Human Population

Chapter 4.2

World Population

• Census is taken every 10 years

• Demography = the study of human population size, density and distribution, movement and its birth and death rates

Human population growth

• Human population growth is different from bacteria population growth in that we can consciously change our environment– ex: we eradicated smallpox– ex: developed methods for producing more food– ex: infant mortality rate has decreased– ex: technological developments improved water

quality

• Result = live longer and produce more offspring that live long enough to produce more offspring

Calculating growth rate

• Determined by many factors: births, deaths, immigration, emigration– Birthrate: number of live births per 1000

population in a given year– Death rate: number of deaths per 1000

population in a give year– Immigration: movement of individuals into a

population– Emigration: movement out of a populations

Calculating growth rate cont.

Formula: (version 1)

(Birth rate + Immigration rate) – (Death rate + Emigration rate) = Population Growth Rate

Formula: (version 2… used often because immigration and emigration rates are not accurate)

Birth rate – Death rate = Population Growth Rate (PGR)

Calculating growth rate cont.

• If birthrate of a population = death rate of a population then PGR = 0– Population is changing, but it is stable

• If PGR > 0, more individuals are entering the population than leaving – Population is growing

• If PGR < 0, more individuals are leaving than entering– Populations might start decreasing

The effect of a positive growth rate

• If PGR = 1.7% in 1995 and then PGR = 1.3% in 2001– The world is populating, but just at a slower

rate

• Unless GROWTH RATE BECOMES NEGATIVE, the population continues to grow (just not rapidly)

Doubling time

• Doubling time: the time needed to double in size

• It depends on current population and growth rate– slow or negative growth rate it will take a long time– often called a “developed country”

• If there is a rapid doubling time often referred to as a “developing country”

Formula:Doubling time (in years) = 70 / annual percent

growth rate

Age structure

• The proportion of the population that are in different age levels

• Age structure graph tells you– how many males and females there are in a

population– how many people there are at each age level

• Rapidly growing countries have a wide base because a large percentage of the population is made up of children and teenagers

• A stable population has a fairly equal percentage of people in each age category

Ecology and growth

• Needs differ throughout the world• Some = concerned w/ basic needs. Others

= concerned about maintaining healthy conditions

• Resources that humans depend on daily– uncontaminated drinking water (and for

agriculture)– adequate sewage facilities– ability to provide food

Ecology and growth cont.

• Resources needed for life (struggling to survive)– food– water– (both can become scarce)

• Other problems = where to properly dispose of waste

• These conditions can lead to stress on current resources and contribute to spread of disease