On Atlantic shores, the dog whelk (Nucella lapillus) has two color forms, white-shelled and brown-shelled. Survival of one form over the other form in a region appears to be related to
Temperature
predation pressure from a common predator, the seagull (Larus sp.).
Predation by seagulls could have a significant impact on the survival of the two color forms of the dog whelk. This has been observed along the Atlantic shores. The white-shelled and brown-shelled forms are preyed upon by seagulls, which have a strong preference for the white-shelled dog whelks.
The preference of seagulls for white-shelled dog whelks is because the white-shelled coloration provides better camouflage against dark rock surfaces. This makes the white-shelled dog whelks harder for seagulls to spot and capture.
In contrast, brown-shelled dog whelks do not provide such good camouflage, making them easier to spot and capture for seagulls. As a result, brown-shelled dog whelks have a lower survival rate than white-shelled dog whelks in regions where seagulls are a significant predator.
Therefore, the survival of the white-shelled dog whelks is higher than that of the brown-shelled dog whelks in regions with high seagull predation pressure. This phenomenon is an example of natural selection, where the selection pressure exerted by the seagulls on the dog whelks has favored the white-shelled form over the brown-shelled form.
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