Recipient Organization
UNIVERSITY OF MONTANA
COLLEGE OF FORESTRY AND CONSERVATION
MISSOULA,MT 59812
Performing Department
College of Forestry and Conservation
Non Technical Summary
Government agencies are increasingly using beavers as tools for restoration of forest ecosystems, streams, wetlands, and floodplains. The main goal of this study is to identify how beavers can influence disease dynamics in populations of amphibians in northwestern Montana. From data collected in 2018 and 2019, we will determine how the chytrid fungus, Batrachochytrium dendrobatidis (referred to as Bd), infections in boreal toads and Columbia spotted frogs differ between beaver wetlands and non-beaver wetlands. While the responses of some amphibian populations to beaver activity have been studied, the responses of amphibian parasites have not yet been studied. These amphibian-parasite dynamics are driven by abiotic factors like canopy cover and temperature and amphibian population density; factors that are directly affected by beaver activity. This study will fill a critical hole in our understanding of how the current trend of beaver reintroductions for forest and watershed management may affect the long-term survival of amphibian populations.
Animal Health Component
30%
Research Effort Categories
Basic
70%
Applied
30%
Developmental
0%
Goals / Objectives
JustificationThe North American beaver (Castor canadensis) is considered an ecological engineer based on its ability to build dams and create patches of disturbance that alter the chemical, physical, and biological structure of the ecosystem (Naiman et al., 1986; Pollock et al., 1995; Majerova et al., 2015). Beaver activity plays a significant role in the disturbance regime in forest ecosystems, contributing to landscape-level habitat heterogeneity and maintenance of biodiversity (Naiman et al., 1986). Prior to European settlement, there were an estimated 60 - 400 million beavers in North America, but the fur trade nearly led to their extirpation by 1900 (Johnson et al., 1974; Jenkins et al., 1979). Conservation efforts since the 1900's have led to an estimated 6 - 12 million beavers in North America today (Naiman et al., 1988). Government agencies are increasingly utilizing beavers as tools for restoration of streams, wetlands, and floodplains (Shoo et al., 2011; Pollock et al., 2015).Amphibians are currently considered one of the most imperiled taxa on the planet, with over 40% of species threatened with extinction (Monastersky, 2014; Catenazzi, 2015). Amphibians are believed to benefit from beaver activity by the creation of aquatic, patch habitat necessary for their survival (Shoo et al., 2011; Hossack et al., 2013b), leading to the increasing use of beavers as a tool for wetland restoration and amphibian population recovery (Shoo et al., 2011; Pollock et al., 2015; Bashinskiy, 2014).Natural disturbances shape and maintain landscape heterogeneity and communities, but they can also provide optimal opportunities for parasite invasions and transmission (Sousa, 1984; Lafferty, 1999; Patz et al., 2000). Disturbances that alter the abiotic and biotic components of an ecosystem (e.g. cyclones, wildfires, logging) can directly or indirectly create conditions that are favorable for parasite survival outside of the host, or favorable for host survival and parasite transmission (Lafferty, 1997; McKenzie, 2017; Joprivnikar et al., 2012; Hossack et al., 2013a). In addition to promoting increases in biodiversity, the increased use of beavers for restoration may also influence parasite abundance and thereby threaten long-term amphibian recovery (Shoo et al., 2011; Pollock et al., 2015).Since its identification almost 20 years ago, the chytrid fungus, Batrachochytrium dendrobatidis (referred to as Bd), has been considered the cause of rapid population declines in amphibians (Richards et al., 1994; Pounds & Crump, 1994; Berger et al., 1998; Lips, 1998). Bd is transmitted through direct contact between amphibians and contact with water contaminated by the microscopic, aquatic zoospores (Berger et al., 1998; Rachowicz & Vredenburg, 2004). Bd's intrinsic growth rates, pathogenicity, and host immune responses are strongly affected by temperature (Piotrowski et al., 2004), and could be affected by temperature changes resulting from beaver activity. Additionally, amphibian community composition may be important in Bd transmission and may be affected by beaver activity. Columbia spotted frogs are suspected reservoir hosts for chytrid fungus, as they can carry and transmit Bd without experiencing mortality (Russell et al., 2010), yet boreal toads experience declines and population extirpations. Columbia spotted frogs were twice as likely to occupy and breed in beaver-engineered wetlands as isolated wetlands (Hossack et al., 2015). Therefore, beaver activity may increase the amplifying host populations (Columbia spotted frogs) leading to a decline in susceptible host populations (boreal toads).The overall goal of this study is to investigate how changes in the environment due to beavers can influence amphibian-parasite dynamics. We aim to document and compare Bd intensity and prevalence between two species of pond-breeding amphibians in northwestern Montana: the boreal toad and the Columbia spotted frog. We will also test whether the presence of Columbia spotted frogs will affect prevalence or infection intensity in western toads.Objectives:We will address the following questions in this study:How do abiotic factors like canopy cover and water temperature in beaver ponds differ from non-beaver ponds?Does Bd prevalence differ in between beaver and non-beaver ponds?Does infection intensity differ between beaver and non-beaver ponds?Does the presence of Columbia spotted frogs