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in practice, it has not precluded the discovery and delimitation of taxa throughout the tree of life. For sound reasons, taxonomists working with different groups of organisms at times adopt different species concepts. However, consistency, utility, and acceptability of a global species list will be maximised if common approaches to delimiting species are adopted as widely as possible, at least within taxonomic groups. At times, governance rules for a global species list will need processes for deciding appropriate approaches to recognising species and clear standards for justifying these decisions. Traditionally, such decisions have been made by following the opinion of responsible experts. However, aggregators need agreed-upon guidance on how to choose when the views of equally responsible experts diverge.
7. A global list must balance conflicting needs for currency and stability by having archived versions
Taxonomy is a dynamic process, and debate about taxonomic circumscriptions and relationships is an irreducible outcome of taxonomic research. As with other scientific hypotheses, taxonomies attain legitimacy (or are overturned) through constant testing, with new, sometimes competing, hypotheses proposed, tested against new evidence, discussed, and ultimately adopted, modified, or rejected. Some users may be institutionally unable to accommodate rapid change and thus may prefer stability over currency. As an example, transaction and opportunity costs of changing national legislation and international conventions to accommodate taxonomic progress can be high if they result in laws, schedules, and agreements lagging taxonomic currency by years or decades [24]. One transparent process that balances the needs of all users is to ensure that dynamic sections of the list are published regularly as versioned, permanently accessible archives. Legislators and others whose need for stability is greater than their need for currency may choose to reference a designated, date-stamped, 'frozen' version of the list or of a single taxon as represented in the list. They must be able to access that version for as long as needed, even while the current list is updated. If a unified list enables the history of changes in taxa and names to be traced between versions, the onus is then on legislators, not taxonomists, to use a version that is acceptable and to update legislation at a rate commensurate with need.
8. Contributors need appropriate recognition
Taxonomy is a vocation for many taxonomists, an activity pursued well beyond the hours of normal employment or, in many cases, not remunerated at all—e.g., amateurs were responsible for 62% of the new terrestrial and freshwater multicellular species described in Europe between 1997 and 2008 [25], and many taxonomists remain active in research and publication long after retirement. Any global list will draw heavily on such dedication. Whilst many taxonomists derive intrinsic pleasure from their work, the most common extrinsic reward is through recognition by peers (and sometimes the broader public) through publications, particularly the description of new taxa. However, list preparation and annotation require effort, which should also be recognised, so any global listing system will need a mechanism for citation and public recognition of the taxonomists and organisations whose skills have been drawn on most heavily to give the list legitimacy. The use of a formal citation of a list that includes editors' names, as conducted by the CoL [21], enhances its authoritativeness and ensures that users immediately know who was responsible for its quality. It also gives formal permanent credit to the people who created it. An attribution mechanism may track fine-scale microcontributions (as in Wikispecies), with periodic publication of parts or revised sections of the list in online open-access journals. Open citation also enhances transparency. Just as the names of authors who erect or revise species names are acknowledged, so too should be the names of those who compile and validate the taxonomic list.
PLOS Biology | https://doi.org/10.1371/journal.pbio.3000736 July 7, 2020
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