Species conservation efforts are often limited by funding for restoration activities, and time in the face of decreasing populations. Therefore, it is critical that restoration activities be prioritized such that the greatest benefit to target species and communities can be achieved. In a paper recently published in Transactions of the American Fisheries Society, co-author Phaedra Budy (Utah State University) and I describe a modeling effort to predict where different restoration activities would have the greatest benefit for imperiled native species in the San Rafael River (Utah).
Flannelmouth sucker, bluehead sucker, and roundtail chub are three imperiled species native to the Colorado River Basin. Populations of each of these species have declined dramatically in the last century in the face of habitat and flow alteration, and invasive species establishment. The states of the upper Colorado River Basin have signed agreements to conserve these three species, but in the face of numerous widespread threats, management agencies need to know where they should focus management and restoration efforts.
In this paper, we fit random forest models biotic and abiotic variables measured at sampling locations to determine the factors most limiting to each of the native species. We then used data from a longitudinal habitat survey of the lower 64 km of river to predict the effect of habitat restoration and non-native species removals at different locations along the San Rafael River. Expanding areas of high quality habitat was predicted to result in greater benefits for the native species than improving isolated patches of habitat. Additionally, the greatest benefit to the native species occurred when non-native species were removed to below about 10% of their current abundance. Non-native species present sources of predation and competition to the native species, and as such can limit the number of native species a habitat unit could support. In fact, our models predicted that habitat restoration without non-native species removals could reduce native species abundances in certain reaches, likely due to increased non-native species following habitat restoration.
Overall, this study highlighted the importance of considering both biotic and abiotic drivers of abundance and persistence of threatened species. Only considering abiotic drivers can lead to unexpected and even negative restoration results, wasting limited time, money, and opportunity. Additionally, river-scale ecological niche models can describe systems at the scale at which endemic species interact with their environment, and can allow for managers to obtain spatially-explicit information at the scale at which restoration activities will occur. Further, we recognize and discuss the importance of restoring the processes that shape river ecosystems (e.g., natural flow regime) in order to ensure the long-term success of any restoration strategy.
Timothy E. Walsworth & Phaedra Budy (2015) Integrating Nonnative Species in Niche Models to Prioritize Native Fish Restoration Activity Locations along a Desert River Corridor, Transactions of the American Fisheries Society, 144:4, 667-681