Macroecological relationships reveal conservation hotspots and extinction-prone species in Australia's freshwater fishes

Aim: We (1) investigate the relationship between range size and body size for all Australian freshwater fish, (2) test whether this relationship changes with dispersal capacity, (3) assess whether this macroecological pattern can be used to detect potentially vulnerable, but currently unprotected, species, and (4) identify hotspots of freshwater fish conservation concern in Australia. Location: All Australian river basins. Methods: We test for relationships between geographic range size and body size in all Australian freshwater fishes, using quantile regression. We then investigate how these relationships vary with conservation status and dispersal capacity. We identify currently unlisted freshwater fishes that share traits with currently listed species and map their distribution, along with freshwater fish research effort, across Australia. Results: We found a positive, triangular relationship between range size and body size. Potamodromous species and species endemic to New Guinea and Australia had the largest geographic ranges, while diadromous and globally distributed species had the smallest geographic ranges. For a given body size, conservation-listed species had a range less than one-tenth the size of unlisted species. Based on this relationship, we identified 55 species that may be vulnerable to extinction. Most of these species are restricted to northern Australia, a climatically sensitive and poorly researched region on the verge of major development. Main conclusion: Despite differences in environments, levels of connectivity and life-history strategies, freshwater fishes exhibit a positive relationship between geographic range size and body size consistent with that found in terrestrial fauna. By identifying northern Australia as a hotspot of potentially vulnerable species, we provide an important context for guiding targeted research and informing future conservation management of Australia's freshwater fishes. We suggest macroecological relationships are likely to be useful for identifying species at risk of extinction across most taxa when detailed ecological data are absent.