Latitudinal gradients of freshwater gastropods from the Western Palearctic

Abstract

We analysed changes in species richness and endemics of freshwater gastropods along the Western Palearctic, within the following boundaries: 10°W–30°E, 32°N–71°N. The aims of this study were to test: (1) the consistency of latitudinal distribution of Western Palearctic freshwater gastropods; and (2) the relationships between freshwater gastropods and environmental factors. Analyses were based on presence/absence data of 911 freshwater gastropod species in 474 sites, located along three bioclimas (boreal, Mediterranean and temperate) and four Koppen–Geiger climatic regions (arid, cold, polar and alpine, and temperate). Five environmental variables were used to assess their influence on the distribution of freshwater gastropods. Relationships between variables were studied using parametric, non-parametric and multivariate statistics, and general regression models. Species number per degree of latitude followed a hump-shaped curve, increasing to 41°N–43°N and, from there, decreasing to reach minimum values in boreal areas. Relationships between species richness and endemics with current and past environmental variables were likewise discussed.