Cœur d’Alene salamander COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Highway Maintenance and Widening
The most imminent threat to at least 20 of the 56 known P. idahoensis sites is highway widening and maintenance. At these sites, watercourses or seepages intercept transportation corridors, and blasting and rock scaling may directly kill salamanders and alter habitat configuration. Dumping of highway wastes may bury individuals, and culvert repair or replacement may cause direct mortality or alter habitat structure. As these are often issues of public safety, it is unlikely that mitigating actions could take place. To offset this, however, is the fact that P. idahoensis has been found at more than one place on a watercourse (Ohanjanian 2002). It is, therefore, unlikely that their only occurrence would be at the highways. Safety and access issues at night created a strong bias to survey at highway locations.
Logging Activities
In coastal British Columbia, Dupuis et al. (1995) found a reduction in populations of terrestrial amphibians after clear-cutting of old growth. Clear-cut harvesting and the consequent reduced canopy cover increases solar gain, creating higher ground temperatures and rates of evaporative water loss (Geiger 1971, cited in Dupuis et al. 1995). The effect of the removal of overstory vegetation on the petrophilic P. idahoensis has not been studied. Loss of forested cover could lead to rapid drying of soil and reduce the time available to salamanders for foraging. Low-flow or ephemeral seepage sites may be particularly vulnerable to subtle alterations in hydrology. Silviculture, including herbicide application and burning, is carried out right up to the banks of these small, non fish-bearing streams. Such activities will alter vegetative composition, soil moisture content, remove coarse woody debris and affect the invertebrate prey base. The degree of threat to these streams cannot be predicted, as it will vary with logging plans over future years. There is a provision to prevent this in the guidelines for Wildlife Habitat Areas (Ohanjanian, 2004).
During logging operations, there is the potential for equipment and machinery to crush salamanders, cause compaction or downstream siltation of interstitial spaces, divert water and deposit debris in gullies. As many P. idahoensis sites are located in gullies or areas of steep terrain, compromised side-slope stability may pose a threat.
Isolation of habitat patches and physiological constraints
Plethodon idahoensis occurs in small subpopulations, thus making it more vulnerable to loss of genetic variation and possibly limiting the species’ ability to adapt to changing conditions. The moist micro-environments required are highly fragmented over the landscape, and the physiology of P. idahoensis is such that dispersal between suitable habitat patches depends on wet weather and the presence of subterranean retreats and/or adequate cover objects on the surface. In the dry southern portions of its range (mean summer precipitation < 200 mm, Braumandl and Curran 1992), the dry logs and soil conditions that typify the landscape between these micro-habitats limit opportunities for genetic exchange. In the northern portions of the species’ range, for example in the Revelstoke area, rainfall is higher (mean up to 400 mm in summer, Braumandl and Curran 1992). Opportunities for dispersal, colonization of new habitats and genetic exchange are therefore greater. Although data are lacking, the degree of risk derived from isolation of habitat patches may be less significant in that area than in the south.
Water diversion and altered hydrological regimes
Small-scale hydro development, which lends itself to the steep topography in the range of P. idahoensis, could alter flow rates at salamander occurrence sites, and reduce moisture levels and humidity in subterranean retreats. This form of private power generation has increased; over 570 additional streams have been identified as having the potential for this type of development (BC Hydro 2000).
In addition to anthropogenic threats, P. idahoensis may be vulnerable to natural catastrophes such as flooding during spring run-off, landslides and flow diversions.
Climate change
The ability of P. idahoensis and other amphibians to respond to anticipated rapid warming of the earth’s climate (Intergovernmental Panel on Climate Change 2001) is a matter of uncertainty at present. Possible responses include movements, behavioural changes, and physiological adaptation. As ectotherms, with a relatively limited ability to move and a highly constrained dependence on low temperatures and humidity, plethodontids may be at risk. Ecological modeling has been used to synthesize what is known about species’ habitat requirements and relate these to possible future conditions (Teixera and Arntzen 2002). If climate change reduces rainfall and alters hydrology in south-eastern British Columbia, those P. idahoensis populations on ephemeral or low-flow watercourses will be at risk, should these dry up.
Of additional concern is a recent mechanistic analysis of the capacity of other montane plethodontid salamanders, such as the genus Desmognathus, to tolerate warming-induced stress (Bernardo and Spotila 2005). The cold-adapted, specialized species studied already live at or near the limit of their physiological tolerances. Montane-adapted salamanders showed dramatic metabolic depression when subjected to higher temperatures. Migration upwards along an elevational gradient in response to warming will lead to range contraction which, in turn, will lead to decreased population sizes and, thereby, the erosion of genetic variability.
There is no aboriginal traditional knowledge of this salamander relevant to assessement (Donna Hurlburt and Henry Lickers, pers. comm.).
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