Reflection: Developing a Conceptual Understanding Mark and Recapture: Population Sampling - Section 2: Getting Started


Because this simulation activity takes place in just one class period and the focus is really on using a formula rather than how the formula works, I ask students to use the simplified formula N = 200/k when calculating their population estimates. 

Some more advanced students may be curious about the math behind that formula, and whether this sampling method always uses that specific simplification.  The quick answer is no.  The simplified formula is based on the particulars of this simulation (taking 20 kernels on the first visit and 10 kernels on each subsequent visit).  Different sample sizes would be calculated differently, so for any groups that are curious about how the actual formula works, I cover the following with them:

The formula used to estimate the population size is the Lincoln-Petersen MethodN = Kn/k

N = Number of animals in the population

K = Number of animals marked on the first visit

n = Number of animals captured on the second visit

k = Number of recaptured animals that were marked

In this simulation, we are going to mark 20 animals on the ”first visit”, so K=20. 

We will capture 10 animals for each “return visit”, so n=10. 

Therefore (because 20 x 10=200), we will estimate the population (N) with the simplified formula: N = 200/k


Example: If you pull out 10 kernels and 4 are marked, then k = 4.  Therefore, N = 200/4. 

N would then equal 50 and that is the estimate of the population.


Admittedly, I only ended up going over this with one group that asked how the formula really worked, but I think it helped them see how this formula could be applied realistically in the field. 

One thing you might try if you want to really focus on the math and go over this formula's applicability in other situations would be to posit a scenario with different parameters.  For example, in a scenario where 15 animals were captured initially but only 5 were captured subsequently, the simplified formula would be N = 75/k

  Got Math? Unpacking the Formula
  Developing a Conceptual Understanding: Got Math? Unpacking the Formula
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Mark and Recapture: Population Sampling

Unit 4: Populations
Lesson 1 of 10

Objective: Students will be able to estimate the size of a population by using calculations based on the mark and recapture method used by ecologists.

Big Idea: Counting every individual in a population is almost always impractical if not impossible. Ecologists can use sampling methods to make reasonable estimates of population sizes.

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