One method for estimating animal populations is known as mark-recapture sampling.

Estimating the population size of an animal population can be important in managing a natural area to see if the population is approaching the carrying capacity of the area.

Carrying capacity: maximum number of individuals of a species that a habitat can support.

For example, we may use traps to capture a particular species of voles. After capture, each vole is marked and released.

After a certain amount of time, the traps are reset to catch another sample of voles. Some of the voles in this second group will be new individuals not caught in the first group, but some may be marked individuals from the first trapping.

We can represent the vole numbers as follows: p. 142

• N = estimated population
• T = number of organisms from first trapping, and marked
• n = number of organisms from second trapping (both marked and unmarked)
• t = number of marked organisms from second trapping

Assuming the captured animals are a random sample of the whole population, N/T should equal n/t:
the ratio of the total number of voles to the total number of marked voles is equal to the ratio of the number of voles in the 2nd sample to the number of recaptured voles.

N/T = n/t
N = (T)(n) / t

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• PART A - MARK AND RECAPTURE EXPERIMENT

  Section 1 - Mark and Recapture Using Beans

  1. Fill tub about 1/2 full of brown beans.
  2. Count 200 - 500 white beans (30 is too few); this is T.
     Mix the white and brown beans; the total number of beans now in the tub is N.
  3. Randomly remove a handful (or cupful - should be about 200 - 500) beans; this is n; try to be consistent with this sample size for each trial.
  4. Count marked (white) beans; this is t. Each sample must have at least one white bean.
  5. Do 10 trials.
  6. After the 10 trials, count ALL of the beans (brown AND white); this is the actual population, A.
  7. Calculate percent error:

     %error = |(A - N)| * 100 / A
     

  Put your group's numbers in Table 4; copy the other groups' numbers in datasheet p. 147. Add a column for T.

  Group #	Population Estimate (N)	Actual Population Size (A)	Sample Size (T)	% error
  1
  2
  3
  4
  5
  6

  NOTE: segregate brown and white beans before returning them to jars.

  Section 2 - Mark and Recapture Using Mealworms p. 142

  SKIP mealworms

• PART B - EXTRA MARK AND RECAPTURE PROJECT p. 144

  SKIP

• PART C - QUESTIONS

  Skip question #6 about mealworms. p. 148

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N

= * /

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N=, A=:

error

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