The function returns a list with three dissimilarity matrices.
bray.baldist object, dissimilarity matrix accounting for the dissimilarity derived from
balanced variation in abundance between sites
bray.gradist object, dissimilarity matrix accounting for the dissimilarity derived from
unidirectional abundance gradients
braydist object, dissimilarity matrix accounting for total abundance-based dissimilarity
between sites, measured as the Bray-Curtis index