Review Responses to Barrier Removals

Here you will find the R code and database to the manuscript: Native and non-native populations respond unevenly to river barrier removals. Dolan et al. Ellen J. Dolan1,*, Ismael Soto2, Julian D. Olden3, Jonathan Tonkin4,5, Fengzhi He6, Laís Carneiro7, Jaimie T.A. Dick1, Ross N. Cuthbert1 Institute for Global Food Security, School of Biological Sciences, Queen’s University Belfast, Belfast, United Kingdom University of South Bohemia in České Budějovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Vodňany, Czech Republic School of Aquatic and Fishery Sciences, University of Washington, Seattle, USA School of Biological Sciences, University of Canterbury, Christchurch, New Zealand Te Pūnaha Matatini Centre of Research Excellence, University of Canterbury, Christchurch, New Zealand Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Société Evolution, Gif-sur-Yvette, France *Corresponding author: [e-mail] Abstract: The multi-faceted threats of habitat degradation and biological invasions are increasing concerns for the integrity of freshwater ecosystems and their associated services globally. Removal of artificial riverine barriers (e.g. weirs and dams) has gained momentum over the last three decades, motivated greatly by the maintenance requirements of the aging infrastructure, while also functioning as a primary means of restoring river connectivity to promote ecosystem recovery and native biodiversity. Although barrier removals are intended to benefit native species dispersal, these actions can simultaneously facilitate the spread of non-native species and increase the risk of facilitating biological invasions, creating a conservation paradox. Using a systematic review and meta-analysis, we synthesised the patterns and trends in responses between native and non-native populations to riverine barrier removals globally. We report that since 1998, research interest in the effects of barrier removals has rapidly accumulated, but with a major geographic imbalance towards North America (80% of studies). Fishes were the most commonly studied taxon (74%), followed by riparian and aquatic plants (24%) and invertebrates (15%). Considering the type of barriers, the removal of dams dominated (85%), most larger in height, compared to road culverts (7%) and weirs (2%). Results from 2,840 reported effect sizes in our meta-analysis showed that both native and non-native population sizes generally increased after barrier removal, but the positive effect was strongest for native species. Moreover, these population responses were highly context-dependent, with taxonomic grouping, sampling directionality, and time since removal affecting outcomes. In particular, non-native population growth outstripped that of native species in the first few years post-removal and non-native invertebrates responded the most favourably to barrier removal. While native species typically benefit from barrier removals overall, our analyses highlight context-specific responses that can simultaneously benefit non-native populations and erode long-term conservation outcomes. As river restoration efforts continue to gain traction globally, further planning and research are required to anticipate and assess long term population recoveries, to reconcile conservation quagmires around interacting global environmental changes.