Ecological study – Cont’d T
HIS WEEK, we continue our study of the environment. How has your week been? Good? I hope so. I hope you will spend some time reflecting on the quote that I have included above. It is vital that we begin to care for our environment. This week, we will look at some more of the pieces of equipment that are used in ecological studies. In our previous lesson, we looked at some of the equipment that we can use to capture animals. In this lesson, we will not be capturing, we will be counting.
One of the most used pieces of equipment is the quadrat. Notice carefully how the word is spelt and do not confuse it with the word quadrant!
WHAT IS A QUADRAT?
A quadrat is a square of a known area, usually 1m2, made out of wood or metal and string. The wood or the metal is used to create the frame and the string is placed at measured intervals on the frame to form individual squares (see Figure 1). It is most commonly used for estimating the density of plant populations, but it can also be used for estimating the density of slow-moving or sessile animals, for example, those on the rocks of the seashore. Quadrats are also used to estimate the frequency of organisms as well as percentage cover.
In order to ensure the accuracy of the results obtained from the use of the quadrat, certain conditions must be met. These include: The size of quadrat to be used. The number of quadrats to be used. The placing or positioning of the quadrats.
At this level of your studies, the third point is the most important of the three for you. In order to reduce bias, the placing of the quadrats should be done randomly. In other words, you cannot look for what you are trying to find and then place the quadrat over it to make your numbers look good! Doing this introduces bias and your results will not be scientifically reliable. Facing away from the field and throwing the quadrat over your shoulder or over your head does not eliminate bias! Bias can be prevented by dividing the area to be studied into squares and using random numbers as coordinates. For example, random numbers can be obtained from random number tables. If random numbers 3, 4 are generated, then walking 3 squares from one corner in a straight line along the edge and then 4 squares down into the field would indicate the position to place the quadrat. The density of a particular species can be determined using the method below.
SPECIES DENSITY
The average number of organisms belonging to a particular species captured in 1m2 found using a 1m2 quadrat. Total number of organisms = 90 Density = 90/10 = 9 per m2 A quadrat can also be used to determine percentage cover. Percentage cover is the area out of 100 parts that is occupied by the organism.
Percentage cover is used to describe the distribution of organisms whose individual units cannot be easily counted. These include organisms such as grass, lichens and small molluscs on the seashore. It is the proportion of a measured ground area covered by that portion of the organism that is above the ground.
ESTIMATING POPULATIONS
Not only is it almost impossible to count the total number of individuals in a population, it could also cause unacceptable levels of damage both to the organisms and to their habitats. However, this is information that scientists need to know in order to study different populations of organisms; hence, estimates of population numbers have to be made. How is this done? It is done using sampling methods. Let us look now at some of these:
TRANSECTS
Transects are useful for estimating populations where one type of habitat is changing to another, e.g., along a shoreline, moving from the water on to land. It can also be used to show zonation of species (zonation describes the geographical habitat of a particular species). A transect is a straight line crossing an area recording all the species that actually touch the line as it crosses the area. Alternatively, the line can be marked at regular intervals, e.g., every 5-10m and the organisms present at these points recorded. The transect can be formed using a rope or a piece of string or a wire. A rope is more commonly used since it is not only flexible, but is also strong. The line transect can be converted to a belt transect by placing a second line at a measured distance, usually 0.5m from the first. All of the species within the two lines are then recorded. The two types of transect can also be used for the placing of quadrats; these are placed at regular intervals along the line and the species within the quadrats are recorded.
“Imagine if trees gave off Wi-Fi signals, we would be planting so many trees, we would probably save the planet too. Too bad they only produce the oxygen we breathe.” – Anonymous