Fig. 6: Influence of host diet type, diet-fibre content, and mean retention time on the absolute abundance of total methanogens.

a Abundance of total methanogens (n = 139) in animals grouped by diet type. The abundance of methanogens is the sum of individual quantifications of Methanobacteriales, Methanomicrobiales, Methanomassiliicoccales and Methanimicrococcus 16S rRNA genes. Two-sided Wilcoxon rank sum test with continuity correction was used to determine differences between diet types, *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p < 0.0001. Significant differences across all groups were determined via the Kruskal-Wallis test, with p < 0.05 set as significant. Correlation between diet-fibre content and (b) absolute abundance of methanogens in mammal species (n = 65) and (c) in primates (n = 12). d Correlation between digesta mean retention time and averaged absolute abundance of methanogens in primates (n = 22). A two-sided, squared Pearson correlation coefficient was computed to assess the relationship between values, unadjusted p-values < 0.05 were considered significant. Grey bands around the lines (panels b–d) represent the 95% confidence interval around the linear regression model. Statistical analyses and representation of the absolute/relative abundance of methanogens were carried out on species where archaea have been detected. Exact p-values of panel (a) are given in Supplementary Data 4.