Name / Period / Date

CHAPTER 2 CHAPTER INVESTIGATION

Estimating Populations

MATERIALS

  • white kidney beans
  • paper bag
  • 2 colored markers
  • calculator

OVERVIEW AND PURPOSE

The number of animals in a wild population cannot be easily counted. Wildlife biologists have developed a formula that can estimate a population's size by using small samples. This method is referred to as mark and recapture. In this lab you will:

  • use the mark-recapture method to estimate population size
  • test the effectiveness of the mark-recapture method by simulating an outbreak of disease in a population

Problem

How effective is the mark-recapture method in estimating population size?

Hypothesize

Write a hypothesis to explain how you will use a sudden change in population size to determine the effectiveness of the mark-recapture method. Your hypothesis should take the form of an "If . . . , then . . . , because . . ." statement.

Procedure

1. From your teacher, obtain a paper bag containing a "population" of white kidney beans.

2. Remove a small handful of beans. Count the sample and record the count in Table 1 under First Capture Total.

TABLE 1: POPULATION SAMPLING BEFORE DISEASE
First Capture Total / Recapture Total / Recapture Marked / Calculated Population Estimate / Actual Population Total

3. Use a RED colored marker to mark your sample population. Return the beans to the bag, and gently shake the bag to mix all the beans.

4. Remove and count a second sample of beans. Record the count in Table 1 under Recapture Total.

5. Count the number of beans from this sample that were marked from the first capture. Record this number in Table 1, under Recapture Marked. Return all the beans to the bag.

6. Use a calculator and the following formula to estimate the population size. Record the estimate in Table 1 as the Calculated Population Estimate.

7. Disease strikes. Remove a small handful of beans from the bag. Count the beans, and record this count in Table 2, under Killed by Disease. Set these beans aside.

TABLE 2: POPULATION SAMPLING AFTER DISEASE
Survivors First Capture Total / Survivors Recapture Total / Survivors Recapture Marked / Survivors Estimate / Killed by Disease / Actual Survivors Total

8. Repeat steps 2–6 to mark and recapture your survivor population. This time use a different BLUE colored marker to mark your sample population, and only include the beans marked in the second color in your counts.

9. Fill in Data Table 2 for the survivor population. Use the formula from step 7 to calculate your estimate of the survivor population.

10. Once you have calculated your estimate of survivors, dump out the paper bag and count all the beans that were inside. Record this count in Table 2, under Actual Survivors Total.

Observe and Analyze

1. Calculate From Table 2 add together the number of actual survivors and the number killed by disease. Put this in Table 1, under Actual Population Total.

2. Calculate Find the percentage of the population affected by the disease using the following formula:

= ______%

Conclude

1. Infer How did the estimated number of beans compare with the actual number? (Table 1)

2. Identify Limits What aspects of this investigation most likely would not be possible in a natural habitat? Why not?

3. Evaluate Compare your results with your hypothesis. Did your data support your hypothesis? (* Hint: Compare Table 1: Actual Population Total/Calculate Population Estimate vs. Table 2: Actual Survivors Total/Survivors Estimate, Closer to 100% = More Accurate)

ANSWER KEY

Hypothesize

Students should hypothesize that a change in the population will decrease the accuracy of a population estimate. Example: If a disease strikes a population of animals, it will make a population estimate less accurate because the population will change greatly.

Observe and Analyze

1. Sample Data: Table 1: First Capture Total, 22; Recapture Total, 28; Recapture Marked, 6; Calculated Population Estimate, 102; Actual Population Total, 100.
2. Sample Data: Table 2: Survivors First Capture Total, 26; Survivors Recapture Total, 22; Survivors Recapture Marked, 4; Calculated Survivors Estimate, 71; Killed by
Disease, 14; Actual Survivors Total, 86 (Percentage affected, 16%).

Conclude

1. Sample Data The estimate should be within 20% of the actual number.
2. It might not be possible to know exactly when disease strikes a population. Also, capturing the required number of animals would be difficult. It most likely would not be possible to catch them all at once. When they are released, they likely would not all stay in one small area.
3. Answers will vary. Students who predicted effective correlation (80% or better) between the estimated and actual count will say the hypothesis was supported by the results.

TEACHER NOTES

Lab Preparation

  • The day before doing the lab, have volunteers make up the bags. Bags should contain around 100 beans, but the number should vary.
  • Prior to the investigation have students read through the investigation and prepare their data tables. Or you may wish to copy and distribute datasheets and rubrics.

UNIT RESOURCE BOOK, pp. 121-129
SCIENCE TOOLKIT, F14

Lab Management

  • Have students work in pairs, with one student handling the beans and the other recording the data. Have them switch roles throughout the lab.
  • Tell students to take small handfuls, or demonstrate what a “handful” means here.
  • White beans work well for marking. Avoid pinto or other spotted beans.

INCLUSION If students have learning disabilities, have them handle and count the “population” samples, while a partner reads directions and records data. If a student has poor fine motor control and is physically unable to perform the population counts, he or she could read and record the procedure aloud, and could present the results.You might use a tape recorder for results if writing is problematic. If a student is colorblind, be sure the two markers are not red and green.