Population Ecology

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 1,000 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
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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

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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

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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 1970s 1980s 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
Age Distribution of the Worlds Population
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 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.
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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