THE VARIED ROLES OF SNAILS - National Universities Commission

of spermatozoa in males or stimulate oogenesis in the
females.. Self fertilization is a common mode of
reproduction and mating is often absent while oviposition
results from the transfer of stimulatory substances with
origin in the reproductive tract during mating.
c. VARIOUS FACTORS AFFECTING
SNAIL DISTRIBUTION
Factors affecting the distribution of gastropods
include the nature of the substratum, certain physical,
chemical and biological factors. Other factors include:
mortality, diversity, turnover, disturbance, and
productivity. It has been observed that the snails’
responses to these factors are species specific and each
species is able to maintain their populations within
certain limits of tolerance.
A habitat can sustain a certain maximum number of
individuals (the carrying capacity) which is determined
by the availability of resources e.g. food quality, as well
as space. The density of species living in a relatively
stable environment fluctuates around the unstable
environments and may never approach the carrying
capacity, they fluctuate severely. In unstable
environment there is regular high mortality caused by
the periodic unfavourable conditions.
The effects of some ecological factors on snail growth
and distribution are difficult to assess as they may be
both of a direct and an indirect nature. Studies show that
snails have distributional patterns in nature which
strongly correlate with the distribution of specific
aquatic macrophytes for freshwater species (Pimentel
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