Table 1. Description of landscape variables considered in analyses evaluating how biotic and abiotic factors influenced wild pig population density across their global distribution.
| Landscape Variable | Category, Description of Variable, and Calculation Method | Predicted Relationship | Supporting Citations for Prediction | Data Source |
|---|---|---|---|---|
| Agriculture | Biotic/Vegetation; all agricultural crop lands; proportional area within 10 km radius buffer | Positive, quadratic | Geisser and Reyer99, Honda59, Ballari and Barrios-García37, Morelle and Lejeune100 | Global Land Cover by National Mapping Organizations (GLCNMO) 2008; cropland cover types |
| Enhanced Vegetation Index (EVI)* | Biotic/Vegetation; plant productivity; mean value within 10 km radius buffer | Positive | Plant productivity: Melis, et al.42. | Google Earth Engine; Landsat 5 TM 32-Day EVI Composite 1984–2012 |
| Forest Canopy Cover | Biotic/Vegetation; all forest over 5 m; mean value of canopy cover within 10 km radius buffer | Positive | Honda59, Morelle, et al.60. | Google Earth Engine; Hansen Global Forest Change v1.0 year 2000 |
| Forest Minus Agriculture* | Biotic/Vegetation; difference between the proportion of forest and agriculture within 10 km radius buffer | Positive | See forest (classified as present or absent for this variable) and agriculture descriptions | See data sources for forest canopy cover and agriculture |
| Normalized Difference Vegetation Index (NDVI)* | Biotic/Vegetation; plant productivity; mean value in 10 km radius buffer | Positive | Plant productivity: Melis, et al.42. | Google Earth Engine; Landsat 5 TM 32-Day NDVI Composite 1984–2012 |
| Unvegetated Area | Biotic/Vegetation; cover types lacking vegetation, including bare, snow and ice, and urban; proportion within 10 km radius buffer | Negative | Plant productivity: Melis, et al.42. | Global Land Cover by National Mapping Organizations (GLCNMO) 2008; sparse vegetation, bare area, urban, and snow and ice cover types |
| Large Carnivore Richness | Biotic/Predation; number of terrestrial large carnivores presented by Ripple, et al.63, excluding the panda bear and adding the dingo; mean value within 40 km radius buffer | Negative | Woodall47, Jedrzejewska, et al.50., Sweitzer101, Ickes48, Melis, et al.42., Mayer and Brisbin36, Massei, et al.58. | Large carnivore distributions from IUCN79, Dingo distribution in Australia102 |
| Actual Evapotranspiration* | Abiotic/Climate; combination of evaporation of water and transpiration from plants; mean value within 40 km radius buffer | Positive, quadratic | Fisher, et al.45. | Global High-Resolution Soil-Water Balance: 1950–2000; Trabucco and Zomer103 |
| Potential Evapotranspiration | Abiotic/Climate; combination of evaporation of water and transpiration from plants; mean value within 40 km radius buffer | Positive, quadratic | Fisher, et al.45. | Global High-Resolution Soil-Water Balance: 1950–2000; Trabucco and Zomer103 |
| Precipitation Annual * | Abiotic/Climate; total precipitation during annual period; mean value within 40 km radius buffer | Positive | Woodall47, Weltzin, et al.104 but see Geisser and Reyer99 | Bioclim WorldClim World Climate Data – Bio 12 Annual Precipitation (mm); 1950–2000 |
| Precipitation Driest Season | Abiotic/Climate; total precipitation during driest 3 month annual period; mean value within 40 km radius buffer | Positive | Mortality related to periods of low precipitation, especially during summer105 | Bioclim WorldClim World Climate Data – Bio 17 Precipitation of Driest Quarter (mm); 1950–2000 |
| Precipitation Wettest Season | Abiotic/Climate; total precipitation during wettest 3 month annual period; mean value within 40 km radius buffer | Positive | Woodall47, Weltzin, et al.104 but see Geisser and Reyer99 | Bioclim WorldClim World Climate Data – Bio 16 Precipitation of Wettest Quarter (mm); 1950–2000 |
| Temperature Annual* | Abiotic/Climate; mean temperature over annual period; mean value within 40 km radius buffer | Positive, quadratic | Jedrzejewska, et al.50. | Bioclim WorldClim World Climate Data – Bio 1 Annual Mean Temperature (C); 1950–2000 |
| Temperature Summer* | Abiotic/Climate; mean temperature over warmest 3 month annual period; mean value within 40 km radius buffer | Positive, quadratic | Geisser and Reyer99, McClure, et al.57., but see Groves106 | Bioclim WorldClim World Climate Data – Bio 10 Mean Temperature of Warmest Quarter; 1950–2000 |
| Temperature Winter* | Abiotic/Climate; mean temperature over coldest 3 month annual period; mean value within 10 km radius buffer | Positive, quadratic | Bieber and Ruf107, Geisser and Reyer99, Melis, et al.42., Honda59, McClure, et al.57., but see Groves106 | Bioclim WorldClim World Climate Data – Bio 11 Mean Temperature of Coldest Quarter; 1950–2000 |
An asterisk (*) indicates landscape variables that were excluded from the final analyses due to high correlation with other variables.