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).