Stream Resource Gradients Drive Consumption Rates of Supplemental Prey in the Adjacent Riparian Zone
Decades of research have revealed the crucial roles of cross-system energy flows (spatial subsidies) in mediating trophic interactions in recipient systems. Food web theory predicts that the responses of subsidized consumers are a key to understanding the net impacts of spatial subsidies on in situ prey/resources of recipient systems. However, less is known about the factors triggering the cascading biotic interactions across coupled ecosystems. Here, we quantify how riverine productivity (donor system) mediates terrestrial food web interactions through spatial subsidies to simplified gravel bar communities. Our comparative study in Japan indicated that higher algal biomass in aquatic systems led to increased supplies of emerging aquatic insects, which were associated with greater densities of terrestrial consumers (Carabid beetles) and enhanced consumption rates of supplemental in situ prey on gravel bars. Our results highlight the potential of donor productivity to drive cascading biotic interactions across coupled ecosystems. Because cross-system energy flows should originate, at least in part, from primary producers of donor systems, our fundamental finding may form the basis of future studies exploring the driving factors of cross-system trophic interactions.
KeywordsProductivity gradients Apparent competition Carabidae River–land interactions Ecotone
We are grateful to B. Nessa, H. Imai, T. Akasaka, A. Agui and student volunteers for their field/laboratory assistance. This study is partly supported by the research fund for the Ishikari and Tokachi Rivers provided by the Ministry of Land, Infrastructure, Transport, and Tourism of Japan.
Data and JAGS code are available as online electronic supplementary material.
- Burdon FJ, Harding JS. 2008. The linkage between riparian predators and aquatic insects across a stream-resource spectrum. Freshw Biol 53:330–46.Google Scholar
- Gelman A, Hill J. 2007. Data analysis using regression and multilevel/hierarchical models. New York: Cambridge University Press.Google Scholar
- Lunn D, Jackson C, Best N, Thomas A, Spiegelhalter D. 2012. The BUGS book: a practical introduction to Bayesian analysis. Boca Raton: CRC Press.Google Scholar
- Nakano S, Miyasaka H, Kuhara N. 1999. Terrestrial-aquatic linkages: riparian arthropod inputs alter trophic cascades in a stream food web. Ecology 80:2435–41.Google Scholar
- R Core Team. 2016. R: a language and environment for statistical computing. Vienna: R Foundation for Statistical Computing. https://www.R-project.org/.
- Sabo J, Power M. 2002. River-watershed exchange: effects of riverine subsidies on riparian lizards and their terrestrial prey. Ecology 83:1860–9.Google Scholar
- Sato T, Egusa T, Fukushima K, Oda T, Ohte N, Tokuchi N, Watanabe K, Kanaiwa M, Murakami I, Lafferty KD. 2012. Nematomorph parasites indirectly alter the food web and ecosystem function of streams through behavioural manipulation of their cricket hosts. Ecol Lett 15:786–93.CrossRefPubMedGoogle Scholar