Usually not possible to count all the individuals of one or a range of species in a habitat. Instead, the habitat is usually sampled to gain an accurate estimate of plant of animal species numbers, or their distribution.
When sampling, a population or a community can be estimated in terms of:
- Density - the number of individuals present. Frame quadrats are often used in sampling to determine density. Density is a useful indicator for many animals but it is not suitable for all plants as it is often difficult to know where one plant starts or ends.
- Percentage cover - mainly used for plants. This gives an estimation of the percentage area covered by a plant specied and is usually rounded up to the nearest 10%.
- Frequency - for each quadrat the species may be recorded as being present or absent. Thus % fequency indicates the percentage of all quadrats that a species occurs in. Sometimes a pin or point quadrat is used to record frequency. If a pin touches a plant of a particular species, it is recorded as being present, if not, it is absent.
Mechanism of sampling
It is important to use an appropriate number of quadrats (sample size) during sampling. Too few will not give a representative value and too many will defeat the purpose of sampling.
Random sampling - if the…