- 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 then 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.
N = Population estimate M = Number of individuals captured in first sample (and marked) 
N = n n = Number of individuals captured in second sample M m m = Number of (n) that were already marked To solve for (N) we re-arrange the formula: N = Mn m 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. Now make a guess as to how many beans are in the sack.
Your population estimate (guess). ______
We will now use the 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 (M). Record your answer.
M = ______
3. To mark these beans merely replace them with colored beans (red). Now release the marked individuals back into the population (sack). The replaced white beans are set aside and never returned to the sack again. They were replaced (marked).
4. Shake the sack, without looking, grab another handful of beans. This represents your second trapping sample (n). Count them and record your answer.
n = ______
5. How many of the beans in your second trapping sample were already marked (red beans)? This is your (m) value. Count them and record your answer. Return this trapping sample (white and red) to the sack.
m = ______
6. Now use the equation from the introduction to calculate your population estimate (N). Record your answer.
Calculated population estimate. N = ______
7. Count the actual number of beans in your sack. Record this number.
Actual population number (counted) = ______
QUESTIONS:
Was your estimate using the ratio (N), closer than your initial guess?
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How could you increase the accuracy of your estimate (N)?
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Back to Lab Dad's Laboratory
- White (enough for 4-6 handfuls per group)
SIMULATION OF A
POPULATION STUDY
Number 1
MARK-RECAPTURE
INTRODUCTION: