Determinants of the tailed frog's range in British Columbia, Canada

The tailed frog is the only stream-breeding frog in Canada. Due to its highly specialized habitat requirements and its vulnerability to habitat degradation, it is of concern through much of its range in the Pacific Northwest. The purpose of this study was to determine the range of the tailed frog in British Columbia, and to generate hypotheses for its current distribution. The tailed frog is resident of steep mountain streams. Along the coast, other than its absence from Vancouver Island and Haida Gwaii, the tailed frog's distribution coincides closely with the Coastal Western Hemlock (CWH) biogeoclimatic zone. In the interior, an area with a continental climate, its distribution is allied with the Engelmann Spruce/Subalpine Fir (ESSF) biogeoclimatic zone. However, streams in the ESSF are likely only suitable to tadpoles if a thick blanket of snow buffers them from winter freezing. Thus, drier subzones of the ESSF are less likely to support tailed frogs. This close association with moist biogeoclimatic zones may reflect the species preference for a humid temperate climate regime. The tailed frog's distribution may also be associated with geology: in contrast to streams underlain by competent plutonic rocks (e.g., granite), which typically have coarse gravel beds with locked boulder steps, areas with highly fractured or weak rock types (e.g. shale) have a finer and more mobile stream bedload, leading to unstable channel conditions. These streams provide less favorable habitat for tadpoles. Along the coast, the presently documented northern distribution lies at the Nass River, and the factors limiting northward dispersal are not apparent. In the interior of British Columbia, northward advancement appears to be limited in part both to underlying rock type and climateDupuis et al "Determinants of the tailed frog's range in British Columbia, Canada." Northwest Science. 2000; 74(2): 109-11