Predation by fish or crustaceans can certainly affect the behavior of
mollusks.  Studies on freshwater and marine mollusks have shown that when
the scent of either the predator or chewed-up mollusks is present in the
water, the mollusks change the way they use their habitat.  If there are
structures to hide under, the mollusks will run for cover.  If no predator
or dead snail effluent is put into the environment that same species
does not hide. Thus, if a prey species has a larger geographic range than
its predator (assuming it has only one), one could potentially observe two
behaviors exhibited by one species in different areas.  Likewise, if the
predator and prey have the same geographic ranges but rocks to hide under
are not available in particular locations, then of course we won't observe
this behavior.  One must then ask how the snail population can survive in
that area without cover.  Then one must consider the possibility of
immigration of snails or larvae from nearby populations with cover or the
possibility that the snails and the crabs are just playing a practical
joke on the observer.
 
Some mollusks, however, may breed fast enough or in such
large numbers that predation is not a factor.  In this case, the evolution
of anti-predatory behaviors might not be advantageous.  Crawling under a
rock could reduce the amount of time needed for grazing and mating giving
other snails that eat and play around in the open with other snails
constantly a decisive advantage in growth and reproductive success.
 
Greg Herbert
Loyola University
 
On Fri, 30 Jan 1998, MR ART WEIL wrote:
 
>     This weeks question has to do with the discussion concerning
> carnivores, herbivoves, and omnivores. What we wonder is if there has
> ever been any observation of mollusks changing their behavior, in
> responce to changing environment. That is, do they change when
> polution changes their environment, or storms upset their biome? Is
> there evidence that separated populations of the same species behave
> differently due to differences in their environment?
>     It seems that such an ability would aid ones evolutionary
> possibilities. Just wondering.
>             Art
>