Population Growth

This lesson will introduce you to some basic concepts of population growth and allow you to experiment with them using the included Java applets.

The term "population growth" refers to how the number of individuals in a population increases (or decreases) with time. This growth is controlled by the rate at which new individuals are added to the population -- the birth rate, and the rate at which individuals leave the population -- the death rate.

There are many types of plants and animals, and different types show different kinds of population growth. In this lesson we will consider a very simple type of growth where the animals in one generation give birth to the next generation and then die. Because the parents die immediately after giving birth, at any given time all individuals in a population are of the same age. This pattern of reproduction is very common in insects and some species of fish.

The number of children a parent gives birth to is known as the birth rate. If all individuals in a population have two children then the birth rate will be 2. However, it is not necessary for the birth rate to be a whole number such as 1, 2, 3, etc. For example, if half the individuals of the population have 2 children and the other half have 3, then on average the birth rate will be 2.5. Likewise, if the population consists of equal numbers of males and females, and if the females give birth to 3 children each (and the males 0), then the average birth rate of the population will be 1.5.

With these basics we can now consider two simple models of population growth:

• Exponential Growth
• Logistic Growth.

These pages describe each growth model and provide several experiments you can perform using the included Java applets. The experiments will help you to better understand that type of population growth. Follow the links and do the experiments there before returning to the discussion below.

Discussion

One of the greatest dangers planet Earth faces today is that of over-population by humans. Since the beginning of human history our population has been growing exponentially (actually a little faster than exponentially). However, there is now little additional land that can be put into use for food production and our wastes are rapidly polluting the environment. Unless major technological breakthroughs are made, we are close to the the Earth's carrying capacity.

Compounding the problem is the fact that our average birth rate is still very high (greater than 2.0). It is possible we will overshoot the Earth's carrying capacity and for the first time in recorded history have massive population decline brought on by disease and starvation. You have seen how sensitive a population's growth is to the its birth rate. The decrease in birth rate needed to avert a disaster is not large, but it is one that everyone needs to work on together to achieve.