Answer:
Over the years, the population of solid brown snails would decrease or extinct whereas the population of striped snails may increase comparatively.
It can be explained with the natural selection.
Striped snails must have some survival advantage over the solid color snails as they account for only 20% of the snails hunted by Seagulls.
It might be hard for the Seagulls to spot striped snails as compared to the solid snails.
Consequently, striped snails would survive and reproduce easily as compared to the solid brown snails.
Thus, the population of strip color snails would increase and that of solid brown snails would decrease.