Litter identity mediates predator impacts on the functioning of an aquatic detritus-based food web
- 636 Downloads
During past decades, several mechanisms such as resource quality and habitat complexity have been proposed to explain variations in the strength of trophic cascades across ecosystems. In detritus-based headwater streams, litter accumulations constitute both a habitat and a resource for detritivorous macroinvertebrates. Because litter edibility (which promotes trophic cascades) is usually inversely correlated with its structural complexity (which weakens trophic cascades), there is a great scope for stronger trophic cascades in litter accumulations that are dominated by easily degradable litter species. However, it remains unclear how mixing contrasting litter species (conferring both habitat complexity and high quality resource) may influence top–down controls on communities and processes. In enclosures exposed in a second-order stream, we manipulated litter species composition by using two contrasting litter (alder and oak), and the presence–absence of a macroinvertebrate predator (Cordulegaster boltonii larvae), enabling it to effectively exert predation pressure, or not, on detritivores (consumptive versus non-consumptive predation effects). Leaf mass loss, detritivore biomass and community structure were mostly controlled independently by litter identity and mixing and by predator consumption. However, the strength of predator control was mediated by litter quality (stronger on alder), and to a lesser extent by litter mixing (weaker on mixed litter). Refractory litter such as oak leaves may contribute to the structural complexity of the habitat for stream macroinvertebrates, allowing the maintenance of detritivore communities even when strong predation pressure occurs. We suggest that considering the interaction between top–down and bottom–up factors is important when investigating their influence on natural communities and ecosystem processes in detritus-based ecosystems.
KeywordsTrophic cascades Litter mixing Litter decomposition Shredder Cordulegaster boltonii
We are grateful to Mark Gessner, Markus Schindler and Brendan McKie who designed and built the enclosures used in this experiment, André Frainer Barbosa for constructive discussion about the experimental design, as well as Barbara Downes and several anonymous referees for their very helpful comments and suggestions on the manuscript. We also greatly appreciate the technical assistance of Sylvain Lamothe and Didier Lambrigot in the field and laboratory. Finally, we thank Jean-Claude Arnaud, Président du syndicat des riverains et pêcheurs de Roquefère et de Labastide, who kindly allowed us access to the Rieutort.
- Brönmark C, Hansson L-A (2012) Chemical ecology in aquatic systems. Oxford University Press, OxfordGoogle Scholar
- Chivers DP, Smith RJF (1998) Chemical alarm signalling in aquatic predator−prey systems: a review and prospectus. Ecoscience 5:338–352Google Scholar
- Graça MAS (2001) The role of invertebrates on leaf litter decomposition in streams − a review. Int Rev Hydrobiol 86:383–393. doi: 10.1002/1522-2632(200107)86:4/5<383:AID-IROH383>3.0.CO;2-D CrossRefGoogle Scholar
- Hooper DU, Chapin FS III, Ewel JJ, Hector A, Inchausti P, Lavorel S, Lawton JH, Lodge DM, Loreau M, Naeem S, Schmid B, Setälä H, Symstad AJ, Vandermeer J, Wardle DA (2005) Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecol Monogr 75:3–35. doi: 10.1890/04-0922 CrossRefGoogle Scholar
- Peckarsky BL, Abrams PA, Bolnick DI, Dill LM, Grabowski JH, Luttbeg B, Orrock JL, Peacor SD, Preisser EL, Schmitz OJ, Trussell GC (2008) Revisiting the classics: considering nonconsumptive effects in textbooks examples of predator prey interactions. Ecology 89:2416–2425. doi: 10.1890/07-1131.1 PubMedCrossRefGoogle Scholar
- R Development Core Team (2012) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar
- Schmid B, Hector A, Huston MA, Inchausti P, Nijs I, Leadley PW, Tilman D (2002) The design and analysis of biodiversity experiments. In: Loreau M, Naeem S, Inchausti P (eds) Biodiversity and ecosystem functioning: synthesis and perspectives. Oxford University Press, Oxford, pp 61–75Google Scholar
- Tachet H, Richoux P, Bournard M, Usseglio-Polatera P (2000) Invertébrés d’eau douce : systématique, biologie, écologie. CNRS Edition, ParisGoogle Scholar
- Terborgh J, Estes JA (2010) Trophic cascades — predators, prey, and the changing dynamics of nature. Island Press, WashingtonGoogle Scholar
- Waringer J, Graf W (1997) Atlas der österreichischen Köcherfliegenlarven. Facultas Universitätsverlag, WienGoogle Scholar