Understanding Population Growth

Earth’s population has boomed in the past years Industrial Revolution and Technology Cheap, reliable fossil fuels Medical advances– TB, influenza, diarrhea Green revolution– huge breakthroughs in biotechnology— we’re producing massive amounts of grain

How many people can Earth support? Very difficult to say…… More the merrier? Technological advances increases are only raising earth’s carrying capacity

How many people can Earth support? 1800– I billion 1927—2 billion (127 year diff.) 1960— 3 billion (33 year diff.) 1974— 4 billion (14 year diff.) 1987– 5 billion (13 year diff.) 1999– 6 billion (12 year diff.) 2011 – 7 billion (12 year diff.) 2050– 9 billion What does these numbers say about carrying capacity?

Some fun with some data..

Source– O’ Neill, Brian Population Scenarios Based on Probabilistic Projections: An Application for the Millennium Ecosystem Assessment. Population and Environment: 2005.

So what affects population? Dependent on: Birth rate (b ) (crude birth rate = b/1000) Birth rate (b ) (crude birth rate = b/1000) Death rate (d ) (crude death rate = d/1000) Death rate (d ) (crude death rate = d/1000) Immigration (i ) Immigration (i ) Emigration (e ) Emigration (e ) Population change = ( b + i) – (d + e)

Fertility So…..women…. having babies…. adds people to the human population….. minus…. how fast people are dying… Replacement level fertility (RLF)– how many babies must be born to replace parents Developed countries ~ 2.1 Developing countries ~ 2.5 Why the discrepancy? If levels were RLF were 2.0, would world population increase?

Fertility Total-fertility rate (TFR)-- # of children woman will have during reproductive ages (13-33) Developed countries – 1.6 Developing countries – 2.9

What factors affect birth/fertility rate? Children as part of working/labor for family Developing countries need children to work/help support family– also think farming families in early US Urbanization– people in cities have access to birth control/family planning Education/job market for women Marriage age Legality of abortions Availability of birth control

What factors affect death rate? Guess…….. Life expectancy Most of world’s increase population is not due to increase birth rates, it’s decreased death rates Infant mortality (baby deaths/1000 before age 1) Used as the best indicator of “developedness” of a country If baby mortality low– medical technology, nutrition, healthcare, infectious disease from drinking water/pollution

Global Total Fertility Rates

Doubling time How fast will a population double with a growth rate of 1.1%? This is current US growth rate Current US pop– 312 million (source: US census 2011)

Doubling time Equation: 70/growth rate % For US: 70/1.2% = 58.3 years SO: in 58 years, current US population will double…!!!!

Doubling Time

Time to take for a population with a stable growth rate to double in size Time to take for a population with a stable growth rate to double in size Doubling Time ( t d ) = t d = 70% or.7 r r r r Ex. Brazil will double its population in how many years with the present growth rate of 1.7%? A:.7/0.017 or 70%/1.7% = 41.2 years

Factors affecting Death rate Population increase is not necessarily due only to increased birth rate, but also decreased death rate. Population increase is not necessarily due only to increased birth rate, but also decreased death rate. 1.Life expectancy 2.Infant mortality rate = # of babies/1000/year Most important measure of quality of life since it is linked to so much of society! Most important measure of quality of life since it is linked to so much of society!

Developed vs. Developing countries Developed countries – USA,

Effect of Fertility Rates of Population Growth Total fertility rate (TFR) = Total fertility rate (TFR) = average number of children that a woman will have in her reproductive years average number of children that a woman will have in her reproductive years Most useful measure of fertility for projecting future populations. Most useful measure of fertility for projecting future populations.

Effect of Fertility Rates of Population Growth in 1998, TFR = 2.9 (greater than 2.1) in 1998, TFR = 2.9 (greater than 2.1) 1.6 in developed countries 1.6 in developed countries 3.3 in developing countries 3.3 in developing countries

Population growth TFR needs to drop to 2.1 in order to stabilize the population.(Takes into account infant mortality)TFR needs to drop to 2.1 in order to stabilize the population.(Takes into account infant mortality) TFR > RLF = pop growth TFR > RLF = pop growth TFR = RLF = steady population TFR = RLF = steady population TFR < RLF = pop slow down TFR < RLF = pop slow down

Demographic Transition Model

Population Pyramids

Demographic Transition Model

10 Factors affecting Birth rate and Fertility rate 1.Average level of education and affluence 2.Importance of children as a part of the labor force 3.Urban areas (wrt access to family planning) 4.Cost of raising and educating children 5.Education and employment opportunity for women 6.Infant mortality rate 7.Average age of marriage and 1st child 8.Availability of pension system 9.Availability of legal abortions 10.Birth control/religion

Population Density # of indiv. of a species unit of area A better way to describe the size of a population A better way to describe the size of a population ex. 270,000,000 people = 29 people/Km 2 in the US ex. 270,000,000 people = 29 people/Km 2 in the US 9,166,605 Km 2 9,166,605 Km 2

Birth and Death Rate b = birth _ or Births per thousand Total population1000 d = death or Deaths per thousand Total population1000 ex. b = 23, 452/942,721 = = 2.5% Same as 25/1000 = = 2.5%

What Causes Populations to Change in Size? Rate of change ( r ) = Four ways to find r:

Rate of change ( r ) = 1. Total births - total deaths/ total population r = 23, , 228 = =.66% r = 23, , 228 = =.66% 942, , birth rate (b) -death rate (d) r = = =0.7% r = = =0.7%

Immigration (i ) = Immigration (i ) = Migration of individuals INTO an area Migration of individuals INTO an area Emigration (e ) = Emigration (e ) = Migration of individuals OUT OF an area Migration of individuals OUT OF an area

Rate of change ( r ) = 3. (Total births + total immigration) - (total deaths + total emigration) / total population (total deaths + total emigration) / total population r = (23, )-(17, ) = 942,721 r = (23, )-(17, ) = 942,721 = = 1.4% = = 1.4% 4. (birth rate (b) + immigration rate(i)) - (death rate (d) + emigration rate (e) ) x 100 r = ( ) - (18 + 3) = = 1.4% r = ( ) - (18 + 3) = = 1.4%

Maximum Population Growth (MPG) Influenced by Biotic PotentialInfluenced by Biotic Potential – different for each species – can change with conditions MPG is always exponential under ideal conditionsMPG is always exponential under ideal conditions

You figure out the growth Rate of a Pop: Remember: r = (b - d ) + (i - e ) b =.01 d =.005 i =.001e =.01 So now: Calculate growth rate and Calculate doubling time

Determining future Pops: Remember: N (t) = N 0 e rt N(t) = population after t years N 0 = initial population size r = growth rate t = time

You Determine the future Pop of Duttania: Remember: N (t) = N 0 e rt The island of Duttania has 435 people. Their growth rate is 2%. What will be the population after 10 years? A: 531 people.