Functional and Taxonomic Structuring of Ground‐Dwelling Spider Communities Under the Combined Effects of the Environment and Metal Contamination

ABSTRACT

Northern regions of France have historically experienced mining and steel production activities, leading to the emergence of multi‐contaminated soils by metals. These metals are a source of indirect disruption to ecosystem functioning through the alteration of biodiversity. We focused on spiders, which are major regulators of terrestrial ecosystems, acting simultaneously as prey, predators and competitors in soil communities. The aim of this study was to assess the impact of metal contamination, among a set of environmental parameters, on the taxonomic and functional structures of spider communities; to identify indicator spider species; and to define trait syndromes specific to metal‐contaminated wastelands. We sampled spiders in 40 sites that represented a metal‐contamination gradient. We have shown that certain environmental parameters largely account for the taxonomic and functional structure of spider assemblages (e.g., soil granulometry, vegetation, pH). The concentrations of metals in the soil (Ag, Al, As, Cd, Mn, Pb, Sb and Zn) also had a significant but less pronounced impact. We have identified Xerolycosa nemoralis (Lycosidae) as an interesting indicator of metal‐contaminated environments. Furthermore, the contaminated sites contained fewer indicator species than the reference areas. Forested and herbaceous landscape promoted the presence of sheet‐ and orb‐web weavers, respectively. Although metal contamination was not the only driver of this trend, stenophagous spiders, which prefer to retreat and hunt on the ground, were selected at most contaminated sites surrounded by sealed ground, which corresponded to a selection of A‐strategists. The observed trends could be explained by the age of the contamination, the low bioavailability of the metals, the spiders' dispersal capacity, or their effective adaptative mechanisms that mitigate the direct impact of soil contamination on spider assemblages. A better understanding of the role of metals in shaping biological communities can provide valuable insights, particularly regarding ecosystem functioning, environmental monitoring and restoration of contaminated areas.