SNOW COVER AS MEDIATOR OF PREDATOR-PREY RELATIONS : Effects of snow on locomotion of lynx and reindeer

Sammanfattning

Animals living in the boreal zone must cope with snow-rich winters, during which snow cover characteristics affect the ability and energy expenditure of animals to move. Sinking depth relative to hind leg length is a good proxy for energetic costs of locomotion. Climate change alters snow cover characteristics and will affect locomotion costs, thus shifting predator-prey relationships. Here, I studied the sinking depth of the protected predator lynx (Lynx lynx) and their prey, semi-domesticated reindeer (Rangifer tarandus) in the surroundings of Umeå in northern Sweden. During mid- and late winter, I sampled snow cover characteristics including snow depth, density and hardness as well as track depth and step length of lynx and reindeer. I used linear models to identify the metrics best predicting sinking depth relative to hind leg length. There was no difference in sinking depth relative to hind leg length between the two species. Snow hardness of the top layer and step length were the best predictors for sinking depth relative to hind leg length. Snow depth and average snow hardness additionally affected the sinking depth for reindeer and lynx, respectively. The study winter was dominated by icy, wet and shallow snow. These conditions seem to facilitate reindeer in escaping their predators as they do not sink deeper into the snow. Even though, climate change seems advantageous for reindeer in terms of sinking depth, combining predatory pressure, further effects of climate change and pasture loss, reindeer husbandry faces a serious threat to its sustainability.