AimGlobal-scale studies are required to identify broad-scale patterns in the distributions of species, to evaluate the processes that determine diversity and to determine how similar or different these patterns and processes are among different groups of freshwater species. Broad-scale patterns of spatial variation in species distribution are central to many fundamental questions in macroecology and conservation biology. We aimed to evaluate how congruent three commonly used metrics of diversity were among taxa for six groups of freshwater species.LocationGlobal.MethodsWe compiled geographical range data on 7083 freshwater species of mammals, amphibians, reptiles, fishes, crabs and crayfish to evaluate how species richness, richness of threatened species and endemism are distributed across freshwater ecosystems. We evaluated how congruent these measures of diversity were among taxa at a global level for a grid cell size of just under 1°.ResultsWe showed that although the risk of extinction faced by freshwater decapods is quite similar to that of freshwater vertebrates, there is a distinct lack of spatial congruence in geographical range between different taxonomic groups at this spatial scale, and a lack of congruence among three commonly used metrics of biodiversity. The risk of extinction for freshwater species was consistently higher than for their terrestrial counterparts.Main conclusionsWe demonstrate that broad-scale patterns of species richness, threatened-species richness and endemism lack congruence among the six freshwater taxonomic groups examined. Invertebrate species are seldom taken into account in conservation planning. Our study suggests that both the metric of biodiversity and the identity of the taxa on which conservation decisions are based require careful consideration. As geographical range information becomes available for further sets of species, further testing will be warranted into the extent to which geographical variation in the richness of these six freshwater groups reflects broader patterns of biodiversity in fresh water.

Aim Species geographic ranges are the 'fundamental units' of macroecology. Range size is a major correlate of extinction risk in many groups, and is also critical in studies of biotic responses to climate change. Despite this, there is a lack of studies exploring the role of environmental, historical and anthropogenic processes in determining large-scale patterns in range size. We perform the first global analysis of putative drivers of range size variation in any group, choosing amphibians as our study taxon. Our aims are to disentangle the many hypothesized causes of range size variation and evaluate support for 'Rapoport's rule' , the observation that range size correlates with latitude. Location Global.Methods We develop a global map of gridded median range size using the International Union for Conservation of Nature (IUCN) distribution maps. From this we perform spatial and non-spatial regressions to explore relationships between range size and nine hypothesized variables in six biogeographic realms. We use information-theoretic model selection to compare multiple competing variables, simultaneously evaluating the relative support for each one.Results Current climate -environmental water and energy, and temperature seasonality -is consistently highly ranked in spatial and non-spatial analyses. Human impacts and other environmental measures (topographic and landscape complexity, effective area, climate extremes) show mixed support, and glacial history is consistently unimportant. Our findings add further evidence to the view that Rapoport's rule is a regional, not global, phenomenon. Main conclusionsThe primary importance of temperature seasonality may explain why Rapoport's rule is largely restricted to northern latitudes, as this is where seasonality is most pronounced. More generally, the dominance of contemporary climate in our analyses (even when accounting for space) has stark implications for the future status of amphibians. Changes in climate will almost certainly interact with the anthropogenic processes already threatening a third of amphibians globally, with the effects being most keenly felt by species with a restricted range.