Beaver dams are associated with enhanced amphibian diversity via lengthened hydroperiods and increased representation of slow‐developing species

Abstract

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.

Beaver: The North American freshwater climate action plan

“…The residence time of water on these flow paths varies; as a result, so does the temperature of the water as it returns to the river. However, the resulting highly heterogeneous thermal profile of the riverscape supports a variety of aquatic life with different temperature needs (Dauwalter & Walrath, 2018;Lowry, 1993;Majerova et al, 2015Majerova et al, , 2020Romansic et al, 2021). Therefore, in-stream structure, or connected floodplains are a critical component of naturally functioning riverscapes.…”

“…But, this key bio‐fluvial component of riverscapes is rare because a long history of anthropogenic impacts has simplified and disconnected streams from their floodplains (Fouty, 2018). Therefore, floodplain reconnection is often invoked to improve the quantity and quality of physical and biological habitat characteristics needed by fish, amphibians, waterfowl, and other aquatic and semi‐aquatic species (Anderson et al, 2015; Baldwin, 2015; Dauwalter & Walrath, 2018; W. G. Hood, 2012; Kauffman et al, 1997; McKinstry et al, 2001; Pollock et al, 2004; Romansic et al, 2021; Snodgrass & Meffe, 1998; Wathen et al, 2019; Wohl, 2021b; Wohl et al, 2021).…”

“…On the seasonally wet floodplain surface, vegetation productivity and plant and animal species richness and diversity are higher than on a disconnected, permanently dry terrace (Stella et al, 2011). In the channels of a connected floodplain reach, primary productivity is higher, macroinvertebrate communities are richer and more productive (Nummi et al, 2021; Robinson et al, 2020), and amphibian and fish productivity is higher (Anderson et al, 2015; Bouwes et al, 2016; Dauwalter & Walrath, 2018; Romansic et al, 2021; Wathen et al, 2019) than in simple channels of a disconnected reach. But, while these internal benefits are independently valuable, they are only a small fraction of the potential benefits that restored riverscapes can provide in the face of climate change.…”

High habitat invasibility unveils the invasiveness potential of water frogs

“…Invasibility was particularly high in sunny, vegetated, and deep ponds that did not dry. These habitat features are important for many amphibians and often increase occupancy for native species (Rowe et al 2019;Falaschi et al 2021;Hamer et al 2021;Romansic et al 2021), suggesting that the most favorable habitats for native amphibians are particularly at risk of invasion. Together, these results call for research on coexistence patterns, which may be facilitated by refuges provided by aquatic vegetation, and the complex consequences of invasion on natives (Bucciarelli et al 2014;Manenti et al 2020).…”

Provisioning of breeding habitat by beaver and beaver dam analogue complexes within the Great Salt Lake catchment

“…Along with a multitude of plant and animal species (Stringer & Gaywood, 2016), beaver enhance both the quantity and quality of breeding habitat for a variety of amphibian species (Arkle & Pilliod, 2015;Dalbeck et al, 2007Dalbeck et al, , 2020Hossack et al, 2015;Karraker & Gibbs, 2009). Their dam building increases wetland hydroperiod, habitat complexity, and pond depths, often leading to improved reproductive habitat for amphibian populations (Dalbeck et al, 2014;Karraker & Gibbs, 2009;Romansic et al, 2021;Zero & Murphy, 2016). The effects of beaver are particularly notable in drier climates, such as the Intermountain West of the U.S.A., where wetlands account for less than 2% of the land area (McKinstry et al, 2004).…”