S. atlantis S. atlantis northern S. hesperis northern S. hesperis southern S. hesperis southern S. hesperis
Predictor variable mean s.e. mean s.e. mean s.e.
terrain ruggedness 6.58 10.07 15.13 10.5 4.06 5.34
heat load 0.84 0.44 0.28 0.62 0.18 0.41
land cover 54.78 13.97 35.04 12.79 39.52 26.7
mean temperature of the coldest month 0 0 0 0 0 0
mean temperature of the warmest month 9.99 15.87 3.1 5.1 0 0
continentality 0 0 0.56 1.26 0 0
chilling degree days 1.89 2.61 0 0 4.46 7.16
growing degree days 19.54 18.74 42.71 20.12 41.59 34.62
extreme minimum temperature 4.73 5.44 0 0 0 0
precipitation as snow 0.19 0.43 0.17 0.38 3.97 6.05
summer (Jun to Aug) precipitation 1.47 1.9 3.02 3.98 6.22 9.61