Sampling
Sampling refers to the gathering of organisms, or verification of their presence, with the purpose of generating data. This data can then be used for scientific studies.
When sampling it is vital to record all available measures to avoid experimental bias, although the choice of method and tools will inevitably induce some bias.
Collecting data for ecological studies in the real world is labour and resource intensive, the methods available are highly variable, depending on the type of organisms, and the area of interest - using methods which are highly reliable for oak-trees, could prove difficult to use on gazelles, and a great method for gazelles such as a remote camera trap, would prove highly inefficient to identify all species of trees in a forest.
The three methods below are not directly comparable but designed for each of their specific organism-groups, they do supplement each other quite well when investigating the biodiversity of an area.