3. ecologist
fluctuation
introduced species
population

4. How can you decide whether a species is successful in its environment?
Record your answer in your notebook.

5. Anticipation guide
Complete the “Before” column of Student Sheet 77.2, “Anticipation Guide: Introduced Species – Zebra Mussels.”

6. Read the introduction and look for key ideas
One example of an
invasive species

7. How do scientists study the size of a population and predict future population changes?
Sea lions on a beach

8. Complete the procedure and record your data

9. SCORING GUIDE: Organizing Data

10. How did your conclusions change?
How do ecologists know that they have sufficient data for a population over time? Share your thoughts with the class.

11. In what ways might being able to predict the future size of a population be useful?
Share your thoughts with the class.

12. Analysis question 1
a. Sketch a line on your graph predicting what you think will happen to the size of this population of zebra mussels during the ten years after b. Explain your prediction. Why do you think the graph will look that way? c. What additional information would make you more confident of your prediction? Explain.

13. Analysis question 1

14. Analysis question 2
a. What factors do you think affect the size of a population? b. Explain how each factor might affect population size: Would it cause the population to increase, decrease, or stay the same? Why?

15. What factors may have caused these very different patterns?
Share your thoughts with the class.

16. Analysis question 3
As you know from your own graph, data were not collected every year. Explain whether you would expect a well-designed experiment to collect data every year. What might prevent the collection of such data?

17. Imagine
Imagine that you are an ecologist collecting data on an introduced species. You are unable to collect data for several years in the middle of your study. What would you do with the data you had collected? Share your thoughts with the class.

18. Analysis question 4
Shown below are graphs of zebra mussel populations in three lakes near Lake Mikolajskie. Describe the population trend in each graph. How does each population change over time?

19. SCORING GUIDE: Analyzing Data

20. Should a rapid population decline automatically be cause for concern?
Share your thoughts with the class.

21. Analysis question 5
The data presented in this activity are similar to actual data collected in Lake Mikolajskie, Poland, between 1959 and Zebra mussels have been found in lakes in that area for over 150 years. Shown below are the data collected from 1977–87. How does this additional information compare to your answer to Question 1?

22. Analysis question 6
Zebra mussels were introduced in the United States in the late 1980s. They first appeared in Lake Erie, one of the Great Lakes. Today, the population of zebra mussels has reached as high as 70,000 mussels per square meter in some parts of Lake Erie.

23. Analysis question 6
a. How does this compare to the populations of zebra mussels found in the lakes in Poland? b. Before 1988, the population of zebra mussels in Lake Erie was zero. Draw a graph showing what you think the data might look like for the population of zebra mussels in Lake Erie from 1985 to the present.

24. Analysis question 6

25. Analysis question 7
Consider the zebra mussel population in Lake Mikolajskie from 1959 to Describe what you think happened to the zebra mussel population from 1987 to Explain your reasons for your prediction.

26. SCORING GUIDE: Analyzing Data

27. Analysis question 8
Fill in the “After” column for Statements 1 and 2 only on Sheet 77.2, “Anticipation Guide: Introduced Species—Zebra Mussels.” Did your thinking change?

28. How do scientists study the size of a population and predict future population changes?
Sea lions on a beach

29. Key vocabulary definitions
Ecologists - Scientists who study relationships between organisms and environments. Fluctuation - A change over time in size, numbers, or other characteristics.

30. Key vocabulary definitions
Introduced species - A species that has been moved by humans from its normal habitat to a new habitat, either intentionally or by mistake. Population - A group of the same species of organisms living in a specific location or habitat.