Human Population Growth

1
Human Population Growth

• The human population is expanding exponentially.
• The doubling time is the length of time it takes
  for a population to double, currently estimated
  at 53 years.
• Only when birthrate equals death rate will there
  be zero population growth.

2
More-Developed Versus Less-Developed Countries

• Most of the expected increase in human population
  will occur in certain less-developed countries
  (LDCs) of Africa, Asia, and Latin America.
• Doubling time in more-developed countries (MDCs)
  is about 100 years because a decrease in death
  rate due to medical advances was followed by a
  decrease in birth rates.

3
Standard of living
4
World population growth
5

• The relationship between decreased death rate
  followed by a slower birth rate is called
  demographic transition.
• Despite introduction of medical care, LDCs still
  have twice the MDC growth rate.
• Support for family planning, social progress, and
  delayed childbearing could help prevent an
  expected increase in population size.

6
Age Distributions

• Many MDCs have a stable age structure, but most
  LDCs have a youthful profilea large proportion
  of the population is younger than age of 15.
• This means their populations will expand greatly
  in the near future.
• Zero population growth or replacement
  reproduction does not occur when each couple has
  only two children because there is momentum from
  younger women entering reproductive years.

7
Age-structure diagram for MDCs
8
Age-structure diagram for LDCs
9

• Summary
• Population size depends upon births, deaths,
  immigration, and emigration.
• Exponential and logistic patterns of population
  growth have been developed.

10

• Life history patterns range from one in which
  many young receive little care to one in which
  few young receive much care.
• The human population is still growing
  exponentially, and how long this can continue is
  not known.

11

• Factors that affect population size are
  classified as density-independent and
  density-dependent.
• Predation often reduces prey population density,
  which in turn can lead to a reduction in predator
  population density.