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In most cases exponential growth halts when an environmental limit is reached.

These are called limiting factors.

What are some examples?

Replacement-level fertility in the US is 2.1

In Uganda it is 5.8

Why would total fertility rate (TFR) vary greatly depending on where you live??

It is not always 2! Demographers have to consider prereproductive mortality into the calculations. In developing countries like Uganda it is much more common for a child to die. To replace the parents, a child has to live to reproductive age.

To understand a changing population demographers look at total fertility rate (TFR)

The average number of children that each woman in a population will bear in her lifetime

Replacement-level fertility

The average number of children a woman must bear in her lifetime to replace herself and her partner.

Other helpful demographic equations

In 2013 TFR for the United Sates was 2.06, meaning that on average each woman of childbearing age would have just over 2 children.

But in Uganda the TFR was 6.06.

Population density = # of individuals

area

% change = new-old x 100

old

New population size =

Population size x (1 + % increase in decimal form)

If demographers wanted to calculate the growth rate for an individual nation and not the globe, then they would have to consider immigrants and emigrants using the following formula:

National growth rate =

(births + immigr) - (deaths + emigr) x 100

total population

Worldwide, there were 20 births and 8 deaths per 1000 individuals in 2009.

So, to calculate the percent growth we use the following formula:

Global population = CBR-CDR x 100

growth rate 1000

The study of human populations, their characteristics and how they change

Demography

To determine birth and death rates demographers use specific measurements.

Crude birth rate (CBR)

Number of births per 1000 individuals per year

Crude death rate (CDR)

Number of deaths per 1000 individuals per year

Demographers use a formula called the Rule of 70 to estimate how long it will take a population to double in size assuming the growth rate stays the same

Doubling time (in yrs) = 70

growth rate

**growth rate is always left as a %**

Human populations can be viewed as systems with inputs and outputs...just like all biological systems.

If there are more births than deaths, then the inputs are greater than the outputs and the system expands.

Other things to consider is immigration and emigration!

Demography measures things like:

birth rate

death rate

fertility

population size

income

There are a few formulas demographers use to measure populations.

One of the most common is to calculate the % growth (or decline) of a population

% growth= births-deaths x 100

total population

Age Structure Diagrams

Anything else you can think of that would affect a populations demographics?

Can also be call histograms or pyramids

Is earth overpopulated?

Demographic Transition

Scientists disagree on Earth's carrying capacity

Pre-Industrial Stage

The maximum population a habitat can sustain indefinitely

Fig. 8-11, p. 169

At first a population grows rapidly because resources are abundant

As a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth

Survivorship Curves

As the population grows, resources become less abundant and the population fluctuates around the carrying capacity

Birth rates are high and death rates are high therefore the population is not growing

Growth and reproduction patterns

r- Selected

Reproduce young, large # of offspring, little or no parental care, short lives

Figure 8-9

K- Selected

Food, water, oxygen, increase in predators, disease

Reproduce later in life, few offspring, a lot of parental care, long lives

Harsh living conditions lead to high birth and death rates

Figure 8-9

Transitional Stage

Birth rates are high and death rates are low therefore the population is growing rapidly

As industrialization begins, food production rises and health care improves

Industrial Stage

Postindustrial Stage

Birth rates decline and death rates are still low therefore the population is no longer growing

Birth rates decline even lower and death rates are still low therefore the population is declining

Industrialization is wide spread, infant mortality declines and use of birth control rises

Health care is wide spread

Earth's carrying capacity for humans

Where are we now?

Some scientists believe we will never reach Earth's carrying capacity for humans because of human intellect and innovation

But, because the human population is growing exponentially, there is major concern how we will be able to feed everyone

7.3 billion

325 million

Human Growth

What caused the increase in human population growth?

Industrial Revolution

&

Medical Advancements

Survivorship Curves

Type I

Type II

Type III

The populations of different species vary in

how long individual members typically live.

So what is the solution??

As a woman's education increases, fertility generally decreases

Educated and working women tend to have fewer children than other women and delay having children because of the demands of school and work.

They also are more likely to have information about and money for contraceptives

Population size is a critical factor in the impact of humans on Earth

In developing countries, the urban areas are lacking safe drinking water, sewage treatments, solid waste disposal

Often the very poor who are unable to afford permanent housing are the residents of urban areas

They quickly become overcrowded and dangerous

Most densely populated place in the US?

10,400 people / sq km

New York

Most densely populated place in the world?

23,000 people / sq km

Mumbai, India

The amount of resources each person uses is also a critical factor!

means per person

Generally the more technology we have the more the environmental impact

*even less straight forward!

(helpful & destructive technology)

Decreased per capita ecological footprint because of public transportation and close proximity to shopping and work

Environmental Considerations with Urban Areas

Increased solid waste, pollution, carbon dioxide emissions, potential for the spread of diseases

Created by economic opportunity.

The more affluent a person or society is, the greater the impact.

*less straight forward

IPAT Equation

Impact = Population x Affluence x Technology

More people means more impact on the environment.

*straight forward

1/2 of the human population lives in urban areas

But, they consume 3/4 of Earth's resources!!

Urbanization

An area has to have 386 people per square kilometer to be considered urban

Human Population Notes

Environmental Impacts of a growing population

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