Tests of robustness

Question

To test whether ED scores are comparable among taxonomic groups, we examined how species' ED accumulates as progressively larger clades are considered. If ED scores are truly comparable, their rank order will be independent of the size of the clade considered. We randomly selected one Critically Endangered species from each of ten mammal orders and measured the cumulative ED score at each node between the species and the root of the mammal supertree, thus redefining and enlarging the clade (and so increasing the number of species it contained) at each step.

Taxonomic changes have the potential to dramatically alter the ED scores of individual species. Splitting a species in two reduces the distinctiveness of all branches ancestral to the split, particularly those near the tips. If ED scores are highly sensitive to taxonomic changes then it may be meaningless to apply them in setting conservation priorities. The effects of taxonomic changes on ED scores were therefore investigated in the primates, which have recently experienced considerable taxonomic inflation [27]. We compared primate ED scores under a biological species concept [35: 233 species] and a phylogenetic species concept [36: 358 species]. We employed a single phylogeny [31], but changed the number of species represented by each tip. We calculated the expected ED for multi-species tips by treating them as if they were descended from a polytomy of {n+r+1} descendent branches, where n is the actual number of descendent branches and r is the number of species represented by the tip.
Extract only the main points for the information given above

Answer 1

- ED scores were tested for comparability among taxonomic groups by examining how species' ED accumulates as larger clades are considered.
- The rank order of ED scores should be independent of the size of the clade considered if they are truly comparable.
- Ten Critically Endangered species from different mammal orders were randomly selected and their cumulative ED scores were measured at each node in the mammal supertree.
- Taxonomic changes can significantly alter the ED scores of individual species, particularly when species are split into multiple entities.
- The impact of taxonomic changes on ED scores was investigated using primates, which have recently undergone taxonomic inflation.
- ED scores were compared under a biological species concept (233 species) and a phylogenetic species concept (358 species) in primates.
- A single phylogeny was used, but the number of species represented by each tip was changed to calculate the expected ED for multi-species tips.