Having accurate maps of species distributions is fundamental to assessing conservation priorities and developing targeted conservation strategies, but also to understanding basic biodiversity patterns.
This study analyses expert range maps of 50,000 animal species to test the assumption that these provide consistent and standardized estimates of species' ranges.
By rasterizing and stacking species range boundaries, they authors created boundary density maps grouped by higher level taxa (mammals, odonates, amphibians, birds and reptiles) and overlayed these with different features such as administrative boundaries.
This exercise demonstrated an average of 20—30 per cent of non-costal species range boundaries coinciding with country borders, many with no clear geophysical boundaries. When considering species richness, 60 per cent of areas with the highest spatial turnover in species occurred at political boundaries.
Finally, the authors compared the expert maps with GBIF mediated data, finding 80 per cent of taxa having more than 30 per cent of their occurrences outside the corresponding range map.
Taken together, these results reveal high bias of expert range maps at administrative borders, suggesting a need for alternative approaches to reconstructing patterns of distribution.