Capture, Mark, & Recapture Lab
Problem: To what extent does sample size affect the amount of error in a population estimate obtained by capture, mark and recapture techniques?
Research / Background: Field scientists have been conducting population “counts” for many decades. Because many animals are continually moving around and seeking shelter and protection in hard to see areas, it is difficult to count them. One commonly used method which attempts to deal with determining population size for an organism in the field is called “Mark and Recapture”, or what might be called “Capture-Mark-Recapture”. As the name implies, a group of animals is captured, tagged, and then released. You then capture another group of the same kind of animals and see how many of them were previously captured and tagged. By knowing how many you caught the first and second time, and how many were caught twice, you can estimate how many animals there actually are in the population.
The formula for estimating population size (X) is: # marked in recapture/ total recaptured = total marked / X .
Therefore, (# marked in recapture)(X) = (total recaptured)(total marked)
Therefore, X = ((total recaptured)(total marked)) / #marked in recapture
Hypotheses: H1:
H0:
Procedure: 1) Take a cup full of beans to your lab table.
2) Take 20 beans from the cup and mark them with a marker (total marked).
3) Put the 20 beans back into the cup. Shake the cup so the 20 beans randomly mix with the beans already in the cup that are unmarked.
4) Randomly spill 10 beans from the cup (this simulates "recapture" of the beans).
5) Count the the total # of beans recaptured including the marked bean (total recaptured).
6) Count the total # of beans marked in the recapture sample (# marked in recapture)
7) Return all beans to the cup.
8) Randomly spill out a total recapture sample size that is 5 larger than the previous one and repeat steps 5 through 7. Always record your data in the data table.
9) Repeat step 8 three more times, until the data table is filled with total recapture samples that increase by 5 beans each time.
10) With data table columns A, B, and C now completed, please calculate column D in the data table.
11) Now count the total number of beans in the cup including the marked ones. Put that number in all blanks for column F.
12) Calculate data table column G.
13) Enter your data into the class spreadsheet so data table 2 can be calculated
14) Graph your group data versus the class data on your own graph paper.
15) Write the two paragraphs of discussion & conclusionsTable 1: Group Data
total marked
total recaptured
#marked in
recapture sample
X = estimated
population size
(A x B)/CF
Actual Population
Size
(actually count the total
number of beans in cup)
Percent Off
|F-D|/F*100
Table 2: Class Data
sample size (B)
Discussion Paragraphs of Conclusion:
1) Did your data support your hypothesis (briefly restate your hypothesis)? Please use data summary figures here. Compare and contrast your group's findings (data table 1) to the entire classes findings (data table 2).
2) What do you now know the relationship between the IV (total recapture sample size) and DV (percent off from truth) to be? What several other things you learned from this lab? How do these results relate to the topics you are studying in class?