Rad. Cameron, Cepaea nemoralis in a hostile environment: continuity, colonizations and morph-frequencies over time, BIOL J LINN, 74(2), 2001, pp. 255-264
In the 1930s Cyril Diver sampled and scored populations of the polymorphic
snail Cepaea nemoralis on the South Haven Peninsula, Dorset. His recording
methods make it possible to be confident about the absence of the species f
rom parts of the peninsula, which has acid soils and changing habitats, and
is generally unfavourable for the species. A resurvey in 1999 revealed a p
attern of retreats and extensions of distribution related to local environm
ental change. Where populations have persisted over the period, the pattern
of morph-frequency distributions has remained the same; there is equivocal
evidence for a small increase in the frequency of midbanded shells. While
most wetland populations have disappeared, new populations have become esta
blished along a roadside, and on newly-stabilized foredune ridges. Morph-fr
equencies in these new populations relate to those of the nearest establish
ed populations, and are sometimes monomorphic. The results are discussed in
relation to the history of the peninsula, and to the role of migration in
determining observed morph-frequency distributions. (C) 2001 The Linnean So
ciety of London.