2.8 Statistics
We used general linear models (GLMs) for ANOVA and ANCOVA models. Multiple comparisons between means after the ANOVA were performed with Tukey–Kramer tests. We tested the significance of all possible interactions between covariates and factors in all ANCOVA models and reported all significant results. The above tests and LOESS smoothing were performed in SAS ver. 9.4 (SAS Institute, Cary, NC, USA). GAM models were fitted with R (ver. 3.3.1; R Core Team 2016).