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What Is Environmental Sampling? | Ecology & Environment | Biology | FuseSchool

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Saint George Catholic College Science Department

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Scientists spend a large amount of time studying the environment. To do this they need to have a good understanding of the techniques needed to sample and analyse the environment.

Ecologists study an environment in terms of its biodiversity - the variety of different species in an area. They will want to know certain information about the species present:

Where an organism is found (distribution)

The number of that organism present (population)

Whenever a scientist studies an area it is usually not possible to look at the entire environment in detail. Therefore, the scientist samples a section or small portion. Sampling several small sections is representative of the whole area. The sampling technique used depends on the habitat and type of organisms present.

Pooters

A pooter is used to catch small insects. The user breathes in through the mouthpiece which has a piece of net covering the end. The insects are sucked into the holding chamber via the inlet tube.

Sweep nets

Sweep nets are used in areas of long grass to catch organisms. They can also be used in ponds.

Pitfall traps

Pitfall traps are used to catch small, crawling insects. They can be set up and left overnight to catch nocturnal species. All organisms caught should be released unharmed.

Quadrats

Quadrats are square frames of a known size eg 1 m ². They are used to sample all the plant species in a particular area.

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Scientists spend a large amount of time studying the environment. To do this they need to have a good understanding of the techniques needed to sample and analyse the environment. Ecologists study an environment in terms of its biodiversity - the variety of different species in an area.

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How to carry out ecological sampling page 1.

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(see picture below). The purpose of using a quadrat is to enable comparable samples to be obtained from areas of consistent size and shape. Rectangular quadrats and even circular quadrats have been used in some surveys. It does not really matter what shape of quadrat is used, provided it is a standard sampling unit and its shape and measurements are stated in any write-up.

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A Piece of the Pie

When you take a bite of your dinner you have a pretty good idea of how the rest of your meal will taste. This is because you have taken a sample or portion that is representative of the entire meal.

Scientists do this when they study things by sampling a portion of the entire population, area, or natural process. Getting an idea of the big picture from a sample is useful because often it is impossible to get a measurement from every single plant or animal that we're studying.

Would you want to count every single tree in a 400 acre forest? Or would you rather sample the forest to get a representative idea of how many trees there are? I'm guessing you'd rather sample!

Assumptions of Sampling

Since we are sampling, we have to deal with making some assumptions. First, we only assume that our sample actually represents the whole. Just one sample of a forest assumes that the whole 400 acres is the same, and that 200 of those acres aren't just fields or lakes.

Therefore, make sure there are enough samples to be representative. Take a sample from each quarter of the forest, or each sixteenth. Do whatever is feasible, but the more the better.

Another important point is that the sample must be random. You can't just walk into the forest and pick the best looking patch of trees as your sample. This would be like picking out all of the chocolate chips in your cookie but leaving the nuts and saying that the chocolate chips are representative of the entire cookie.

Randomly choosing your samples is the best way to fairly represent the characteristics of the bigger picture, and when done in its simplest form this method is called simple random sampling.

Systematic Sampling

A good way to avoid bias in your sampling efforts is to use systematic random sampling. This is when samples are taken at fixed, predetermined intervals. What makes this type of sampling random is that the start point is randomized for the predetermined intervals.

For example, you might want to sample every fifth tree that you come across as you go through the forest. By sampling every fifth tree, the trees you do and don't sample are not biased by your choice because they are still random. But it is systematic because for every one tree you sample there are four that you don't. Essentially this guarantees that your sample is equally random over time.

A good way to systematically sample is to walk a transect line. Here, a line is laid out along an environmental gradient. This could be down the slope of a hill, along the edge of a stream, or something similar. Everything that is touching the line gets measured. Along a transect you might count every single organism of interest, or you might systematically sample by counting organisms that occur every three feet.

Belt transects are similar to line transects but they allow for a greater area of sampling. With this method, instead of counting along the line, you count the abundance or percent cover within the area of a quadrat. This is a grid that is a known size (for example, 1 foot by 1 foot), and is laid out on the ground.

Stratified Sampling

Another method of random sampling is called stratified sampling, which allows us to randomly select from different categories, or strata. We would use this type of sampling when we need to sample individuals within similar, smaller units.

Stratified sampling is used when it is better to divide a population into smaller groups and sample within those groups. Just like when you identify your age, gender, and race in a survey, we can create sub-groups for our ecological sampling.

For example, if the trees you are sampling in your forest grow best in a particular kind of soil, instead of randomly sampling trees throughout the forest, you might want to divide the forest into areas of similar soil type and sample trees within those divisions.

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ecological sampling: definition & example | study.com

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Ecological Sampling: Definition & Example | Study.com

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When you take a bite of your dinner you have a pretty good idea of how the rest of your meal will taste. This is because you have taken a sample or portion that is representative of the entire meal. Scientists do this when they study things by sampling a portion of the entire population, area, or natural process.