UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 23/05/2023 [SEARCH]

Surveying ecology : 3. Biodiversity surveying: Method 2 using transects

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There are various sections to work through,

after 1 they can be read and studied in any order.

INDEX of biology notes on ecological surveying

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(3) Biodiversity surveying: Method 2 Surveying using transects in ecology

A belt transect is a path/gradient along which one counts and records occurrences of the species of study.

You might wish to study how the distribution of organisms changes by sampling across a transect.

A transect is used to survey a wider area in a more systematic way than just doing a few quadrats.

e.g you can use a sequence of quadrats along a transect to find out how organisms are distributed across a change in habitat due to an abiotic factor - bright light to shade, damp to dry ground, change in soil composition (due to underlying differences in geology e.g. limestone and sandstone)

Below is a photograph of a field of wild flowers.

I've drawn on the photograph how you use a 1 m2 quadrat along the line of a transect to survey the species of wild flowers from the hedge at the top to the bottom of the field.

You can visually see that the distribution (concentration) of white and yellow flowers changes as you come down the field and these can be accurately counted to give you quantitative data.

Photo of the Cornfield wild flower project Hutton-le-Hole - Ryedale Folk Museum (August 2019) well worth a visit.

20 cm x 20 cm squares in the 1 m2 quadrat

You can count the number of each species in 1 m2 (100 x 100 = 10,000 cm2) areas or randomly sample the smaller 0.04 m2 (20 x 20 = 400 cm2) areas.

 

Doing a transect survey

In the preceding section I've described how to use a quadrat.

Here you lay out a long string line from the starting point to the end point.

Using a long tape measure you measure out 1, 2, 3 m etc. and place a 1 m2 quadrat at these points.

Count the organisms e.g. plant species you are interested in and then move the quadrat on 1 m further down the line.

You can survey every metre or 2 or 3 metres if its a very long transect.

From your results you can plot graphs of organism density (species/m2) versus distance down the transect (m).

You could also measure the light intensity down the transect using a light meter, at the same distance intervals you were measuring the plant density.

You can then compare the two graphs and see if there is any connection between the plant species density and the intensity of light falling on the transect.

The calculations are just the same as I've shown in the preceding (1) Quadrats section.


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