Species, Mimicry and Phylogenetic Diversity

We used several metrics to measure different aspects of ithomiine diversity in each grid cell, as outlined below:

– Species richness is the most commonly used measure of diversity, and is computed as the number of species present in each grid cell.

– Mimicry richness corresponds to the number of mimicry patterns in each grid cell.

– Mimicry vulnerability is a relative vulnerability index based on the hypothesis that the smaller a mimicry ring, the more vulnerable it is (i.e., the more likely it is to lose species). Specifically, we define the vulnerability of mimicry ring i as 1/ni, with ni the number of species in the mimicry ring. The total vulnerability of a grid cell is the sum of vulnerabilities of each of its constituent mimicry rings

Σ1/ni. The relative vulnerability of a grid cell (i.e., scaled by its species richness), is (Σ1/ni)/Σni. The smaller this index is, the more robust the community of the grid cell.

– Faith's Phylogenetic Diversity (PD, Faith 2002, 2008) is recognised as the most complex measure of phylogenetic diversity. It is a group measure calculated as the total branch length connecting the species present in each grid cell.

– Equal-Splits (ES, Redding et al. 2008) is a measure of evolutionary distinctiveness, and it reflects how evolutionarily isolated a species is. Unlike the other measures used, it is a species property measure obtained by dividing the evolutionary time represented by a branch equally among its daughter branches. So, species that diverge early in the tree have higher ES values because much of their evolutionary time is not shared with any other species. The ES of a grid cell is given by the sum of the ES of all species occurring in it.

– Mean PhylogeneticDiversity (MPD) is the mean phylogenetic distance between all pairs of species occurring in a grid cell. While PD and ES are expected to be influenced by species richness (see Rodrigues et al. 2005; Nipperess chapter “The Rarefaction of Phylogenetic Diversity: Formulation, Extension and Application”), MPD is totally decoupled from it. High values of MPD indicate the presence of pairs of distantly related species in the grid cell.

For all metrics, we present only results for species present in the phylogeny (i.e., we ignore the single and seven species missing from the phylogenies of Ithomia and Oleria, respectively). Including all extant species for the metrics that do not depend on the phylogeny does not affect our results and conclusions (results not shown).