The Role of Environmental Heterogeneity in Maintaining Reproductive Isolation between Hybridizing Passerina (Aves: Cardinalidae) Buntings

Table 3

List of environmental variables used in our analyses.

Data Record	Instrument	Ecological attributes	Variables derived
Normalized Difference Vegetation Index (NDVI)	Satellite-MODIS	Vegetation density	NDVI mean
Vegetation Continuous Field (VCF)^*§	Satellite-MODIS	Forest cover + heterogeneity	Tree cover
Scatterometer-Backscatter^*†	Satellite-QSCAT	Surface moisture + roughness (forest structure), seasonality	QSCAT aug
DEM*	SpaceShuttle SRTM	Topography + ruggedness	SRTM
WorldClim^¶	Station-Network	Bioclimatic variables	Bio1, Bio2, Bio10, Bio11, Bio12, Bio15, Bio17, Bio18

*Data at native resolutions smaller or larger than 1 km have been aggregated to 1 km.
^†QSCAT is based on data from 2001.
^§Based on MODIS data from 2001 [41].
^¶WorldClim data are based on monthly climatologies from 1950–2000 [39]. The bioclimatic variables are annual mean temperature (Bio1), mean diurnal temperature range (Bio2), mean temperature of the warmest quarter (Bio10), mean temperature of the coldest quarter (Bio11), annual precipitation (Bio12), precipitation seasonality (Bio15), precipitation of the wettest quarter (Bio17), and precipitation of the warmest quarter (Bio18).