The freshwater amphipod (Gammarus pulex) is an important detritivore that helps maintain the health of stream ecosystems by recycling organic matter.
Freshwater ecologists used a choice chamber to investigate the effects of blue light and red light on the movement behaviour of Gammarus pulex.
Table 1 shows their results. The P-values show results from a chi-squared statistical test.
Table 1 | Behaviour of Gammarus pulex | Type of light used in choice chamber | | :--- | :---: | :---: | | | Blue light | Red light | | Moving towards the light | 11 | 23 | | Moving away from the light | 39 | 27 | | P-value | 0.005 | 0.62 |
State a null hypothesis the ecologists tested in this investigation.
The natural habitat of Gammarus pulex is cool, fast-flowing freshwater streams. Suggest two factors (other than light) that should be kept constant in the choice chambers so that the amphipods display normal behaviour.
A researcher studying Table 1 suggested that either wavelength of light could be used to cause Gammarus pulex to move away from the light. Evaluate the researcher's suggestion.
At dawn, Gammarus pulex move rapidly away from light into deeper gravel beds to hide from fish predators. Table 2 shows the maximum speeds recorded of these amphipods.
Table 2
| Response to light | Maximum speed / mm min−1\text{mm min}^{-1}mm min−1 |
|---|---|
| Amphipods moving towards blue light | 25 |
| Amphipods moving away from blue light | 48 |
Calculate the shortest time one Gammarus pulex would take to move from an exposed shallow pool at 0.5 m0.5\text{ m}0.5 m depth to a deep gravel bed at 9.3 m9.3\text{ m}9.3 m depth at dawn. Give your answer to the nearest hour.