Increasing importance of nocturnal arboreal interactions in plant-frugivore networks with island isolation

Seed dispersal by frugivorous animals is essential for maintaining biodiversity and ecosystem functionality, yet nocturnal frugivores and their interactions remain understudied, particularly in arboreal habitats. Here, we explored plant-frugivore interactions (PFIs) in fragmented arboreal habitats of the Thousand Island Lake, China, focusing on the roles of the two monitored nocturnal frugivores, <i>Niviventer confucianus</i> and <i>Paguma larvata</i>. We continuously monitored PFIs using camera traps for 24 hours a day during the fruit ripening period across 202 individual fruiting plants on 13 forested islands over seven months, recording 1,333 nocturnal frugivory events, which comprised 20% of total PFIs. Our findings indicate that island isolation positively influenced the proportion of nocturnal PFIs, reaching up to 31% on the most isolated island, while island size had no significant effect. Network analyses revealed that including nocturnal frugivores did not significantly alter network structure (connectance, modularity, specialization, and nestedness) but showed trends toward lower connectance and nestedness and higher modularity and specialization. Biogeographic patterns of network structure remained stable regardless of the inclusion of nocturnal PFIs. Our results highlight the importance of incorporating nocturnal frugivores in ecological assessments, particularly in fragmented landscapes, while suggesting that their roles may not fundamentally reshape network structures. Future studies should further investigate the contributions of nocturnal frugivores to frugivory networks and examine the impacts of environmental changes on these interactions.