Schoolyard Capture/Recapture Experiment

Connecting Outdoor Instruction to Innovative Learning Standards

(COIILS)

View Existing Data Login to Enter Data Critter Links Collected Data Pages/Downloads Experiment Home Page

Schoolyard Capture/Recapture Experiment

Contributors to this activity are: Jill Carter and Mike Schneider

Grade Levels: 4-12 (Note: This experiment can be simplified or made more challenging depending on the developmental levels of your students. See Teacher Information.)

Description: By using an already tested scientific research method, students can determine the numbers of a mobile population of insects. Grasshoppers, pill bugs, or other arthropods are captured, marked, and then recaptured. Students learn how to use an algebraic formula to determine their populations.

Approximate Time Involved: One 30-minute classroom planning session; (first day outside)10 minutes to conduct sweep or check pill bug traps; 20 minutes to count, mark and release animals; (second day outside) 10 minutes to conduct sweep or check pill bug traps; 10 minutes to count and release animals); 20 minutes to enter data online, one or two 30-minute classroom sessions to examine results, state conclusions, draw inferences, and make recommendations.

Teacher Information:

Schoolyards, prairies, fields, forests, parks and other areas provide students with a great opportunity to examine and test the capture/recapture method used by scientists to determine the population size of a mobile animal such as the grasshopper or pill bug. The capture/recapture process is just one way to determine animal population sizes and it, like the others, is not 100% perfect. NOTE: Encourage your students to search the Internet and other sources for more information about ways in which scientists determine animal populations.

SIDEBAR: Remember that every season may show major changes in the number of organisms you will collect. This is why it is important to compare the populations from year-to-year so students can recognize these population fluctuations.

A number of grasshoppers* or pill bugs will be captured, marked and released during the first day of the experiment. The next day a second sample of grasshoppers or pill bugs will be captured from the same area. The following assumptions must be met in order for this sampling technique to be valid and useable:

All of the grasshoppers or pill bugs in the population of a given area have an equal chance of being caught.
There is no change in the ratio of marked to unmarked grasshoppers or pill bugs. To make certain this holds true, there must be no significant additions or subtractions to the marked population of grasshoppers or pill bugs that is different from that found in the overall population of grasshoppers or pill bugs.
Marked grasshoppers or pill bugs distribute themselves equally throughout the population so that both marked and unmarked grasshoppers or pill bugs have the same opportunity to be captured in the second go-around.

*It was thought that grasshoppers would be the most prevalent organism, but you may choose to capture/recapture another organism that is more common to your schoolyard - the pill bug. (Other possible arthropods for a population study include ladybugs, box elder bugs, ground beetles, crickets, wood roaches, etc.)

If the above assumptions are met, the number of grasshoppers or pill bugs caught in the second sampling will be proportionate to the number of grasshoppers or pill bugs in the entire population. The total population of grasshoppers or pill bugs for a given area can then be estimated using the following formula:

If N/M = n/R, then N = (M)(n)/R
Where N is the total population size to be estimated
M is the sample of grasshoppers or pill bugs that was captured, marked, and released
n is the number of grasshoppers or pill bugs captured the second day
and R is the number of marked grasshoppers or pill bugs that were recaptured on the second day.

What the capture/recapture equation is saying is that the ratio of the total population of grasshoppers or pill bugs to the total number marked on the first day is equal to the ratio of the total number caught on the second day to the number of marked grasshoppers or pill bugs that were recaptured.

(Example: M = 32 grasshoppers or pill bugs caught, marked & released on the first day, n = 40 grasshoppers or pill bugs caught on the second day, R = 20 recaptured, marked grasshoppers or pill bugs. Therefore N/32 = 40/20 and N = (32)(40)/20 or 64.

Challenging Your Students to Be Problem Solvers:

To make this experiment more challenging to your students, you might just want to pose a question or problem such as: Based on the research information you have collected on capture/recapture techniques, design and conduct an investigation to determine the size of a population of mobile animals living in the schoolyard. OR Using the information provided above, design and conduct an investigation to determine the population size of the grasshoppers or pill bugs living in the schoolyard. OR Conduct the grasshopper or pill bug capture/recapture experiment in two or more different habitats (schoolyard, prairie, grassy field, forest, park) and compare your results. What factors may have influenced the difference in grasshopper or pill bug population size found in each habitat?

This should become a team exercise where your student groups might each conduct Internet research on capture/recapture techniques, design or choose the investigation and habitat, develop and write a question or hypothesis, list the materials they will use, the number of each item, and a procedure. NOTE: An excellent way to assess this activity is to have the teams repeat each other's experiment to see if they achieve the same results. This will also replicate the real world challenges facing a research scientist.

