When sampling a population, the numbers of organisms are counted within a sample site, and then the results multiplied to estimate the total number in the entire habitat. Large animals and plants can often simply be counted. However, many smaller animals like insects and smaller mammals need to be trapped first so they can be counted and then released afterwards.

Collecting organisms

Organisms can be collected using a variety of methods, including:

• nets
• pooters
• pitfall traps

Nets and pooters

Nets are useful for collecting flying insects such as butterflies and moths. They are swept through long grass or leaves of trees in a process called sweep netting. The organisms are caught in the net. To catch aquatic organisms, nets are often held downstream of the area to be studied and then the riverbed is gently disturbed by the person doing the sampling. The small animals float into the net. This is called kick-sampling.