the value of r is at a much lower value than prior to the transition. Population size is much greater and longevity has increased during transition. 80% of world population is in developing countries, but they generate 96% of population growth. Have they completed their transition? No 8. How long did it take Sweden to complete its transition? about 150-170 years. When was its peak period of growth? about 1850 when b>>d. Is it growing today? Little, if any. Explain in terms of the value of B-D. Today, B = D, so r = 0. The growth rate is 0. Has Mexico completed its transition? No 1900 1925 1950 1975 2000Birth rate 48 45 46 45 22Death rate 34 25 17 6 5“r” 14 20 29 41 17Pop Increasing Increasing Increasing Increasingthe fastestIncreasingbut less fast9. Is the doubling time of Costa Rica higher or lower than Haiti? higher Are both countries undergoing a demographic transition? Yes Which one is at a later stage? Costa Rica Why is Costa Rica doubling time higher than Haiti?Birth rate Death rate Doubling timeHaiti 46 20 30 yrCosta Rica 41 9 Higher or lower than Haiti?The value of r =32 for CR and 26 for Haiti. CR is higher because it has dropped its death rate to a lower value than Haiti What is the main take-home point here? Demographic transitions take time. Population explosions occur when only the death rate is altered. The more the death rate is slowed without lowering of the birth rate, the faster the population growth (= faster doubling time).10. Figure 5. What is on the Y-axis? Average annual rate of change (%) How does this variable relate to Figure 1? It refers to the annual % change in population size (Nt+1-Nt)/Nt)100 Draw a horizontal line for a non-growing population. at 0 Worldwide population growth is 1.1% per year (=11 per thousand per year) What population parameter does this represent? r or Ro? r Complete this table. Doubling time = 70/% growth per year. What is T? Generation time How does it relate to doubling time? Generation time parallels doubling time; greater generation time greater doubling time.% growth/yr Double time TMost develop 0.3 233 years 28Worldwide 1.1 64 20Least develop 2.4 29 1611. Prospects for the future What is expected to happen to the death rate? Stay the same birth rate? decline Then why is the population expected to increase? The world-wide demographic transition is not complete. Birth rate still exceeds death rate so the population continues to increase until B = D. If B = D, is zero population growth (ZPG) automatically achieved? Explain. No. A population that has been growing in the past will have a high proportion of young people in their pre-reproductive + reproductive years. As it is younger people who have children there is a large time lag between the point at which the birth rate equals or falls below the death rate and the point at which the population stops
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