How wide is a stream? Spatial extent of the potential “stream signature” in terrestrial food webs using meta‐analysis

Abstract

The magnitude of cross-ecosystem resource subsidies is increasingly well recognized; however, less is known about the distance these subsidies travel into the recipient landscape. In streams and rivers, this distance can delimit the "biological stream width," complementary to hydro-geomorphic measures (e.g., channel banks) that have typically defined stream ecosystem boundaries. In this study we used meta-analysis to define a "stream signature" on land that relates the stream-to-land subsidy to distance. The 50% stream signature, for example, identifies the point on the landscape where subsidy resources are still at half of their maximum (in- or near-stream) level. The decay curve for these data was best fit by a negative power function in which the 50% stream signature was concentrated near stream banks (1.5 m), but a non-trivial (10%) portion of the maximum subsidy level was still found > 0.5 km from the water's edge. The meta-analysis also identified explanatory variables that affect the stream signature. This improves our understanding of ecosystem conditions that permit spatially extensive subsidy transmission, such as in highly productive, middle-order streams and rivers. Resultant multivariate models from this analysis may be useful to managers implementing buffer rules and conservation strategies for stream and riparian function, as they facilitate prediction of the extent of subsidies. Our results stress that much of the subsidy remains near the stream, but also that subsidies (and aquatic organisms) are capable of long-distance dispersal into adjacent environments, and that the effective "biological stream width" of stream and river ecosystems is often much larger than has been defined by hydro-geomorphic metrics alone. Limited data available from marine and lake sources overlap well with the stream signature data, indicating that the "signature" approach may also be applicable to subsidy spatial dynamics across other ecosystems.

Variation in reciprocal subsidies between lakes and land: perspectives from the mountains of California

“…After emergence, amphibians and aquatic insects are expected to be unevenly distributed in surrounding terrestrial landscapes, with the highest abundances likely to occur near the water (Sabo and Hagen 2012;Bartrons et al 2013;Muehlbauer et al 2014;Dreyer et al 2015). Our data from a set of 16 lakes in the Klamath Mountains confirmed this pattern -aquatic insect biomass was inversely proportional to distance from the lake shore, with a power law best describing the distribution (K.L.…”

Artificial Light at Night Affects Organism Flux across Ecosystem Boundaries and Drives Community Structure in the Recipient Ecosystem

“…The presence of artificial light adjacent to water bodies may affect the distance that organisms move away from the water and therefore the spatial scale of the aquatic-terrestrial subsidy signature in a river landscape (Perkin et al, 2011;Gurnell et al, 2016). A recent review found the density of aquatic insects was reduced by 50% within the first 1.5 m from the water's edge (Muehlbauer et al, 2014). Our traps were located 3 m from the water and collected 85-fold more aquatic insects compared to unlit controls.…”

Species traits reveal effects of land use, season and habitat on the potential subsidy of stream invertebrates to terrestrial food webs

“…The transfer of aquatic resource subsidies into terrestrial food webs via the winged adult stages of aquatic insects is recognized as a key component in the functioning of riverine networks (Moldenke and Linden 2007;Lamberti et al 2010;Muehlbauer et al 2014). Not only do aquatic insects often emerge with very high abundance and biomass, but they also carry nutrients and essential lipids produced within aquatic environments (Baxter et al 2005;Gratton et al 2008;Gladyshev et al 2009;Torres-Ruiz and Wehr 2010).…”

“…The potential for land use effects on the composition of aquatic invertebrate communities to alter the composition of dispersal related traits is seen in research by Muehlbauer et al (2014), who found that greater stream-to-land subsidy distances were partly explained by the presence of longer lived and/or stronger flying taxa. Similarly, Carlson et al (2016) found that dispersal distances of adult aquatic insects were longer when abundances of blood-feeding taxa (which disperse widely in search of food) were higher, although the bulk of variation in dispersal distances was explained by characteristics of the terrestrial abiotic environment (wind, insolation etc).…”