Resource subsidies between stream and terrestrial ecosystems under global change

Abstract

Streams and adjacent terrestrial ecosystems are characterized by permeable boundaries that are crossed by resource subsidies. Although the importance of these subsidies for riverine ecosystems is increasingly recognized, little is known about how they may be influenced by global environmental change. Drawing from available evidence, in this review we propose a conceptual framework to evaluate the effects of global change on the quality and spatiotemporal dynamics of stream-terrestrial subsidies. We illustrate how changes to hydrological and temperature regimes, atmospheric CO2 concentration, land use and the distribution of nonindigenous species can influence subsidy fluxes by affecting the biology and ecology of donor and recipient systems and the physical characteristics of stream-riparian boundaries. Climate-driven changes in the physiology and phenology of organisms with complex life cycles will influence their development time, body size and emergence patterns, with consequences for adjacent terrestrial consumers. Also, novel species interactions can modify subsidy dynamics via complex bottom-up and top-down effects. Given the seasonality and pulsed nature of subsidies, alterations of the temporal and spatial synchrony of resource availability to consumers across ecosystems are likely to result in ecological mismatches that can scale up from individual responses, to communities, to ecosystems. Similarly, altered hydrology, temperature, CO2 concentration and land use will modify the recruitment and quality of riparian vegetation, the timing of leaf abscission and the establishment of invasive riparian species. Along with morphological changes to stream-terrestrial boundaries, these will alter the use and fluxes of allochthonous subsidies associated with stream ecosystems. Future research should aim to understand how subsidy dynamics will be affected by key drivers of global change, including agricultural intensification, increasing water use and biotic homogenization. Our conceptual framework based on the match-mismatch between donor and recipient organisms may facilitate understanding of the multiple effects of global change and aid in the development of future research questions.

Stream network geometry and the spatial influence of aquatic insect subsidies across the contiguous United States

“…Indeed, others have reported nonlinear relationships (i.e., shifting between positive and negative along continuous precipitation gradients) between drainage density and runoff (Moglen et al 1998, Smith et al 2013, Sangireddy et al 2016) that are inconsistent with the positive parameter estimates reported here. Though future efforts are needed to clarify the exact relationship between basin features and stream network geometry, the linkage we have uncovered here could highlight a potential understudied impact of climate change on aquatic-to-terrestrial resource exchange that could affect some regions more than others (Larsen et al 2016). The Pacific Northwest (VPU17) for instance spans a precipitation gradient large enough to produce both positive and negative relationships observed in other studies (Sangireddy et al 2016).…”

“…Further, we suspect climate, hydrology, soils, topography, and vegetation are related to stream network geometry (Moglen et al 1998, Smith et al 2013, Sangireddy et al 2016) and could underlie regional differences in the spatial influence of aquatic insect subsidies. Disentangling relative role of basin features (i.e., climate, hydrology, soils, topography, and vegetation) could highlight macroscale constraints on aquatic-terrestrial resource exchange (Heffernan et al 2014, Larsen et al 2016.…”

Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams

“…As riparian forest conditions continue to change, it is essential to understand how cross-ecosystem resource subsidies that link riparian forests to streams may also be changing (Larsen et al, 2016;Warren et al, 2016). The effects of invasive riparian species are unique in that they can transcend ecosystem boundaries via stream-riparian linkages (Hladyz et al, 2011).…”

Crossing boundaries: Shigeru Nakano's enduring legacy for ecology

“…These investigators have assessed how the effects of human land uses such as cattle grazing Fausch 2007, 2012), logging (Inoue et al 2013), and mining (Kraus et al 2016), as well as the introduction and invasion of species like nonnative trout (Baxter et al 2004(Baxter et al , 2007Benjamin et al 2011Benjamin et al , 2013Lepori et al 2012) and global climate change (Larsen et al 2016), can all have strong effects on the processes that produce or shape the flux of invertebrate prey across the stream-riparian boundary. For example, Benjamin et al (2013) reported that nonnative brook trout reduced the emergence of adult aquatic insects by 55% compared to native cutthroat trout (O. clarkii), and projected that this was sufficient to eliminate emerging insects from the diets of two-thirds of riparian birds that depend, in part, on this food source.…”