Here is an opportunity for your students, especially those in a high school biology or ecology class, to present and defend their capture/recapture results to a professional in the field:

Dr. Elaine AbuSharbain, Science Educator at Southern Illinois University at Edwardsville, has agreed to review any student designed experiments and their results, conclusions, inferences, and recommendations. Elaine's Email Address is: eabusha@siue.edu

Student Instructions Available to download as a PDF file.

Needed Materials: Sweep nets, collection jars or half-gallon resealable plastic bags, pencil and clipboard, small paint brushes and several colors of model paint or nail polish, four uncooked potatoes, carving knife, rubber-band or toothpicks. (NOTE: The number of each item needed will be determined by the number of student groups you plan to have perform the investigation.) (NOTE: You can purchase inexpensive 5-gallon paint straining bags for around a $1.00 each at your local Sherwin Williams paint store, or other paint stores. They can then be sewn onto coat hangers to make inexpensive sweep nets.)

Pill Bug Traps: Pill bug traps can be made by cutting a potato in half and then hollowing out a portion of each half to create a cavity when the halves are joined back together. A small hole (5 mm.) will need to be cut in one end of the potato through to the internal cavity to create an entrance for the pill bugs. When you have completed the carving you can use toothpicks or a rubber-band to rejoin the two potato halves to complete the pill bug trap.

Safety Rule: When using a sweep net it is likely that some stinging insects and spiders may be captured in the process. Pill bug traps could also produce some small spiders. Remind your students to use caution when removing organisms from the sweep net and/or the pill bug trap. Special care must be taken not to injure the organisms that are to be marked and released. When carving a potato, make sure the knife is always cutting away from you and others.

Procedure :

Student Information: The following information will provide you with the steps for conducting your capture/recapture investigation and marking the organisms you have caught. It is important to hold all of the variables constant except for those that are being manipulated. Constant (or controlled variables) would be such things as: the size of the capture/recapture area, the size and shape of the sweep net, the size and number of pill bug traps placed in each location, the time of day the experiment is conducted, the way in which the sweep is performed, etc. Manipulated (or independent) variables would be those things that we change to see if the response will be different. In this case it might be different locations, habitats, weather conditions, times of the day, etc. NOTE: To guarantee accurate results, you should only have one manipulated (independent) variable during an investigation.) The responding (or dependent) variable for this experiment might be the number of animals you catch in each of your locations or habitats. To get an idea of the types and numbers of mobile animal populations in other schoolyards, you will want to compare your capture/recapture data with other online classes to see if there are similarities or differences in your results.

The reporting form for this experiment is set up so that you can identify the locations or habitats you want to test, identify the animal population(s) you plan to count, and provide additional information about your experiment. NOTE: Remember that a good scientific experiment is repeated a minimum of three times. To accomplish this, several student groups can each conduct the investigation in several identical locations or habitats and then compare their data to check for accuracy. If their data is similar, they may want to compile an average and submit it as a group. If there are major differences, a discussion should follow to determine what may have caused these differences in the results.

Steps to Conducting a Capture/Recapture Investigation

Click on “Login to Enter Data” at the Schoolyard Capture/Recapture Experiment web page link provided above (Note: You will need you user name and password to do this). Once you are there, click on “Add New”. What comes up is the data collection sheet that will be used in this investigation. Complete any pertinent information and also choose the appropriate choice listed in each "dropdown" box (Ex. The location for your trap, your bait, etc).

Print the form and place it on your clipboard. Click "Add" so that your form, and your completed work, to this point, will now be in the list when you return to enter your data.

Grasshopper Instructions:

1. To capture grasshoppers, try to choose a location approximately 50 meters long and wide enough so that all of the groups' sweepers can stand at an arm's length away from each other.

2. Each student group should have a different color paint or nail polish.

3. The individuals with the sweepnet (sweepers) will walk the length of the study area, sweeping the net back and forth in a consistent figure-eight manner so that the opening of the net is first to sweep the area.

3. Stop every five meters and place your captured organisms (grasshoppers) in your collection jar or resealable half-gallon bag.

4. Other members of the group can take the jar or bag and carefully begin marking the grasshoppers by placing a small spot of paint or nail polish on the top thorax of the grasshopper just behind the head region. NOTE: Paint or nail polish placed on the arthropod's thorax will be shed the next time it molts.

5. Use the pencil and clipboard to record the number of grasshoppers you are marking as you go.

6. Carefully release the grasshoppers back into the same approximate area as soon as the paint or marker dries.

7. Complete the sweep of the entire area length, capturing, counting, marking, and releasing the grasshoppers as you go.

8. Return all equipment to the classroom and complete an inventory to make sure nothing was left in the study area.
9. On day two, repeat the procedure described in steps 1-3 at the same location.
10. This time, keep track of the total number of both marked and unmarked grasshoppers as you go. Once you have taken a count, carefully release the grasshoppers back into the same area.

