organism with these types of adaptations (eg the blue periwinkle)
is well suited to the stressful upper zones of the rock platform.
It should be remembered that it can also cope with the physical
parameters which exist at lower levels.
are periwinkles only found at upper levels? The answers lie
in the interactions which exist between the periwinkle and
the other organisms along the tidal continuum.
periwinkle has similar food and shelter requirements as another
snail (eg, the conniwink), they will be in competition for
these resources. If the conniwink is a more successful competitor
it will restrict the numbers of periwinkles in an area or
exclude them altogether. Distribution patterns are therefore
a result of adaptations and interactions.