Synergistic effects of primates and dung beetles on soil seed accumulation in snow regions

This study aimed to reveal the soil seed accumulation processes for endozoochorous plants in the heavy-snowfall forests of Japan, where seed dispersal agents are few when compared to tropical forests. We assessed (1) primary seed dispersal by Japanese macaques (Macaca fuscata) by identifying dispersed seeds found in their feces, and (2) secondary seed dispersal by dung beetles by using beads (as seeds mimics) of different sizes, to quantify the frequency of seed burial and burial depths. We studied this diplochorous system in different forest types (undisturbed beech forest, conifer plantation, and secondary beech-oak forest) and during the spring and summer seasons. The key findings were as follows: (1) macaques dispersed the seeds of 11 and 14 plant species during spring and summer, respectively; (2) seeds dispersed by macaques in the spring were smaller and twice as abundant than those dispersed in the summer; (3) although no differences were observed in the amount of beads buried by beetles between seasons, all bead sizes tended to be buried in deeper soil layers in the spring than in the summer; and (4) the seed supply to the soil in undisturbed beech forest and conifer plantation was greater than the one in secondary beech-oak forest. Similar to what has been observed in tropical forests, seeds defecated by frugivorous mammals can be successfully incorporated into the underground soil seed bank through a diplochorous macaque-beetle system in temperate forests of deep snow regions.