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 Availability of food and water Invasion of parasites, pathogens, or disease Over-crowding Sudden Climate changes 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 resources Improving sanitation and medicine Expanding habitat Increasing capacity in existing habitats Increasing 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/LEDC MEDC’s LEDC’s industrialized little or no industry high GDP (gross domestic product) low GDP relatively rich population provide 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 rates most 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 Pre-industrial (Stage 1) LEDC (Stage 2) Wealthier LEDC (Stage 3) MEDC (Stage 4) MEDC (Stage 5) Birth rate High Declining Low Very low Death rate Moderate Life expect Short Medium 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