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.