How To Use Percent Cover Quadrat Data

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Field investigations

Ecologists report the distribution of living organisms in habitats to find out how healthy it is. They use many different sampling methods to provide quantitative data which is then analysed.

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Using quadrats in sampling

Quadrats are square frames of wire usually 0.25 g ² . They may contain further wires to mark off smaller areas inside, such as 5 cm × 5 cm or 10 cm × x cm squares.

These are placed on the ground to look at the plants or slow-moving animals inside them. When looking at plants in a quadrat, the following sampling can be used:

Number of an private species - the total number of individuals of one species (eg daisies) is recorded.
Species richness - the number of different constitute or brute species is recorded but not the number of individuals within a species.
Per centum comprehend - the per centum of the quadrat area that is covered by one species (eg grass). This is easier to guess if a quadrat has wires making smaller sections. Percentage encompass rather than number of individuals is used when estimating plant frequencies if information technology is hard to place individual plants, such as grasses or moss.

A school student testing a selected quadrat

Random sampling

Random sampling using a quadrat involves the placing of quadrats at random coordinates. Regardless of whether yous are investigating the number of individual species, the diversity of species or the percent cover in different areas, you would use random sampling.

Almost sampling is random, but systematic sampling can exist used if at that place is a trend or pattern across the habitat, such equally distance upward a beach, or altitude on a hillside. If you are using the incorrect kind of sampling method for your experiment, this tin can lead to biased results.

Random sampling using quadrats

Sampling of the area yous are studying must be random. It must prove no bias – for example, choosing to sample where there are lots of plants.

When yous have chosen a sampling area, first divide it upward into a grid, for instance, having x × 10 divisions.
Utilise a suitable method – you could draw numbers out of a hat – to generate a pair of random coordinates on your grid.
Place the first quadrat on your grid using these coordinates.
Count the number of different species within this quadrat (the species richness).
Repeat steps 1-iv and so that y'all have a total of at to the lowest degree ten counts.

Using quadrats and transects in systematic sampling

Sometimes we want to see if the number of species or percent encompass changes within an surface area. This is oftentimes equally a effect of a change in an abiotic gene such as soil pH.

An example of this is an investigation into whether the growth of seaweed depends upon the altitude information technology is found on the seashore from the tide. We would use systematic sampling as nosotros are looking to link a linear change (in this case the number of hours the seaweed is covered by the tide).

A quadrat could be placed at regular distances, for example every five metres, forth an imaginary line called a transect , which would run downwardly the shore. Systematic sampling would be used along the transect to link changes in species to abiotic factors, such as immersion by water, temperature fluctuations and light intensity, all of which are influenced by the tide.

The results from transects can be fatigued into kite diagrams. The width of the bar from the centre at whatever altitude shows how many individuals were observed at that betoken.

Kite diagram showing grasses and dandelions over 25m. Grasses rise slightly and fall slightly over long period then rise and fall steeply to 25m. Dandelions rise steeply, then fall gradually to 20m.

Question: At what distances were the most grasses and the most dandelions seen?
: The most grasses were seen at 20 metres. The most dandelions were seen at five metres.