Biology Fieldwork

A Level

Sampling mobile organisms

Using a sweep net to capture invertebrates in long grass

1. Sampling

Why sample?

It is not practical to record every single invertebrate. Instead you can take a representative sample.

Since many woodland invertebrates are mobile, the number of individuals at a particular site can change rapidly. Woodland iinvertebrates are rarely distributed evenly. So to take an unbiased sample, you must use the same sampling technique at all sites.

If you are comparing two or more areas, take several random samples at each area. If you are investigating the effect of an environmental gradient, take a stratified sample. Here are some examples of sensible sampling strategies:

  • Investigation question: is there a difference in ground invertebrate species between the oak wood and the beech wood?
    Sampling strategy: 5 samples are taken in oak wood, and 5 samples are taken in the beech wood.
  • Investigation question: what is the impact of position on slope on ground invertebrate species?
    Sampling strategy: 10 locations are chosen at 20 metre intervals.