Unravelling Regional Patterns in Freshwater Turtle Diversity: Insights From the Western Palearctic and Nearctic

ABSTRACT Aim Turtles are widely distributed across continental freshwater systems in the Western Palearctic and Nearctic regions. Nevertheless, the two regions differ markedly in species richness, with 55 species in the Nearctic assemblage and only seven in the Western Palearctic. This study investigated the interplay between environmental filters (hydrological, climatic, and landscape factors), species traits, and species phylogenetic relatedness in shaping the spatial patterns of Holarctic freshwater turtles. Location Western Palearctic and Nearctic. Time Period Present day. Major Taxa Studied Freshwater turtles (order Testudines). Materials and Methods Locality data for 62 turtle species were collected from open‐access databases. Distance‐based redundancy analysis was conducted to assess the influence of environmental, species trait, and phylogenetic components on species spatial distribution matrices. Results In the Western Palearctic and Nearctic regions, climate and landscape variables were highly associated with the spatial patterns, with these relationships being stronger in the Nearctic than in the Western Palearctic. In both regions, phylogenetic relatedness was also correlated with the structuring of species distributions, although this association appeared more marked in the Western Palearctic. Hydrological factors and species traits showed only weak relationships with the spatial configuration. Conclusions The Western Palearctic and Nearctic regions differ significantly in the richness of their freshwater turtle assemblages. In the Nearctic, the spatial relationships among species show stronger associations with environmental conditions than in the Western Palearctic. This pattern is consistent with a high diversity of assemblages composed of closely related species that exhibit fine‐scale turnover along environmental gradients.