Investigating Population; Random sampling; what is transects? How does it work?

A group of interbreeding organisms of one species in a habitat is referred to as a population. Investigating the population is part of ecology, which is the study of inter-relationships between organisms and their environment. Eventually, it is necessary to count the number of individuals of a species in a given habitat. However, it is impossible to count all the number of individuals of a species of given habitat because the process is time consuming and could cause damage to the habitat. To overcome these issues, random sampling using quadrates and systematic sampling along transects are used.

Random sampling can be carried out by dividing the study into a grid of numbered lines, e.g. by setting two long calibrated rulers at right angles to each other. Then random coordinates can be obtained by either using log chart or random number generator in a calculator. Finally, we take samples from the intersection of each pair of coordinates. This process prevents sampling bias by eliminating human involvement of choosing the sample. {Figure 1 shows a diagram that briefly describes the method of random sampling}.

There are two types of quadrats that can be used in random sampling: ...

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There are two types of quadrats that can be used in random sampling: 1. point quadrat – consists of a horizontal bar supported by two legs. A point frame consisting of a group of 10 pins set about 5 cm apart is normally used. The pins are lowered in turn and the number of hits and misses on the particular species of plant under consideration is recorded. 2. A frame quadrat – a square frame divided by string or wire into evenly sized sections. Altogether, both types of quadrates produce quantitative results.

Systematic sampling along transects is more informative to measure the number of individuals of a species in a given space in a systematic rather than a random manner. This method of using transects are particularly useful in situation such as sea shores and sand dunes where conditions and species vary across the area being studies. A line transect sampling method comprise of a string or tape stretched across the ground in a straight line. Any organism over which the line passes is recorded. It is usually a belt transect (strip) is marked by putting a second line parallel to the first. The species occurring within the belt between the lines are recorded. {Figure 2 represents a frame quadrat}.

Both the process involves reasons, such as chance affecting the sampling. Therefore the results may not be representative. For example, the 50 buttercup plants selected might just happen to be the tallest in the population. Even though we cannot remove chance from the sampling process completely, we can minimise the effect by using a large sample as well as analysis the data that is collected carefully. Using a large sample size will reduce the effect of chance; as more individuals are selected, the results are less deviating far from accurate mean value. at the same time, analysing the data collected carefully, which involve accepting that chance will play a part and using statistical tests to determine the extend to which chance may have influenced the data could also minimise the effect of chance.

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