Range-weighted metrics of species and phylogenetic turnover can better resolve biogeographic transition zones

Understanding changes of biodiversity across the landscape underlies biogeography and ecology and is important in land management and conservation. Measures of species and phylogenetic turnover used to estimate the rate of change of assemblages between sets of locations are more often influenced by wide-ranging taxa. Transition zones between regions that are associated with range-restricted taxa can be obscured by wide-ranging taxa that span them. We present a set of new range-weighted metrics of taxon and phylogenetic turnover, as modifications of conventional metrics, where the range-restricted components of the assemblages are assigned greater weight in the calculations. We show how these metrics are derived from weighted endemism and phylogenetic endemism and demonstrate their properties using a continent-wide data set of Australian Acacia. The range-weighted metrics result in better delineated transition zones between regions, in that the rate of turnover is steeper than with conventional turnover measures. These metrics provide important complementary information for the interpretation of spatial turnover patterns derived from conventional turnover metrics. Additionally, the phylogenetic variant incorporates information about phylogenetic relatedness while also not saturating at high values of turnover, thus remaining useful for comparisons over greater distances than conventional turnover metrics.