 for phylogenetic diversity, the objects are species, the units are evolutionary features and the phylogenetic/feature diversity of the 3 (solid dots) species is indicated by the summed lengths of the blue branches on the phylogenetic tree. Note that this set of 3 species has greater phylogenetic diversity / feature diversity than the set of two hollow-dot species (red branches). [An  extended description of figure (a)  is in the supplement.]