Earthworm ecological categories are not functional groups
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POSITION AND OPINION PAPERS
Earthworm ecological categories are not functional groups Nicolas Bottinelli 1,2 & Yvan Capowiez 3 Received: 8 June 2020 / Revised: 28 August 2020 / Accepted: 15 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Seven earthworm ecological categories, including anecics, endogeics and epigeics, were defined by Marcel Bouché in 1972 based only on morpho-anatomical characteristics measured on European lumbricids. These categories had an outstanding success, and their use was generalized even outside of Europe. However, most of the time, only the three main categories are used, and over two decades, these categories have been considered functional groups, i.e. to presume how earthworms influence the soil functioning. Moreover, this relationship between ecological categories and functional groups is seldom tested and often uncritically accepted by soil biology researchers. It is then not surprising to observe unexpected trends when earthworm species are gathered in ecological categories to, for instance, analyze burrow systems or cast properties. We believe it is time to acknowledge that ecological categories are not functional, because they were not made for this purpose. We also propose three future directions in order to either improve our knowledge on the functional effects of earthworms or to build new authentically functional groups: (i) going back to the seven initial ecological categories to provide greater accuracy than the usage of the simplified three-level classification; (ii) testing, for a set of selected species, the functionality of the groups, being ecological categories or new tailored ones; and (iii) using trait-based approach in order to study the correlation between some earthworm traits and main soil functions. Keywords Anecic . Endogeic . Epigeic . Ecological traits . Burrow . Cast . Earthworms
In his 1972 seminal book ‘Lombriciens de France’, Marcel Bouché initially described seven earthworm ecological categories (anecic, endogeic, epigeic, epi-anecic, endo-anecic, epi-endogeic and intermediate) (Bouché 1972). Five years later, he simplified the explanation of these categories by describing a ternary plot in which the three major categories (anecic, endogeic and epigeic) represent the three poles (Bouché 1977). This classification system, which was initially applied to French lumbricids, has been an outstanding success in the earthworm research community and is now commonly used for non-lumbricid species as well. However, Bouché only applied earthworm morpho-anatomical traits to describe * Yvan Capowiez [email protected] 1
IRD, UMR iEES Paris, Sorbonne Université - Institute of research for Development (IRD), 32 av. H. Varagnat, 93143 Bondy, France
2
Soils and Fertilizers Research Institute (SFRI), Duc Thang, Bac Tu Liem, Hanoi, Vietnam
3
INRAE, UMR 1114 EMMAH, INRAE - Université d’Avignon, Domaine Saint Paul, 84914 cedex 09 Avignon, France
each species and did not try to relate these categories to some soil functions. For
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