Water Resources Research Act Program

Details for Project ID 2019MT156B

The Influence of Beavers on Amphibian Parasite Dispersal in Glacier National Park

Institute: Montana
Year Established: 2019 Start Date: 2019-04-01 End Date: 2019-12-01
Total Federal Funds: $1,000 Total Non-Federal Funds: $440

Principal Investigators: Leah Joyce

Project Summary: Over the past several decades, amphibian populations have undergone major declines across the world that are largely attributed to habitat alteration and parasites (Collins & Crump, 2009; Monastersky, 2014; Catenazzi, 2015). Host-parasite dynamics are strongly influenced by environmental factors that change the rates of transmission and affect host or parasite survival. For example, factors that increase the abundance of the host may increase parasite transmission, or abiotic changes in temperature and water flow that improve parasite survival outside of the host. The North American beaver (Castor canadensis) may strongly affect host-parasite dynamics because of its ability to completely alter the aquatic ecology of a system through damming water, trapping sediment, slowing the velocity of flow, and altering the temperature regime in a river network (Pollock et al., 1995; Majerova et al., 2015). Beavers shape riverine ecosystems and existing wetlands into more diverse water bodies with longer hydroperiods that generally support higher occupancy and abundance of amphibians relative to wetlands that are unaffected by beavers (Shoo et al., 2011; Hossack et al., 2015; Pollock et al., 2015). Government agencies are increasingly utilizing beavers as tools for restoration of streams, wetlands, and floodplains and current management efforts in Yellowstone National Park and Rocky Mountain National Park are focusingon increasing the abundance of beavers in order to promote overall biodiversity and amphibian recovery (Peinetti et al., 2002; Smith & Tyers, 2012; Pollock et al., 2015). However, these habitat alterations by beavers may also promote parasites which can impair amphibian immune function, cause mortality, and lead to population declines (Monzingo & Hibler, 1987; Koprivnikar et al., 2012). One aquatic parasite of particular concern is the chytrid fungus, Batrachochytrium dendrobatidis (referred to as Bd). Since its identification almost 20 years ago, Bd has been considered the cause of rapid and enigmatic population declines in amphibians (Richards et al., 1994; Pounds & Crump, 1994; Berger et al., 1998; Lips, 1998). Bd causes the amphibian disease chytridiomycosis, and affects amphibian populations around the world in both developed areas, where habitat stressors are abundant, and remote areas like national parks and conservation areas (Blaustein & Bancroft, 2007; Collins & Crump, 2009; Becker & Zamudio, 2011). 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). Bd can only be detected using expensive DNA analyses, and most studies focus on host tolerance and transmission by quantifying Bd infections on amphibian skin swabs. This approach, while important for understanding host responses to Bd, fails to address the freeliving zoospore stage that also plays an important role in infecting hosts. 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). In Glacier National Park, beaver populations have been considered stable and 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 (Meentemeyer & Butler, 1995; 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. The main goal of this study is to investigate how changes in the environment due to beavers can influence amphibian parasite dispersal, particularly Bd. Understanding the influence of beavers and their environmental alterations on host abundance and zoospore density in the water column can allow us to understand the effects of beavers on long-term amphibian survival and parasite persistence in regions where beavers are being reintroduced.