Organisation & Trophic Levels - Quadrat and Transect Sampling (GCSE Biology)
Quadrat and Transect Sampling
Sampling
Sampling is a technique used to find a small proportion of a population and use this to small section in order to draw conclusions regarding the rest of the population. Transects and quadrats are measurement tools that can be used for sampling.
Quadrat Sampling
- Quadrats can be used for sampling. Quadrats are wooden, or wire tools that form a 0.25 metres squared area. You can place a quadrat over an area and use it to sample. This can be done by counting the number of a certain organism, the percentage cover of an organism – the area within the quadrat covered by the organism, or the diversity of species in the area.
- Random sampling must be done. In order to produce valid results, care must be taken to make sure sampling is random. This can be done by throwing the quadrat over an area with eyes closed to avoid bias, or a better method involves two measure tapes. Place two measuring tapes across an area like two axes of a graph. Then use a telephone number or a random number generator to make random coordinates. Place the quadrants in the random area. Repeat this at least three times for reliability. You can use these steps to do quadrat sampling to investigate the effect of a factor on the distribution of a species.
Transect Sampling
- Transects can be used to sample. Belt transects can be used to sample changes in diversity across a range of areas. For example, you can use them to monitor species diversity along a rocky shore line. You can do this by placing a measuring tape along the shore line then placing a quadrat at different distances along this line and recording the species and their numbers.
- Transects can be used systematically. You can use a transect to see the effect of different abiotic and biotic factors on species diversity along a habitat. You can then use this information to draw a kite diagram.
Kite Diagrams
- Kite diagrams can be used to map data from transects. If we look at this data, we can analyse the species diversity across the transect. This data was taken from along a habitat. We use the width of the bar from the midline to see how many individuals are present. Therefore, we can see here that at the first site, lithics were the most abundant organism, however as we went further along the transect, other organisms, such as trees and shrubs become more and more common, whilst the lithic reduced in number. At the final site, we see that reeds and rushes were the most abundant.
Other Sampling Methods
- You can also use the capture-recapture method. You would capture a sample of a population and mark them using a harmless method then release them back into the environment. After a while, you would recapture a sample of the population then count how many of the organisms are marked. You can estimate the size of the population by doing the following:
- You make assumptions when using the capture-recapture method. You assume there have been no changes in the population size e.g. births/ deaths. You assume that marking the individual hasn’t had an impact on the individual’s chance of survival.
- Other equipment can be used to sample. Nets can be used to collect organisms from water and long grass. Pooters (jars with a rubber bung with tubes) can help collect ground insects. Insects can be aimed at with the long tube. The shorter tube is used to suck the insects into the jar (the short tube has mesh so you won’t breathe in the insect). Pitfall traps are containers placed in a hole in the ground. Insects fall into the traps and are unable to get out.
Using Keys
When sampling, keys are useful as they can help you identify organisms when you find them. They are sets of questions you can ask to help you identify an unknown organism.
Keys can be statements as well as questions. An example of a key is ‘how many legs does the organism have?’ This will be followed by a set of options.
Keys help you narrow down the options of what the organism might be. You start with the first question and you look at the organism to help you answer it. Then you move to the next question followed by the next and eventually you narrow down the options so much that you’re only left with one species that the organism could be.
Calculations
Mean
- The arithmetic mean is a method of calculating the average. If we have many sets of data, we can attain one average value by calculation a mean. For example, if you have taken data from 3 randomly placed quadrats, regarding the number of lichens, you can work out the average number of lichens.
Median
- The median is another measure of average. In order to calculate the median, you place all of the numbers in ascending order. The number in the middle is the median. For example, if you have 9 quadrats and have counted the number of lichens, and get the following data: 1,1,3,4,5,6,7,7,7. The median would be 5.
Mode
- The mode is a measure of average. The mode is the most common number. If we use the same data as above, the mode would be 7, as it is the value that we see the most.
- You can draw bar charts in order to plot such data. You must use appropriate numbers on the axes, as the data must take up at least 50% of the graph area.
Scaling Up
You can estimate the population size of an organism:
Population size = mean no. organisms in sample area x total area
For example, we will use the previous example and assume that the quadrat size was 1m2. You are asked to estimate the population of lichens in a field with an area of 500m2. We’ve already worked out that the mean number of lichens in the sample is 14. So now you simply do the following:
Population size = 14 x 500 = 7,000 lichens
FAQs
Organisation in ecology refers to the way different species are arranged and interact with each other in an ecosystem. It includes the way organisms are grouped into populations, communities, and ecosystems.
Trophic levels in ecology refer to the different levels of the food chain, from producers to top predators. Producers are organisms that make their own food, such as plants, while consumers are organisms that eat other organisms, such as herbivores and carnivores.
Quadrat sampling is a field-sampling method used in ecology to estimate the abundance and distribution of organisms in a particular area. It involves the use of a series of quadrats, which are square or rectangular frames of a known size, placed systematically within the study area to sample the target population.
To carry out the quadrat sampling method, researchers first define the area to be sampled and then divide it into a grid of equal-sized quadrats. They then randomly select a predetermined number of quadrats within the grid to sample, and record the number of organisms or species observed within each quadrat. By extrapolating the data from the sampled quadrats to the entire study area, researchers can estimate the abundance and distribution of the target population.
Quadrat sampling is commonly used to study plants, but it can also be used for animals or other organisms that are relatively immobile. The method is simple, non-invasive, and cost-effective, making it a popular choice for ecological research.
Transect sampling in ecology is a method used to study the distribution and abundance of organisms along a line or pathway. A transect line is established and data is collected at regular intervals along the line to determine the presence and abundance of different species.
Quadrat and transect sampling methods are two different techniques used in ecology to study populations of organisms. While both methods involve measuring the abundance and distribution of organisms in a given area, they differ in how they collect and analyze data.
Quadrat sampling involves selecting several square or rectangular frames of a known size, called quadrats, and systematically placing them within the study area to sample the target population. The quadrats are then surveyed to record the number of individuals or species present within them. Quadrat sampling is a non-destructive method that is useful for studying organisms that are stationary or do not move much, such as plants or sessile animals.
Transect sampling, on the other hand, involves moving along a straight line or path through the study area, and recording the abundance and distribution of organisms that intersect the line. This method can be used to study both mobile and immobile organisms and is particularly useful for studying population density or species composition across a gradient, such as an environmental or habitat gradient.
In summary, the main difference between quadrat and transect sampling methods is that quadrat sampling is a stationary method that uses a series of fixed frames to sample organisms in a given area, while transect sampling involves moving along a line or path to survey the distribution and abundance of organisms that intersect the line.
Quadrats and transects are used in ecology to study the distribution and abundance of organisms in a specific area. They allow ecologists to gather data on the number and types of organisms present and their distribution patterns.
The benefits of using quadrats and transects in ecology include the ability to gather precise data on the number and types of organisms present, their distribution patterns, and changes in their populations over time.
The purpose of using quadrat and transect sampling in ecology is to study the distribution and abundance of organisms in a specific area and to determine how these populations change over time. This information is important for understanding the interactions between different species and the dynamics of ecosystems.
The results from quadrat and transect sampling are used in ecology to study the distribution and abundance of organisms in a specific area and to determine how these populations change over time. This information can be used to make predictions about the future of ecosystems and the interactions between different species.
Some limitations of using quadrat and transect sampling in ecology include the small sample size, the potential for human error in data collection, and the fact that they provide limited information on the behavior and interactions of organisms. These limitations must be considered when interpreting the results from quadrat and transect sampling.
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