Pill Bug Instructions:

1. To capture pill bugs, place four potato traps strategically no more then 2 meters apart in the location you have chosen.

2. Cover the potatoes with natural litter or

bury them partially in the ground, making sure the entrances are still accessible.

3. After waiting for twenty-four hours, retrieve the potato traps, open them and carefully remove the pill bugs.

4. Use model paint or nail polish to place a dot on each pill bug's thorax (NOTE: The thorax makes up the seven segments across the pill bug's back that have legs attached to them.)
5. NOTE: If you are having trouble marking the pill bugs, you might want to refrigerate them to temporarily slow their movements. NOTE: Paint or nail polish placed on the arthropod's thorax will be shed the next time it molts.
6. Use a pencil and clipboard to record the number pill bugs you have marked.
7. Release the pill bugs back into the location they were captured.
8. After twenty-four hours, reset your potato traps in their original locations.
9. After another twenty-four hours, retrieve the potato traps, open them and carefully remove the pill bugs.
10. This time, keep track of the total number of both marked and unmarked pill bugs. Once you have taken a count, carefully release the pill bugs back into the same location where they were caught.

Grasshopper and Pill Bug Instructions:

11. Each collaborative group should now have the data you need to plug into the formula described above. Once your group has completed the formula, compare your results with other collaborative groups.

12. After group and classroom discussions have occurred, login to enter your data online at the correct location. NOTE: Only numbers must be inserted into the boxes where data is being entered and then used in an Excel chart or graph. Words can be used in other boxes where the information is not being quantified.

13. Choose your group's investigation from the existing list and choose "Edit". Enter your remaining data that was collected and any other requested information that has not yet been entered. Click "Update".
14. Once all classroom data is submitted you can download all submitted Schoolyard Capture/Recapture Experiment data and develop charts and graphs in Excel by following the general directions provided at "Downloading and Analyzing Collected Data Using an Excel Spreadsheet"

Below is a list of questions that can be used to stimulate student discussions. If your students are at a developmental level where you are able to challenge their higher level thinking skills, then only present them with the first set of questions from each group below. Use the second list of questions as a way to stimulate thinking when you students seem unable to expand their knowledge on their own.

Examining Local Results

Discussion Questions that Require More Critical Thinking Skills:

What were your results and conclusions for this experiment?
What could your infer based on your conclusions?
How would you design and/or conduct this experiment differently the next time?

Discussion Questions that Require Less Critical Thinking Skills

Did your results match those of the other collaborative teams?
If your results were different, what do you think might have been the reason?
Did all of the collaborative groups end up with the same results? Why do you think this was the case?
Were the results somewhat similar to each other? Why do you think this was the case?
If you were able to compare your data to that taken at a different location in the schoolyard, were the results somewhat similar? Why do you think this was the case?
Did the outside temperature have any impact on the number of animals caught?
If you were able to conduct this investigation in other habitats, what comparisons and differences were you able to note?
What factors might impact the number of animals captured and recaptured? How could you test your assumptions experimentally?

Examining Local and Online Results

Discussion Questions That Will Require Critical Thinking Skills to Compare Local Data to the Online Data of Others

How did your results compare with the results of others?
What conclusions can you make when you compare your results with the results of others?
What inferences can you draw from your additional conclusions?
How would you design and/or conduct this experiment differently based on the information you now have?

General Discussion Questions that May Occur as a Result of Comparing Local Data to the Online Data of Others

Where is the geographic location of the schools who have provided online data?
How did the types of animals you captured/recaptured compare with those captured/recaptured by others?
What external factors may have contributed to different capture/recapture results?
What similarities existed among those schools that captured/recaptured the same types and numbers of animals?
Did others have the same success with the same habitats? If not, what could be the reason for the differences?

Performance and Multiple Choice Assessment Options

Critter Links

Entomological Society of America This site has a special "kids" page for insects.
Monarch Watch Participate in a migratory census of butterflies.
Iowa State Department of Entomology This is a good source for information on insects, including some insect recipes.
Children's Butterfly Site This butterfly site is maintained by the United States Geological Survey.
The Butterfly WebSite Learn more about the facinating world of butterflies.
Butterflies, Moths, and Cool Bugs Browse this collection of insects from Havana Junior High's annual Adopt-An-Insect Project.
Young Entomologists' Society, Inc. If you really like to explore the insect, spider, and minibeast world, check out this site and become an amateur entomologist.
Copyright, 2005
by Prism Press
ALL RIGHTS RESERVED The text of this publication or any part thereof, may not be reproduced or transmitted in any means, electronic or mechanical, including photocopying, recording, storage in an information retrieval system, or otherwise, without the prior written permission of the authors.

Back to COIILS Main Page

Back to SPLASHD Web Page