Cœur d’Alene salamander COSEWIC assessment and status report: chapter 4

Distribution

Global range

The global range of P. idahoensis (figure 2) is the product of postglacial events and the species’ ability to disperse under conditions that largely no longer exist in today’s forested landscape. Recent genetic work has shown that the species dispersed north into Canada from a Pleistocene refugium at a rate of averaging around 50 m per year (Carstens et al. 2004) as conditions became favourable. This movement was possible due to the salamander’s ability to exploit wet, ephemeral habitats, in the form of glacial moraines, created during glacial retreat.

Figure 2. Global distribution of Plethodon idahoensis.

Figure 2. Global distribution of Plethodon idahoensis.

In the United States, P. idahoensis is found in northwestern Montana and northern Idaho (Wilson et al. 1997; Wilson and Ohanjanian 2002, Maxell et al. 2003). There are 209 documented occurrence sites in the U.S. sites: 164 in northern Idaho and 45 in Montana (Cassirer et al. 1994; Maxell et al. 2003). In Montana, the southern limits of its range are in the Bitterroot River drainage (Maxell et al. 2003). In Idaho P. idahoensis is found south to the Selway River drainage (Wilson and Ohanjanian 2002). To date, it has not been found in Washington.

Canadian range

Plethodon idahoensis is known from south-eastern British Columbia (figure 3), in the Purcell and Selkirk mountain ranges (Charland 1992, Ohanjanian 1997, 2001b, 2002, Dulisse 1999, Ohanjanian and Beaucher 2002, Dykstra 2004, Adama and Ohanjanian 2005). It was first discovered in British Columbia some 20 years ago, and by 1998 was known from 15 sites (Dupuis and Ohanjanian, 1998). The 56 occurrence sites now known are situated in seven general areas along the Columbia and Kootenay Rivers and their tributaries. The largest number of sites is on the eastern shore of Kootenay Lake, continuing north along the east shore of the Duncan Reservoir. Other sites are located along the east shore of Upper Arrow and Lower Arrow Lakes, the Moyie drainage, the St. Mary River drainage, the east shore of the Columbia River north of Revelstoke, along the Trans Canada Highway east of Revelstoke and on a tributary of the Pend d’Oreille River. The northernmost (and most westerly) limit of the species’ range is a small tributary of the Columbia River, 95 km north of Revelstoke, although recently the species has been reported at a site on the west side of the Arrow Lakes (Dave Fraser, pers. comm.). The most southerly occurrence is near the U.S. border. The distance between these two points is approximately 320 km. The most easterly occurrence is south of Kimberley on a tributary of the Kootenay River.

Figure 3. Distribution of Plethodon idahoensis in British Columbia. From Matsuda et al. (2006).

Figure 3. Distribution of Plethodon idahoensis in British Columbia. From Matsuda et al. (2006).

The Extent of Occurrence (EO) for P idahoensis in British Columbia, if calculated using the minimum convex polygon method and encompassing all recorded sites, is approximately 17,000 km². However, because the species occurs in highly disjunct areas, a more biologically relevant calculation of EO may be done by adding together each of the areas in which the species occurs and excluding large extents of unsuitable habitat such as lakes and farmland. Considering that the species has been found from 500 m to 1365 m elevation in British Columbia, high elevation alpine and tundra habitats in the region should also be excluded. EO for P idahoensis in British Columbia is only 2,000 km² when estimated in this way. It should be noted, though, that the Flathead Valley, the Rocky Mountains and tributaries of the Columbia River in the Monashee range might contain salamanders but remain un-surveyed

Area of occupancy (AO), when calculated based on a 2 km x 2 km grid, without buffers, using known occurrences, comes to 100 km². A minimum estimate of AO based on known occurrence sites, with a 1 km buffer, is 336 km².

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