Good News; there are usually less of them in a habitat, Bad News; they move, may detect your presence and hide or fly away
Must trap them and then estimate the total population, larger animals may be carefully observed, they also may leave droppings, footprints or damage trees in an identifiable way
Collect data e.g. counting animals in several areas/paths, at different times of day/year in different weather conditions (data collected is a one point in time sample)
Use a specific and relevant sampling technique e.g. sweepnet for flying insects, and a method to ensure individuals are not counted twice
Use mark-release-recapture technique to estimate population size of species in the area (unsuitable technique for aquatic organisms and for very small invertebrates in soil)
Tullgren Funnel: Device, used in lab to collect small invertebrates from sample (e.g. soil), it is placed in a funnel in exposed light for a period of time, as it heats and dires organisms move away from the light falling into a container with alcohol
Pitfall traps (e.g. plastic cup): Left buried in soil so crawlinginvertebrates fall in; a little water should be at bottom so they can’t escape, also a cover/canopy used in case it rains, the organisms are examined, identified, counted, and set free
Bush and Tree Beating: White sheet is placed on the ground (or in an open umbrella) under bush/tree, and it is knocked with a stick to dislodge organisms; problem organisms could move away, they need to be trapped for identification and counting
Light Trap: Collects night flying insects, attracted by UV lamps and they fall into a jar of alcohol
Mark and recapture
Capture a sample of animals (e.g. woodlice) and mark each so it can recognised if re-caught (C_1)
Release them and return later to count animals in second sample (C_2)
