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Population Ecology

Population Ecology. Population = Demography =. Ways of Expressing Population Growth. Net birth rate = Births per unit time Net death rate = Death per unit time Net population increase = Net Birth rate – Net Death rate World Population mid-year 2007 6.625 billion people

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Population Ecology

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  1. Population Ecology Population = Demography =

  2. Ways of Expressing Population Growth • Net birth rate= Births per unit time • Net death rate= Death per unit time • Net population increase= Net Birth rate – Net Death rate • World Population mid-year 2007 • 6.625 billion people • Net birth rate/ year = 139, 125,000 • Net death rate/year = 59,625,000 • Net Increase/year = 78,500,000 • USA Population mid-year 2007 = 302,200,000 • World Increase = USA Population - 3.85 years

  3. Expressing Population Growth • Births/1,000 = • (Births per year/ mid-year population size) X 1,000 • Deaths/1,000 = • (Death per year /mid-year population size) X 1,000 • Natural Rate of Increase = • Births/,1000 – Death/1,000

  4. World Population mid-year 2007 • Birth rate= 21 • Death rate= 9 • Rate of Natural Increase = 12 • Percent Growth = • 1. Rate of Natural Increase/10 • 2. 12/10 = 1.2% • Approximate doubling time = • 70 years/ % Growth • World Doubling Time =70 yrs/1.2 % = 58 yrs

  5. Comparison of Ways to Express Population Growth A. Population size = 1,000B. Population size = 1,000,000 1.Net birth = 10Net births = 100 2. Net deaths = 5 Net deaths = 50 3. Net increase = 5Net increase = 50 1. Birth /1000 = 10= 0.10 2. Death/1000 = 5= 0.05 3. Rate of natural increase = 5= 0.05 4. % growth = 0.5%= 0.005%

  6. Rate of Natural Increase and % Growth do not include net immigration • United States • Birth per 1000 = 14 • Deaths per 1000 = 8 • Net Immigration per 1000 = 4 • % Growth with Immigration = 18-8 = 1.0% • % Growth w/o immigration = 14-8 = 0.6%

  7. Population Growth(Basic Growth Curves) • “J-shaped” growth or exponential growth • Sigmoid or “S-shaped” growth

  8. J-shaped or exponential growth curve EXPONENTIAL GROWTH Population Size LAG BEND TIME

  9. EXPONENTIAL GROWTH • Population increase • Fixed percentage of population size at the beginning of the period • Example of exponential growth is geometric growth - • Growth by doubling • Fixed percentage is 200 percent

  10. Geometric Growth of a Sheet of Paper • Number of doubles Thickness • 1 2/254 inch • 2 4/254 • 3 8/254 • 4 16/254 • 5 32/254 • 6 64/254 • 7 128/254 • 8 256/254

  11. Geometric Growth of a Sheet of Paper • Number of doubles Thickness • 12 1.25 foot • 20 340 feet • 35 3,000 miles • 42 384,000 miles (reaches the moon) • 50 93,000,000 miles (reaches the sun)

  12. Exponential Growth • Initially, no limit placed on growth • Population grows at max possible rate • Intrinsic growth rate (biotic potential) • r = biotic potential • Maximum rate/individual • Growth is halted abruptly: • Depleted resource (food or space) • Epidemic disease • Environmental resistance • Applied all at once

  13. J-shaped Growth Curve Carrying Capacity Environmental resistance – applied abruptly POPULATION SIZE Time

  14. J-shaped growth curves are characteristic of populations in environments of • Low diversity • Few predators or competitors (few ecological controls) • Simple food webs

  15. Sigmoid or S-shaped Growth Curve Biotic Potential Carrying Capacity Population Size Time

  16. Sigmoid Curve • Detrimental factors (environmental resistance) • Increases in proportion to population increase • Characteristic of environment • High diversity • Predators, competitors exert biological control

  17. AGE STRUCTURE DIAGRAMS • Graphically • % of individuals within various age categories • Three age categories • Prereproductive (Age 0-14 years) • Reproductive (Age 15-44 years) • Postreproductive ( Age 45+) • Plot males on left and females on right

  18. Age % males in the age group % females in the age group Age Structure Diagrams Post-reproductive Reproductive Younger to older Pre-reproductive

