Résumé
An increasing number of studies are simultaneously investigating species
diversity (SD) and genetic diversity (GD) in the same systems, looking for
‘species– genetic diversity correlations’ (SGDCs). From negative to
positive SGDCs have been reported, but studies have generally not
quantified the processes underlying these correlations. They were also
mostly conducted at large biogeographical scales or in recently degraded
habitats. Such correlations have not been looked for in natural networks
of connected habitat fragments (metacommunities), and the underlying
processes remain elusive in most systems. We investigated these issues by
studying freshwater snails in a pond network in Guadeloupe (Lesser
Antilles). We recorded SD and habitat characteristics in 232 ponds and
assessed GD in 75 populations of two species. Strongly significant and
positive SGDCs were detected in both species. Based on a decomposition of
SGDC as a function of variance–covariance of habitat characteristics, we
showed that connectivity (opportunity of water flow between a site and the
nearest watershed during the rainy season) has the strongest contribution
on SGDCs. More connective sites received both more alleles and more
species through immigration resulting in both higher GD and higher SD.
Other habitat characteristics did not contribute, or contributed
negatively, to SGDCs. This is true of the desiccation frequency of ponds
during the dry season, presumably because species markedly differ in their
ability to tolerate desiccation. Our study shows that variation in
environmental characteristics of habitat patches can promote SGDCs at
metacommunity scale when the studied species respond homogeneously to
these environmental characteristics.