3.1 Human population growth. The Population Explosion – Exponential Growth

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