Banded snails (Cepaea nemoralis) have evolved variations in shell colour and banding to survive in different environments.
Scientists have tried to find out why some snails have bands on their shells.
One theory is that having no bands keeps snails cooler in sunny, open grasslands. Scientists did an experiment to test this. They placed empty snail shells of different designs, filled with water and a temperature sensor, under a heat lamp. They measured the temperature of the water after 15 minutes.
The results are shown in Fig. 1.1.
Fig. 1.1
Do the results in Fig. 1.1 support the theory that having no bands keeps yellow snails cooler? Explain your answer.
The scientists were aiming to investigate if it was only the colour and banding of the shell that affected temperature regulation.
Suggest one improvement the scientists could make to ensure they only investigate the colour and banding of the shell. Explain your answer.
Another theory says that the bands act as camouflage, making snails less likely to be detected and eaten by birds, such as song thrushes.
To test this theory, scientists made models of snails out of plasticine and painted them. One model was plain yellow (unbanded). Other models had different widths of dark bands.
Fig. 1.2 shows the number of model snails that were attacked by birds.
Fig. 1.2
Describe what Fig. 1.2 shows about the link between shell band width and protection from bird attacks.
In areas with very high bird populations, suggest what band width a snail population should ideally have to minimise bird attacks. Explain your answer using Fig. 1.2.
Predators like birds can significantly reduce snail populations. Use the theory of natural selection to explain how banded snails could have developed in woodland habitats.