Drawing lines: Spatial behaviours reveal two ecotypes of woodland caribou

Abstract

Ecotypes offer an essential framework for conservation and ecological understanding, but their identification can be problematic. These challenges are exemplified by the sedentary and migratory ecotypes of woodland caribou (Rangifer tarandus caribou). In Ontario, Canada, reliable discrimination based on morphology, pelage, or genetics has been unsuccessful. We tested the discriminatory power of locational and movement metrics as candidate indicators of discrete behaviours for 132 GPS-tracked female caribou. We assigned each animal to an ecotype each year using two variables which demonstrated the strongest bi-modality and the best discriminatory power: percent of calving season locations within the Hudson Bay Lowland and mean distance to treeline during calving season. The analysis revealed two distinct modes. None of 101 caribou tracked for more than 1year switched behaviours, implying the distinction may be permanent. Although there was no significant difference in morphology between ecotypes, mean aggregation metrics and calving dates were significantly different. Geographic distribution of these ecotypes showed substantial range overlap, particularly during winter, which presents challenges for conservation of the sedentary ecotype, a threatened designatable unit under federal and provincial legislation. Woodland caribou − with its cryptic ecotypes, discernible from differences in spatial behaviour − illustrate the importance of this type of analysis for identifying significant units for protection, understanding habitat relationships, and delineating ranges for habitat protection.