Fig. 2

Measuring ɑ-diversity with Hill numbers. ɑ-diversity indices were first unified by ecologist Mark Hill as the inverse of mean proportional abundances in a community [123, 124]. The value of q (or order of diversity) describes how this mean is calculated, affecting the sensitivity of diversity indices to rare species. In a–c, Hill numbers are shown for a metabarcoding data obtained from the fecal sample of an Ecuadorian finch (publicly available in NCBI with accession number SRR6486665 [125]). When q=0, the weighted harmonic mean of species’ proportional abundances is measured, and richness is assessed (a). When q=1, the weighted geometric mean is measured, and Shannon’s entropy is assessed (b). When q=2, the weighted arithmetic mean is measured and inverse Simpson’s richness is assessed (c). All Hill numbers are expressed in units of effective numbers of species, or the number of species that would be expected in a community in which all species are equally abundant