Required practical 12: Investigation into the effect of a named…

The idea

This practical investigates how an environmental factor affects species distribution. Choose a measurable factor: light intensity, soil moisture, pH, or temperature. Where the factor changes along a gradient, use a belt transect by running a tape measure along the gradient and placing quadrats at regular intervals to capture the pattern. At each quadrat, record species abundance (e.g., percentage cover or frequency) and measure the environmental factor, taking repeat readings to calculate a mean. If comparing two uniform areas without a gradient, sample randomly within each area using coordinates generated by a random number calculator to avoid bias.

What earns the marks

• Name the environmental factor being investigated and state suitable apparatus to measure it accurately.
• Specify a belt transect with quadrats placed at regular intervals when sampling along an environmental gradient.
• Specify random sampling using randomly generated coordinates when comparing areas without an environmental gradient.
• State a valid measure of abundance, such as percentage cover or frequency, ensuring repeats are taken to calculate a mean.
• State clearly that a correlation between the environmental factor and species distribution does not establish causation.

Common mistakes and how to put them right

• Concluding that the measured factor causes the distribution.

  Put it right: State that other abiotic or biotic factors may change along the same transect and influence distribution.

• Using random quadrats where there is an obvious environmental gradient.

  Put it right: Use systematic sampling (a belt transect) to observe changes along a gradient.

• Taking a single reading of the environmental factor.

  Put it right: Take multiple repeat readings at each sampling site to calculate a reliable mean.

Exam tips

• When asked for conclusions about distribution, give one specific statement per species and tie each to a feature shown on the provided map or figure.
• Name the specific statistical test used (e.g., Spearman's rank correlation) and state exactly what it tests for, rather than just saying 'do a stats test'.