The biogeography of home range size of woodland caribou Rangifer tarandus caribou

Abstract

Aim: Population-limiting factors represent the core of conservation biology. Because animal space use is affected by ecological constraints that can vary among populations, limiting factors might be revealed from intraspecific variation in home range size. We evaluated biogeographic variation in the home range size of woodland caribou (Rangifer tarandus caribou), a threatened species inhabiting the boreal forest, in relation to land cover, topography, snowcover and disturbance across the species’ range. Location: Twenty-five populations in Canada, spanning the contiguous boreal forest (an east–west extent of 4,400 km), including the southern fringe of the species’ range, adjacent to a broad region of extirpation. Methods: We compiled the average annual home range size of adult female caribou (5–68 home ranges per population) and 18 putative predictor variables in each population range. We uncovered major gradients using principal components analysis and then evaluated models of home range size using multiple regression, with orthogonal variables representing vegetation, human disturbance and snowcover. Results: Average home range size varied 28-fold among populations (range: 312–8,838 km 2 ). Home range area was most strongly and negatively correlated with anthropogenic disturbance in the population range (R 2  = 0.391), a variable in all seven top models (ΔAIC c  ≤ 5.99). Among populations, where human disturbance in the population range was low (≤10%), mean home range sizes consistently exceeded 1,400 km 2 . Conversely, where human disturbance was high (>55%), especially at the species’ southern range margin, mean home range sizes did not exceed 1,500 km 2 . Main Conclusions: In the boreal forest, female caribou may constrict their home ranges amid human-caused disturbances. We speculate that smaller home ranges may lower the risk of encounter by predators, a key limiting factor. Among populations, smaller home ranges may serve as a signal of anthropogenic habitat loss.