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UBC Theses and Dissertations

Movements of adult western toads, Bufo boreas, in a managed forest landscape and the incidence of a disease in southwestern British Columbia Deguise, Isabelle Emiola


Amphibians are declining dramatically around the globe, due primarily to two major threats: habitat destruction and emerging infectious diseases. The western toad, Bufo boreas, is an IUCN red-listed species thought to be affected by both these factors. The objectives of this thesis were to (1) determine how forest fragmentation affects western toad movement behaviour; and (2) determine if there is any evidence of the infectious disease, the chytrid fungus (Batrachochytrium dendrobatidis), in this species in British Columbia. I used radio-telemetry to follow daily movement patterns of 23 adult male toads in a fragmented landscape near Vancouver, BC, composed of forest patches and small, recent clear-cuts. Movement parameters were analyzed using a Geographic Information System (GIS) and mixed effects models. Results showed that toads in forests were able to perceive clear-cut edges from as far as 150 m. Greater than 60% of toads released in forest patches actively chose to enter the clear-cuts from adjacent forests, indicating high boundary permeability. In addition, toad movement parameters were not significantly reduced in these disturbed environments, suggesting that clear-cuts do not restrict movement. Although toads appear to favour these disturbed environments, further research is required in larger, more realistically sized clear-cuts. To investigate the prevalence of the chytrid fungus in southwestern British Columbia, I tested a breeding population of western toads in a protected area. Results showed a 28% infection rate, although no toads showed any visual signs of the disease. These results provide the first evidence of the chytrid fungus in western toads in British Columbia and suggest that the disease is potentially more widespread that currently documented. The results of my research suggest that the western toad may not be affected by small scale forest harvesting. In addition, my results support the hypothesis that western toads are reservoirs for the chytrid fungus. Although most populations in Canada appear to be faring well, long-term population monitoring and further testing for chytrid prevalence are required. To minimize the likelihood of western toads experiencing the dramatic declines that are presently taking place in the United States, protecting vital habitats and preventing the spread of chytrid through public awareness are required.

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