Characterization of habitat requirements of European fishing spiders

Abstract

Wetlands are among the most threatened habitats in the world, and so are their species, which suffer habitat loss due to climate and land use changes. Freshwater species and arthropods receive little attention in research and conservation, and the goals to stop and reverse the destruction of wetlands published 25 years ago in a manifesto by the Union of Concerned Scientists have not been reached. In this study, we investigated the occurrence and habitat requirements at two spatial scales of two species of European fishing spiders Dolomedes, which rely heavily on declining wetland habitats in Sweden and southern Norway.We collected occurrence data for Dolomedes plantarius and Dolomedes fimbriatus, using a live-determination-method. We modelled the placement of nursery webs to describe fine scaled habitat requirements related to vegetation and microclimate. Using a machine learning approach, we described the habitat features for each species, and for co-occurrence sites, to provide insight into variables relevant for the detectability of Dolomedes.We found that habitat requirements were narrower for D. plantarius compared to D. fimbriatus; that the detection of nursery webs can be affected by weather conditions and that nursery placement is mostly dependent on the proximity to water, the presence of Carex sp. (Sedges) and of crossing vegetation structures, and on humidity. Furthermore, co-occurring sites were more similar to D. plantarius sites than to D. fimbriatus sites, whereby surrounding forest, water type and velocity, elevation and latitude were of importance for explaining which species of Dolomedes was present.We provide a detailed field protocol for Dolomedes studies, including a novel live-determination method, and recommendations for future field protocols.

Contrasted propensity for waterborne and airborne dispersal between two closely related semi‐aquatic spider species

“…Moreover, D. fimbriatus is less restricted by the absence of water, except when females carry their eggsacs, which must be dipped into water to keep the eggs moist. D. plantarius is more dependent to the presence of water in the site than D. fimbriatus (Dickel et al, 2022; Duffey, 2012).…”

“…We used the 'sponge-box' technique on the female guarding the nursery to identify the species. The female was gently pressed between a sponge and the bottom of the box to inspect her epigyne (see Dickel et al, 2022 for detailed technique). We sampled 11 sites in July/August 2019 (See Figure S1 in Appendix 1).…”

“…Studying the propensity to sail for different stages might help to identify the age at which the fishing spiders are more prone to disperse on the water. D. fimbriatus can occupy a wider variety of wet habitat while D. plantarius lives in site constantly wet, for example, along streams or on ponds (Dickel et al, 2022;Duffey, 2012;van Helsdingen, 1993).…”

“…Indeed, Vugdeli c (2006) observed in the United Kingdom that two populations of D. plantarius distant by less than a kilometre from each other were genetically isolated. Regarding their habitat requirements, D. plantarius is less habitat generalist and his limited to more open habitat, fenlands or riverbanks with a constant presence of water (Dickel et al, 2022;van Helsdingen, 1993). D. fimbriatus is more tolerant to more oligotrophic wetlands with lower pH and is less dependent to water.…”

The presence of Dolomedes plantarius (Clerck, 1757) (Araneae: Pisauridae) in the Ebro Delta extends its distribution in the Iberian Peninsula southwards

“…Both D. fimbriatus and D. plantarius live in wetlands and marshes, and they need the presence of water at some point of their life cycle, but they differ considerably in their habitat requirements, so they rarely coexist (Helsdingen, 1993, Duffey, 2012Lecigne, 2016;Dickel et al, 2019). In this sense, D. fimbriatus needs water only during the mating period, and it can inhabit marshy sites without permanent open water surfaces, peat bogs or small water bodies, whereas D. plantarius lives on the water surface, the overhanging or surrounding aquatic vegetation, usually associated with large water bodies (for example, slow flowing rivers or marshy areas with open waters; Duffey, 1995;Dickel et al, 2019). Tolerance to shade constitute a second difference between these two species, since D. fimbriatus tolerates shade to a large extent, while D. plantarius selects open tree-free habitats due to its preference for higher temperatures and light availability (Helsdingen, 1993;Duffey, 2012).…”