Range mapping to assess extinction risk of species in Canada

Government agencies and conservation organizations often determine the conservation status of plant and animal species based on factors such as changes in a species’ geographic distribution (or range). Species with large reductions in range are often proposed for legal protection.

Two NCASI scientists, Dr. Craig Loehle and Dr. Darren J.H. Sleep, recently examined how geographic range changes are used in the listing process for species, with an emphasis on terrestrial vertebrates in Canada. The authors found that geographic range is not a clearly defined metric and no two studies reviewed by the authors used the same methods and/or data for mapping ranges.

Historic data reliability was particularly problematic. Most seriously, many of the listed species examined in the study only had a small part of their total range in Canada, and actually were globally secure.

The abstract for the paper follows.

“When a species potentially at risk of extinction is considered for legally protected status, changes in geographic range over time are often evaluated and utilized in listing decisions. Range changes are also used to guide conservation management decisions. Although changes in geographic range may provide information relevant to conservation decisions, many factors affect estimates of geographic range. We investigated how geographic range change is estimated and used in the listing process. We evaluated all terrestrial vertebrates in Canada whose assessment as threatened or endangered was based at least partially on small range or range reduction. The 39 cases of birds, mammals, reptiles, and amphibians (including 2 populations of 1 species) used a variety of historical and recent data, including natural history archives, special surveys, and standardized surveys. Little mention was made in the reports of the methods used for range delineation or the limitations of geographic range maps. Of the 39 cases listed by the reports as being threatened or endangered in Canada at least in part due to geographic range, 32 (82%) had ≤10% of their current global range in Canada (i.e., most had wide ranges in the United States), resulting in the listing of species with marginal and sometimes nonviable populations within Canada even when the global population was not at risk. We identify several ways that listing decisions could be improved.”



Loehle, C., and D.J.H. Sleep. 2015. Use and application of range mapping in assessing extinction risk in Canada. Wildlife Society Bulletin 39:658-663. http://dx.doi.org/10.1002/wsb.574