The objectives of this activity are to make the student aware of the difference between exponential and logistic growth, how the growth rate impacts the existing population, and the importance of studying the world's population growth.

As you are working through this activity, write the answers to the questions on a printed copy of this web page and hand the completed activity to your instructor.

Name:

1. Use the links  http://www.jump.net/~otherwise/population/logistic.html
and  http://www.jump.net/~otherwise/population/exponent.html
to describe the difference between exponential and logistic growth.

• Question: What is the difference between exponential and logistic growth?

2.   Use the link http://www.jump.net/~otherwise/population/population.html
to give a definition of birth rate.

• Question: What is the definition of birthrate?

Experiment 1:

•  Run the Applet. You should leave the applet in the Graph view to help you interpret the results.
• Click Reset All to clear any past data. Now do a series of simulations using birth rates of 1.0, 1.2,1.4, 1.6, 1.8, and 2.0. Step or Run the population for 30 to 40 generations, or until the graph goes off the top of the window. Be sure to click the Reset button between each simulation in order to start over but leave the past results in place. Do this now.
• Question: What happens with an average birth rate of 1.0?

• Question: What happens with a birth rate of 1.2?

• Question: What happens as the higher birth rates get larger?

 Experiment 2:

• Click Reset All to clear any past data. Set the average birth rate to be 1.5 and Step the population through 15 generations. Now without clicking either reset button change the birth rate to 0.8. This change means that each individual is now only producing (on average) 0.8 individuals in the next generation. You would expect the population size to decline. Step through 20 or 30 more generations and observe the results.

• Question: What happens?

Use the link http://www.jump.net/~otherwise/population/logistic.html for Experiments 3, 4 and 5

 Experiment 3:

• In this experiment and those following, you should leave the applet in the Graph view to help interpret the results.  Click Reset All to clear any past data. Make sure the birth rate is set to 1.5. Now do a series of simulations using carrying capacities of 200, 400, 600, 800, and 1000. Step or Run the population for about 30 generations with each value of carrying capacity. Be sure to click the Reset button between each simulation in order to start over but leave the past results in place. Do this now.

• Notice that all the curves look similar for the first 10 or 12 generations. It is not until the population begins to near its carrying capacity that the curve deviates from the exponential growth curve.

• Question: What does the term carrying capacity mean?

• Click Reset All to clear any past data. Reset the carrying capacity to 1000. Now do a series of simulations using birth rates of 1.2, 1.4,1.6, 1.8, and 2.0. Step or Run the population for about 30 to 40 generations with each value of birth rate. Be sure to click the Reset button between each simulation in order to start over but leave the past results in place. Do this now.

• Question: Does changing the birth rate affect how quickly the population reaches its carrying capacity?  Does it have an affect on the final population size achieved?

Experiment 5:

• Click Reset All to clear any past data. Make sure the carrying capacity is set to 1000. Set the birth rate to 3.0 and Step or Run the population for 40 generations. Here we see something new!

• The population appears to be oscillating around the carrying capacity. Notice that with birthrates greater than 2.0 the population will overshoot the carrying capacity and have more offspring than the environment can support. The following generation, because of this overcrowding, the effective birth rate will be much less than 1.0 and the population will decline below the carrying capacity. Then it will overshoot again and the cycle will be repeated. You will notice that with time the overshoots get less and less and the population still appears to converge to its carrying capacity.