Species ranges and boundary density maps
ERMs were downloaded for mammals, odonata and amphibians (https://www.iucnredlist.org/resources/grid/spatial-data); BirdLife maps, and GARD reptile maps (Roll et al. 2017). Each species polygon boundary was converted to a polyline, then split to produce independent polylines per species within each taxa.
To generate species boundary density maps, species were rasterized at 1km spatial resolution with the Eckert-IV projection, and stacked them into a single raster per taxon. The values indicate the number of species whose distribution boundaries overlapped with each cell, enabling overlay with other features to examine overlaps in R. These species boundary density maps underlie most subsequent analyses. R code, and caveats are given in supplements.
Geographic boundaries
Exploration of species range boundaries suggested numerous geographic datasets were used for different regions and taxa (Ficetola et al. 2014), so analysis was performed for a core set of taxa for all variables, in addition to specialist analysis for groups where other biases were evident.
For all taxa, we assessed the intersection of species range boundaries with national and provincial boundaries, with and without coastal boundaries. An international map was used because international (Western) assessors use them, and do not necessarily denote agreed country boundaries. A 2.5km buffer was added on each side of these boundaries in ArcMap to account for potential insignificant deviations from political boundaries.
Species range boundary densities were reclassified into richness classes using the ArcMap quartile function, and the percentage of the top-two, and top-three quartiles of range densities within different buffers (500m, 1000m, 2500m, 5000m) calculated per country to determine what percentage of top-quartile data within countries approximated borders. Several buffers were used to assess if there were fewer species range boundaries at greater distances from political boundaries as species ranges may be digitized with differing precisions even if tracking physical or administrative boundaries.