Temporal niche partitioning by nocturnal arboreal mammals increases the modularity of plant–frugivore networks in a fragmented subtropical landscape

Animal-mediated seed dispersal sustains plant diversity and ecosystem functioning, particularly in fragmented landscapes. However, the specific contributions of nocturnal frugivores, particularly in above-ground (arboreal) strata, are often overlooked, leading to incomplete characterization of seed-dispersal networks. In a dam-created archipelago in subtropical China (Thousand Island Lake), we used arboreal camera traps to quantify the role of nocturnal mammals in plant–frugivore networks and to examine how island area and isolation shape these nocturnal interactions and overall network structure. We monitored frugivory events on fleshy-fruited plants across 13 forest islands and constructed quantitative bipartite networks to compare diel (i.e. day–night) interaction patterns and their response to island biogeographic variables. Despite being represented by only two families (Muridae and Viverridae), nocturnal arboreal mammals accounted for ~20% of all interaction events, a substantial share second only to the dominant diurnal avian family Pycnonotidae (bulbuls). Island area positively predicted nocturnal interaction richness and its proportional contribution, whereas isolation had no significant effect. Incorporating nocturnal interactions increased network modularity and decreased nestedness, indicating temporal niche partitioning, while connectance remained unchanged. This network reorganization was consistent across the island area gradient. Our study demonstrates that nocturnal arboreal mammals substantially influence the structure of seed-dispersal networks. Omitting their interactions underestimates network compartmentalization and overlooks key dispersal pathways. We emphasize the conservation value of large forest fragments for supporting temporally complementary disperser assemblages and robust mutualistic networks, and we recommend the integration of diel-scale, vertical-strata sampling into ecological network studies, while noting that generalizations to bat-rich tropical systems should be made cautiously. Read the free Plain Language Summary for this article on the Journal blog.