Abstract
Estimating the overall number of species for a given taxon is a central issue in ecology and conservation biology. It should be particularly topical in the case of soil organisms, which represent the majority of known species, but it still suffers from a considerable taxonomic knowledge deficit. We propose here an estimation of the global number of earthworm species based on the Joppa approach, which models taxonomic effort over time in order to estimate the total number of known and, as yet, unknown species in a given taxa. We also conducted regional assessments of species numbers, which allowed us to refine global estimates by providing an accurate overview of the taxonomic deficit in different latitudinal locations on the planet. Our results allow us to propose a conservative estimation of global diversity of the order of 30,000 species. This means that the 5,679 species and subspecies already described represent at best around 20% of the global number of earthworm species. Considering the current rate of new species description, we calculate that it would take at least 120 years to describe all the species existing on Earth. We discuss the strategies that could be developed to reduce the magnitude of this taxonomic deficit.
Significance statement Earthworms are emblematic soil organisms performing critical ecological functions in terrestrial ecosystems, which contribute to the providing of goods and services for humanity. Paradoxically, our understanding of their global diversity remains limited, representing a significant shortfall in our capacity to build ecological and evolutionary knowledge for these organisms. Here, we demonstrate that the approximately 5,700 species currently known likely represent less than 20% of global earthworm diversity. At the current rate of species description, it could take more than a century to identify the tens of thousands of species yet to be discovered. Our findings underscore the urgent need for a rapid and substantial improvement in taxonomic efficiency and a revaluation of taxonomy as a critical scientific discipline.
Competing Interest Statement
The authors have declared no competing interest.
