Mark and Recapture Method
Objective:
To learn the mark and recapture method of estimating population size.
Time:
This lab will take several days to complete. Part 1 will take approximately 30 minutes
and Part 2 will take approximately 30 to 45 minutes on the first day and less than 30
minutes on each of the next 3 days.
Materials:
·
·
·
50 beans (30 white and 20 brown)
Jar with lid
Nail polish
Background Information:
A researcher visits a study area and uses traps to capture a group of individuals alive.
Each of these individuals is marked with a unique identifier (e.g., a numbered tag or
band), and then is released unharmed back into the environment. The researcher then
uses the Lincoln index to estimate the size of the population.
Part 1
Procedure:
1.
2.
3.
4.
5.
6.
Take 30 white beans and 20 brown beans and put them in the jar.
Shake the jar; without looking, remove 10 beans.
Count the number of brown beans left in the jar and record in Data Table 1.
Repeat step 3 until the data table is complete (10 times).
Use the Lincoln index to estimate the population size for each trial. (Multiply the
total number of brown beans in the jar (20) by the number of beans you removed each
time (10); then, divide this number by the number of brown beans you “caught” for that
trial.)
Add up the population estimate column and then divide the total by 10 (the number
of trials) to get your average population estimate.
Formula:
Lincoln Index
P
P
N1
N2
R
=
=
=
=
=
(N1 x N2)/ R
total size of population
size of first sample (all brown beans in jar)
size of second sample (recapture: some will be brown and some won’t)
number of brown individuals recaptured or “caught” each time
Data and calculations:
Data Table 1
Trial number
Number of
marked beans
in sample
Populatio
n estimate
1
2
3
4
5
6
7
8
9
10
Average
Analysis:
1.
2.
How close was the average value compared to the actual population size?
What things do animals in the wild do that beans do not? Why does this behavior
make a researcher’s job more difficult?
Part 2 (Optional)
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Select an area of your campus where the ground is slightly damp. A good place to
look is in flower beds or planters where the ground is frequently watered.
All students in the class should work together to catch pill bugs and put them into a
box for later use. Try to catch at least 50.
Mark the top of each pill bug with a small spot of nail polish. Use a toothpick rather
than the nail-polish brush to put a very small dot on each bug.
Allow the paint to dry. When all of the pill bugs are marked, release them back into
the area.
Return to the area each of the next 3 days and capture 10 pill bugs.
Count the number of pill bugs that you catch that have polish on them and record
that number in Data Table 2. Then, re-release your captured pill bugs.
Estimate the population size from each day’s data by multiplying the number of pill
bugs you marked (probably 50) by the number of pill bugs in each sample (10). Divide
by the number of marked pill bugs you “caught” each time.
After finding the population estimates for each day, find the average estimate by
adding up the daily estimates and dividing by the number of samples.
Data and calculations:
Data Table 2
Number of pill bugs in first sample (marked): _______
Date
Number of
pill bugs
captured
Number
of
marked
pill bugs
Population
size
estimate
Average
Analysis:
1.
2.
Do you think your population estimate is correct? Why or why not?
What difficulties did you encounter during this activity? What did you do to help this
problem?
3.
What other methods could you have used to estimate the number of pill bugs other
than the mark and recapture method?