  19. What Does the Age Structure Diagram Indicate? • Growth Patterns • Proportional Distribution in Age Categories

  20. Three general types of age structure diagrams • Expanding • Stabilizing • Diminishing

  21. Expanding Growth 2.7% Stabilizing 0.6% Diminishing –0.2% Post-reproductive Reproductive Pre-reproductive

  22. Changes in USA Age Structure • Last century USA • Expanding population to a stabilizing population • Total fertility rate (2007 USA 2.1) • Post war baby boom (1946 and 1964) • Peaked 1955-1959 • 75 million bulge in population • Large affect on social and economic structure

  23. Effect of Post War Baby Boom • 1960-1975 – expansion of schools • Late 1970’s – 1980’s high unemployment • 2,005-2025 – Dominance of middle age (Pension cost begin to rise) • 2,025 – 2,040 – Period of Senior Citizens

  24. Changes -USA Birth Rates and Death Rates • Year BR DR RNI %Growth • 1947 26.6 15.0 11.6 1.16 • 1977 14.7 9.0 5.7 0.57 • 1987 16.0 9.0 7.0 0.70 • 1996 14.6 8.8 5.8 0.58 • 2000 15.0 9.0 6.0 0.60 • 2004 14.0 8.0 6.0 0.60 • 2007 14.0 8.0 6.0 0.60 • Over the last 50 years births and death rates have declined • BR = Birth Rate, DR = Rate, RNI = Rate of Natural Increase

  25. Implications of Death Rates and Birth Declining • Fewer Births = fewer young people • Fewer Deaths = More Older People • Birth rates declined more rapidly than death rates = fewer young people more older people

  26. Results of declining growth in USA • USA has an aging population: • Proportionately fewer young people and more older people • Median Age of the USA Population • 1970 -- 29 years • 1990 -- 33 • 2,000 -- 36 • 2010 -- 39

  27. United States’ Aging Population • Population 1950 1985 2020 • Ages 65-84 (Millions)11.7 25.8 44.3 • 85 and over (Millions)0.6 2.7 7.1 • 65 and older % total 7.7% 12% 17.3% • LIFE EXPECTANCY • Total Pop. (years) 68.2 74.7 78.1 • Federal Spending • Pension & Health-care As a % of GNP 1.6% 9.3% 11.8%

  28. Social Security • Continued adjustments in Social Security Social Security • Not a pay as you go system. • Pay while you work get benefits later • As the populations ages: • Future retirees will have few workers supporting their retirement than current retirees or retirees in the past

  29. Ratio: retirees/worker • Date Retiree/workers • 1950 1/16 • 1960 1/5 • 1965 1/4 • 1985 1/3 • 2025 1/2

  30. Social Security: Current Status • 2018 – More expenditures than income • 2042 –Trust Fund Depleted • Pay out all in coming funds • 75 % of current benefits • Reality Trust fund is not fully funded

  31. Suggested Solutions • Raise FICA Tax (Federal Insurance Contributions Act) – Current (7.65%) • Tax income over $90,000 (current cap) • Tax one-half of Social Security Income over $32,000 • What changes have occurred?

  32. Birth Year & Age for Full SS Retirement Benefits Birth Year Age for full benefits 1937 or earlier 65 1939 65 and 4 months 1941 65 and 8 months 1943-1954 66 1955 66 and 2 months 1957 66 and 6 months 1959 66 and 10 months 1960 and later 67

  33. Cunningham, Cunningham and Saigo, “Environmental Science, 8th ed.” McGraw Hill, Fig. 7.9

  34. Population Structures by Age and Sex, 2005 Millions Age Distribution of the World’s Population 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 17-19 10-16 5-9 0-4 Male Female Male Female Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003. Provided online by the Population Reference Bureau Graphics Bank, The Graphics Bank was prepared by Allison Tarmann, senior editor, and Theresa Kilcourse, senior graphics designer. Please visit www.prb.org.

  35. Examples of Age Structure Diagrams • Rapid Growth: Kenya, Nigeria, Saudi Arabia (doubling times 20-35 years) • Slow Growth: United States, Australia, Canada (doubling times 88-175) • Zero Growth: Denmark, Austria, Italy • Negative Growth: Germany, Bulgaria, Hungary

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