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Diagram showing mean darkness scores for the shaded habitats compared with the corresponding open habitats (for convenience, darkness score set to zero for the open habitat). Statistical significances (Kruskall–Wallis one-way analysis of variance): NS P>0.05; *P<0.05; **P<0.01; ***P<0.001. The overall pattern of a change towards darker shells in shaded habitats is significant (P<0.001; Fisher's combined probability test).
