Structure of Epiphyte–Phorophyte Networks and Their Robustness to Species Loss in White-Sand Ecosystems in the Amazon

Abstract

The Amazon is the world's largest tropical forest, has a great diversity of species, and provides essential ecosystem services. However, anthropic exploratory processes have intensified and are seriously influencing this biome. Approaches that are based on ecological network theory are an excellent tool for describing the structure of communities, interactions between species, and the stability of ecosystems. Using a specific set of network metrics; the first epiphyte–phorophyte commensal network for the fragile white-sand ecosystems of the central Amazon was created. The structure and organization of interactions were analyzed and described; we also tested the stability of the system to simulate species loss. A total of 725 interactions between 52 phorophyte species and 118 vascular epiphytes were recorded in the white-sand ecosystem (WSE). The epiphyte–phorophyte network exhibited a nested structure, with a low degree of specialization (H₂′), connectance, modularity, and robustness. When the elimination of highly connected phorophytes was simulated, secondary extinctions in epiphytes were high, which indicates low stability of the system when disturbances occur. The generalist phorophyte Aldina heterophylla was particularly important, interacting with 89.0% of the species and hosting 75.0% of the epiphytes. Our results indicate that the richness and abundance of vascular epiphytes in WSEs is concentrated in a few phorophytes species, especially in large trees. As such, removing this species from the system can disrupt interactions, change the network's structure, and unbalance the entire ecosystem.