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Populations . AP Environmental Review Caroline, Kristina, Lauren, Gwen, Colby . Populations…. All members of a species inhabiting a specific geographic area (at a time) Size dictated by Emigration Immigration Birth Death. Density. Individuals in a population per unit habitat area

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AP Environmental Review

Caroline, Kristina, Lauren, Gwen, Colby

  • All members of a species inhabiting a specific geographic area (at a time)
  • Size dictated by
    • Emigration
    • Immigration
    • Birth
    • Death
  • Individuals in a population per unit habitat area
  • Dependent on
    • social/population structure
    • mating
    • time of year


  • Distribution/Dispersion types
    • Random
    • Clumping – uneven groups
    • Uniform – rare, even
exponential growth
Exponential Growth
  • “Geometric” growth
  • J-shaped Curve
  • Starts slowly but then accelerates with population increase
logistic curve
Logistic Curve
  • S-shaped Curve
  • Begins exponential
  • Environmental resistance comes into play
  • Growth slows to accommodate carrying capacity (K)
carrying capacity k
Carrying Capacity (k)
  • Maximum number of species which may survive together at a given time
  • Determined by resources and biotic potential
  • Exceeding leads to a dieback or crash
biotic potential r
Biotic Potential (r)
  • How a population might grow without presence of environmental resistance (limiting factors)
  • Density - independent
  • Exponential
k strategists
K Strategists
  • Early reproduction
  • Large bounties of offspring
    • accounts for high instance of death
  • Little care provided
  • Generally lower tropic levels
r strategists
R Strategists
  • Reproduce later in life
  • Few offspring
  • Large energy input for care
  • More prone to extinction
  • More specialized
survivorship curves
Survivorship Curves
  • Show the number/proportion of group individuals surviving at specific ages
  • Reflection of reproductive strategies
    • I. Late loss: K-strategist that produce few young and care for them until they reach reproductive age, reducing juvenile mortality.
    • II. Constant loss: Intermediate reproductive strategist with fairly constant mortality.
    • III. Early loss: r- strategists with high infant mortality
other growth rates
Other Growth Rates
  • Crude birth rate
    • live births occurring (per 1,000) in given time


  • Crude death rate
    • amount of deaths (per 1,000) in given time


  • Doubling Time (Rule of 70)
    • Time it would take for a population to double in size



Total Fertility Rate (TFR)

    • Average offspring a woman will have in her lifetime
  • Replacement Fertility Rate
    • Number of children which must be born to replace those creating them
zero growth
Zero Growth
  • The ultimate goal of a population
  • Occurs at two phases
    • When both rates (birth/death) are equally high
    • When both are equally low

(birth+ immigration)= (death+ emigration)


Rapid Growth

    • Appears “bottom-heavy”
    • Large portion of population which will soon move to the reproductive stage
  • Slow Growth
    • General evenness with growth
  • Negative Growth
    • Large portion of population post-reproductive
    • Small portion to move into reproductive
demographic transitions
Demographic Transitions
  • Societal change in birth and death rates
    • Both change as industrialization develops
stage 1 pre industrial
Stage 1: Pre Industrial
  • Slow population growth
  • Due to high birth rate and high death rate
  • Living conditions are poor
stage 2 transitional
Stage 2: Transitional
  • Improvements bring a decline in death rate
    • Medical, sanitation, food
  • Birth rate remains high
  • Rapid population growth
stage 3 industrial
Stage 3: Industrial
  • Birth rate slows
    • Due to further innovation
  • Meets death rate
  • General growth slows
stage 4 post industrial
Stage 4: Post-Industrial
  • Birth rate falls below death
  • Zero population growth