Estimating an animal population
Random quadrat
The animal population we are
going to estimate is a crustacean commonly called a nipper. These
animals live in holes in the ground and at low tide it is easy to
count the holes. By using a random quadrat you can take 10 measurements
and then calculate the average number of holes per square
metre. The average is then multiplied by the area covered
with the nipper holes. For
the purpose of this exercise we will equate one hole to one nipper.
However nippers often have more than one hole.
Nipper
male and female.
The male has one large claw that is being held firmly in the picture
(for obvious reasons!). The female is smaller and doesn't have the claw.
A quadrat as the name suggests is usually a square. A metre square
is a convenient size to use.
Now I want you to count the
number of nipper holes that appear in the following images. You
may like to print out the page and use a pencil to mark the holes
as you count them. When you have finished there is a table to
fill in with your results.
Quadrat 1
Quadrat 2
Quadrat 3
After you have counted the number of holes add them to the table below. A
further seven quadrats have been counted for you.
|
Quadrat number
|
Nipper Holes
|
|
1
|
|
|
2
|
|
|
3
|
|
|
4
|
30 |
|
5
|
24 |
|
6
|
36 |
|
7
|
22 |
|
8
|
12 |
|
9
|
27 |
|
10
|
23 |
|
Total
|
|
Take the total and divide by ten which is the number of quadrats you
took. This will give you the average.
Average =
The total area of nipper holes is 100 metre x 130 metre =
13000sq
metre
Multiply this by the average in 1 square metre.
You estimate for the total population is
When estimating a population it is necessary to make sure that the sample
size is large enough to make the estimate accurate. Obviously the best
number of quadrats would cover the entire area. There has to be a balance
between the sampling effort and the accuracy of the estimate.
