A string character specifying dissimilarity index to be used in calculating pairwise distances (Default index is "bray".).
"unifrac","wunifrac","manhattan", "euclidean", "canberra", "bray", "kulczynski", "jaccard", "gower", "altGower",
"morisita", "horn", "mountford", "raup" , "binomial", "chao", "cao" or "mahalanobis".