A species of land snail has a shell that can be either plain or banded with dark stripes. A bird predator hunts the snails by sight and eats the ones it sees most easily. Biologists recorded the percentage of plain-shelled snails in two habitats with different backgrounds.
| Habitat | Background | Plain-shelled snails / % |
|---|---|---|
| Woodland floor | dark, uniform leaf litter | 74 |
| Grassland | pale, patterned grass stems | 21 |
Using the data, analyse the relationship between the habitat background and the percentage of plain-shelled snails.
[2]
Explain how predation by the bird leads to the differences in shell type between the two habitats.
[3]