Population ecology
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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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Population ecology

Population Ecology

Population =

Demography =


Ways of expressing population growth

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


Expressing population growth

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


World population mid year 2007

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


  • Comparison of ways to express population growth

    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%


    Rate of natural increase and growth do not include net immigration

    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%


    Population growth basic growth curves

    Population Growth(Basic Growth Curves)

    • “J-shaped” growth or exponential growth

    • Sigmoid or “S-shaped” growth


    J shaped or exponential growth curve

    J-shaped or exponential growth curve

    EXPONENTIAL

    GROWTH

    Population

    Size

    LAG

    BEND

    TIME


    Exponential growth

    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


    Geometric growth of a sheet of paper

    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


    Geometric growth of a sheet of paper1

    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)


    Exponential growth1

    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


    J shaped growth curve

    J-shaped Growth Curve

    Carrying Capacity

    Environmental

    resistance – applied

    abruptly

    POPULATION SIZE

    Time


    J shaped growth curves are characteristic of populations in environments of

    J-shaped growth curves are characteristic of populations in environments of

    • Low diversity

    • Few predators or competitors (few ecological controls)

    • Simple food webs


    Sigmoid or s shaped growth curve

    Sigmoid or S-shaped Growth Curve

    Biotic Potential

    Carrying Capacity

    Population

    Size

    Time


    Sigmoid curve

    Sigmoid Curve

    • Detrimental factors (environmental resistance)

      • Increases in proportion to population increase

    • Characteristic of environment

      • High diversity

      • Predators, competitors exert biological control


    Age structure diagrams

    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


    Population ecology

    Age

    % males in the

    age group

    % females in the

    age group

    Age Structure Diagrams

    Post-reproductive

    Reproductive

    Younger to older

    Pre-reproductive


    What does the age structure diagram indicate

    What Does the Age Structure Diagram Indicate?

    • Growth Patterns

    • Proportional Distribution in Age Categories


    Three general types of age structure diagrams

    Three general types of age structure diagrams

    • Expanding

    • Stabilizing

    • Diminishing


    Population ecology

    Expanding Growth 2.7%

    Stabilizing 0.6%

    Diminishing –0.2%

    Post-reproductive

    Reproductive

    Pre-reproductive


    Changes in usa age structure

    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


    Effect of post war baby boom

    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


    Changes usa birth rates and death rates

    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


    Implications of death rates and birth declining

    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


    Results of declining growth in usa

    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


    United states aging population

    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%


    Social security

    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


    Ratio retirees worker

    Ratio: retirees/worker

    • DateRetiree/workers

    • 19501/16

    • 19601/5

    • 19651/4

    • 19851/3

    • 20251/2


    Social security current status

    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


    Suggested solutions

    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?


    Population ecology

    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


    Population ecology

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


    Age distribution of the world s population

    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.


    Examples of age structure diagrams

    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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