Studying the environment

WELL, HELLO again, students. How are you all this week? Now that we have completed our lessons on Section C, we need to focus our attention on another topic. I hope everything went well for you last week and that this week will be equally good! Right now, we will be looking at some of the practical principles involved in the study of the environment. These, along with the identification and classification of organisms, form the basis of many of the structured questions on Paper 02. Before we begin, you will need to familiarise yourself with some key terms. These are terms that will be used in the questions that you will be asked to answer; if you do not know what they mean, then you will not be able to answer the questions adequately.

KEY WORDS AND TERMS

Population: A group of organisms of the same kind (species) found in a particular area. Community: Several populations living together in a particular place, e.g., all the organisms living under a fallen tree or all the organisms living on a Barbados cherry tree. Niche: The position occupied by a particular type of organism within the community. Habitat: This is the place where the organism lives. Habitats can be either terrestrial – on land – or aquatic - fresh water (rivers, lakes), sea water (marine), brackish water (estuaries). Ecosystem: The interaction of living organisms with their environment. Species density: The average number of organisms belonging to a particular species captured in 10 throws of a 1m2 quadrat. e.g., Calculation of the species density of grasshoppers in an abandoned playing field. Percentage cover: This is used to describe the distribution of organisms that are not easily separated into individual units and cannot be easily counted. These include organisms such as grass lichens, and small molluscs on the seashore, such as periwinkles. Percentage cover 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, but doing so would also cause unacceptable levels of damage, both to the organisms and their habitats. However, population numbers is information that one needs to know in order to study populations, hence estimates of population numbers have to be made. How do we estimate population numbers? It is done using sampling methods. Let us look now at some of these methods:

QUADRAT SAMPLING

A quadrat is a square of a known area, usually 1m, made out of wood or metal. It is most commonly used for estimating the size of plant populations, but it can also be used for estimating the size of slow-moving or sessile (not mobile) animals, e.g., those on the rocks of the seashore. This square of 1m can be further subdivided into smaller squares (see diagram below). In order to use the quadrat accurately, 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. In order to reduce bias, the placing of the quadrats should be done randomly. Simply throwing the quadrat over your shoulder will give some degree of randomness, but there are more accurate ways of doing this. This can be done by dividing the area to be studied into squares and using computer-generated random numbers as coordinates. For example, if random numbers 3, 4 are generated, then walking 3 squares from one corner in a straight line along one edge and then 4 squares down into the field would indicate the position to place the quadrat.

TRANSECTS

Transects are useful for estimating populations where one type of habitat is changing to another, for example, along a shoreline moving from the water on to land. They can also be used to show the zones different species occupy. The line transect is a straight line crossing an area, recording all the species that actually touch the line as it crosses the habitat. Alternatively, the line can be marked at regular intervals, for example, every 5 to 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. A line transect can also be used to place quadrats; the quadrats are placed at regular intervals along the line and the species within the quadrats are recorded.

Next week, we will look at some of the different methods that can be used to collect animals. In the meantime, read through this information a few times until you become comfortable with it, because you will soon be using it to answer questions.

Have a blessed week!