Understanding Understanding Population GrowthPopulation Growth

Age Structure

Pre-reproductive ReproductivePost-reproductive

This group has a large economic impact

Mostly older people

Declining quickly

Is a declining population a problem?

YES!

Problems

Decreased economic growth

Labor shortage – so more immigrant labor

Less taxes – fewer workers

health care costs

pension costs – burden to taxpayers

retirement age

Other countries with these problems

Germany

Russia

Poland

Italy

Spain

Greece

AIDS

25 million people dead as of 2008

Kills adults

8 African countries have 16-39% of their adults infected with HIV

Loss of workers

Loss of people to raise kids and care for elderly

How Does Industrialization How Does Industrialization Affect Population Size?Affect Population Size?

The The

Demographic Demographic

TransitionTransition

Overall

Shows what happens to countries as they move from developing to developed nations

Economic development and family planning are key factors

Overall: first the death rate goes down, then the birth rate

FactorsFactorsInfant Mortality Infant Mortality

RateRate number number of babies per of babies per 1000 that 1000 that don’t don’t make it to make it to their 1st yrtheir 1st yrreflect reflect quality of lifequality of life

Average Average Crude Birth Crude Birth & Crude & Crude Death Death RatesRates

Stage 1: Pre-Stage 1: Pre-IndustrialIndustrial

High birth rate (high IMR)High birth rate (high IMR)High death rateHigh death rateLow pop growthLow pop growth

Stage 2: TransitionalStage 2: TransitionalIndustrialization Industrialization food availabilityfood availability Health careHealth careBirth rate stays Birth rate stays

highhighDeath rate Death rate

begins to fallbegins to fallPop grows Pop grows

quicklyquickly

Some countries get stuck here

Stage 3: Stage 3: IndustrialIndustrial

Birth rate falls to near Birth rate falls to near death ratedeath rate

better jobs and better jobs and education for womeneducation for women

Decline in IMRDecline in IMRPop growth rate Pop growth rate

continues, but is lowcontinues, but is low

Stage 4: Stage 4: Post-IndustrialPost-Industrial

Birth rate falls Birth rate falls moremore

birth rate = birth rate = death ratedeath rate

ZPGZPG

Stage 4: Post-IndustrialStage 4: Post-IndustrialThen, birth rate declines Then, birth rate declines

more; less than death more; less than death rate, negative pop growthrate, negative pop growth

UnUnsustainability to sustainability to sustainabilitysustainability

Very fewVery few countries have countries have made it heremade it here

Calculations

Population DensityPopulation Density

# of indiv. of a species # of indiv. of a species

unit of areaunit of area

A better way to describe the A better way to describe the size of a populationsize of a population

Dependent on:Dependent on:

Birth rate (Birth rate (bb ))

Death rate (Death rate (d d ))

Immigration (Immigration (i i ))

Emigration (Emigration (ee ) )

What Causes Populations to What Causes Populations to Change in Size?Change in Size?

Rate of change ( Rate of change ( r r ) =) =

birth rate (birth rate (bb)-death rate ()-death rate (d d ) x 100) x 100

r = 40 - 20r = 40 - 20

1000 10001000 1000

r r =0.04 - 0.02 x 100 = 2% per year=0.04 - 0.02 x 100 = 2% per year

What Causes Populations to What Causes Populations to Change in Size?Change in Size?

Rule of 70

A way to estimate the number of years it takes for a certain variable to double.

The rule of 70 states that in order to estimate the number of years for a variable to double, take the number 70 and divide it by the growth rate of the variable.

Time to take for a population with Time to take for a population with a stable growth rate to double in a stable growth rate to double in sizesize

Doubling Time ( Doubling Time ( ttd d ) =) =

ttd d = 70= 70

rr

Doubling TimeDoubling Time

Doubling TimeDoubling Time

Growth Rate of a Pop.Growth Rate of a Pop.

rr = ( = (b - db - d ) + ( ) + (i - ei - e ) )b = .01b = .01 d = .005d = .005

i = .001i = .001 e = .01e = .01

Calculate growth rateCalculate growth rate

Calculate doubling timeCalculate doubling time

Proportion of a population to Proportion of a population to survive to survive to breeding agebreeding age

Type Type II= = survival survival decreasesdecreases with age with age

Type Type IIII = = survival survival doesn’t changedoesn’t change with with age age

Type Type IIIIII = = survival survival increasesincreases with age with age

SurvivorshipSurvivorship

Questions to consider

1. What kind of survivorship do humans have? Explain why you think this.

2. How does parental care affect the survivorship curves?

3. What kind of curve for a redwood tree? A sea turtle? A squirrel? Why?