Magnitude and direction of stream-forest community interactions change with time scale

Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering datasets collected at the deciduous forested Horonai Stream and conducted ecosystem-level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathway demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal time scale to negative at the annual time scale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top-down control that is not revealed in short-term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating non-linear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales.The first tab of this worksheet contains metadata, including the sources for any data that were previously published. Each other tab contains a different dataset. If more appropriate, the first worksheet could be transoformed into a ReadMe file. It's important for readers to know that although all of these data were collected from the same 1.2km study segment, they were not collected from the same reaches or with the same level of replication. Detailed collection and analysis methods, including the location of samples, scale and extent of study reaches for each metric are all described in detail in the Ecology MS identified above, which is currently in production. Funding provided by: Japan Society for the Promotion of ScienceCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001691Award Number: Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-1451919Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-0516136Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-1754224Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-0516133The study segment of Horonai Stream was located in the Tomakomai Experimental Forest (TOEF; 42 deg 43' N, 141 deg 36'E), Hokkaido, Japan. This small, spring-fed stream drains 15.4 square km in drainage area with an average discharge of 0.25 cubic m / sec over the study period. The study site is described in additional detail by Nakano and Murakami 2001 PNAS 98:166-170 (https://doi.org/10.1073/pnas.98.1.166). The field work for this study was carried out during 14 months from May 1997 to June 1998, over a full annual cycle of seasons in a stream draining a temperate deciduous forest. Additional field work was completed to measure stream primary production and respiration during field campaigns led by Marcarelli in Oct 2008 during leaf fall and in March-April 2009 during snowmelt. The dataset archived here includes new analyses and calculations completed for this paper (e.g., fish and invertebrate production, trophic basis of production), or time series of data that were not presented the same way in earlier papers (leaf litter, terrestrial prey flux, chlorophyll a). It does not include the original data that was summarized from other publications - e.g., it does not include the full data from the organic matter budget, as most of that was taken directly from Shibata et al. 2001. It also does not include fish density or biomass data or benthic macroinvertebrate data that are reported in full in Nakano and Murakami 2001. Detailed collection and analysis methods, including the location of samples, scale and extent of study reaches for each metric are all described in detail in the Ecology MS identified above, which is currently in production