Counting by sub-sampling.

Often there are too many organisms in the entire quadrat to count, and so you have to sub-sample the quadrat using smaller quadrats, and calculate the number in the entire area using the formula

Total number = Sum of no. in all subquadrats x  Area large quadrat/ sum area subquadrats

Do you think this method would work better when the organisms were randomly distributed, or when they were clustered together in clumps?

Use this Excel spreadsheet to help you estimate the population of Red dots in the diagram.
The large quadrat is 1m2, the small ones are 10 cm x 10 cm.
Now try counting the all dots. How close is the estimate?