Interaction Network Between Frugivorous Birds and Plants in Karst Habitats

Abstract

The karst region of southwest China is characterized by fragmented habitats featuring high plant diversity but low biological resource availability. Furthermore, high-intensity human activities degrade natural vegetation, reduce landscape connectivity, and alter the bird–plant interaction network. To characterize plant–frugivorous interaction networks in karst habitats, we established six 3 to 5 km transects within Guangxi's Chongzuo White-headed Langur National Nature Reserve, conducting year-round observations of 18 frugivorous birds foraging on 14 fruiting plant species. We calculated four network-level metrics (characterizing network structure) and three species-level metrics (evaluating bird and plant contributions to network structure). Then, we analyzed how species traits influenced their network roles. Compared with the networks (N = 1000) generated by the null model, the observed network exhibited lower connectance (C_z-score = −24.86), higher weighted nestedness (wNODF_z-score = −1.34), higher specialization (H₂´_z-score = 75.39), and higher modularity (Q_z-score = 35.85). Rainy seasons showed higher z-scores for these metrics than dry seasons. Under three extinction scenarios, bird robustness ranged from 0.459 to 0.936, while plant robustness ranged from 0.404 to 0.872. Network stability was compromised when bird or plant species with the highest centrality values were removed, with plant removal being more detrimental. Pycnonotus jocosus, P. aurigaster, and P. sinensis showed the highest species degree and species strength among birds. Meanwhile, Ficus altissima, F. concinna, and Camphora officinarum exhibited the highest values among plants. Bird body mass correlated negatively with species degree and species strength but positively with specialization. Body length correlated positively with species degree and negatively with specialization. The fruit abundance index (FAI) correlated positively with plant species degree and species strength. Our findings highlighted the seasonal differences in the frugivorous bird–plant network in karst habitats and the species traits affecting network functional roles. These results enrich the theoretical framework of the plant–frugivorous interaction network in karst ecosystems, providing a foundation for further analysis of the impact of karst habitat fragmentation on network structure.