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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
Scientists disagree on Earth's carrying capacity
Pre-Industrial Stage
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
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
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