Novel splitting/lumping index reflects the history of species concepts applied to bumblebees (Insecta: Apidae)

Splitting or lumping of species is a concern because of its potential confounding effect on comparisons of biodiversity and on conservation assessments. By comparing global lists of species reported by previous authors to lists of the presently recognized species that were known to those authors, a simple ratio can be used to describe their relative splitting or lumping of species. One group of 'model' organisms claimed for the study of what species are and how to recognize them is bumblebees. A comparison of four bumblebee subgenera shows: (1) an early phase (up to and including 1931) showing splitting, in which taxonomy was dominated by a typological concept of invariant species with heavy reliance on colour-pattern characters; (2) a middle phase (1935-98) showing lumping, associated with a shift to a polytypic concept of species emphasizing morphological characters, often justified with an interbreeding concept of species, but only rarely associated directly with process-related characters; and (3) a recent phase (after 2000), using a concept of species as evolutionarily independent lineages, as evidenced by corroboration from integrative assessment, usually including evidence for coalescents of species in fast-evolving genes compared with morphology. Analysis of splitting or lumping should help to improve biodiversity comparisons and conservation.

Automated summary

The splitting or lumping of species can have confounding effects on comparisons of biodiversity and conservation assessments. By comparing global species lists reported by previous authors to presently recognized species lists, a simple ratio can describe the relative splitting or lumping of species. Bumblebees are used as a model organism group to study species recognition and definition. The analysis of splitting or lumping can help improve biodiversity comparisons and conservation assessments.