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Human Population Principles

Slide 1 – Human Population Principles
Now that we have learned about the basics of ecology and the impact humans have on the
biosphere, let’s turn our attention to the principles and concepts related to population growth.
The growth of a population, or lack thereof, can have a significant impact on the individuals
within that population. In this lecture you will learn about population growth curves, population
demographics, and population pyramids. Once you complete this lecture you should be able to:
1. Discuss the effects of biotic potential and environmental resistance on population growth.
2. Define carrying capacity and explain what happens when animal populations exceed their
carrying capacity, as well as discuss how this principle is related to human population
3. Analyze population pyramids and compare the age distribution of the populations of less
developed and more developed countries, as well as, explain how age distribution affects
population growth and economic states.

Slide 2- J Curve
If we look at this graph, we will see a J curve. This J curve represents the maximum rate a
population can increase under ideal conditions. People in this type of population have as much
food as they need as much water as they need as much space as they need; this is known as the
biotic potential.

Biotic potential is influenced by food, birth rate, death rate, access to medicine etc. This J curve
is not very realistic.

Slide 3 – Limiting Factors
Because our environments are not always ideal, a J curve is really not the way populations grow.
At some point things become limited and a population reaches what is known as its carrying

Some of the limiting factors that increase the death rate of a population include interspecies
competition, intraspecies competition, disease, predators, and natural disasters. All of these play
an important role in controlling population size. One of the more interesting things that control
population size is the age of reproduction.

If a girl has a baby at the age of 12, then her child has a baby at the age of 12, and that girl has a
baby at the age of 12, the first girl will be a great, great grandmother by the time she is 60. On
the other hand, if a girl waits until she is 30 to have her first child and then that child waits until
she is 30 to have a child; the first girl will only be a grandmother at 60.

Slide 4 – S Curve
When we graph a population showing size controlled by limiting factors we get an S shaped
curve as opposed to the J curve we discussed earlier. Looking closely at the S curve you can see
that initially the population grows very rapidly, but as limiting factors increase the death rate, the
population begins to level off.

Slide 5 – Carrying Capacity
Population growth is also affected by carrying capacity. Carrying capacity is the number of
organisms an ecosystem can support indefinitely without using up its resources faster than they
can be replaced. The carrying capacity is the leveling off that we show in the S curve in the
previous slide.

Slide 6 – Island Picture
This is an island off the coast of Washington State. It was purchased by a group interested in
making it a private hunting island. The problem was that the island is in the middle of a busy
shipping channel. When the businessmen went to get the permits, they were denied by the Coast
Guard because of the potential for injury to vessels in the shipping channel. The sheep and deer
that live on the island began to overpopulate the island and have eaten most of the vegetation. If
something is not done to remove these animals, many are in danger of starving to death because
of the lack of food.

Slide 7 – Check Your Understanding
Now that we have learned about world population growth, let’s check your knowledge of the
subject. The following slides will have a series of questions on the topic. Be sure to click
“Submit” after answering each question.

Slide 8 through 13 – Human Population Growth Interactive Quiz
A non-graded assessment to test your understanding of human population growth.

Slide 14 – Human Population Growth
Now we will turn our attention to the topic of Human Population Growth.

Total fertility rate is the average number of children per woman (in a particular area or country).
Replacement level TFR = 2.1, if TFR drops below 2.1 and no immigration occurs, the population
size will decrease. A TFR of 2.1 indicates zero population growth. The population will not grow
or shrink, but stay at the same size.

Slight changes in the TFR for a country can have a tremendous impact in the world population.
For example if the world’s TFR is 2.1, by 2150 there will be a human population of >11 million,
however if the world’s TFR is 2.6, just a 0.5 difference, then the world’s population would be
>27 million by 2150.

Slide 15 – Population Pyramids
If we look at these population profiles, we can see a graphical representation of the age
distribution in a population.

On the left is a graph for a less developed nation. Most of the wide bars on the graph are at the
bottom, indicating that there is a broad base at the younger ages. In these countries 40-50% of
the population is under the age of 15. This could result in rapid population increases.

The graphs in the center and the right represent more developed nations. The wider bars are in
the middle and top, indicating that the heaviest part of the population is in their mid thirties to
forties. The chances for a large population booms to occur here are much, much lower.

These population profiles can help people figure out how to best utilize their resources. In the
less developed nation, they would need to increase education about birth control, increase the
number of schools for the children, and increase the roads and transportation systems to allow
access to education and medical facilities.

In the more developed nations, they will need to provide better services for the elderly including
nursing and rehabilitation homes, transportation and affordable medicine and medical care.

Slide 16 – Population Pyramid Video
A YouTube video about Population Pyramids

Slide 17 – Overpopulation
What happens when a population exceeds its carrying capacity? Think about the island we
discussed a few slide ago off the coast of Washington state. A population exceeding its carrying
capacity is similar to an individual living beyond their means. Eventually that individual will be
in severe debt. Instead of debt, populations that exceed their carrying capacity can crash. In
addition, overpopulation can lead to the loss of resources.

Slide 18 – Religion and Babies
A Ted Talk showing the statistics of population growth and religion.

Slide 19 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this lecture.
Be sure to review the questions you answered incorrectly.

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