Land managers are increasingly using beavers to restore hydrological function, provide wildlife habitat, and mitigate the effects of climate extremes on water balances and ecosystems. Although North American beavers (Castor canadensis) and Eurasian beavers (Castor fiber) both hold great potential for landscape‐scale benefits, more information about the interactions between beavers and wildlife is necessary to maximise the ecological benefits and minimise the social and ecological costs of beaver‐centred management. Beaver dams create large, deep pools with long hydroperiods, which could benefit aquatic and semi‐aquatic species, especially pond‐breeding amphibians, which breed in still and slow‐moving water.
We studied the relationship between beaver dams and pond‐breeding amphibians in the southern Washington Cascade Range of the north‐west U.S.A. by surveying 29 beaver‐dammed and 20 undammed lentic sites in three mid‐elevation (560–1,010 m) spatial blocks.
We found that mean amphibian species richness was 2.7 times higher in dammed sites than in undammed sites (2.4 vs. 0.9 species). This increase in species richness was driven by increased occupancy of slow‐developing species—red‐legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile)—which were also more abundant at sites with dams. These two species were detected almost exclusively in beaver‐dammed sites, suggesting that some amphibians rely heavily on beaver‐dammed sites for successful reproduction in areas such as our study blocks where ponds and wetlands with long hydroperiods are otherwise scarce. Species with highly variable development periods—long‐toed salamanders (Ambystoma macrodactylum) and rough‐skinned newts (Taricha granulosa)—showed nonsignificant trends of higher site occupancy and, in the case of newts, higher number of mating events per hectare in dammed sites compared to undammed sites.
Compared to undammed sites, dammed ponds were consistently deeper and had longer hydroperiods, consistent with beavers benefitting slow‐developing amphibians primarily by increasing the quality of lentic breeding habitat. We suggest that slow‐developing amphibians and some variable‐rate developers might benefit greatly from beaver restoration, especially in areas where climate change is predicted to reduce summertime water levels. Beavers could therefore be useful and important components of ecosystem‐based restoration, management, and climate adaption, especially in parts of their native ranges in North America or Eurasia predicted to undergo climatic drying.
1. Surveys for environmental DNA (eDNA) can provide an efficient and effective means of detecting aquatic organisms in various types of aquatic systems. 2. In the summer of 2017, the efficacy of a new, integrated eDNA backpack sampler to detect two native amphibians (Rana sierrae and R. cascadae) at risk was tested in complex mountain meadows in California. Samples were collected at 65 locations in 15 meadows where the target species were known to be present or were historically present. 3. Collection and preservation of individual samples took less than 10 min on average. Environmental DNA analysis methods detected each species at all meadows with visual detections (N = 11) except one with one frog seen away from sampling sites. Bayesian multi-scale occupancy modelling indicated that conditional detection probabilities at the sample level ranged from 0.30 (CL 0.07-0.65) at meadow heads where no frogs were observed during visual surveys to 0.93 (CL 0.77-1.00) at the meadow foot with at least one frog observed in the vicinity. 4. Compared with visual surveys, eDNA methods more frequently detected amphibians at the sampling-location scale. The improvement in detection using eDNA methods was most pronounced for samples collected at the downstream ends of meadows where water converges, where eDNA methods detected target species at 10 of 11 occupied meadows. 5. These results suggest that the addition of eDNA sampling to visual surveys in mountain meadows will improve survey accuracy and increase the probability of detecting rare frogs.
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