Distribution and trophic dynamics of riparian tetragnathid spiders in a large river system

Abstract

Development and agriculture are increasingly encroaching into riparian areas, with largely unknown effects on nearshore arthropods, which are important components of linked aquatic–terrestrial food webs. To assess the environmental determinants of the distribution and trophic dynamics of riparian spiders of the family Tetragnathidae, we characterised riparian habitat, collected emergent aquatic insects, and surveyed spiders in developed and rural landscapes of the Scioto River system, Ohio, USA, which provided a range of riparian land cover, nearshore vegetation types and habitat complexity. We also estimated the trophic position (TP) of Tetragnathidae and the proportion of energetic and nutritional subsidies derived from benthic algae (EBA) using naturally abundant carbon (C) and nitrogen (N) stable isotopes. Model-selection results revealed that tetragnathid spider density (1.57–3.80individualsm–1) was more sensitive to differences in overhanging vegetation than to those in aquatic food resources (i.e. emergent aquatic insects). Tetragnathidae TP, which averaged 3.16 across all 12 study reaches (range: 2.35–3.98), was largely driven by canopy density, shoreline shape, percentage overhanging vegetation and emergent-insect density. Emergent-insect density was the strongest driver of tetragnathid spider EBA (0.04–0.54, µ=0.24). Our study reinforced the notion that riparian spiders ecologically link aquatic and terrestrial ecosystems. In particular, our results further current understanding of the mechanisms affecting riparian spider distribution and trophic dynamics, particularly in the context of larger stream and river systems, given that the propensity of related research has occurred in small streams.

Fluvial geomorphology and aquatic‐to‐terrestrial Hg export are weakly coupled in small urban streams of Columbus, Ohio

“…Although in this study, Tetragnathidae Hg body burdens were unrelated to emergent insect Hg body burdens, tetragnathid spiders are known to be dependent on emergent insects as a nutritional subsidy, although the degree of this dependence can vary based on a suite of both in‐stream and riparian factors [ Sanzone et al ., ; Wesner , ; Tagwireyi and Sullivan , ]. Thus, potential variability in the reliance of tegtragnathid spiders on emergent insects across the study reaches may have obscured a statistical relationship between Tetragnathidae and emergent insect Hg body burdens, although the bioaccumulation pathway may still be significant.…”

Local and landscape drivers of aquatic‐to‐terrestrial subsidies in riparian ecosystems: a worldwide meta‐analysis

“…). A positive relationship between prey body size and Tetragnatha use of aquatic subsidies has been previously demonstrated (Tagwireyi and Sullivan ).…”

“…Several studies have highlighted body size-trophic level linkages (Cohen et al 2003). A positive relationship between prey body size and Tetragnatha use of aquatic subsidies has been previously demonstrated (Tagwireyi and Sullivan 2015).…”

Responses of riparian tetragnathid spiders to wildfire in forested ecosystems of the California Mediterranean climate region, USA

“…Factors that influence web placement by riparian orb-web spiders include access to open water (Gillespie 1987) and web-building substrate (Tagwireyi and Sullivan 2015). Web-building substrate at our study sections included overhanging vegetation, which did not differ between fire-severity treatments, and large and small wood, which was ∼30% more abundant at study sections in high-than in low-severity riparian fire reaches but was highly variable (SD = 47.9%) and not related to tetragnathid spider density in any of our models.…”