Quantifying climatic niche breadth.
We quantified the temperature and precipitation niche breadth of each
species as follows, using custom scripts in the R statistical computing
environment (R Core Team, 2020) and the resulting climatic niche breadth
distributions were contrasted among species occupying different
elevations. Having parsed the SDMs among small increments of each
climatic variable, we interpreted these climatic vectors as representing
states a species could occupy within its range. We used Levins’ (1968)
niche breadth index to quantify SDM uniformity across the full suite of
possible climatic states for either MAT or MAP using: