Evaluation of secondary seed dispersal by dung beetles in a temperate region

The survival of seeds dispersed by primary dispersers is determined by seed predation and secondary movement from deposition sites. The aim of this study was to clarify the role of dung beetles (Scarabaeidae) as secondary dispersers in northern Japan, with a focus on the burying ability of seeds within the feces of the sympatric primate Japanese macaque (Macaca fuscata) and its seasonal patterns. We conducted field and laboratory experiments to evaluate the seed-burial ability of dung beetles in parallel with investigations into the composition of seeds in dung and the capture of dung beetles. The experiments demonstrated that large tunnellers, mainly Phelotrupes spp. in summer and Copris spp. in fall, buried experimental seeds (plastic beads) at a depth of 0.5–5 cm regardless of size, implying that the buried seeds had a high probability of escaping predation and desiccation. Therefore, the large dung beetles at our study site seem to contribute more to secondary seed dispersal. We found that the percentage of seed-burying was greatest in summer when the abundance of Phelotrupes spp. was higher. This implied that secondary dispersal in the temperate region exhibited a clear seasonality originating from the life history of the dung beetles. The role of secondary dispersers in each season should be accurately evaluated to estimate seed dispersal effectiveness, especially in temperate regions where environmental seasonality is clear.