Riverine Landscape Patches Influence Trophic Dynamics of Riparian Ants

Food webs in riparian corridors are increasingly viewed as embedded in complex riverine landscapes characterized by an amalgam of aquatic, semi-aquatic, and terrestrial habitats. However, the influence of riverine landscape pattern on trophic dynamics of riparian consumers remains largely unknown. We used naturally abundant stable isotope ratios (N-15) to compare trophic structure of ants (Formica subsericea) among riparian patch types (crop, grass/herbaceous, gravel bar, lawn, mudflat, shrub, swamp, and woody vegetation) at 12 riverine landscapes distributed along an urban-rural landscape gradient of the Scioto River, Ohio, USA. We expected that the diet of F. subsericea, a common generalist consumer, would reflect local prey availability and thus differences in trophic dynamics among patch types. Mean ant N-15 was higher in crop patches than in any other patch type, and was lowest in grass/herbaceous, lawn, shrub, and woody vegetation patches, suggesting that patch type was associated with trophic position of F. subsericea. We also found that the range of N-15, and thus trophic breadth, was significantly different by patch type, with woody vegetation exhibiting the greatest spread. Variability in canopy, tree and shrub cover, and the degree of urban development was positively correlated with N-15 range (R-2=0.78), pointing to the role of habitat structure in mediating trophic breadth of riparian ants. These findings provide evidence that riverine landscape pattern can strongly influence trophic dynamics of riparian arthropods. Copyright (c) 2016 John Wiley & Sons, Ltd.