Dietary partitioning and competition between sika deer and Japanese serows in high elevation habitats

Abstract

How environmental conditions promote interspecific niche overlap and the occurrence of competition has long intrigued ecologists. In native ungulate assemblages, dietary partitioning based on interspecific differences in diet preferences has often been reported, but dietary overlap indicating competition is relatively rare. In Japan, native sika deer (Cervus nippon) have invaded high-elevation mountain areas and negatively affected the vegetation there, whereas native Japanese serows (Capricornis crispus) have declined in these areas. However, diet-related interspecific relationships between these species remain unclear in these areas. We examined the diets of deer and serows, and the forage availability in a subalpine forest and an alpine desert of Mt. Fuji, central Japan. The subalpine forest provided both graminoids and coniferous trees, while the alpine desert provided a homogeneous supply of dicot leaves, and forage abundance of both habitats was quite limited. In the subalpine forest, deer fed mainly on graminoids while serows fed mainly on conifer leaves, suggesting partitioning of food resources. By contrast, in the alpine desert, both species fed mainly on dicot leaves, resulting in dietary overlap. We show for the first time that the diets of these two species overlap when shared food resources are limited, suggesting that food resource competition is likely to occur in the alpine desert. These results suggest that food resource competition can occur when both food resource diversity and abundance are limited, even among native species with different diet preferences.