Model evaluation
For BRT models, evaluation of model performance included measures of residual deviance, k-fold cross validation and the area under the receiver operator characteristic curve (AUC) (De’ath, 2007; Elith & Leathwick, 2009). GLM model performance was evaluated with AUC and adjusted D2 (a measure of the difference between null deviance and model deviance adjusted for degrees of freedom) and Akaike information criterion (Guisan et al., 2002; Franklin, 2010). Maxent models were evaluated by comparative training and test AUC, and omission on test and training samples against random prediction (specificity-sensitivity curves) (Hijmans, 2012; Elith & Leathwick, 2017).
For predictions of current habitat suitability, maps showing the predicted probabilities of presence or absence are presented for the best model with soil type and without soil type. Plots of the partial response of C. halei to each of the environmental variables and the proportional contribution of each variable to model performance are also presented.