correspond with a higher infection load or prevalence in western toads?Previous Work and Present Outlook Bd is transmitted through direct contact and contact with water contaminated by the microscopic, aquatic zoospores. Bd is a complex parasite to detect and control because it affects both adult and larval stages without obvious symptoms of infection and most species vary in their tolerance to Bd (Berger et al., 1998; Rachowitz & Vredenburg, 2004; Blaustein et al., 2005; Carey et al., 2006). Free-swimming Bd zoospores are sensitive to environmental alterations like increasing temperature, stream connectivity, and decreasing canopy cover - all factors directly influenced by beaver presence (Naiman et al., 1988; Piotrowski et al., 2004; Becker et al., 2012; Sapsford et al., 2012). Although the history of beavers in GNP is not well understood, their populations are thought to have avoided the dramatic extirpations observed in other areas of North America, and are generally considered to be stable today (Jonas, 1955; Meentemeyer & Butler, 1995). Government agencies are increasingly utilizing beavers as tools for restoration of streams, wetlands, and floodplains (Shoo et al., 2011; Pollock et al., 2015). Management efforts in other regions of the Rocky Mountains, like Yellowstone National Park and Rocky Mountain National Park, are focusing on increasing the abundance and density of beavers to promote overall biodiversity (Peinetti et al., 2002; Smith & Tylers, 2012).In Glacier National Park, amphibian populations have not experienced the sudden, devastating declines like those observed in other regions of the U.S. (e.g., boreal toads in Rocky Mountain National Park), despite the presence of Bd (Muths et al., 2003; Corn et al., 2005; Hossack et al., 2013; Hossack et al., 2015). The positive responses of amphibian populations to beaver activity have been well documented, particularly in the park, but these increases in host abundance and occupancy have not led to any apparent increases in parasite-induced mortality (Hossack et al., 2015; Pollock et al., 2015). In addition to providing wetland habitat for amphibians, beavers could potentially provide refuge from parasites like Bd.In addition, the presence of certain species of amphibians has been shown to amplify, or increase, infections in other species (Scheele et al., 2017). Amplification usually occurs in reservoir hosts, or species that are more tolerant to a disease than others. In this study system, western toads are thought to be more susceptible to chytrid fungus than Columbia spotted frogs due to the dramatic noted declines (Muths et al., 2003). Columbia spotted frogs also spend more time in aquatic habitats than western toads, increasing their chances of being exposed to, and exposing other species to, chytrid fungus infections. This study will also investigate whether this species of amphibian acts as an amplifier for chytrid fungus infections in western toads.
Project Methods
Study AreaGlacier National Park (GNP) in northwestern Montana comprises part of the Crown of the Continent Ecosystem, a transboundary region of the Rocky Mountains internationally managed by the U.S. and Canada (Darrow et al., 1990). There are approximately 700 lakes, ponds, marshes, bogs, and wetlands in GNP, which are responsible for most of the biodiversity in the park and provide vital habitat for beavers and amphibians (NPS). This montane landscape, classified as the Western Cordillera, is dominated by dry ponderosa pine forests and mixed conifer forests consisting of various zones of grand fir (Abies grandis), white fir (Abies concolor), western larch (Larix occidentalis), Douglas fir (Pseudotsuga menziesii), Englemann spruce (Picea engelmannii), western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), lodgepole pine (Pinus contorta), aspen and cottonwood (Populus spp.), and subalpine fir (Abies lasiocarpa). We surveyed 44 wetlands (23 beaver-engineered wetlands and 21 non-beaver wetlands) on the eastern side of the Continental Divide from 1400m-1800m in elevation.Data Collection and AnalysisTo examine the effect of beaver activity on amphibian communities and prevalence and intensity of Bd infections, PhD student in Wildlife Biology, Leah Joyce, has collected data at 44 ponds in northwestern MT on the presence of beavers, tree cover and vegetation composition, water and air temperature, and pond depth. Sites were visited between late May and early August in 2018 and 2019. At each pond, she estimated population abundance of the boreal toad (Anaxyrus boreas) and the Columbia spotted frog (Rana luteiventris), and has swabs from up to 15 frogs and 15 toads per site to quantify prevalence (proportion of the population infected) and intensity of infection (number of spores per host) and relate it to individual characteristics such as sex, mass, and snout-vent-length.Leah will process amphibian skin swabs in November and December 2019 using quantitative PCR to detect pathogen load among individuals. By the end of the semester she will begin analyzing the dataset to determine which abiotic factors are associated with beaver activity and how they relate to Bd infection dynamics. Leah will analyze her data using generalized linear models to determine how abiotic factors such as water temperature are affected by beaver activity, and which abiotic and biotic factors are correlated to population densities and both pathogen prevalence and intensity.Evaluation The results of this research and its products will be evaluated with an analysis of the number of downloads of the graduate student dissertation via the University of Montana's Mansfield Library, as well as published research paper views, downloads, and citations noted on the PI's page on ResearchGate.