To link abiotic environmental variation with host specialization (Q3), we identified areas with optimal conditions for specialization using environmental niche models (ENMs). ENMs are a widely used tool for characterizing suitable habitat for a species based on correlation between environment and observed occurrences of an organism (Elith et al. 2010). An implicit assumption is that organisms should have higher fitness in locations with higher habitat suitability predicted by ENMs (Nagaraju et al. 2013, Wittmann et al. 2016).