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Sampling with quadrats and transects
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You cannot count every plant in a field. Sampling with quadrats gives a reliable estimate.
Quadrats
A quadrat is a square frame, often 1 m2. Place it randomly (using random coordinates) to avoid bias and count the organisms inside.
Mean per quadrat × total area (in m2) = estimated population.
Mean per quadrat × total area (in m2) = estimated population.
Transects
A transect is a line across a habitat, such as from a pond's edge to a field. Place quadrats at regular intervals along it to see how distribution changes with an abiotic factor, like light or moisture.
Reliability
Use more quadrats for a more reliable estimate. Measure abiotic factors at each point to explain patterns.
10 quadrats (each 1 m2) contain a total of 6 daisies. The field is 2000 m2. Estimate the number of daisies.
- Mean per quadrat = 6 ÷ 10 = 0.6
- 0.6 × 2000
Answer: 1200
Place quadrats randomly to estimate population: mean per quadrat × area. Use a transect with quadrats at intervals to study how distribution changes across a habitat.
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