Geographic variation in range size and beta diversity of groundwater crustaceans: insights from habitats with low thermal seasonality

AIM: Three broad mechanisms have been proposed to explain geographic variation in species range size: habitat area/heterogeneity, climate seasonality and long‐term climate variability. However, it has proved difficult to disentangle their relative role, particularly as temperature seasonality often covaries with the amplitude of long‐term temperature oscillations. Here, we shed new light onto this debate by providing the first continental‐scale analysis of range size and beta diversity in groundwater habitats, where taxa are not exposed to latitudinal variation in temperature seasonality. LOCATION: Europe. METHODS: We compiled and mapped occurrence data for 1570 groundwater crustacean species. Generalized regression models were used to test for latitudinal variation in geographic range size and to assess the relative role of the three broad mechanisms in shaping present‐day patterns of range size. We partitioned beta diversity into its spatial turnover and nestedness components and analysed their latitudinal variation across Europe. RESULTS: Median range size increases with latitude above 43° N and the range size of individual species is positively correlated to latitude, even after accounting for phylogenetic effects. Long‐term temperature variability accounted for a substantially higher variation in median range size of groundwater crustaceans across Europe than precipitation seasonality and habitat heterogeneity, including aquifer area, elevation range, climatic rarity and productive energy. Spatial turnover contributes significantly more to beta diversity in southern regions characterized by stable historic climates than it does in northern Europe. MAIN CONCLUSIONS: Our findings add support to the historic climate hypothesis which suggests that patterns of increasing range size and decreasing species turnover at higher latitudes in the Palaearctic region are primarily driven by long‐term temperature oscillations rather than by climatic seasonality and the availability and heterogeneity of habitats.