populations

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 timeCBR =

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 size70/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