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Transcript of Population Pyramids
- 1. Population Pyramids = graphicdevice that represents apopulations age and sexcomposition.Pyramid describes diagramsshape for many countries in1800s when was created.
2. A broad base of younger age groups andprogressively narrowing to apex as olderPopulations were thinned by death.Now there are many different shapes. 3. Quickly growing population of Kenya jas,most people in lowest age cohortsPercentage in older age groups declinessuccessively with markedly sloping sides.Typically female life expectancy isdecreased in older cohorts of lessdeveloped countries 50 for Kenya proportion of females in older age groupsis less than in Sweden or U.S. 4. In wealthy countries with very slow rate ofpopulation growth population is nearlyequally divided - so pyramids haveAlmost vertical sides.War can be reflected by showing depleted agecohorts and male female disparities.The % of a countrys population in each agegroup strongly influences demand for goods andservices within that national economy.Country with high % of young has high demandfor educational facilities and health deliveryservices. 5. Dependency Ratio = measure of # ofdependents old and young that each100 people in productive years (15 64)Must support.Population Pyramids show this.Population pyramids also foretell futureproblems from present population policiesor practices. Ex. Chinas populationpolicies skewed in favor of males. 6. Natural Increase = Rate of NaturalIncrease of population derived bysubtractingThe Crude Death Rate from the CrudeBirth Rate.Natural means increases or decreasesdue to migration are not included.This rate is usually expressed as a % orrate per 100 rather than 1,000.Doubling Time = Time it takes forpopulation to double. 7. Ex. 2% rate of increase recorded1999 by developing world except ChinaPopulation would double in 35 years since 1% rate would take 70 years todouble.Population Doubling Time estimated bydividing the Growth Rate into the number70 = ( 70 divided 2 = 35 years).Globally Rates of Increase have risenover history. Thus doubling time hasdecreased. 8. Should world fertility rates decrease - - ashave recently population doubling timeWill correspondingly increase as it hassince 1990.Even small annual additions accumulateto large total increments because ofgeometric or exponential (1,2, 4, 8)instead of arithmetic growth.Inevitable consequences of doubling or J-CurveGrowth. 9. The Demographic Transition someform of braking mechanism must operateto control totally unregulated populationGrowth voluntary or involuntary.Demographic Transition voluntaryrelation between population growth andeconomic development. traces changinglevels of human fertility and mortalityassociated with industrialization andurbanization. 10. This model assumes over time highbirth and death rates will slowly bereplaced by low rates.The 1st Stage = of process and demographictransition model characterized by high birthand high but fluctuating death rates. Whenbirths only slightly exceed deaths thepopulation will grow only slowly.From 1 AD to 1650 for population to increasefrom 250 million to 500 million = Doubling Timeof over millenium and a half. Offset bysometimes catastrophic decline like bubonicplague. This 1st Stage no longer found in anycountry. 11. This model was developed to explainpopulation history of Western Europe.Western Europe entered 2nd Stage withindustrialization 1750 its effects decliningdeath rates with high birth rates have dispersedworldwide without universal industrialeconomies.Rapidly increasing population during 2nd Stageresults from dramatic increases in lifeexpectancy. This reflects falling death rates dueto advances in medical and sanitation practices,rising per capita incomes, urbanization thatprovides environment where medicine and fooddistribution improvements are concentrated. 12. Birth rates dont fall as soon as deathrates cultural patterns change moreslowly than technologies.Many Latin American and South andSouthwest Asian countries showcharcteristics of 2nd Stage.Annual rates of increase of thesecountries are near or above 30 per l,000and their population will double in 20 to 25years. Means underdeveloped societieshave been beneficiaries of lifepreservation techniques. 13. Third Stage = when birth rates decline aspeople begin to control family size.Urban, industrialized societies may view kids aseconomic liabilities, instead of assets asagrarian societies do.When birth rate falls and death rate remains low population size begins to level off.4th Stage End of model final stage characterized by very low birth and death rates.This results in very slight % increases inpopulation and doubling times stretching to l,000years or more. 14. Extension of 4th Stage into 5th Stage population decrease has so far beenconfined to rich, industrialized countriesThroughout the world Europe andJapan.By 2010 most worlds population growthwill result from Demographic Momentum not 2nd Stage expansion.Original model made to describeNorthwest European countries as wentfrom rural-agrarian to urban industrial. 15. Beginning 1860 lst death rates thenbirth rates began gradual decline.= Mortality Revolution first came asepidemiological transition echoeddemographic transition to which itsassociated.Many formerly fatal epidemicdiseases became Endemic = continualwithin a population. As people developedpartial immunities mortalities with themdeclined. 16. Health of European population increasedwith improving animal husbandry, croprotation, etcSewage systems, sanitary water supplies common in larger cities hygieneimproved everywhere.Deaths associated with chronic illnessesassociated with maturing and agingpopulation increased.Passed to Age of Degenerative andHuman-Origin Diseases. 17. Increases recently in drug and antibioticresistant diseases, pesticide resistanceOf disease-carrying insects, and AIDScast doubt on finality of ultimate stage.In Europe decrease in death rates wasechoed by decreases in birth rates associeties altered traditional concepts ofideal family size.