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3.1 Human population growth
The Population Explosion – Exponential Growth
The Population Clock• Population Clock•The global population reached 6 billion in
fall of 1999•In 2013 Global Population Topped 7
billion!
Limiting factors of population Growth
1. Availability of food and water2. Invasion of parasites, pathogens, or
disease3. Over-crowding 4. Sudden Climate changes5. Pollution of air, soil and water•If we do not take steps to control
population it is likely one of these factors will forcibly reduce our population for us!!
Humans Avoid Limiting Factors by…
Importing resourcesImproving sanitation and medicine Expanding habitatIncreasing capacity in existing habitatsIncreasing in agricultural technology
Key Terms•Population: number of persons•Population change: a change (increase or
decrease) in the number of persons (per year)
•Growth rates: rate of change (per year) includes births, deaths and immigration, and emigration
Crude Birth Rate Crude Birth Rate (CBR)= number of births
per 1000 population Example: US Births = 3,999,386 and the total
population is 307,645,076 people (Births / Total Population) x 1000
Crude Death Rate•Crude Death Rate (CDR)= number of
deaths per 1000 population Example: US Deaths = 2,468,435 and the
total population is 307,645,076 people (Deaths/ Total Population) x 1000
Natural Increase Rate (NIR)Rate of Natural Increase (RNI) Rate Natural Increase is % growth rate based
only on birth and death
(Totally ignores immigration and emigration)
RNI = (crude birth rate – crude death rate) 10 Example: The CBR of USA is 13.0 and the CDR is 8.0.
Calculate the RNI of USA
Fertility •General Fertility-(# live births / female
reproductive population (15-44) x 1000•Example: US Births = 3,999,386 and female
population ages 15-44 is 62,071,000
Fertility Continued •Replacement Fertility: Number of children
adults need to have to replace themselves▫MEDC ~ 2.1 ▫LEDC ~ 2.3 +
•TFR (total fertility rate) = ▫number of children born to a woman during
her reproductive years (or life time)▫USA TFR is 2.06▫Mali TFR is 7.38 !
Total Fertility Rate
Infant Mortality Rate•IMR (infant mortality rate) =
▫infant deaths per 1000 live births (infant < 1 yr)
▫Used as overall indicator of health
Infant Mortality rate
Doubling Time •Number of years in which a population
doubles its size•Doubling time can be approximated using
growth rates and the rule of 70•Doubling time (T) = ___70_____
% growth rate
Calculate Doubling Time Below▫rate: 1.4% doubling time = 50 years▫rate: 2.0% doubling time = ______ years▫rate: 0.5% doubling time= _______ years▫rate: -0.5% doubling time = _______years
Growth Rate•Human Population Growth Per Year = 1.4%•LEDC (least economically developed
country)=1.7%•MEDC (more economically developed
country) = 1.0%
Rate of Population Increase
Factors affecting fertility Rates
•Urbanization•Importance of children in workforce•Cost of raising a child•Education/Employment for women•Average age of marriage •Availability of abortion•Availability of birth control•Religious beliefs, traditions and culture
Determining Future populations•Use Ne(rt) formula
▫N= Current population▫e= constant 2.71828…▫r = growth rate as a decimal!!! (Divide by 100!)▫t = time in years
•Example: 2010 data reports that a population of 2,350,000 has a growth rate of 1.2%. What will the population be in 2025?
Carrying Capacity•The maximum population that can be
sustainably supported without running out of resources.
Population Pyramids
Characteristics of MEDC/LEDCMEDC’s LEDC’s
industrialized little or no industry
high GDP (gross domestic product)
low GDP
relatively rich populationprovide raw materials but few processed or manufactured goods
access to education and health care
limited access to education and health care
high resource use per capita
fewer resources consumed per person
low population growth ratesmost have high population
growth rates
What is a Population Pyramid? Graphic device: bar graph Shows the age and gender composition of a
region Horizontal axis: gender
male: left-hand female: right-hand absolute number of people or %
Vertical axis: age 5-year or 10-year age groups
Three age population categories Pre Reproductive- (0-14) Reproductive- (15-44) Post Reproductive- (45 +)
Why a population Pyramid?
•Helps to determine specifics of potential future populations
•Shape of pyramid indicates future growth•Can point to future changes in social
conditions of a country
Population Pyramids
Demographic Transition Model
Stages of Demographic Transition Model
StagePre-
industrial(Stage 1)
LEDC(Stage 2)
Wealthier LEDC
(Stage 3)
MEDC (Stage 4)
MEDC(Stage 5)
Birth rate High High Declining Low Very low
Death rate High Moderate Low Low Low
Life expect Short Medium Long Long Long
Pop’l growth Slow Rapid Slowing Stable Shrinking
Reason for changes in the DTM•Birth rates, death rates and growth rates
systematically change through time as societies change:▫Modernize, urbanize▫Gain access to new technology▫Births, deaths, migration ▫Fertility rates play huge role
Stage 1•High birth rates,
high death rates, low growth rates
•Stage for much of human history, traditional societies
•Practically no country today
Stage 2•High birth rates,
declining death rates, rising growth rates
•Improvements in sanitation (water) and medicine
•Europe during Industrial Revolution
•LEDC countries since the 1950’s
•Much of Africa today, some countries of Asia (Afghanistan, Nepal)
Stage 3•Continued decline of
death rates, declining birth rates, growth rates decline from high to lower levels
•Change in behavior: adaptation to lower death rate, in particular infant mortality rate
•Economic change: urbanization (incentive to have fewer children)
•Mexico today
Stage 4 & 5•Stage 4: low birth
rates, low death rates, low growth rates▫United States today
•Stage 5: low birth rates, rising death rates, declining growth rates (if birth rates drop below death rates: negative growth rates)▫Western Europe,
Japan
Population Pyramid and Demographic Transition
•Stage 2: wide base
Population Pyramid and Demographic Transition
•stage 3: wide middle
Population Pyramid and Demographic Transition
•stage 4: slender
Population Pyramid and Demographic Transition
•stage 5: narrow base
Demographic Transitions in China
China Population Pyramid 2005
Models for Predicting Population growth
Computer simulations: Can be highly accurate with many variables Cant include unforeseen events (i.e. natural disaster,
terrorist strike, warfare)? Statistical and/or demographic tables
Include actual field measurements based on past trends.
Past trends may not always predict future trends. How large/representative are the sample populations?
Age/sex pyramids ( see above)
Population curves Mathematical extrapolation from graphs based on
real data Less complex than computer models