世界人口分布.ppt

世界人口分布 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望 http:/ 起重机 立体停车设备 电动葫芦 http:/ 衬塑复合管 涂塑复合管 钢塑复合管 消防涂覆钢管World populationPopulation growthn nDefinition:how the number of individuals Definition:how the number of individuals in a population increases or decreases in a population increases or decreases with timewith timen nGrowth is controlled by rates of birth,Growth is controlled by rates of birth,immigration and death and emigration.immigration and death and emigration.n nOpen or closed population:no immigration Open or closed population:no immigration and emigration,or immig.=emig.and emigration,or immig.=emig.n nIn closed population,growth is determined In closed population,growth is determined by birth rate and death rate.by birth rate and death rate.10.1 Population growth reflects the difference between rates of birth and deathn nModel developmentModel developmentn nA population of freshwater hydra growing in an aquarium in A population of freshwater hydra growing in an aquarium in the laboratory.the laboratory.n nPopulation size N(t)when time is t.Population size N(t)when time is t.n nThis is a closed population.This is a closed population.n nPopulation size change is related to birth rate(b)and death Population size change is related to birth rate(b)and death rate(d)rate(d)n ndN/dt=(b-d)N=rN dN/dt=(b-d)N=rN n nThe difference between birth rate and death rate is the The difference between birth rate and death rate is the intrinsic growth rate(r)(instantaneous per capita rate of intrinsic growth rate(r)(instantaneous per capita rate of growth).growth).r=b-d r=b-dn nIn a closed population,population size In a closed population,population size change is related to birth rate(b)and change is related to birth rate(b)and death rate(d)death rate(d)n nThe difference between birth rate and The difference between birth rate and death rate is the intrinsic growth rate(r)death rate is the intrinsic growth rate(r)(instantaneous per capita rate of growth).(instantaneous per capita rate of growth).r=b-d r=b-dn nPopulation growth is related to this Population growth is related to this intrinsic growth rate(r).intrinsic growth rate(r).Exponential population growthn nEquations:1)dN/dt=rN(differential equation form)1)dN/dt=rN(differential equation form)2)N2)N(t)(t)=N=N(0)(0)exp(rt)(exponential growth exp(rt)(exponential growth model)model)n nConditions:Initial population is smallInitial population is small No food or resource limitationNo food or resource limitationAn exampleReindeer,St.Paul,Alaska.Started in 1910 with only 4 males and 22 femalesIn 1940,there were nearly 2000 Whooping crane,an endangered speciesrecovered from near extinction in 1941How to calculate r?Software,Excel(trendline)Aransas National Wildlife RefugeProperties of exponential growthr determines the shape of the growth.r=0,no change in population sizer0,increase in population size.Properties of exponential growthWidely used in biologyN(t)=N(0)Exp(rt)Give a time t,we can predict the population size.An Example:Deer population:N(0)=300,r=0.5,after 5 years,whats the population size?N(5)=N(0)Exp(rt)=300*exp(0.5*5)=3655(495,815,1344,2216,3655)t=10,?Prediction of population growth4452410.2 Life tablen nLife table is an Life table is an age-specific age-specific account of account of mortality.mortality.n nPurpose of life Purpose of life table:to provide a table:to provide a clear and clear and systematic picture systematic picture of mortality and of mortality and survival within a survival within a populationpopulationHow to construct a life table?n n1.start with a 1.start with a cohort:a group of cohort:a group of individuals born in individuals born in the same period of the same period of time;time;n n2.Add a column of 2.Add a column of l lx x as the probability as the probability at birth of at birth of surviving to any surviving to any given age;given age;How to construct a life table(cont.)?n n3.calculate d3.calculate dx x,a,a measure of age-measure of age-specific mortalityspecific mortalityn n4.Calculate age-4.Calculate age-specific mortality specific mortality rate,qrate,qx x10.3 Different types of life tablen nTwo typesTwo types Cohort or dynamic life tableCohort or dynamic life tablen nas the above gray squirrelas the above gray squirrel Time-specific life tableTime-specific life tableElf opine10.4 Life tables provide data for mortality and survivorship curvesn nTable is better than words,but a graph is worth one thousand words.n nMortality curve and survivorship curve.Mortality curvesSurvivorship curvesLog scale for Y axisThree basic types of survivorshipType I(convex)Humans and other mammals and some plants (k-selection)Type II(survival rates do not vary with age)Adult birds,rodent,and reptiles,perennial plantsType III.ConcaveMortality rate high in the beginning(r-selection)Oysters,Fish,many plant species(most trees)10.5 Birthrate is age-specificCrude birthrate(demographers):#of birth over a period of time divided by population size at the beginning of the period*1000Age-specific birthrates,bxMean#of females birth to a female in each age group.