1

Human PopulationGrowth

(a)time

(minutes)0

20406080100120140160180200220

number ofbacteria

1248

163264

128256512

10242048

carrying capacity

(biotic potential)

rapid growth

(environmental resistance)

equilibrium

Demography

• includes details of:– natality- birth rate (new births per unit time)– mortality- death rate (deaths per unit time)– age structure

• natality related to fertility rate and age structure of population

• mortality related to age-specific survivorship and age structure of population

• studied with respect to geography

• crude birth rate = # births/1000 people/yr• crude death rate = # deaths/1000 people/yr• Natural increase of a population

= (crude birth rate - crude death rate) (x 100)• Zero Population Growth Rate

crude birth rate = crude death rate• Total Growth Rate

includes immigration and emigration

2

Doubling Time• = number of years it takes a population to

double• calculate approximately by:

70 / annual growth as percentage• Examples:

70/35% growth rate=2 year doubling time70/4% growth rate=17.5 year doubling

time

Fertility Rates

• Total Fertility Rate = average number of children a woman will have during her entire reproductive life (based on current statistics)

• Replacement-level Fertility rates = average number of children a woman would have for replacement– varies between 2.1 and 2.5

Current Human Population• World population size > 6 billion people• World Natural rate of increase ~ 1.55 %• In one year,

(6 billion)(1.55%)=89.9 million added• World population doubling time

= 70/1.55 = 45.16 years• World Average Total Fertility Rate=3.0

children per woman

Cultural advances Agricultural advances Industrialandmedicaladvances

1999

1987

1975

1960

1930

1830

Is human population growth an environmental problem?

• Consider the following:• What are our “necessary” resources and do they

have unlimited availability?• Does earth have a carrying capacity for

humans?• How do we value the rights of other organisms?• environmental impact = (#people)(# units of

resources per person)(impact per resource unit)

• “developed country”, “more-developed country”, “MDC”– highly industrialized and high per capita GNP– examples: United States, Canada and Western

Europe, Japan, Australia, New Zealand • “developing country”, “less-developed

country”, “LDC”– low-to-moderate industrialization and low-to-

moderate per capita GNP– examples: most countries in Africa (e.g., Kenya,

Nigeria), Asia (e.g., India, Bangladesh, China), Latin America (e.g., Bolivia, Guatemala), former Soviet Union

3

Disparity between rich and poor

• developed nations have 21% of population but 80% of wealth

• developing countries have 79% of population but 20% of wealth

• 10-15% of people in developed countries are “poor”

• 90% in developing countries are “poor”

World average 1.4%

Developed countries 0.1%

Developing countries 1.7%

Africa 2.4%

Latin America/Caribbean 1.8%

Asia (excluding China) 1.7%

China 0.9%

N. America 0.6%

Europe – 0.1%

4

U.S. population (in millions)(1790-2000)

• fertility rates have declined• mortality rates have declined• population growth continues because

fertility rates still higher than replacement rates (which includes mortality)

• LDC’s tend to have higher fertility rates than MDC’s and higher population growth

In general:

5

• life expectancy = probable number of years of survival for an individual of a given age

6

Population Age Structure

• age structure diagrams are snapshots of populations at particular moment

• expanding population- lots of new births• stable population- few births• diminishing population-

natality<replacement

7

Population Momentum

• even once replacement level reached, population will continue to grow 50-60 years

• pyramid shaped age structure means that few move into upper age classes and many moving into reproductive age classes

Demographic Transition

High Birth RatesHigh Death Rates

Low Birth RatesLow Death Rates

Factors influencing family size

• security in one’s old age• infant and child mortality (overcompensate)• economic assets of having children• importance of education• status of women: education and jobs• availability of contraceptives

Birth Reduction Measures• decrease poverty• increase access to health care for infants,

children, women• increase access to family planning services• improve status of women

– education– job opportunities– increase involvement of men in family-

planning and child-rearing