Scientists investigated why some spittlebug morphs are dark (melanic) while others are pale.

One theory (the thermal melanism hypothesis) is that melanic body coloration allows spittlebugs to absorb more solar radiation, keeping them warmer in cooler climates. To test this, scientists placed realistic models of three different spittlebug morphs, each containing an internal micro-thermocouple probe, under a heat lamp. They recorded the internal body temperature of each model after 10 minutes.

The results are shown in Fig. 1.1.

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Fig. 1.1

Do the results in Fig. 1.1 support the theory that being melanic keeps spittlebugs warmer? Explain your answer.

The scientists aimed to investigate if it was only the color and pattern of the body that affected temperature regulation.

Suggest one improvement the scientists could make to ensure they only investigate the color and pattern. Explain your answer.

Another theory suggests that longitudinal stripes on pale spittlebugs act as disruptive camouflage, making them less likely to be detected and attacked by insectivorous birds, such as blue tits.

To test this theory, scientists created lifelike plasticine models of spittlebugs. One model was plain pale (unstriped), while other models were painted with dark stripes of varying widths.

Fig. 1.2 shows the percentage of model spittlebugs that were attacked by birds during the study.

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Fig. 1.2

Describe what Fig. 1.2 shows about the link between stripe width and protection from bird attacks.

In grasslands with very high bird populations, suggest what stripe width a spittlebug population should ideally have to minimise bird attacks. Explain your answer using Fig. 1.2.

Predators like birds can significantly reduce spittlebug populations. Use the theory of natural selection to explain how striped spittlebugs could have developed in grassland habitats.