Name___________________
Introduction:
Mark and Recapture Lab
In this lab exercise, you will simulate a population estimate technique used by wildlife
biologists in the field. The first step is to trap a random sample of animals of the species
being studied. These animals are the n marked in some manner appropriate to the
species and released. Then the next step is to do another trapping. Some of the
animals captured may have been marked from the first sample. Using a simple ratio,
the biologist can come up with a quick population estimate using the following formula:
Estimate of Total Population = (total number captured) x (number marked)
(total number recaptured with mark)
Pre-lab Questions:
1) If you were in charge of a team given the responsibility to determine the number of
sunfish in Kyle Lake, how would you accomplish this task? Explain in great detail in
the space provided!!!
A technique called sampling is sometimes used to estimate population size. In this
procedure, the organisms in a few small areas are counted and projected to the entire
area. For instance, if a biologist counts 10 squirrels living in a 200 square foot area, she
could predict that there are 100 squirrels living in a 2000 square foot area.
2) A biologist collected 1 gallon of pond water and counted 50 paramecium. Based on
the sampling technique, how many paramecium could be found in the pond if the pond
were 20,000 gallons. SHOW YOUR WORK OR YOU GET NO CREDIT!
3) What are some problems with sampling? What could affect its accuracy?
4) A biologist originally marked 400 butterflies in a park. Over a month long period,
butterfly traps caught 200 butterflies. Of those 200, 80 were found to be marked.
Based on this information and using the equation above, what is the estimated
population size of butterflies in the park?
5) In what situations would sampling work best for estimating population size? In what
situations would mark and recapture work best? You will have to think about this one.
Materials:
Beans (Black and White) or Beads of different colors
250 mL beaker
Plastic spoon
Procedure:
1) Put 4-6 spoonfuls of black beans into the beaker. Do not count them. Now make a
guess as to how many beans are in the beaker.
Population Estimate (guess) _____
2) Pick out a spoonful of beans from the beaker and count them (do not return them to
the beaker). This will be the number marked.
Number marked _______ B
3) To “mark” these beans, simply replace them with white beans. Now release the
marked individuals back into the population. The replaced black beans are set aside and
never returned to the beaker again.
4) Shake the beaker. Without looking, grab another spoonful of beans. Count the
beans and record your answer.
Total Number captured _______ A
5) How many of the beans in the above sample were white?
Number of marked beans ______ C
6) Now use the equation from the introduction to calculate your population estimate.
Show your work and record your answer.
Calculated population size ______
7) Repeat this procedure 9 more times and record your data in the chart below.
Trial
A
C
#
captured
# of
marked
beans
Population
Estimate
1
2
3
4
5
6
7
8
9
10
8) Use the data above and the equation from the introduction to calculate the population
estimate based on the totals from your ten trials. Show your work and record your
answer.
Population Estimate from 10 trials ______
9) Count the actual number of beans in your beaker.
Actual population number _______
Conclusion:
1) How far off was your estimate using the equation from the actual number when you
counted them?
2) Do you think mark and recapture is an effective way to estimate
population size? Why or why not?
3) How could you increase the accuracy of your estimate?