A synthesis on cave-dwelling spiders in Europe

Abstract

We provide the first overview on spiders living in subterranean habitats in Europe, including the first European subterranean spider checklist. In Europe, there are 486 spider species known to dwell in caves and other subterranean habitats, distributed across 22 families. Despite a few species being able to colonize caves across the whole continent, approximately 90% of the species show a restricted distribution, occurring exclusively in one or two countries. From a biogeographic perspective, southern Europe emerges as the main hot spot of subterranean spider diversity, showing the highest richness of endemic species. Compared to other temperate regions of the world, some families appear to be well represented and other poorly represented (or lacking) in European subterranean habitats. Overall, it appears that the taxonomical knowledge on subterranean spiders in Europe is sufficient, but not evenly distributed. As this checklist represents a useful baseline for advances in this field, we point out specific areas of interest for future research.

Tracking the ice: Subterranean harvestmen distribution matches ancient glacier margins

“…For example, the absence of a native subterranean fauna in the northernmost European regions mirrors the severe effects of the compact ice shield covering Northern Europe during the Last Glacial Maximum (LGM, about 22,000 years ago) (Ehlers, Gibbard, & Hughes, ). As a result, subterranean species occurring in these areas mostly exhibit weak adaptations, because northernmost subterranean habitats have been actively undergoing recolonization in recent times (Holdhaus, ; Růžička, Smilauer, & Mlejnek, ; Mammola, Cardoso, Ribera, Pavlek, & Isaia, ; Mammola, Goodacre, & Isaia, ; but see McInerney et al., ). Conversely, where the ice shield was more fragmented, such as in the Alps, marginal areas and mountain peaks protruding through the surface of the glaciers supported the survival of a specialized subterranean fauna (e.g., Latella, Verdari, & Gobbi, ; Mammola, Cardoso, et al., ; Mammola, Goodacre, et al., ).…”

“…As a result, subterranean species occurring in these areas mostly exhibit weak adaptations, because northernmost subterranean habitats have been actively undergoing recolonization in recent times (Holdhaus, ; Růžička, Smilauer, & Mlejnek, ; Mammola, Cardoso, Ribera, Pavlek, & Isaia, ; Mammola, Goodacre, & Isaia, ; but see McInerney et al., ). Conversely, where the ice shield was more fragmented, such as in the Alps, marginal areas and mountain peaks protruding through the surface of the glaciers supported the survival of a specialized subterranean fauna (e.g., Latella, Verdari, & Gobbi, ; Mammola, Cardoso, et al., ; Mammola, Goodacre, et al., ). As a consequence, when observing the distribution of these species, especially the most cold‐adapted ones, it should be theoretically possible to detect the signature of these past climatic events.…”

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

“…Indeed, researchers are not always able to consider the connections that exist between the habitats accessible to humans and the voids of smaller size. The use of such sampling tools has proven to provide a reliable means to characterise subterranean communities, especially if implemented in properly executed experimental protocols involving a wide spatial and/or temporal scale of investigation , Rendoš et al 2012, Ortuño et al 2013, Halse and Pearson 2014, Nitzu et al 2014, Jiménez-Valverde et al 2015, Mammola et al 2018a. Some authors have relied on markrecapture techniques for estimating the real population size of subterranean species sampled in caves (Moldovan and Fejér 2013, Jugovic et al 2015, Băncilă et al 2018, as well as for estimating species longevity (Venarsky et al 2012a).…”

“…Alternatively, this disadvantage can be overcome by using specific sampling devices for collecting the fauna inhabiting the network of fissure, whether air-filled (Mammola et al 2016a), temporarily water-filled (Ortuño et al 2013) or constantly water-filled (Brancelj 2004). The use of such sampling tools has proven to provide a reliable means to characterise subterranean communities, especially if implemented in properly executed experimental protocols involving a wide spatial and/or temporal scale of investigation , Rendoš et al 2012, Ortuño et al 2013, Halse and Pearson 2014, Nitzu et al 2014, Jiménez-Valverde et al 2015, Mammola et al 2018a). More recently, the use of indirect molecular evidence for the presence of the species (environmental DNA) was also discussed (Gorički et al 2017, Vörös et al 2017, Niemiller et al 2018.…”

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

“…Following this criterion, we calculated the abundance and species richness of external and subterranean elements (Next, Rext, Nad, Rad, respectively) for each trap in each sampling survey. Species represented by less than three individuals were not classified, and thus excluded from the analysis, unless if we possessed a solid literature background testifying the species ecological requirements -e.g., Lana (2001) for a few subterranean species in Piedmont and Mammola et al (2017) for most spider species.…”