Effects of lichen biomass on winter diet, body mass and reproduction of semi-domesticated reindeer Rangifer t. tarandus in Finland

Winter food supply very likely influences the life history of reindeer Rangifer t. tarandus. We therefore examined how lichen biomass affects winter diet composition, body mass and reproduction in 14 herds of semi-domesticated reindeer in northern Finland. Diet composition was assessed microhistologically on faeces collected from the actual winter feeding sites of reindeer. When lichen was scarce at these sites reindeer included vascular plants and mosses in their diet. Calf dressed weight depended on both ground lichen biomass and the intensity of supplemental feeding, doe dressed weight depended on lichen biomass alone. One explanation for this difference between calves and does is the connection between food supply and calf mortality: low lichen biomass may promote newborn mortality, which, in turn, frees breeding females from investing further in current reproductive investment. Relative offspring weight (calf/female weight ratio) depended on both lichen biomass and supplemental feeding. Low lichen availability appeared to enhance the impact of density-independent factors on reproduction, because the annual variation in reproductive rate increased with decreasing lichen biomass.