F2Adonis2 - PERMANOVA using the F2 Statistic

Implements the F2 statistic of Anderson et al. (2017) <doi:10.1111/anzs.12176> for permutational multivariate analysis of variance (PERMANOVA) on dissimilarity matrices. The F2 statistic uses group-specific dispersion estimates, so group centroids can be compared when dispersions differ and group sizes are unequal. P-values are obtained by permutation, bootstrap, or bias-adjusted bootstrap. The formula interface follows 'adonis2()' in the 'vegan' package.