Differentiation and adaptation among fishers in Western Canada: Evidence for validity of Pekania pennanti columbiana subspecies

Recent work has shown that fishers (Pekania pennanti) in Western Canada are split into at least 2 populations, with the endangered Columbian population that occurs in central British Columbia being genetically distinct from fishers in the Boreal population of northern and northeastern portions of the province. To better understand other differences that may exist between these populations, I examined morphological, diet, and age-structure differences using data collected from 329 carcasses collected from trappers between 1989-1993 and live-captures of 105 fishers by researchers between 1996 and 2023. Fishers from the Columbian population had significantly different axial and appendicular skeletons from those in the Boreal population and were significantly smaller in body mass, body and tail length, foot area, neck girth, and chest girth. Despite their smaller overall body mass, fishers in the Columbian population had significantly higher foot-loading than did fishers from the Boreal population. Fishers in the Columbian population also had significantly different winter diets than those in the Boreal population, ingesting mid-sized mammals, grouse, and squirrels more often and ungulates and small mammals less frequently than did fishers in the boreal forest. Age structures were not significantly different between populations but were dominated by juvenile and subadult individuals. These significant differences in morphology and diet were coincident with numerous significant differences in the biotic and abiotic environments in which each population occurred and, when coupled with the genetic and possible biogeographical history of the 2 populations, suggested considerable adaptive differentiation that substantiates the subspecies concept for P. p. columbiana.