# Investigating Ecosystems

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## Investigating Ecosystems

Scientists use different sampling methods to investigate the abundance of organisms and their distribution in a given area. Common sampling methods include the use of quadrats and transects. The distribution of organisms is often affected by a variety of environmental factors

Quadrats are square frames of a known size, e.g. $1\text{m}^2$, that are usually divided into smaller segments. They are placed on the ground and used to measure the abundance of certain small organisms in an area.

This can either be done by counting the number of the particular organism in the quadrat or by estimating the percentage of the quadrat that is covered by the organism. Which method you use depends on how easy it is to count all the organisms in the quadrat.

Example:

Counting the number of daisies within a quadrat is relatively easy but counting the amount of grass would be incredibly difficult. In this case it would be best to estimate the percentage cover instead.

To calculate percentage cover of grass in a quadrat, count the number of squares that are more than half covered with grass. Divide that number by the total number of squares in the quadrat and times the whole thing by 100

Quadrats are often used to randomly sample different areas so their species abundances can be compared, eg. the amount of flowers in the sun compared to the shade.

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## Transects

Transects are used to study the distribution of organisms across an area, in a straight line. A tape measure is laid out across the area that is to be studied. You can then either count all the organisms that touch the line or place quadrats at regular intervals along the line and count/calculate the abundance of organisms at each point.

Example:

You can investigate how the abundance of marram grass changes as you move up a beach by placing quadrats at regular intervals along a transect. Notice how the abundance of marram grass increases with distance from the sea.

To make the results more reliable you could carry out many transects along the beach and calculate a mean abundance at each interval

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## Measure population size and species distribution using sampling techniques.

You should be able to put these methods into practice to find the population size of different species in a habitat and how specific factors affect the distribution of organisms.

Calculating population size

1. Divide the area that you want to sample into a grid and use a random number generator to select coordinates in the chosen area.
2. Find each coordinate and place a quadrat on the ground.
3. Count and record the number of organisms of the particular species in the quadrat
4. Repeat using many randomly generated coordinates.

5. Calculate the mean number of organisms per $\text{m}^2$

$\text{mean number of organisms}$$\text{per m}^2 =$$\dfrac{\text{total number of organisms}}{\text{number of quadrats}}$

6. Calculate the population size

$\text{number of organisms}$$\text{in whole area} =$$\text{mean number of organism per m}^2$$\times \text{total area (m}^2\text{)}$

The effect of a factor on the distribution of a species

In this example we will investigate the effect of light on grass coverage

1. Mark out a transect line along the ecological gradient using a tape measure, e.g. from the base of a tree.
2. At regular intervals along the line, place a quadrat on the ground and estimate the percentage cover of grass as well as measuring the light intensity using a light meter
3. Continue until you reach the end of the transect.
4. Plot the light intensity against the percentage cover of grass on a graph to discover any trends in the data. Percentage grass cover increases with light intensity
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## Environmental Change

The distribution of organisms within a habitat can be affected by many factors and investigated using quadrats and transects, as seen above.

Changes to the environment can also affect the distribution of organisms on a wider scale. These changes can be seasonal, geographic or as a result of human activities

• Temperature changes, often due to climate change, can cause organisms to migrate, e.g. some Mediterranean bird species have been spotted in parts of Europe where the temperature is more suitable.
• The availability of water can affect the distribution of organisms, e.g. there is often a big difference in the distribution of organisms on the African savannas between the wet seasons and the dry seasons. Some mammals will migrate every year in accordance with the rainfall patterns.
• The composition of gases in the atmosphere can affect the distribution of certain species, e.g. certain lichen cannot grow if there are high levels of sulfur dioxide in the atmosphere which is released during some industrial processes.
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## Investigating Ecosystems Example Questions

$13$ out of $25$ boxes are more than half covered in grass.

$\dfrac{13}{25} \times 100$ $= 52 \%$

Gold Standard Education

Calculate the mean number of dandelions per quadrat

$\dfrac{4+6+9+2+6+0+7+5+4+6}{10} \\= 4.9 \text{ dandelions per m}^2$

Calculate the area of the field.

$20\times30 = 600 \text{ m}^2$

Calculate the population size of dandelions in the field.

$600\times 4.9 = 2940 \text{ dandelions in the field}$

Gold Standard Education

Seasonal, geographic or as a result of human activities.