Population Estimation Lab
Purpose
To compare the mark-recapture and quadrant methods of estimating population
size. (In this lab activity, the population you will be examining is beans.)
Background
The ability of scientists to accurately estimate the total population of a target
organism is fundamental to any ecological study. Species and resource management
is closely tied to population size counts performed in the field. Because counting
each individual in a population can be impractical and very difficult, field biologists
have developed a variety of techniques and mathematical formulas for estimating
populations. Several of these methods require counting a portion of the population
while others involve successive captures of individuals.
Method 1: Mark & Recapture
One common population sampling technique is the mark-recapture method. This
technique involves capturing a number of individuals in such a way as to identify
them if recaptured, and then release them back into the population. A subsequent
capture is performed, and the ratio of marked to unmarked individuals is noted. For
this method to be effective:
 Each individual in the population must have an equal and independent
chance of being captured
 Except for while being captured, the population must not increase or
decrease in size during the sampling period
If these conditions are met, a simple formula can be used to estimate the size of a
population, where:
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
𝑁 𝐾
=
𝑛 𝑘
Method 2: Quadrant Method
Sometimes it is effective to examine a
relatively small area in which the
population exists and apply the findings
to the entire area. This can be done by
creating a grid to cover the entire area
the population inhabits. By counting the
individuals in certain squares of the grid
and extrapolating those numbers to the
entire area, the population size can be
estimated.
Question
Which method of estimating population size will yield a more accurate result?
Lab Report
In a formal lab report, please include the following sections:
 Objective ( /1)

Hypothesis ( /1)

Materials ( /1)

Procedure ( /4)

Results ( /2)

Analysis ( /2)
o Compare your results to the “true” number of beans in your sample.
Use the formula below to calculate the error of each method.
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =

|𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑉𝑎𝑙𝑢𝑒 − "𝑇𝑟𝑢𝑒" 𝑉𝑎𝑙𝑢𝑒|
𝑥100%
𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑉𝑎𝑙𝑢𝑒 + "𝑇𝑟𝑢𝑒" 𝑉𝑎𝑙𝑢𝑒
2
Follow Up Questions ( /2)
1. List three populations that the mark-recapture technique would work
well for. Why is this the case?
2. List three populations that the quadrant method would work well for.
Why is this the case?

Conclusion ( /1)