Intraspecific range dynamics and niche evolution in Candidula land snail species

The range dynamics of a species can either be governed by the spatial tracing of the fundamental environmental niche or by adaptation that allows to occupy new niches. Therefore, the investigation of spatial variation in the realized environmental niche is central to the understanding of species range limit dynamics. However, the study of intraspecific niche variation has been neglected in most phylogeographical studies. We studied the spatial distribution of the realized environmental niche in three land snail species of the genus Candidula, integrating phylogeographical methods, morphometrics, and spatial biodiversity informatics. The phylogeographical analyses showed significant range expansions in all species. These expansions were accompanied in Candidula gigaxii by a shift in the realized environmental niche, the species Candidula unifasciata followed its ancestral niche during expansion while the climate changed in the area of origin and Candidula rugosiuscula tracked the ancestral environmental conditions. The significant niche shifts were associated with potentially adaptive changes of shell morphology. We propose our presented approach as a practicable framework to test hypotheses on intraspecific niche evolution. (c) 2007 The Linnean Society of London.