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Flow regime alteration degrades ecological networks in riparian ecosystems

Abstract

Riverine ecosystems are governed by patterns of temporal variation in river flows. This dynamism will change due to climate change and the near-ubiquitous human control of river flows globally, which may have severe effects on species distributions and interactions. We employed a combination of population modelling and network theory to explore the consequences of possible flow regime futures on riparian plant communities, including scenarios of increased drought, flooding and flow homogenization (removal of flow variability). We found that even slight modifications to the historic natural flow regime had significant consequences for the structure of riparian plant networks. Networks of emergent interactions between plant guilds were most connected at the natural flow regime and became simplified with increasing flow alteration. The most influential component of flow alteration was flood reduction, with drought and flow homogenization both having greater simplifying community-wide consequences than increased flooding. These findings suggest that maintaining floods under future climates will be needed to overcome the negative long-term consequences of flow modification on riverine ecosystems.

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Fig. 1: Conceptual diagram outlining the workflow used in the analysis, from data collection to projection.
Fig. 2: Examination of riparian plant networks across a spectrum of possible flow regime futures.
Fig. 3: Summary metrics of full ecological networks spanning the spectrum of flow extremes from extreme drought to flood.
Fig. 4: Degree (number of links connected to the node) of each network node in relation to flow state.

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Acknowledgements

We thank N. L. Poff, A. Ruhi and members of the OSU Integrative Biology journal club for comments on earlier versions of the manuscript. Dinosaur National Monument and the US Bureau of Reclamation supported the research that led to the vital rate data. Funding was provided in part by the US Department of Defense (SERDP RC-2511) and the US Department of Agriculture Forest Service.

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J.D.T. and D.A.L. designed the study, developed the model and ran analyses; D.A.L. and D.M.M. compiled vital rate information; J.D.T. wrote the first draft of the manuscript in close collaboration with D.A.L., and all authors contributed substantially to writing in subsequent drafts.

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Correspondence to Jonathan D. Tonkin.

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Tonkin, J.D., Merritt, D.M., Olden, J.D. et al. Flow regime alteration degrades ecological networks in riparian ecosystems. Nat Ecol Evol 2, 86–93 (2018). https://doi.org/10.1038/s41559-017-0379-0

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