(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 (section 2) Quadrats section.

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Key points - ecological surveying using transects

Based on the syllabus-specifications for students taking the UK AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10 biology).

Revision notes specifically for biology students on Surveying Using Transects - a vital fieldwork technique in ecology for investigating the distribution of organisms.

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What Is a Transect?

A transect is a straight line across a habitat along which observations or measurements are taken.

It helps study how the distribution of organisms changes in relation to abiotic factors (like light, moisture, or temperature).

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Why Use a Transect?

• To study how species vary across a changing environment (e.g., from a shaded area to a sunny patch).

• To identify patterns of distribution related to gradients or zonation (e.g., seashore to inland, forest edge to open field).

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Types of Transects

1. Line Transect

   • A tape measure is laid out in a straight line.

   • You record any organism that touches the line at set intervals or continuously.

   • Used for quick surveys where visibility is good.

2. Belt Transect

   • Place quadrats at regular intervals along the transect line (e.g., every 1 meter).

   • In each quadrat, count or estimate species abundance.

   • Provides more detailed data, ideal for measuring changes in population density.

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How to Carry Out a Belt Transect

1. Mark a straight line across the study area using a tape measure or rope.

2. Place quadrats at fixed intervals (e.g., every metre).

3. In each quadrat:

   • Record all species present.

   • Count individuals or estimate percentage cover.

4. Record abiotic factors at each point if necessary (e.g., light intensity with a light meter).

5. Repeat for reliability and compare patterns across the transect.

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What You Might Measure

• Species distribution (where species are found or absent).

• Abundance (how many individuals or % cover).

• Environmental gradient (e.g., soil pH, temperature, moisture).

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Exam Tips

• Link species distribution to abiotic factors. Example: “The moss species were more abundant in areas of higher moisture.”

• Understand why a belt transect gives more data than a line transect.

• Be prepared to draw or interpret graphs showing changes in distribution along the transect.

• Use appropriate terminology like “zonation,” “gradient,” and “sampling.”

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Keywords, phrases and learning objectives for this part on ecological surveying and biodiversity

Be able to describe surveying using transects to measure the abundance and biodiversity of species in an ecosystem.

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