Redes de frugivoría ave-planta en dos etapas sucesionales de bosque secundario de araucária

Abstract

Mutualist networks can present variations in their structure related to different degrees of specialization and organization of interactions. In the present investigation we evaluate two frugivorous networks in the secondary Araucaria forest, and we test how the succession stage influences the network size, level of specialization, modularity and species centrality. We categorized two areas of secondary forest (in initial and advanced successional stages) of Araucaria forest in at Reserva Particular do Patrimônio Natural Pró-Mata, Rio Grande do Sul, Brazil. In these areas we collected feces from birds captured in mist nets, to determine the interaction events between species of birds and plants. We generate bipartite networks from quantitative matrices and use species and network level descriptors for comparisons between succession stages. We identified 23 species of birds (19 in the initial network and 13 in the advanced network) interacting with 14 species of plants (11 in the initial network and 10 in the advanced network). It was remarkable that the Myrsine lorentziana plant maintained its structural representativeness in both stages. Observed networks were more specialized and modular than expected by chance. The advanced network presented a higher degree of specialization (H2': 0.43) compared to the initial network (H2': 0.30); with respect to modularity, the initial network presented a higher degree (Z-score: 6.55) compared to the advanced network (Z-score: 4.47). The average specialization at the species level showed that plants had a higher degree of specialization (d'initial: 0.36 and d'advance: 0.45) than birds in both networks (d'initial: 0.24 and d'advanced: 0.38). The local abundance of birds did not show a relationship with their degree of specialization, but with their degree of interaction in the initial network. Two species remained in the core of central species: M. lorentziana and Turdus albicollis, plant and bird, respectively. We also detected that migratory birds were part of the core species in both networks. We found that the secondary araucaria forests in advanced stage harbor smaller, slightly more specialized, and less modular frugivory networks compared to the forest in the initial stage, which present a higher concentration of interactions by a plant species.