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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
{(𝑖𝑚𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛+ h𝑏𝑖𝑟𝑡 )−(𝑒𝑚𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛+ h𝑑𝑒𝑎𝑡 𝑠)
Density
Individuals in a population per unit habitat area
Dependent on social/population structure mating time of year
Density= Distribution/Dispersion types
Random Clumping – uneven groups Uniform – rare, even
Exponential Growth
“Geometric” growth J-shaped Curve Starts slowly but then accelerates with
population increase
Logistic Curve
S-shaped Curve Begins exponential Environmental resistance comes into play Growth slows to accommodate 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)
How a population might grow without presence of environmental resistance (limiting factors)
Density - independent Exponential
POPULATION GROWTH REFLECTS REPRODUCTIVE
STRATEGIES
K Strategists
Early reproduction Large bounties of offspring
accounts for high instance of death Little care provided Generally lower tropic levels
R Strategists
Reproduce later in life Few offspring Large energy input for care More prone to extinction More specialized
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
Standard Growth Rate
(r) =*100
Other Growth Rates
Crude birth rate live births occurring (per 1,000) in given time
CBR = Crude death rate
amount of deaths (per 1,000) in given time
CDR= Doubling Time (Rule of 70)
Time it would take for a population to double in size
70/r
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
GROWTH TRENDS
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
HUMAN POPULATION NUMBERS VARY ACCORDING
TO INDUSTRIALIZATION
Demographic Transitions
Societal change in birth and death rates Both change as industrialization develops
Stage 1: Pre Industrial
Slow population growth Due to high birth rate and high death rate Living conditions are poor
Stage 2: Transitional
Improvements bring a decline in death rate Medical, sanitation, food
Birth rate remains high Rapid population growth
Stage 3: Industrial
Birth rate slows Due to further innovation
Meets death rate General growth slows
Stage 4: Post-Industrial
Birth rate falls below death Zero population growth
Demographic Transition