MarkRecapture Laboratory
by G Lyon
Name_______________________ Date___________ Per.______
This is a laboratory that simulates a population census technique commonly used by
wildlife biologists in the field. The first step is to trap a random sample of animals
of the desired species. These animals are then eartagged or marked in some other
manner and released. The next step is to trap once again. 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.
N n
____ = ____
M m
N=Population estimate
M=Number of animals captured and marked in first sample
n=Number of animals captured in second sample
m=Number of "n" that were already marked
 Put 46 large handfulls of pinto beans into a shoe box. Do not count them. Then
make an estimate as to how many beans are in the box. Write your estimate here___________.
 Now we shall use the mark recapture technique to get an estimate of the population.
 Pick out a handful of beans and count them. This is your first trapping sample,
M. M=_________
 To mark these beans merely replace them with colored beans (white or red). These
marked individuals must be released back into the population (shoe box).
 Shake the box and, without looking, grab another handful of beans. This is your
second trapping sample, n. n=__________
 How many of the beans in your second trapping sample were already marked (colored
beans)? m=__________
 Now use the equation above to calculate your population estimate, N. N=__________
 Count the actual number of beans in your box. Write the number here ___________.
 Was your estimate using the ratio closer than your initial guess?
 How could you increase the accuracy of your estimate?
 What species of animal would this technique work well for? What species of animal
would this technique not work for? Why?
 Can you think of a better way to estimate the number of beans in the box?


