Range Extent CommentsRange extends from portions of southern Canada southward through much of the western United States and as far south as Puebla, Mexico. The ranges of A. mavortium and A. tigrinum meet in the Great Plains region, where their distributions meld. This species is absent from most of the Great Basin and most of the far western United States west of the Rocky Mountains. It has been introduced in many localities west of the Rocky Mountains. Elevational range extends to about 3,660 meters (12,000 feet).
Threat Impact CommentsThese salamanders occur throughout their historical range in the Rocky Mountains and Great Plains of Colorado and adjacent states. They remain easy to find and locally abundant in suitable habitat statewide. Ponds often contain up to several thousand larvae. Recent surveys found no evidence of significant declines in distribution or abundance (Corn, Stoltzberg, and Bury 1989; Hammerson 1989a, 1992; Corn, Jennings, and Muths 1997). In the Rocky Mountains, a local decline in numbers over several years, reported by Harte and Hoffman (1989), turned out to be a temporary fluctuation from which the population subsequently recovered (Wissinger and Whiteman 1992). Hovingh (1986) reported that tiger salamanders remain quite common in aquatic systems in glaciated portions of the Uinta Mountains in northeastern Utah. The widespread creation of small, fishless artificial bodies of water has provided much suitable habitat where previously there was little, and these salamanders have been quick to colonize it (Norris 1973; pers. obs.).
Many mountain lakes formerly inhabited by tiger salamanders now have few or none of these amphibians due to the stocking of trout, which easily consume and deplete the larval populations (e.g., Blair 1951; pers. obs.). Geraghty and Willey (1992) found that fish absence was the most important factor influencing tiger salamander presence in Gunnison County and vicinity, and Corn, Jennings, and Muths (1997) reported that trout and tiger salamanders rarely occur together in Rocky Mountain National Park. Trout and tiger salamanders do coexist in some lakes (Dartt 1879; Blair 1951), especially where vegetated shallows provide habitat not easily accessible to the fishes. Levi and Levi (1955) surmised that trout may conflict with paedomorphic salamanders but not with metamorphosing populations.
Some have suggested that breeding-pond acidification related to atmospheric pollution may cause periodic failure of tiger salamander reproduction in the mountains of Colorado (Harte and Hoffman 1989, 1994). Low pH, even if not fatal to salamander larvae, may result in reduced growth rates and ultimately could diminish salamander populations through decreased survival or feeding success (Kiesecker 1996). However, recent water chemistry data, together with information on acid tolerances of salamander larvae, suggest that eggs and embryos in the wild do not experience harmful levels of acidification (Corn, Stoltzenburg, and Bury 1989; Corn and Vertucci 1992; Wissinger and Whiteman 1992; Vertucci and Corn 1994).
Under certain conditions, larval populations may be vulnerable to bacterial infections associated with livestock grazing. In the mountains of Utah, Worthylake and Hovingh (1989) observed recurrent mass mortality of larvae associated a bacterial infection and suggested that increased nitrogen levels due in part to sheep grazing may have been involved. Bryant (1995) observed a mass mortality event in the summer of 1993 that appeared to be associated with an opportunistically pathogenic bacterium. In Arizona, similar die-offs, apparently associated with bacterial pathogens, have been reported (Pfennig, Loeb, and Collins 1991). Cannibal morphs seemed particularly vulnerable, probably due to their feeding on diseased larvae. Again, fecal contamination of ponds by introduced livestock was suggested as a possible cause of the fatal outbreaks. In contrast to these reports, larvae sometimes do thrive in large numbers in manure-laden ponds in Colorado (Hammerson 1999). Nevertheless, die-offs of larvae, apparently associated with pathogenic bacteria, have been observed in Colorado (Hammerson 1999).
Infection by chytrid fungus, which has been associated with amphibian declines in several areas, has been observed in southern Arizona. Observations and experiments with salamanders and frogs indicated that chytridiomycosis does not always lead to mortality, individuals within a species vary in susceptibility to infection, animals appear to recover from the infection, and syntopic salamanders and frogs may act as reciprocal pathogen reservoirs for chytrid infections (Davidson et al. 2003).
Populations in the southeastern United States have been detrimentally affected by deforestation and loss of wetland habitats (Petranka 1998). Similarly, populations in the Great Plains have declined in the extensively cultivated portions of the Great Plains.