Simulated high-intensity phorophyte removal mitigates the robustness of epiphyte community and destroys commensal network structure

Abstract

Interspecies interactions deserve more attention in biodiversity conservation since the elimination of only one species can indirectly impede the dependent species through ecological networks. Phorophytes, which provide physical support, constitute the basis for the occurrence of epiphytes. Epiphytes and their host phorophytes thus form a typical commensal interaction network. However, the impacts of phorophyte removals on the diversity and stability of epiphyte communities are poorly understood. Such understanding may illuminate guidance on forest protection and management. In this study, two species-based networks (raw species-based network and standardized species-based network) and one raw individual-based network between vascular epiphytes and phorophytes were analyzed in a tropical rainforest in Southwest China. Based on the construction of second extinction models, the robustness of epiphyte community and the dynamic of network structure were calculated for raw species-based network and individual-based network under different phorophyte removal scenarios. As a result, all three epiphyte-phorophyte networks exhibited low connectivity and moderate modularity; the nestedness of the standardized species-based network was lower than that of the raw species-based network, but remained higher than that of the raw individual-based network. The removal of the strongest interactor could lead to the rapid collapse of epiphytic communities, while the reverse order increased community robustness. Most importantly, for raw species-based and individual-based networks, we found the curves of modularity and nestedness started changing drastically and fluctuated frequently when the phorophytes’ removal rate approaches 80%. Our results suggest that the keystone phorophytes (such as generalists, large individuals and abundant species) should receive special attention in conservation efforts to sustain tropical epiphytic systems; and when subject to removal, the intensity of phorophyte removal should be kept below certain threshold to achieve long-term stability of epiphytic communities.