An identification key is also known as a dichotomous key. The word ‘dichotomous’ means ‘divided or dividing into two parts’. This name reflects that at each stage in the process of identifying a species, you are always given two choices.
No
Segmented body? No
Yes Shell? No Slug Yes Snail Worm No Oval-shaped body? No
One pair of legs per segment?
No Millipede Yes Centipede
All the species identified during the qualitative survey are put into a list. Step 3: Quantitative survey of species present in the habitat
A quantitative survey collects numerical data about the species in the habitat. Quantitative surveys are always conducted for a single species at a time. The following techniques can be used to collect this data.
zz
Calculating the area covered by a quadrat
The length of each side of a standard quadrat is 0.5 m. Calculate the area covered by a single quadrat. How many quadrats must be positioned side by side to cover an area of 1 m2?
Frequency is the percentage chance of a species being present in a randomly chosen standard quadrat. Mark out the area under survey and select at least ten quadrats at random. Record if the species is present or absent using a single tick for present and a single cross for absent.
Percentage frequency is calculated using the following formula: Percentage frequency =
( zz [Total no. of quadrats]) x 100 [No of ticks] 1
It is important to use enough quadrats to give a reasonable idea of the frequency of a species in a habitat.
Percentage cover is the area of ground covered by plants or by animals. Percentage cover can be measured using a grid quadrat with a wire grid stretched across it to form smaller sample squares. A record is kept of the number of squares the species under survey is found in.
Percentage cover is calculated using the following formula: Percentage cover =
([No. of squares species found in] [Total no. of small squares] 104 ) x 100 1
Percentage cover is a useful way of finding out the most dominant plant or animal in a habitat.
