Browsing by Author "Johnson-Bice, Sean"

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    Factors Influencing Beaver (Castor Canadensis) Population Fluctuations, And Their Ecological Relationship With Salmonids
    (2019-08) Johnson-Bice, Sean
    Within the western Great Lakes (WGL) U.S. region (Michigan, Minnesota, Wisconsin), the ecological impacts that North American beavers (Castor canadensis) have on cold- water streams are generally considered to negatively affect salmonid populations where the two taxa interact. Here, we review the history of beaver-salmonid interactions within the WGL region, describe how this relationship and management actions have evolved over the past century, and review all published studies from the region that have evaluated beaver-salmonid interactions. Our review suggests the impact beavers have varies spatially and temporally, depending on a variety of local ecological characteristics. We found beaver activity is often deleterious to salmonids in low-gradient stream basins, but generally beneficial in high- gradient basins; and ample groundwater inputs can offset the potential negative effects of beavers by stabilizing the hydrologic and thermal regimes within streams. However, there was an obvious lack of empirical data and/or experimental controls within the reviewed studies, which we suggest emphasizes the need for more data-driven beaver-salmonid research in the WGL region. Resource managers are routinely faced with an ecological dilemma between maintaining natural environmental processes within cold-water ecosystems and conducting beaver control for the benefit of salmonids, and this dilemma is further complicated when the salmonids in question are a non-native species. We anticipate future beaver-salmonid research will lead to a greater understanding of this ecologically-complex relationship that may better inform managers when and where beaver control is necessary to achieve the desired management objectives. Understanding how wildlife populations respond to density-dependent (DD) and density- independent (DI) factors is critically important for wildlife management and research, as this knowledge can allow us to predict population responses to forcing mechanisms such as climate, predation, and exploitation. Recent advancements in statistical methods have allowed researchers to disentangle the relative influence each factor has on wildlife population dynamics, but this work is ongoing. Using a long-term dataset collected from 1975 to 2002, we sought to evaluate the relative influence DD and a suite of covariates (weather, harvest, habitat quality, and wolf [Canis lupus] predation) had on annual rates of change in the number of beaver (Castor canadensis) colonies among 15 populations in northern Minnesota, USA. We modeled changes in beaver colony densities using a discrete-time Gompertz model within a Bayesian inference framework, and compared model performance among three global models using Deviance Information Criterion (DIC) widely available information criterion (WAIC): a DI model without covariates; a DD model without covariates; and a DD model with covariates. Our results provide strong evidence for compensatory (negative) DD within beaver colony dynamics. We found no evidence that covariates related to harvest, wolf predation, or habitat quality significantly influenced beaver colony growth rates, but cold winters (lag-0), spring drought (lag-0), and fall drought conditions (lag-2) were correlated with greater colony growth rates. Despite strong evidence of the effect of environmental covariates on beaver colony dynamics, prediction of colony dynamics using these covariates showed only minimal improvements. We suggest the lack of improvement in prediction was the result of model over-fitting, indicating our significant covariate effects may not be biologically relevant. Our analysis demonstrates how reliance on information criterion values may lead to erroneous conclusions in time-series analyses, and using a hindcasting approach like the one we present here may help determine whether model results are biologically relevant or merely statistically significant. Our results highlight the importance of long-term monitoring programs for evaluating the efficacy of predictive ecological models. That beaver populations are primarily intrinsically regulated has important management implications depending on whether the objectives concern eradicating beavers from unwanted regions, mitigating conflicts, or facilitating rewilding or colonization efforts.
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    Predicting Potential Beaver Dam Sites on Lake Superior's North Shore
    (University of Minnesota Duluth, 2020-04) Johnson-Bice, Sean; Gorzo, Jessica; Kovalenko, Katya; Brown, Terry; Host, George E
    Beavers (Castor canadensis) play a substantial role in coastal Lake Superior ecosystems, as the creation of beaver dams and ponds results in riparian habitat that can be vastly different from habitats before beaver activity (Naiman et al. 1988, Rosell et al. 2005). Beaver dams can influence water temperatures, flow regimes, channel morphology, and sediment dynamics (Gurnell 1998, Pollock et al. 2003, Westbrook et al. 2006, Burchsted et al. 2010, Bouwes et al. 2016). Understanding where beavers are likely to build dams and ponds has many practical implications for resource managers and citizens. Current climate models have predicted an increase in the prevalence of extreme precipitation events that may cause an increase in erosion and flooding events in the North Shore (Herb et al. 2016). Beaver dams have been shown to mitigate the downstream effects of high-precipitation events by reducing stream energy and increasing water retention time (Law et al. 2016, Puttock et al. 2017, Karran et al. 2017); their presence in the North Shore may be an important natural mechanism for minimizing impacts from natural hazards. But they also may have an adverse effect on fisheries, particularly steelhead (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) (Johnson-Bice et al. 2018), leading to controversy within coastal communities and complex management decisions. The goal of this study was to create a model that predicts potential beaver dam locations based on existing habitat characteristics, stream gradient, and stream power and flow estimates. Building from an existing data set that includes spatial information of beaver-created wetlands within five North Shore watersheds, we also conducted a rapid assessment of water and sediment storage contained within beaver ponds across the North Shore. The key deliverables of this project are: ● An interactive online map showing historic and potential beaver dam locations ● Estimates of water and sediment storage in North Shore beaver wetlands ● A downloadable spatial database of existing and predicted beaver dam locations, with FGDC-compliant metadata ● This report describing methods, results, and interpretations These products will be important for resource managers that make land-use decisions based on current and future hydrologic and sediment pathways in Lake Superior tributaries.