First evidence of the formation of secondary strongholds of threatened epigeic spiders (Araneae) in oligotrophic anthropogenic wetlands that form in sand pits and gravel-sand pits

The absence of evidence regarding the ecosystem services of habitats affected by sand mining has had direct effects on the destiny of landscapes affected by human disturbances. Active sand pits and gravel-sand pits cover 0.1% of the study area, the Czech Republic. In many sand pits, various types of oligotrophic wetlands may form; these range from periodic pools to peat bogs and purposefully formed water bodies. In the present study, we aimed to provide the first conclusive evidence of ability of sand pit wetlands to serve as secondary strongholds for both common and threatened wetland-associated epigeic spiders. We examined 21 anthropogenic wetlands in Czech sand pits and gravel-sand pits using pitfall trapping (17,764 trap-days) for the presence of spiders, and characterized various abiotic variables and the cover and composition of plants in the analyzed microhabitats. We found 5,842 individuals from 224 spider species, including 52 Red-Listed species and one previously undescribed Scutpelecopsis sp. All types of examined anthropogenic wetlands were associated with low dominance and high entropy, with the least stable assemblages present in gravel-sand pit tailing ponds. The examined anthropogenic wetlands hosted 60% of the species that were previously found in (near-)natural wetlands within the study region, and hosted numerous species that were absent from (near-)natural wetlands. During the sampling period, four study sites were affected by severe June floods, which caused prominent changes in species-specific spider abundances but caused a disappearance of only a few species, including Pardosa prativaga and Xerolycosa miniata. Oligotrophic anthropogenic wetlands occurring in sand pits and gravel-sand pits serve as local biodiversity hotspots, and their value should be taken into consideration when planning restoration and rehabilitation of areas affected by sand and gravel-sand mining.