POPULATION GROWTH • For most of human history, humans have not been very numerous compared to other species. • It took all of human history to reach 1 billion. • 150 years to reach 3 billion. 12 years to go from 5 to 6 billion. Human population tripled during the twentieth century. • Changes in population size, density, dispersion, & age structure are known as population dynamics.
Population Doubling Times • Rule of Thumb: • In exponentially growing populations: • 70/annual % growth = Doubling Time • 70/2.0% = 35 years
Sample problems • r=1.7% in 1995, when does this population double? 70/1.7%=41years, so • 1995+41=2036
LIMITS TO GROWTH • Thomas Malthus (1798) argued human populations tend to increase exponentially while food production is plentiful. • Humans inevitably outstrip food supply and eventually collapse. • Human population only stabilized by positive checks. Human populations utilize resources that are not evenly distributed, this results in a clumped dispersion pattern.
Checks and Balances limit growthA. Resources not yet limited, can grow at intrinsic rate of increaseB. Stabilizing at carrying capacityC. Capacity for growthD. Limiting abiotic factors
Humans have extended the Earth’s carrying capacity, manifesting as exponential growth • By controlling many diseases • Improved hygiene • Using energy resources at a rapid rate • Using material resources at a rapid rate • Increasing our life spans • Expansion of agriculture • Increased industrial production
The Role of Technology • Technological optimists argue that Malthus was wrong in his predictions because he failed to account for scientific progress. • Current burst of growth was stimulated by the scientific and industrial revolutions.
Can More People be Beneficial? • More people mean larger markets, more workers, and increased efficiency due to mass productions. • Greater numbers also provide more intelligence and enterprise to overcome problems. • Human ingenuity and intelligence.
HUMAN DEMOGRAPHY • Demography - Encompasses vital statistics about people such as births, deaths, distribution, and population size. • October 12, 1999, UN officially declared the human population reached 6 billion. • Estimation at best.
Estimated Human Population Growth: more than 90% of all growth in the twentieth century and projected for this century is in less-developed countries.
Logistic growth of sheep, S shaped curveA. results from reproductive time lagB. Results from biotic potential & environmental resistance
Exponential growth of reindeerA. low carrying capacity B. area of sustained indefinite growth, but organisms have exceeded the carrying capacity C. Dieback after overshoot
Survivorship curve - probability of newborn individuals surviving to a particular age • Late Loss (Type I) ex. primatesConstant loss (Type II) - death is often unrelated to age, ex. Many bird speciesEarly loss (Type III) ex. Most fish and reptiles
Two Demographic Worlds • First is poor, young, and rapidly growing. • Less-developed countries. • Africa, Asia, Latin America • Contain 80% of world population, and will account for 90% of projected growth. • Second is wealthy, old, and mostly shrinking. • North America, Western Europe, Japan • Average age is about 40. • Populations expected to decline.
Fertility and Birth Rates • Crude Birth Rate - Number of births in a year per thousand. (Not adjusted for population characteristics) • Total Fertility Rate - Number of children born to an average woman in a population during her reproductive life. • Zero Population Growth - Occurs when births plus immigration in a population just equal deaths plus emigration.
Total Fertility Rates in the U.S.A. signifies increase in birth rates B. # of children to keep a constant population growth rate. Is the most useful measure of fertility used for projecting the future of a population.
Practice problems • 1. What is the annual % rate of natural change for a population in a city, say Calera, OK, if b=25/1000 & d=7/1000? • r= (25-7)/1000 x 100% • =18/1000 x 100%=1.8%
2. Predict the new population • N=20,000 in 2011 r=1.8% • i=600/yr and e=200/yr • N1 = N0 x r + (i-e) + N0 • (20,000x1.8%) +400+20,000 • (20,000x0.018) + 20,400 • 360 + 20,400= 20760
3. Net growth rate R0=N1/N0 • From previous problems N1= 20,760 and N0= 20,000 so R0= 20,760/20,000 =1.038 OR use this! r= (b-d)/1000 + (i-e)/20,000 So r= (25-7)/1000 + (600-200)/20,000 r= 0.018 + 0.02 = 0.038 or .38% Total would be 100% + .38% or 1.0 + 0.038= 1.038 Wanna check? .038 x 20,000 = 760 people from original problem!!!!!