(Only females give birth;birth rates vary with ages)Gross reproduction rate:sum of the bx values across all age classes,provides an estimate of average offspring born to a female over her lifetime.10.6 Birth rate and survivorship determine net reproductive raten nFecundity table:Fecundity table:take survivorship take survivorship column,lcolumn,lx x,from life,from life table and add age-table and add age-specific birthrate,bspecific birthrate,bx x.n nNet reproduction Net reproduction rate,Rrate,R0 0:number of female number of female offspring a female at birth can offspring a female at birth can produce (or average#of produce (or average#of females that will be produced females that will be produced(left)during a lifetime by a(left)during a lifetime by a newborn females.)newborn females.)n nR R0 0:depends on:depends on survivorship and survivorship and fecundityfecundityn nR0=1,1 or 1 or 110.7 Project population growthn nGiven a population with age structure and Given a population with age structure and some other information(age-specific some other information(age-specific mortality rates and birthrates),we can mortality rates and birthrates),we can project future changes of the population project future changes of the population size.size.n nFor example,a population of squirrel with For example,a population of squirrel with 10 adults(1-yr)and 20 juveniles 10 adults(1-yr)and 20 juveniles females,what would happen in the next females,what would happen in the next 10 years?10 years?n nWhat do we need to project future population size change?Calculate age-specific survivor rate:sx=1-qxbx is age-specific birthrateHow to construct a population projection table?How to construct a population projection table?Population size(N)increases every year.Lambda(finite multiplication rate):=N(t+1)/N(t).Age distributionStable age distribution:by year 7,the proportion of each age group remain the same year after year.Population is still growing.Geometric growth vs exponential growthn nN(t)=N(0)N(t)=N(0)t tn nN(t)=N(0)exp(rt)N(t)=N(0)exp(rt)n n =exp(r)or r=ln(=exp(r)or r=ln()n nThese models are used to describe These models are used to describe dynamics of populations.Geometric dynamics of populations.Geometric growth is used for population generations growth is used for population generations not overlap(discrete time interval),not overlap(discrete time interval),exponential growth model is for exponential growth model is for continuous population.continuous population.Fig.11.3Fig.11.310.8 Stochastic processes can influence population dynamicsn nWhats stochastic process?Whats stochastic process?n nDeterministic process:Given a set of Deterministic process:Given a set of initial conditions(N(0),r),the initial conditions(N(0),r),the exponential growth will predict only one exponential growth will predict only one exact outcome.exact outcome.n nBut the age-specific mortality rates,birth But the age-specific mortality rates,birth rates represent probability and averages rates represent probability and averages derived from the cohort or population derived from the cohort or population under study(bx=2?0,1,2,3).under study(bx=2?0,1,2,3).Stochasticityn nDemographic stochasticity:stochastic(or Demographic stochasticity:stochastic(or random)variations in birth and death random)variations in birth and death rates that occur in populations from year rates that occur in populations from year to year.(Cause change in r).to year.(Cause change in r).n nEnvironmental stochasticity:Random Environmental stochasticity:Random variation in the environment,such as variation in the environment,such as annul variation in climate and natural annul variation in climate and natural disasters can have a direct influence on disasters can have a direct influence on average birth and death rates within the average birth and death rates within the population.population.10.9 Population extinctionn nIf r becomes negative If r becomes negative(birth rate death(birth rate death rate),population rate),population declines and will go declines and will go extinction.extinction.n nFactors:Extreme Factors:Extreme environmental events environmental events(droughts,floods,cold(droughts,floods,cold or heat etc),or heat etc),loss of loss of habitat habitat(human).(human).n nSmall populations are Small populations are susceptible to extinctionsusceptible to extinctionAllee effect,genetic drift,inbreeding(mating between relatives)Overgraze,only 8 in 1950n nHackney and McGraw(West Virginia University)examined the reproductive limitations by small population size on American ginseng(Panax quinquefolius)Fruit production per plant declined with Fruit production per plant declined with decreasing population size due to decreasing population size due to reduced visitation by pollinationreduced visitation by pollinationn nSmall population size may result in the breakdown of social structures that are integral to successful cooperative behaviors(mating,foraging,defense)n nThe Allee effect is the decline in reproduction or survival under conditions of low population densityn nThere is less genetic variation in a small population and this may affect the populations ability to adapt to environmental changeENDGeometric Growthn nWhen generations do not overlap,growth can be modeled geometrically.N Nt t=N=No ot t N Nt t=Number of individuals at time t.=Number of individuals at time t.N No o=Initial number of individuals.=Initial number of individuals.=Geometric rate of increase.=Geometric rate of increase.t=Number of time intervals or t=Number of time intervals or generations.generations.Exponential Growthn nContinuous population growth in an unlimited environment can be modeled exponentially.n nAppropriate for populations with overlapping generations.As population size increases,rate of As population size increases,rate of population increase gets larger.population increase gets larger.