Bird-plant frugivory networks in two secondary Araucaria forests in southern Brazil.

The properties of mutualistic networks may vary depending on the habitat structure in which partners interact. In this research, we evaluated two plant-bird frugivorous networks from the South Brazilian Atlantic Forest (Araucaria Forest) and tested how different past disturbance history and present successional stage can influence the structure of these networks. We sampled six secondary forest sites within a protected area in Rio Grande do Sul, Brazil-three in early succession following clear-cutting (CC), and three in late succession following selective logging (SL), all with similar disturbance timing in the past. Bird feces were collected from individuals captured with mist nets to identify plant-bird interaction events. We constructed bipartite networks from quantitative matrices and compared network- and species-level descriptors across habitats. We identified 19 bird species interacting with 11 plant species in the CC network, and 13 bird species with 10 plant species in the SL network. Myrsine lorentziana, an important pioneer species for the local forest ecosystems, was a key species in both networks, concentrating the highest number of bird interactions. Both networks were more specialized and modular than expected by chance but did not exhibit significant nestedness. Specialization was generally low, with no significant difference between networks. Modularity was higher in the CC network. On average, plants were more specialized than birds in both networks. Bird abundance did not correlate with species-level specialization, but it did correlate with the number of interactions in the SL network. The same two species, Myrsine lorentziana (plant) and Turdus albicollis (bird), were central in both networks. Additionally, migratory birds were part of the core group of interacting species. Our results showed that plant-bird mutualistic networks of frugivory were structured according to forest type, differing in modularity, composition, and species centrality. Furthermore, the persistence of Myrsine lorentziana and Turdidae as central nodes of interaction throughout successional stages suggests their key role in stability and connectivity in the disturbed remnants of the Araucaria Forest.