Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Co-chair

Angela D. Luis, Winsor H. Lowe

Commitee Members

Lisa A. Eby, Blake R. Hossack, Taegan A. McMahon

Keywords

amphibian, amphibian decline, Batrachochytrium dendrobatidis, beaver, chytrid fungus, disease ecology

Publisher

University of Montana

Abstract

Environmental variation plays an important role in shaping patterns of parasite and pathogen infections within ecosystems and populations. Effective management of wildlife diseases hinges on the detection of parasites and pathogens, followed by the identification of trends in infections that can be used for predicting their spread and implementing control measures. Beavers are ecosystem engineers and keystone species that serve as important sources of environmental variation. In North America, beavers are promoted for the conservation of imperiled taxa like amphibians which are facing declines driven by habitat loss, parasites, and pathogens. Beavers create diverse habitats that attract amphibians, but these habitat variations have the potential to influence the dynamics of their parasites and pathogens.

In Chapter 1, I highlight the potential bias introduced by environmental sampling in understanding pathogen occurrence and detection probability. I found that the use of eDNA water filters to detect the amphibian pathogen Batrachochytrium dendrobatidis (Bd) overestimated detection probability and underestimated Bd occurrence compared to direct-host swabbing methods. This suggests that eDNA approaches are less reliable than direct-host sampling for pathogens, thus influencing monitoring strategies. In Chapter 2, I demonstrate how different habitat modifications by beavers influence Bd prevalence in western toads (Anaxyrus boreas) and Columbia spotted frogs (Rana luteiventris) in Glacier National Park, Montana. Beaver activity both increased and decreased Bd prevalence by lengthening hydroperiod and reducing canopy cover, respectively. These opposing effects led to no net differences in Bd prevalence between beaver-modified and non-beaver wetlands, indicating that beaver reintroductions may not significantly change amphibian-Bd interactions. In Chapter 3, I found that there was lower prevalence and abundance of the intestinal nematode Gyrinicola batrachiensis in beaver-modified wetlands compared to non-beaver wetlands. While various environmental factors, not linked to beavers, primarily predicted prevalence, I found some evidence that flowing water in beaver-modified wetlands corresponded to reduced nematode prevalence. Tadpole developmental stage was a predictor of nematode abundance, which also did not vary by wetland type. Collectively, the findings from these chapters emphasize the significance of reliable sampling methods in detecting pathogen patterns and highlight how beaver-associated environmental variation may shape parasite and pathogen infections in amphibians.

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