- In the first simulation, you estimated population size by trapping an initial sample. Then you marked the captured sample (replaced white beans with red), and released them back into the ecosystem (sack). A second trapping was made, and calculations based on the ratio for re-captures gave a population estimate (N).
- You were asked how you could increase the accuracy of your estimant (N). The two good answers would have been to 1. trap larger samples, and 2. have more than two trappings.
- In this lab exercise we will investigate the use of more than two trappings, to obtain a more accurate population estimate. This will require a little more data collection, and a different formula for calculation. This method is called, repeated marking and recapture (Cox, 1980).
- On the first date, a sample of individuals will be captured, marked, and released back into the population. On each subsequent date (i), a sample (Ci) will be captured. The number of marked re-captures (Ri) will be recorded and the remaining individuals marked and returned to the population. Thus, the total number of marked individuals (Mi) increases through time. From the data obtained, a population estimate (N) can be calculated, using the following formula:
N = 
MiCi Ri is the symbol for sum-of-all).MATERIALS:
Beans (2 colors that are the same shape and size)
- White (enough for 4-6 handfuls per group)
- Red (enough for 1-2 handfuls per group)
Small paper bagsPROCEDURE:
1. Put 4-6 handfuls of white beans into a sack. Do not count them.
We will now use the repeated mark-recapture technique to get an estimate of the population.
2. Pick out a handful of beans and count them (do not return them to the sack). This is your first trapping sample (C1). Record the count in the DATA TABLE. Now mark individuals (replace them with red beans). Put the number of ( marked individuals in population) in the DATA TABLE for the next trapping time. In this case, it will be the same number as (C1). Return the marked individuals (red beans) to the sack.
3. Shake the sack well. Now take out a hand full for your second trapping time. Record in the DATA TABLE, the total captured (red and white) in (C2), and the number of recaptures (red) in (R2).
- Now replace the white beans with red ones. You are marking previously unmarked individuals. Add the number of individuals you just marked, to the (M2) number, and record this for (M3). This is the total marked individuals. Return all the second trapping (now all red) to the sack.
4. Repeat step 3 for the third and fourth trappings. Record the information as before. The number of individuals you mark (replace with red) in trapping 3, needs to be added to the (marked individuals in population) and recorded in (M4).
DATA TABLE: 
Trapping
timeMarked Individuals in
Population
(Mi)Captured
(Ci)Recaptures
(Ri)
1
0
0
2
3
45. Now use the formula given, to calculate the population estimate.
Because M1 = 0, and R1 = 0, the data for the first trapping period is not used in the calculation. The formula as you will use it, is as follows:N = (M2C2) + (M3C3) + (M4C4) R2 + R3 + R4 Your population estimant (N) = _______
6. Now count all the individuals in the population (sack).
Counted Population Number = _______
LITERATURE CITED:
Cox, George W.. 1980. Labratory Manual of General Ecology, fourth edition. William C. Brown Company. Dubuque, Iowa.
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- You were asked how you could increase the accuracy of your estimant (N). The two good answers would have been to 1. trap larger samples, and 2. have more than two trappings.
SIMULATION OF A
POPULATION STUDY
Number 2
REPEATED MARK-RECAPTURE
INTRODUCTION: