Evaluating the effects of beaver-related restoration on aquatic ecosystems: Outcomes and risks of beaver reintroductions

Jesse A. S. Burgher

doi:10.7273/000007329

Reversing or stemming declines in ecosystem function and biodiversity are main areas of focus for restoration ecology and conservation biology. Conservation and restoration ecologists have increasingly shifted towards restoring ecosystem processes rather than specific community compositions or habitat conditions. Rewilding is a promising strategy for restoring ecosystem processes at the landscape scale through reintroductions of species that regulate ecosystem processes. Beavers (Castor canadensis and Castor fiber) are well studied ecosystem engineers that have profound impacts on biotic and abiotic components of ecosystems. Beaver-related restoration (BRR), including beaver reintroductions and mimicry structures, is increasingly used to restore ecosystem processes and increase biodiversity in freshwater systems of the United States and Europe; however, implementation has outpaced research on aspects of the rewilding and ecosystem restoration process. In this dissertation, I focus on aspects of rewilding reintroductions and restoration ecology using BRR as a study system. Specifically, my research focuses on developing tools to assess population establishment, assessing disease risks associated with animal reintroductions, and synthesizing how ecosystem engineer reintroductions impact ecosystem processes and biodiversity across ecological contexts. For my first project, I evaluated the efficacy and spatial inference associated with environmental DNA (eDNA) techniques for detecting reintroduced beaver presence in natural wetland and stream systems. I conducted eDNA sampling paired with radio-tracking of translocated beavers to elucidate spatial patterns of site use, eDNA detection probability, and eDNA quantity. I find that eDNA techniques detect beaver rapidly over long distances and reliably detect upstream beavers. These findings suggest that eDNA methods could be a valuable tool for rapid inventory and assessment of beaver occupancy and highlight important implications for using eDNA to monitor other semi-aquatic mammal species that share similar life histories. For my second project, I evaluated whether one important fungal pathogen, Batrachochytrium dendrobatidis (Bd), maintains viability on beaver pelts and assess effects of neutralization treatments on Bd viability. I conducted a laboratory experiment by inoculating small sections of beaver pelt with high concentrations of live Bd zoospores, incubating them to observe viability and growth, and applying realistic neutralization treatments to pelt sections to evaluate the effects of treatment on Bd. I find the first evidence that Bd can adhere to and maintain viability on mammal hairs up to 21 days after initial exposure and provide evidence that simple treatments may be effective for reducing the risk of transmitting Bd during beaver relocation. My findings provide evidence that co-dispersal of external pathogens may be an important process to consider during animal reintroductions and mitigating these risks may be important for protecting recipient ecosystems from unintentional pathogen introductions. For my third project, I conducted a comprehensive literature review focused on beaver-related restoration’s (BRR) influence on habitat and biodiversity attributes that confer climate resilience across western North America. I used 161 sources, assigned confidence scores for specific outcomes, and identified climatic and hydrogeomorphic contexts where BRR may be most impactful at building climate resiliency. I find substantial evidence that BRR increases climate resiliency of stream and riparian ecosystems by reducing summer water temperatures, increasing water storage, and enhancing floodplain connectivity. However, benefits are only likely to accrue under certain climatic and hydrogeomorphic conditions, and I highlight the deficit of peer-reviewed literature at the spatial and temporal scope necessary bridge our understanding of the aspirational potential and the realized benefits of BRR. My findings suggest that rewilding and ecological restoration efforts require a deeper understanding of the ecological contexts that produce desired outcomes and recommend that future research needs to consider appropriate spatial and temporal scales.

Evaluating the effects of beaver-related restoration on aquatic ecosystems: Outcomes and risks of beaver reintroductions

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