2. Population Ecology Population = Demography =

3. 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

4. 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

5. 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

6. Comparison of Ways to Express Population Growth A. Population size = 1,000 B. Population size = 1,000,000 1. Net birth = 10 Net births = 100 2. Net deaths = 5 Net deaths = 50 3. Net increase = 5 Net 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%

7. 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%

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

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

10. 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

11. Geometric Growth of a Sheet of Paper Number of doublesThickness 12/254 inch 24/254 38/254 416/254 532/254 664/254 7128/254 8 256/254

12. Geometric Growth of a Sheet of Paper Number of doublesThickness 121.25 foot 20340 feet 353,000 miles 42 384,000 miles (reaches the moon) 5093,000,000 miles (reaches the sun)

13. 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

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

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

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

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

18. 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

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

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

21. Three general types of age structure diagrams Expanding Stabilizing Diminishing

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

23. 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

24. 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

25. Changes -USA Birth Rates and Death Rates Year BR DR RNI %Growth 194726.615.011.61.16 197714.7 9.05.70.57 198716.0 9.07.00.70 199614.6 8.85.80.58 200015.0 9.06.00.60 200414.0 8.0 6.00.60 200714.0 8.06.00.60 Over the last 50 years births and death rates have declined BR = Birth Rate, DR = Rate, RNI = Rate of Natural Increase

26. 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

27. 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

28. United States’ Aging Population Population 19501985 2020 Ages 65-84 (Millions ) 11.725.844.3 85 and over (Millions) 0.62.77.1 65 and older % total7.7%12%17.3% LIFE EXPECTANCY Total Pop. (years)68.274.778.1 Federal Spending Pension & Health-care As a % of GNP1.6%9.3%11.8%

29. 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

30. Ratio: retirees/worker DateRetiree/workers 19501/16 19601/5 19651/4 19851/3 20251/2

31. 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

32. 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?

33. Birth Year & Age for Full SS Retirement Benefits Birth YearAge 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

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

35. Population Structures by Age and Sex, 2005 Millions Less Developed Regions More Developed Regions MaleFemaleMaleFemale 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 Age Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003. Age Distribution of the World’s Population 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.

37. 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