Question

One way to determine the density of animals in an area is to use the mark-recapture technique. A number of individuals from a population are captured, marked so they are easily identifiable, and released back into the population. It's assumed that the captured and marked animals will randomly mingle with the rest of the population. Later, the population is re-sampled and the number of marked and unmarked animals is recorded. The following equation can then be used to estimate the size of the entire population.
Number of individual marked in first catch/Total population size, N = Number of individual marked in 2nd catch / Total number of 2nd catch

If 25 Prairie Dogs were captured, marked, and released back into their population, and then subsequently 135 Prairie Dogs were captured, of which 18 were marked, what is the approximate total population size, N?

Answer 1

Answer:

N = 187.55

Explanation:

Here you just need to replace the terms and clear the equation.

You already know that,

• First capture: 25 prairie dogs.
• First marked animals: 25 (the whole first capture)

You let these animals leave and then you made another capture.

• Second capture: 135 prairie dogs
• Already Marked animals: 18 (these 18 dogs were caught in the first capture and marked before releasing them)  

To know the size of the prairie dogs population you just need to use the following equation and clear N, which is the value that you are looking for.  

Number of individual marked in first catch/Total population size, N = Number of individual marked in 2nd catch / Total number of 2nd catch

• Number of individual marked in first catch = 25 dogs
• Total population size, N = this is what we want to know
• Number of individual marked in 2nd catch = 18 dogs
• Total number of 2nd catch = 135 dogs

So now, we need to replace terms

25 / N = 18 / 135

25 / N = 0.1333

N = 25 / 0.1333

N = 187.55