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Sampling Techniques

AQA A2 Biology 4.1 - Sampling Ecosystems

Peter Fearon

on 8 February 2012

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Transcript of Sampling Techniques

SAMPLING TECHNIQUES Random Systematic Random sampling means that you have no control over where the sample is taken from within the study area. Random samplings allows that each part of the sample area has exactly the same chance of being sampled. Systematic sampling allows you to decide where to take your samples, for example, at set intervals along a transect. BENEFITS If you wanted to sample the population of a plant species in a meadow and the meadow looked like it had similar vegetation growing throughout it, then random sampling will give data that is representative of the whole meadow. If you can see a gradation in the habitat that you wish to sample, a randomised sample would not be appropriate as there it wouldn't give an accurate picture of how the distribution of species changes in the habitat. In this case, a belt transect would be suitable, with samples taken at predetermined intervals. This would be particularly useful if you were to return to the site at a later date to resample. How? Random number generators can be used to generate co-ordinates of quadrats or the sample area. QUADRATS TRAPPING NETTING Frame Point - a quadrat is a defined area within which you can collect data best used to sample plants

or sessile animals best for sampling plants Random number generators allow
random plots to be chosen based on
a co-ordinate system. random systematic What are the limitations of this approach? the point quadrat can be placed at

set intervals along the line transect the percentage of each species within

the quadrat can be estimated estimating percentage cover using the grids within the quadrat you can

estimate the coverage by a single species Do's & Don'ts it is important to standardise the procedure in this case, flowers occuring >50% inside the quadrat are counted, whereas flowers occuring <50% inside the quadrat are not. Sweep Netting Kick Sampling a net is held downstream so that the

disturbed stream bed flows into the net this sampling method is recommended for targetting aquatic invertebrates
and some small species of fish Mist Netting the net is swept over plants

such as the soybean shown here this method is ideal for sampling insects Mist netting is used for catching birds as part of mark, release and recapture programs such as bird ringing. Pitfall Traps Longworth Traps used for catching insects used for catching small mammals trapping small mammals is usually as part of a mark, recapture and release program
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