Overview & Lesson Sequence

Focus on Standards & Assessment

Materials Needed, Preparation & Planning, Management Strategies

Background Info

Intro Activity
Why Study Populations?

Meet the Aphids

Research Project
Aphid Population Growth

Data Analysis I

Data Analysis II

Optional Activity
The Power of Exponential Growth

References

Glossary

Suppliers

Resource Sheets

Great Gravidity Home

CISEO Home

Data Analysis II

Materials Needed per group

• Flip chart paper, poster boards or
• other display materials
• Marker pens

Class Time Required
30 minutes for groups to finalize their data and develop their presentation

15 minutes for each group to present their data to the class

30 minutes for a final class discussio

At the end of the long-term project, use this activity to help students interpret their data. This activity helps students make final interpretations of their data and present their conclusions formally to the class. Interpretations of their aphid population data lead to making generalizations about populations, which illustrate students' understanding of population ecology concepts.

Procedure
Have each student group complete their data analysis and finalize graphs drawn in Data Analysis I or draw new graphs. Ask the following questions to help students prepare for their formal presentations to the class:

How close did your predictions (graphs and results of exponential growth calculation) come to reality? Why or why not?

What does the shape of your graphs tell you about the change in the population over time? (Change over time will be small at first, then increase over time and may level off at some point.)

What is the rate of change for your population? (Rate is always a change in a variable over some time period, e.g., miles per hour. A population may grow or recede depending on the birth rate, death rate, immigration rate, and emigration rate. The independent variable is always the number of individuals and the dependent variable is always time.)

What affects rate of change? (In a closed system, the population grows or recedes based only on number of birth and deaths. These births and deaths result from the environmental conditions.)

Ask each student group to present their graphs and results to the class (see the Rubric for Group Presentations). Once all the student groups have made their formal presentations, facilitate a discussion of the major concepts in population growth.

At the beginning of the long-term project, the aphid population growth most likely represented exponential growth or a "J" curve. On the board, represent exponential growth as some number with an exponent (e.g., 9² = 81). You may want to graph or have students graph the numbers so they observe the mathematical expression as a "J" shape . Ask them what would happen if this "population" grew unchecked. (The population would continue to grow exponentially.) Assuming the population is insect pests, what might be the best time to control the population? (Somewhere near the beginning, before the population grows out of control.)

At least one or two graphs should start to show a leveling off. What might have caused this? (The leveling off is called "carrying capacity." When populations reach their carrying capacity the graph resembles an "S".)

What then is the number that represents carrying capacity of the aphid population? (Students should give the number on the Y-axis where the population levels off. This number corresponds to births minus deaths.) How might the graph change after the carrying capacity is reached? (Adverse conditions increase the death rate; beneficial conditions may increase the birthrate.)

Some populations may decrease dramatically, i.e., all individuals may die. Ask students what factors may have caused this and (approximately) how low the number of individuals could go before extinction is threatened. What does extinction look like on a graph? (Generally, a rapid, sometimes exponential decline to zero; reverse of the "J" curve.)

Facilitate a discussion of environmental factors that affected, or would affect, the birth and death rates of aphids. These will include the availability of water/moisture, light, and food as discussed in Meet the Aphids. What else affects birth and death rates? (Disease, predation, random events)

Your students might be bewildered because their data and graphs don't resemble others in the class. Remind them that results are alike only when the conditions of the experiment are exactly the same. Have students pool their data in a computer spreadsheet program such as Excel. Discuss the relationship between data outliers, sample size and reliability. Also ask the students: What is a "right" answer in scientific research? How does variability affect finding the right answer? Ask the students if they think the system (pea plant and aphids) is really a "closed" system.

Finally, review students' questions about populations and population growth listed at the beginning of the lesson and those which may have been added later in the lesson. Unanswered questions may be assigned for extra credit and/or research projects.

Assessment
Over the course of this activity use the Observation Check sheet to record the students' ability to describe the relationship of a

population to its environment, and population growth rates using graphical analysis.

Use a rubric to assess presentations. (See Rubric for Group Presentations.) Share the rubric with the students. You might want to ask them for input in constructing their own rubric.