Assessing the Impacts of Agricultural Land Use on Wood Frog (Lithobates sylvaticus) Presence and Health in Central Saskatchewan

• Main Author: Ruso, Gabrielle Elise 1993-
• Other Authors: Jardine, Timothy D, Hogan, Natacha S, Morrissey, Christy A, Wickstrom, Mark L, Brook, Ryan K
• Format: Thesis
• Language: unknown
• Published: 2019
• Subjects: Saskatchewan; wood frog; agriculture; Tadpole; Tundra
• Online Access: http://hdl.handle.net/10388/12057

Globally, amphibian populations are declining in response to many factors including habitat loss and degradation, environmental contamination, invasive species, emerging diseases, climate change, and overexploitation. Amphibians are particularly susceptible to habitat loss and contaminants because of their diverse habitat requirements and unique life histories and ecologies. The Canadian Prairie Pothole Region (PPR) is home to several amphibian species, but they are threatened by large-scale conversion of habitat to agriculture. One of the more common amphibians in this region is the wood frog (Lithobates sylvaticus), a wide-ranging species that occupies a variety of ecosystems, from forests to prairies to tundra. This makes it an ideal model species to compare results in ecological and toxicological studies. Given anecdotal reports of their abundance in the PPR and simultaneous exposure to a number of anthropogenic stressors, I investigated the effects of environmental variables across multiple scales on wood frog presence and tadpole and metamorph health in central Saskatchewan. I visited wetlands at five sites near Saskatoon, SK along a gradient of agricultural intensity with two grassland sites (Allan and St. Denis) and three cropland sites (Burr, Colonsay, and Humboldt). I collected data on water quality including nutrients and pesticides, wetland habitat, and surrounding land use and used environmental DNA (eDNA) to detect the presence of ranavirus and wood frogs. To assess the effects of these variables on both wood frog presence and health (condition, mass, and neutrophil to lymphocyte (N:L) ratios), I used boosted regression trees, a relatively novel but growing modelling technique in the ecological sciences. Wood frogs were present in both grassland and cropland sites. eDNA was more successful at detecting wood frogs in wetlands compared to traditional survey methods – visual encounter surveys and dipnetting. However, for both wood frogs and ranavirus, detection varied seasonally with greater success ...