Towards a biologically meaningful classification of subterranean organisms: a critical analysis of the Schiner-Racovitza system from a historical perspective, difficulties of its application and implications for conservation

Abstract

Citation: Trajano E, Carvalho MR (2017) Towards a biologically meaningful classification of subterranean organisms: a critical analysis of the Schiner-Racovitza system frpm a historical perspective, difficulties of its application and implications for conservation. Subterranean Biology 22: 1-26. https://doi.org/10.3897/subtbiol.22.9759 Abstract Subterranean organisms always attracted the attention of humans using caves with various purposes, due to the strange appearance of several among them and life in an environment considered extreme. According to a classification based on the evolutionary and ecological relationships of these organisms with subterranean habitats, first proposed by Schiner in 1854 and emended by Racovitza in 1907, three categories have been recognized: troglobites, troglophles and trogloxenes. The Schiner-Racovitza system has been discussed, criticized, emended, the categories have been redefined, subdivided, original meanings have changed, but it is used until now. Herein we analyze in a conceptual framework the main ecological classifications of subterranean organisms, from Schiner to Trajano, in 2012, so far the last author to introduce a relevant conceptual change on the categories definitions, incorporating the source-sink population model. Conceptual inconsistencies are pointed, especially with regards to the generally ill-defined trogloxene category, and the correspondence between categories according to the original sense and in alternative classifications is discussed. Practical criteria for distinction between these categories and difficulties for their application are presented. The importance of rightly classifying subterranean populations according to the Schiner-Racovitza system for conservation of these fragile and mostly threatened habitats is discussed.

Finding answers in the dark: caves as models in ecology fifty years after Poulson and White

“…Over the years, different classification criteria have been proposed (reviewed by Sket 2008, Trajano 2012, Trajano and Carvalho 2017, Giachino and Vailati 2017. This facilitates the analysis of subterranean patterns and processes and to generalise the results to distinct subterranean communities.…”

“…Recently, Trajano (2012) proposed to introduce a source-sink population model in the classification process, providing a more objective method for sorting subterranean species in one of the ecological categories mentioned above (details in Fig. Although the applicability of this classification is often hindered by the scarcity of distributional and genetic data for most subterranean species, the introduction of this idea certainly represents a significant improvement 'towards a biologically meaningful classification of subterranean organisms' (Trajano and Carvalho 2017). Although the applicability of this classification is often hindered by the scarcity of distributional and genetic data for most subterranean species, the introduction of this idea certainly represents a significant improvement 'towards a biologically meaningful classification of subterranean organisms' (Trajano and Carvalho 2017).…”

“…Moreover, the investigation of these habitats is important for understanding the biogeography and the evolutionary patterns of the subterranean fauna (Christian 1987, Howarth 1993, Arnedo et al 2007, Ružička et al 2013. occasionally washed into caves during flooding or temporary exploiting the underground domain in search specific environmental conditions, are not considered in the classification (Trajano and Carvalho 2017). (2012) recently proposed to incorporate a source-sink population model to obtain a more objective ecological classification of subterranean organisms.…”

A synthesis on cave-dwelling spiders in Europe

“…We relied on the online taxonomic resources on spiders (Nentwig, Blick, Gloor, Hänggi, & Kropf, ; WSC, ) and the associated literature data to compile the checklist of the European subterranean spiders. In the absence of detailed information on the epigean/hypogean distribution and the natural history of the taxa of interest (Trajano & de Carvalho, ), we based the ecological classification of species (troglobionts or troglophiles as defined in Table ) on troglobiomorphic traits reported in the original description of each species. When available, ecological information was also considered.…”

An ecological survey of the invertebrate community at the epigean/hypogean interface

“…trogloxenes, troglophiles, troglobionts) according to their preferred habitat and general association with the subterranean domain (Sket 2008, Trajano andCarvalho 2017). However, most ecological classifications, such as the Schiner-Racovitza system, are deemed to oversimplify real cases given that boundaries between the categories are often vague and difficult to attribute (Martìn et al 2001, Giachino andVailati 2016).…”