The Structure of Sunbird Floral Visitation and Pollen Transport Networks From an Afrotropical Agricultural Landscape

Abstract

Plant-pollinator interactions are among the most studied mutualistic interactions in terrestrial ecosystems. However, little is known about them from the agricultural landscapes within tropical forests of Africa, including the East Usambara Mountains in Tanzania. This study provides the first description of sunbird-plant pollination networks from the East Usambara Mountains. We compared the sunbird floral visitation network and pollen transport network in the agroforestry of Amani Plateau near Amani Nature Forest Reserve. For the floral visitation network, we included a network with nectar robbers and one without. Our results show that the floral visitation and pollen transport networks are structurally similar, and sunbirds visit flowering plants with a wide range of pollination syndromes. Both networks are nested, connected, and modular, so they are relatively robust and less prone to secondary extinctions. Nectar robbers affected the modularity of the network structure and confirmed the reliability of the pollen transport network in defining the most robust plant-pollinator networks. We found that sunbirds with longer beaks transport more pollen, and sunbirds can transport pollen from robbed plants. The findings of this study underscore the vital role of agricultural landscapes in conserving avian pollinators. Therefore, sustainable agricultural practices should be prioritised to mitigate agriculture's negative impact on avian pollinators.