Long-distance endozoochory of fleshy-fruited trees by sika deer in Hokkaido, Japan

Deer affect their habitats in various ways. Many previous studies on the ecological functions of deer have investigated the impact of herbivory on vegetation but have rarely focused on other functions. In this study, we evaluated the seed dispersal function of the sika deer (Cervus nippon yesoensis) in Hokkaido Island, examining the process from foraging to germination. We (1) surveyed the composition of seeds dispersed by wild deer, (2) measured seed recovery rate and gut passage time by feeding trials using three fleshy-fruited trees (Vitis coignetiae, Actinidia arguta, and Rosa rugosa), (3) conducted germination tests using defecated intact seeds, and (4) estimated seed dispersal distance and its seasonal changes using GPS movement data. In total, 73 seedlings of at least 10 species emerged from 181 fecal samples, each weighing ~1 g. The proportion of intact seeds after gut passage varied greatly with plant species and among trials (0.0%–55.0%). The germination rate of intact defecated seeds was similar to (R. rugosa and V. coignetiae) or higher (A. arguta) than that of manually washed seeds. The average seed dispersal distances during the resident period were 594 m for V. coignetiae and 610 m for A. arguta. The average seed dispersal distances during the migration period increased to 3140 m for V. coignetiae and 3617 m for A. arguta, and sometimes exceeded 18,000 m. These findings highlight that sika deer can disperse seeds over long distances, thus contributing to gene flow between distant populations and range expansion to suitable habitats.