Confluence configuration of river networks controls spatial patterns in fish communities
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Given the importance of spatial heterogeneity in altering dispersal, interspecific interactions, and population persistence, high rates of habitat homogenisation across the globe are a concern. In river ecosystems, confluences likely act as heterogeneity ‘hotspots’ by creating discontinuities in longitudinal processes and influences that are propagated both up and down stream networks.
We predicted the layout of abiotic conditions around confluences would influence the presence and configuration of spatial heterogeneity, and strongly influence spatial patterns in fish abundance and evenness.
Twelve replicate mainstem and tributary stream combinations in Canterbury, New Zealand, were electrofished to evaluate how the configuration of flow disturbance (i.e. flooding) characteristics around a confluence (i.e. stable mainstem and disturbed tributary versus disturbed mainstem and stable tributary) influenced fish communities.
The configuration of abiotic conditions around confluences, and position of a sampled reach with respect to the confluence, significantly interacted to create configuration-specific patterns in fish abundance and evenness. Fish abundances were particularly high in disturbed tributaries juxtaposed with stable mainstems, suggesting certain confluence configurations are disproportionately ecologically important. Evenness scores differed significantly downstream of confluences, depending on configuration, with highest fish evenness in reaches downstream of confluences between a stable and a disturbed stream.
These results reveal strongly context-dependent spatial patterns in communities and demonstrate the role of spatially transferred influence in river systems. Understanding importance of not just the presence of heterogeneity, but its configuration and context-dependence in the landscape will assist in identifying sites of ecological significance for management and conservation purposes.
KeywordsSpatial heterogeneity Habitat configuration Habitat homogenization Riverscapes Fish conservation Flooding disturbance
We are grateful to Castle Hill, Brooksdale, Flock Hill and Glenthorne Stations and to the Department of Conservation for allowing access to sampling sites. Funding was provided by a subcontract from the New Zealand National Institute for Water and Atmospheric Research under the Freshwater & Estuaries Research Programme 2, Sustainable Water Allocation (2014/15 SCI). We thank Richard White, Brandon Goeller, Sophie Hale, Simon Howard and Tom Moore for field assistance, Linda Morris for Technical support, Jenny Ladley for logistical support, and the University of Canterbury for use of the Cass Field Station. Discussions with Erin Peterson at the Queensland University of Technology, Peter McHugh and Carl Saunders at Utah State University, Phillip Jellyman from the New Zealand National Institute for Water and Atmospheric Research and the Freshwater Ecology Research Group (University of Canterbury) enhanced this manuscript. Procedures were conducted under Animal Ethics permit 2014/28R from the University of Canterbury.
- Barton K (2016) MuMIn: multi-model inference. R package version 1.15.6. https://CRAN.R-project.org/package=MuMIn
- Jackson DA, Peres-Neto P, Olden JD (2001) What controls who is where in freshwater fish communities — the roles of biotic, abiotic, and spatial factors. Can J Fish Aquat Sci 58:157–170Google Scholar
- McIntosh AR, McHugh PA, Dunn N, Goodman JM, Howard SW, Jellyman PG, O’Brien LK, Nyström P, Woodford DJ (2010) The impact of trout on galaxiid fishes in New Zealand. N Z J Ecol 34:195–206Google Scholar
- MEA (2005) Millennium Ecosystem Assessment. Ecosystems and human well-being: synthesis. Island Press, Washington DCGoogle Scholar
- Oksanen J, Blanchet FG, Friendly M, Kindt R, Legendre P, McGlinn D, Minchin PR, O’Hara RB, Simpson GL, Solymos P, Stevens MHH, Szoecs E, Wagner H (2017) Vegan: community ecology package. R package version 2.4-3. https://CRAN.R-project.org/package=vegan
- Pfankuch DJ (1975) Stream reach inventory and channel stability evaluation. United States Department of Agriculture Forest Service, Region 1Google Scholar
- R Development Core Team (2016) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. R Foundation for Statistical Computing. https://www.R-project.org/