Seed-Bird co-occurrence networks in cocoa agroforests: Morphological matching analysis reveals shading effects on network organization

Abstract

Tropical forests are highly vulnerable to ongoing deforestation, which often involves converting land for agricultural use. While tropical agroforests have been promoted as wildlife-friendly systems, limited information is available on the ability of agroforests to provide diverse fruits that attract birds and thus contribute to essential ecological processes, such as seed dispersal. Here, we evaluated the organization of tropical seed-bird co-occurrence networks in cocoa agroforests of the Brazilian Atlantic Forest. Specifically, we investigated the influence of (i) landscape and local predictors in shaping the structure of seed-bird co-occurrence networks; and (ii) species traits in explaining their interactive role in the networks. We constructed matrices of presence-absence interactions based on morphological matching among the beak width of frugivorous bird species and the size of ornithochorous seed species (both native and exotic species), using field data of seed rain and understory bird surveys from 15 cocoa agroforests. We further evaluated both the effects of landscape forest cover and local shading on five network indices and how functional traits of birds and seeds explain their importance to the network. In total, we obtained 467 events of potential plant-bird interactions, which revealed a modular pattern. We also observed that only canopy shading significantly affected network connectance, and seed diameter was a significant predictor in explaining tree species contribution in the network. Therefore, our findings show that cocoa agroforests with greater shading will have greater opportunities for interactions between frugivorous birds and plants. We also observed that plants with small seeds play a more relevant role in the co-occurrence interaction network. Based on findings, we emphasized that cocoa agroforests likely maintain certain mutualistic relationships to ensure ecosystem functionality and demonstrate that co-occurrence networks have great potential for future seed dispersal networks in agricultural ecosystems.