Environmental determinants of freshwater mollusc biodiversity and identification of priority areas for conservation in Mediterranean water courses

This study evaluates which environmental factors influence the biodiversity, distribution and conservation of freshwater mollusc communities in a Mediterranean Biosphere Reserve in the south-western Iberian Peninsula. Habitat features and two biodiversity indices (native species richness and diversity) were evaluated at 109 locations. Environmental gradients were assessed using principal component analysis, which orders the habitat variables along two gradients: headwater characteristics and water availability. According to a canonical correspondence analysis, the main environmental factors related to the distribution of species and community structure were, also, climate and headwater habitat features (precipitation, order, channel width, slope and pH), and heterogeneity and trophic features (IHF index and instream macrophytes cover). Relationships between biodiversity indices and environmental variables were best explained by a regression model incorporating, basically, aridity index and precipitation as the variables that accounted for most of the variance. This study demonstrates that distribution of freshwater molluscs along a highly stressed by drought Mediterranean region mostly depends on the local pool of species and their adaptive patterns to water availability.