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Research article2016Peer reviewed

Strong land-use effects on the dispersal patterns of adult stream insects: implications for transfers of aquatic subsidies to terrestrial consumers

Carlson, Peter; Mckie, Brendan; Sandin, Leonard; Johnson, Richard

Abstract

The dispersal of terrestrial adults of freshwater insects is a key process regulating the transfer resources from aquatic habitats to terrestrial consumers, including high-quality lipids synthesised in the aquatic environment. However, the efficiency of these transfers depends strongly on both subsidy production in the aquatic source habitat and permeability of the aquatic-terrestrial boundary. We assessed how land use (agriculture versus forest) affects stream riparian habitats and the dispersal of adult aquatic insects. Flying insects were sampled alongside eight streams (four agricultural, four forested) in central Sweden using sticky traps, placed from 1 up to 100m from the stream edge. Environmental variables including temperature, wind, vegetation structure and canopy cover were also quantified. Abundances of adult aquatic insects were greater at agricultural than at forested sites, but most (64%) were caught close to the stream edge. In contrast, catches of adult aquatic insects declined relatively little with increasing distance from the forest streams. Overall, dispersal of the dominant aquatic insect order (Diptera) was positively associated with greater tree density and canopy shading and negatively associated with higher wind speeds and soil temperatures, more open habitats and steeper topographies. Taxonomic differences among assemblages, reflecting differing dispersal capacities, were also important, but less so than environmental factors. Our results indicate that adult aquatic insects in our forested landscapes are more likely to subsidise near-ground food webs at a greater distance from stream channels, whereas the abundant subsidy emerging from the agricultural sites is likely to be most influential near the stream channel. A key question for future research is whether the deposition of large quantities of aquatic subsidy in agricultural riparian habitats exceeds the resource requirements and processing capacities of terrestrial consumers.

Keywords

aquatic insects; dispersal capacity; epigeal; resource transfers; stream ecosystems

Published in

Freshwater Biology
2016, Volume: 61, number: 6, pages: 848-861
Publisher: WILEY-BLACKWELL