Topic 8: Human Populations

consequences of exponential growth

* increased demand for food/water/land
* demand for food → raising livestock → deforestation
* loss of habitat endangers species
* loss of forest degrades air/water quality
* congested areas promote spread of disease
* more pollutants released
* more waste generated

crude birth rate (CBR)

number of live births per 1,000 people in a population per year

CBR = births / population \* 1,000

crude death rate (CDR)

number of live deaths per 1,000 people in a population per year

CDR = deaths / population \* 1,000

natural increase rate (NIR)

rate of population growth, not accounting for immigration of emigration; percentage

NIR = (CBR - CDR) / 10

doubling time (DT)

time (years) for a population to double

DT = 70 / NIR

replacement level fertility

the number of children a couple must have to replace them (2.1)

total fertility rate (TFR)

estimate of the average number of children a woman will have per year, if she passes through her childbearing years conforming to the age-specific fertility rates of a given year

TFR > replacement level

population growth

TFR < replacement level

zero/negative growth

contributing factors to total fertility rate (TFR)

* urbanization
* increasing opportunities for women
* reduce infant mortality rate
* delay women’s age when she first gives birth
* pensions for retirees
* availability of abortions & birth control
* avoiding dogmatic religion & tradition statutes

factors that reduce death rates:

* urbanization (more resources/medicine)
* better healthcare
* increased access to food
* sanitation and potable water

first stage of the demographic transition model (DTM)

* ex: a few remote groups
* CBR: high
* CDR: high
* increase: stable/slow
* reasons for changing birth rate:
* children work
* high infant mortality rate
* religion/societal pressures
* no family planning resources
* reasons for changing death rate:
* disease/famine
* little to no medical care

second stage of the demographic transition model (DTM)

* ex: Egypt, Kenya, India
* CBR: high
* CDR: falling rapidly
* increase: rapid
* reasons for changing birth rate:
* children work
* high infant mortality rate
* religion/societal pressures
* no family planning resources


* reasons for changing death rate:
* medical care
* good water/sanitation
* more children live

third stage of the demographic transition model (DTM)

* ex: Brazil
* CBR: falling
* CDR: falls slowly
* increase: slower
* reasons for changing birth rate:
* more medicine/food
* reasons for changing death rate:
* medical care
* good water/sanitation
* more children live

fourth stage of the demographic transition model (DTM)

* ex: US, Japan, UK
* CBR: low
* CDR: low
* increase: stable/slow
* reasons for changing birth rate:
* urbanization
* healthcare
* family planning
* reasons for changing death rate:
* healthcare
* reliable food source

age-gender pyramids

shows the proportion of the population, by sex, at each for different age levels

How do predictions made about population growth by age structure diagrams influence economic decisions?

* pensions
* social security
* job competition
* more people = more consumers = greater need for jobs
* large population provides a taxable base for supporting retirees
* more people = greater environmental footprint

factors contributing to population growth

* universal access to family planning
* better healthcare for pregnant women/children
* equality- more opportunities for women
* increased access to education
* increased involvement in child-rearing for men
* eradicate poverty
* sustainable use of natural resources
* cultural attitudes about family size
* government policies

abiotic factors

* light
* temperature
* nutrient level

biotic growth factors

* high reproductive rates
* generalized niche
* adequate food supply
* suitable to habitat
* ability to compete for resources
* ability to hide/defend from predators
* ability to migrate/live in other habitats
* ability to adapt to environmental change

biotic decrease factors

* low reproductive rate
* specialized niche
* inadequate food supply
* unsuitable/destroyed habitat
* too many competitors
* can’t run/hide from predators
* can’t resist disease/parasites
* can’t migrate
* can’t adapt to environmental change