Plant and Fruit Traits Drive the Structure of Bird-Frugivore Networks in a Simplified Coastal Forest of Eastern China.

Plant and fruit functional traits fundamentally structure mutualistic networks in forest ecosystems. However, it remains unclear how these traits affect the network structure in the coastal forests. Understanding the relationship between plant traits and network structure is crucial not only for fundamental ecology, but also for the effective conservation and management in the coastal forest ecosystems. Here, we examined avian-frugivory networks in the coastal forests of Dafeng, eastern China, by integrating key plant (height, canopy density, and fruit yield) and fruit traits (water content, crude fat, sugar, starch, and phenolics). The frugivory network exhibited a specialized and modular structure with significantly lower connectance and nestedness than null model expectations. Generalist species, particularly the light-vented bulbul (Pycnonotus sinensis), acted as the main forager in the network, interacting with all 12 plant species. The results of generalized additive models revealed complex nonlinear relationships between plant functional traits and network structure: fruit yield exhibited a threshold effect on species degree, while water content showed a unimodal effect. Crude fat and tannin content further influenced specialization through saturating and unimodal patterns, respectively. Overall, our study highlight that both structural and nutritional traits critically shape frugivory networks in coastal forests. Our findings also provide a trait-based framework for conservation of coastal forests, underscoring the need to preserve generalist frugivores and prioritize plant species with key functional traits to maintain ecosystem resilience.