17.0147.014Lecture 29 & 30:Lecture 29 & 30:Population GrowthPopulation GrowthApril 30 & May 2April 30 & May 220072007Population Age DistributionMore Developed CountriesAge IntervalNumber of people (Millions)FemalesMales80 - 9070 - 8060 - 7050 - 6040 - 5030 - 4020 - 3010 - 20 0 -10Long periods ofno net growth lead toeven distributionPopulation Summary forthe US200020252050http://blue.census.gov/Population Age DistributionLess Developed CountriesAge300300Number of people (Millions)FemalesMales2Population Summary forUganda200020252050http://blue.census.gov/Very high reproductive rateLife Tablesx = age or interval (defined)N0 = number of individuals in original cohort (defined)dx = number of original cohort dying during intervalNx = number of individuals surviving to age x (measured)lx = proportion of individuals surviving to age xlx = Nx / N0mx = per capita births during age interval x to x+1 (measured) “age specific fecundity” = female offspring produced per female Age Number Surviving Proportion Surviving X Nx lx 0 100 1.0 1 50 .5 2 40 .4 3 30 .3 4 0 0 A COHORT LIFE TABLE (for Unicorns)N0 = 100lx = Nx/NoSURVIVORSHIP CURVESAgeLog (Number Surviving)Type IType IIType IIIHigh Probabilityof SurvivalSteady SurvivalHigh Probabilityof SurvivalLow Probabilityof SurvivalLow Probabilityof Survival3SURVIVORSHIP CURVESHomo sapiensSpergula vernalis(grass)Common BirdSpeciesAgeLog (Number Surviving)AgeLog (Number Surviving)AgeLog (Number Surviving)SeeFig 5 4 . 1Purves Age Number Surviving Proportion Surviving Average Offspring per female of age x (age-specific fecundity ) X Nx lx mx 0 100 1.0 0 1 50 .5 4 2 40 .4 2.5 3 30 .3 0 4 0 0 0 A COHORT LIFE TABLE (for Unicorns)N0 = 100 Age Number Surviving Proportion Surviving Average Offspring per female of age x (age-specific fecundity) Realized Fecundity Values X Nx lx mx lxmx 0 100 1.0 0 0 1 50 .5 4 2 2 40 .4 2.5 1 3 30 .3 0 0 4 0 0 0 0 R0 = ! lxmx = 3 A COHORT LIFE TABLE (for Unicorns)N0 = 100R0 = Net Replacement = 3What if you can’t follow cohort?Mastodon Skeletonhttp://www.state.nd.us/ndfossils/Education/animals/mastodon%20%20030612.html4 Age Interval X Number Surviving at Beginning of X Nx Number Dying dx Proportion Surviving by Age X lx 0 100 50 1.0 1 50 10 .5 2 40 10 .4 3 30 30 .3 4 0 0 0 A STATIC LIFE TABLE (for Unicorns)Sample of 100 unicorns N0 = 100measuredNx – dx = Nx+1lx = Nx/NoLecture 30Lecture 30Equilibrium Densityr = (b – d)b = d thus r = 0Density-Dependant Factors Regulate Population Sizeb = dPopulation Density (N)Density-dependent deathrate, dDensity-dependent birthrate, bstabilizingb> d, N b< d, NNOTE:Ignore slide on websiteUS Population ClockUS Population Clockhttp://www.census.gov/cgi-bin/popclock12122626131388295,974,238295,974,2382005200511 seconds11 seconds13131111Net gain of oneNet gain of oneperson everyperson every27 seconds27 seconds25252222One internationalOne internationalmigrant (net) everymigrant (net) every13 seconds13 seconds12121313One death everyOne death every8 seconds8 seconds9988One birth everyOne birth every301,723,494301,723,494Total PopulationTotal Population2007200720042004200320034/29/2007 at 14:13 AM EDT5Simulation of Human Population Growthover Earth HistoryTake a Look….moviestart at 53 secondsjump to 2:11Human Population GrowthYearPopulation (Billions)123456Agriculture &domestification ofanimals4 million7 millionHunterGatherersAdapted from: Cohen, “How Many People Can the Earth Support”10,000 BC 8,000 BC 2,000 AD04,000 BCBubonic PlagueIndustrial Revolution(1400)(1800)Modern Medicine(reduced mortality)(1900)FossilFuel6,591,890,041(4/29/2007)http://www.census.gov/main/www/popclock.html6,363,174,549(4/28/2004)6,432,150,287(4/22/05)Now projected toreach 9 Billionand level off6 Billion(1999)6,289,870,258(4/30/2003)Four “Evolutions” in Human Population GrowthAdapted from: Cohen, “How Many People Can the Earth Support”Evolution Driver Midpoint Population (billions) Doubling Time (years) before after Local Agriculture 8000 B.C. 0.005 40,000 - 300,000 1,400 – 3,000 Global Agriculture 1750 A.D. 0.75 750 – 1,800 100 – 130 Public Health 1950 2.5 87 36 Fertility Control 1970 3.7 34 (peak) >40 (since 1990) F and recall from an earlier lecture and recall from an earlier lecture …………Population size (billions)Population size (billions)COCO22NN22O (310 x COO (310 x CO22))CHCH4 4 (21x CO(21x CO22))Population sizePopulation size38038034034030030026026018001800140014001000100060060000 10001000500500 15001500 20002000COCO22 and N and N22O O ppmVppmVTime, Calendar years (A.D.)Time, Calendar years (A.D.)CHCH44 ppbVppbV66442200Falkowski and Tchernov 20046Demographic TransitionDemographic Transitionextremely important concept!extremely important concept!Stage 1High birth rateHigh, but fluctuatingdeath rateStage 2Declining death ratesContinuing high birthratesStage 3Declining birth anddeath ratesStage 4Low death rateLow, but fluctuatingbirth rateDemographic TransitionKrebs, 2001 (Figure 28.2)b >> db >> db = db = dhttp://www.census.gov/ipc/prod/wp02/wp02-1.pdfTime it takes to add a billionTime it takes to add a billiondoubling time52 yearsdoubling time54
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