Demographic transition: accompanies economic development & stabilization.A. High birth rate & high death rateB. Death rates decrease & birth rates are highC. Growth continues by slows D. ZPG
Mortality and Death Rates • Crude Death Rate - Number of deaths per thousand persons in a given year. • Poor countries average about 20 while wealthier countries average about 10 per 1,000 people. • Some rapidly growing countries have very low crude death rates compared to slower growing countries, due to a higher proportion of young people in the population. Highest b and d are in Africa.
r, intrinsic rate of increase r, intrinsic rate of increase is the rate at which a population would grow if it had unlimited resources. Also called population change. r= b-d or (b-d)+(i-e) b= birth rate/1000 d= death rate/1000 i= immigration e= emigration (emigration: a one-way movements out of a particular population to another area) For example, .0019 or 0.19%=r, resulting in slow population growth
Life Span and Life Expectancy • Life Expectancy - Average age a newborn can expect to attain in any given society. • Worldwide, average has risen from 40 to 65.5 over the past century. • Greatest progress has been in developing countries. • Annual income and life expectancy are strongly correlated up to about $4,000.00 (U.S.) per person.
Sample problem • Uganda crude birth rate = 48/1000 • Crude death rate= 18.4/1000 • r= b-d or (48-18.4)/1000 x 100%=2.96% • r= ? When b=22/1000 and d=9/1000 • r= 100% x 13/1000= 1.3%
As income rises, so does life expectancy up to about $4,000, with a few exceptions.
Demographic Implications of Living Longer • A population growing rapidly due to natural increase has more young people than a stationary population. • Natural Increase • (Crude Birth Rate - Crude Death Rate) • Both rapidly and slowly growing countries can have a problem with dependency ratio. • The number of non-working compared to working individuals in a population.
Age Structure DiagramsA. Increasing rapidly (unless d increases)B. Demographically divided (not socially equal)C. Stable, similar # of pre & reproductive ages D. Declining population Age structure is the # or % of persons of each sex at each age level.
ZPG • ZPG zero population growth: countries with ZPG show little variation in population by age= age structure diagram C
Age structure Diagrams • Rapid growth= broad base, more people at or below reproductive age, thus the greatest built in momentum for population growth.
Population Growth : Opposing Factors • Pronatalist Pressures • Factors that increase the desire for children. • Source of pleasure, pride, comfort. • Source of support for elderly parents. • Current source of family income. • Social Status • Replace members in society as they die. • Boys frequently valued more than girls.
Children in extremely rural areas often work at an early age.
Birth Reduction Pressures • Higher education and personal freedom for women often result in decisions to limit childbearing. • When women have more opportunities to earn a salary, they are less likely to have children: therefore birthrates decrease as development increases. • Education and socioeconomic status are usually inversely related to fertility in wealthier countries.
Birth Reduction Pressures Cont’d • In developing countries, higher income often means families can afford more children, thus fertility often increases. • In less-developed countries, adding another child to a family usually does not cost much, while in developed countries, raising an additional child can carry significant costs.
DEMOGRAPHIC TRANSITION • Model of falling death rates and birth rates due to improved living conditions accompanying economic development, or industrialization. • Pre-Developed Country - Poor conditions keep death rates high, thus birth rates are correspondingly high. • Economic Development brings better conditions and standard of living thus death rates fall. Birth rates stay constant or even rise.
DEMOGRAPHIC TRANSITION CONT’D • Eventually, birth rates begin to fall. • Populations grow rapidly in time between death rates and birth rates fall, this is due to economic development. • Developed Countries - Transition is complete and both death and birth rates are low and population is in equilibrium.
Children under 15 WILL make up a smaller percentage of world population than over 65.
By the numbers • Current fertility: 2.7 • Replacement level fertility: 2.1 • Infant mortality: # of children per 1000 that die by their first birthday. • 2 useful indicators of overall health of a country are: life expectancy & infant mortality rates. • Life expectancy: U.S. 78.3 (75.6m & 80.8f) • World 67.2 (65.0 males & 69.5 females)
Fast growth • 500,000,000 people with r=1.5% • 500,000,000 x .015= 4,500,000 each year • Slower growth, but higher r will be when the population starts smaller: • 10,000,000 with r=2.5% • 10,000,000 x .025= 250,000
Optimism or Pessimism • Some demographers believe the demographic transition is already taking place in developing countries, and world population should stabilize during the next century. • Others argue that many poorer countries are trapped in the middle phase of transition, and their populations are growing so rapidly that human demands exceed sustainable resource yields.
Social Justice • Still other demographers believe that in order for the demographic transition model to work, resources must be distributed more equitably. • The world has enough natural resources, but inequitable social and economic systems cause maldistribution.