2.3.2 Network roles of fruit plants and frugivore birds
We characterized the network roles of plants and birds based on five parameters: (1) degree (D), which describes the proportion of available partners a species interacts with and is related to the importance of the species for network cohesion and stability of the total number of connected species (Costa et al., 2020); (2) species strength (Ss), which represents the sum of the dependencies of each species’ relevance across all partners (reflecting quantitative importance of a species for the other) (Bascompte & Jordano, 2007); and (3) partner diversity (Pd), which represents the diversity of interaction partners for each species. It is a quantitative analog to the qualitative species degree, the richness of interaction partners (Kaiser-Bunbury & Blüthgen, 2015); and (4) effective partners (Ep), which interpret the variety of partners a species interacts with in a given network (Quitián et al., 2017); and (5) specialization ( ), which measures how strongly a species deviates from a random sample of interaction partners, assuming that all species interact according to their total frequencies (Rumeu et al., 2020). All analyses were performed using the function “species-level” in the “bipartite” package version 4.20 (Vollstädt et al., 2018).
We conducted a correlation analysis between species traits and network parameters to test whether the role of plants and birds in the network were driven by species traits. Plant traits included fruit mass, fruit length, fruit diameter, fruit volume, and fruit color, whereas bird traits included body mass, body length, bill length, wing length, and wing-loading. Their network parameters included degree, species strength, partner diversity, effective partners, and specialization. The analysis between them was performed in the “cor” package version 4.2.0 (R Core Team, 2022), the function “pairs” were used to realize graphic visualization, and the statistically significant difference was set asP <0.05.