False colour satellite image of Nanaimo, BC

2009 Submission

Shari Willmott
Advanced Diploma in GIS Applications

American Bullfrogs

Areas at Risk from Colonization

The American bullfrog (Rana catesbeiana) is an invasive species in British Columbia and in many countries throughout the world.  Bullfrogs are of conservation concern because of their negative impacts on native fauna mediated through resource competition and direct predation.  The Bullfrog Project, a partnership between the School of Environmental Studies at the University of Victoria and the Centre for Coastal Health in Nanaimo, was formed in 2007 with the goal to control range expansion of bullfrogs in British Columbia and to mitigate their impacts. In an attempt to protect native frogs and toads, which (on Vancouver Island) include the Red-legged Frog (Rana aurora), the Pacific Chorus Frog (Hyla regilla) and the Western Toad (Bufo borealis), the project has developed a three level management plan to control range expansion: eradication, population control and mitigation of impacts (web.uvic.ca/bullfrogs, 2008). In addition it has also been determined that public education is a key factor in preventing further range expansion and should be the first step in any bullfrog management plan.

In order to prioritize management actions, it is essential to assess habitat suitability and highlight areas that are most vulnerable to colonization by bullfrogs. Through the use of GIS spatial analysis, a breeding habitat suitability model was created to predict which areas in the Capital Regional District (CRD) on Vancouver Island offer potential breeding habitat for American bullfrogs. Further analysis created a cost-distance surface using distance to water as the cost variable and current known colonized water bodies as the sources.  Areas at risk for future colonization in the CRD can now be identified.  With this information, the initiatives of the Bullfrog Project can be implemented more resourcefully, using available funds in the most critical areas to effectively control the spread of the American bullfrog.

Human assisted relocation is the primary mechanism that is allowing bullfrogs to spread in BC and is the reason why public education remains an important first step in controlling further range expansion.  The development of the poster style map submission was a primary focus of a nine week practicum for the Advanced Diploma in GIS Applications program at Vancouver Island University.  The idea was to combine the results from the cost distance spatial analysis with facts about bullfrogs to produce a visually appealing poster-style map to help educate the public about this invasive species.