Final answer:
The color forms of dog whelk are likely influenced by predation, with the coloration serving as camouflage to protect against predators in their native regions. Variants that blend in with their environment have higher survival rates than those that do not.
Step-by-step explanation:
The question asks about the survival rates of different color forms of the dog whelk (Nucella lapillus) and their relation to what environmental factor contributes most to the prevalence of one form over the other. The possible factors given are temperature fluctuations, wave exposure, predation, and salinity changes. Among these options, predation is the most likely factor influencing the survival of white-shelled and brown-shelled color forms, as these forms can provide different levels of camouflage against predators in different regions. A hypothesis related to this suggests that the coloration is an adaptation for camouflage to protect the snails from predators in their native region. Hence, snails with coloration that blends in with their surroundings would have a higher survival rate than those that stand out. This is supported by experimental setups where both mottled and solid snails are released into regions they are not native to, and their survival rates are measured against each other.