Secondary seed dispersers of <i>Morella rubra</i> on Yakushima and Tanegashima islands

<p>Abstract: Because primates and large birds can be the sole seed dispersers for plants with large seeds or fruits, as well as being the seed dispersers of a wide variety of other plants, seed dispersal collapse in defaunated forests has become a concern. In Japan, a dramatic reduction in the seed dispersal of Morella rubra has been reported on Tanegashima Island, where its main seed disperser, the Japanese macaque (Macaca fuscata), has become extirpated, unlike on Yakushima Island, which is still inhabited by Japanese macaques. A previous study of seed dispersal collapse focused on arboreal animals that consume M. rubra fruits in the canopy; however, secondary seed dispersal of M. rubra by terrestrial animals remains unclear. The objective of this study was to identify animal species that consume fallen M. rubra seeds and fruits on Yakushima and Tanegashima islands, and to explore the possibility of secondary seed dispersal by these animals. In June 2022 and 2023, we established infrared-triggered cameras at experimental M. rubra fruit patches at 10 sites each on Yakushima and Tanegashima islands, and recorded the terrestrial animal species that visited the sites, together with their visitation frequency. All individuals that consumed or removed fruits were considered foragers, and their species and the numbers of fruits foraged were recorded. The results show that seven animal species on Yakushima Island and ten on Tanegashima Island visited M. rubra seeds or fruits, including five foragers, Japanese macaques, Cervus nippon, Apodemus spp., Nyctereutes procyonoides, and Corvus macrorhynchos, with C. nippon and Apodemus spp. accounting for the highest foraging rates. Considering their feeding style and small faeces, C. nippon may chew M. rubra seeds when feeding on the fruits, and are therefore unlikely to contribute to secondary seed dispersal. By contrast, Apodemus spp. were observed to consume the fruit pulp and seeds, and sometimes held the fruits in their mouths before removing them. This behaviour implies that Apodemus spp. may hoard M. rubra seeds, which could play an important role in the secondary seed dispersal of M. rubra, particularly on Tanegashima Island, where Japanese macaques are absent. Future studies should comprehensively evaluate the amounts of dispersed seeds, seed dispersal distances, and survival and germination rates of dispersed seeds to reveal the role of Apodemus spp. as a secondary seed disperser of M. rubra.</p>