The Structure of Riparian Vegetation in Agricultural Landscapes Influences Spider Communities and Aquatic-Terrestrial Linkages

Ellinor Ramberg,Geta Rîşnoveanu,Danny C P Lau,Richard K Johnson,Jasmina Sargac,Brendan G Mckie,Benjamin Kupilas,Francis J Burdon

doi:10.3390/w12102855

Abstract

Riparian habitats are important ecotones connecting aquatic and terrestrial ecosystems, but are often highly degraded by human activities. Riparian buffers might help support impacted riparian communities, and improve trophic connectivity. We sampled spider communities from riparian habitats in an agricultural catchment, and analyzed their polyunsaturated fatty acid (PUFA) content to quantify trophic connectivity. Specific PUFAs are exclusively produced by stream algae, and thus are used to track uptake of aquatic resources by terrestrial consumers. Riparian spiders were collected from 10 site pairs situated along agricultural streams, and from five forest sites (25 sites total). Each agricultural site pair comprised an unshaded site with predominantly herbaceous vegetation cover, and a second with a woody riparian buffer. Spider communities differed between site types, with web-building spiders dominating woody buffered sites and free-living spiders associated with more open habitats. PUFA concentrations were greatest overall in free-living spiders, but there was also evidence for increased PUFA uptake by some spider groups when a woody riparian buffer was present. Our results reveal the different roles of open and wooded riparian habitats in supporting terrestrial consumers and aquatic-terrestrial connectivity, and highlight the value of incorporating patches of woody vegetation within riparian networks in highly modified landscapes.

Highlights

Streams and their adjacent riparian zones are recognized as important habitats supporting high biodiversity and providing a range of ecosystem services [1,2,3,4]
We focused on the role of spider taxonomic identity in regulating polyunsaturated fatty acid (PUFA)
Our results demonstrate that unforested, herbaceous riparian zones and forested buffers play different roles in agricultural catchments, harboring different functional types of spiders in an otherwise impacted landscape

Summary

Introduction

Streams and their adjacent riparian zones are recognized as important habitats supporting high biodiversity and providing a range of ecosystem services [1,2,3,4]. These habitats are closely linked through multiple exchanges of organisms, nutrients and materials, which often act as “resource subsidies” in the recipient habitat [5]. To some degree fungi, are the main sources of PUFAs for consumers, with several types of especially long-chain (with ≥20 carbon) PUFAs produced almost exclusively in aquatic environments by algae [7,13,14] This aspect makes PUFAs suitable biomarkers for tracking the uptake of aquatic subsidies into terrestrial food webs [15]. PUFAs may be useful for studying trophic connectivity in stream-riparian networks where the ecosystem boundary is relatively well-defined, and the spatial scale for conducting research is tractable [16]

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Methods

Discussion

Conclusion