Gray ratsnake (Elaphe spiloides) COSEWIC assessment and status report: chapter 11

Special Significance of the Species

The Canadian populations of Gray Ratsnakes represent only a small proportion of this species’ total global range. Despite this fact, there are a number of genetic, ecological and cultural factors that make both the Great Lakes/St. Lawrence and Carolinian populations significant.


Genetic

It is widely accepted that species conservation depends in part upon preserving the genetic diversity within species. Genetically diverse species are better able to adapt and survive in changing environments (discussed in Lesica and Allendorf, 1995; Keller and Waller, 2002). Although peripheral populations may have reduced genetic diversity, they often contain a proportionately higher amount of rare alleles (Gapare et al. 2005), and are considered to be the most active areas of speciation (Simpson, 1944; Carson, 1959; Levin 1993). These factors often make peripheral populations proportionately more important in preserving the total genetic diversity, especially when the peripheral populations are disjunct, genetically differentiated and under different selection pressures (Lesica and Allendorf, 1995).

The Carolinian and Great Lakes/St. Lawrence ratsnake populations are geographically disjunct and genetically distinct from each other, and from populations in the United States. The Canadian populations are also at the northern extreme of the species’ range and face more extreme temperatures than most populations. Furthermore, studies using RAPD markers and microsatellite DNA have estimated the amount of genetic variation accounted for by differences between regional populations to be as high as 13% (Prior et al. 1996) and 20% (Lougheed et al. 1999) respectively. All of these factors make preserving the Canadian populations important for preserving the total genetic diversity of Gray Ratsnakes.


Ecological

Although their importance is often under-estimated, snakes play an important role in their ecological communities. Ratsnakes are major predators of many species of small mammals and birds (Weatherhead et al. 2003) and have also been shown to be major prey items for birds of prey (Fitch, 1963). Gray Ratsnakes also require and occupy a wide variety of habitats (See Habitat –Habitat requirements) and have relatively large home ranges. Ratsnakes can disperse as far as 4 km from their hibernacula and, therefore, efforts to preserve hibernacula could encompass as much as 50 km2 of surrounding habitat and would benefit many other species.


Cultural

The Gray Ratsnake is Canada’s largest snake and the presence of populations in Ontario is widely recognized by herpetologists and naturalists. This is especially true for the Great Lakes/St. Lawrence population, which is recognized as a distinct population in many field guides and textbooks (e.g. Ernst and Barbour 1989; Conant and Collins, 1998; Futuyma, 1986).

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