Floral visitation network versus pollen-transport network between bees and flowers in the atlantic forest in south Brazil.

Abstract

The establishment of plant-pollinator interactions is of great importance for the functioning of ecosystems. These interactions can be recorded directly, by focal observation, or indirectly, by the pollen load on the pollinator body. Thus, the evaluation of the specialization and dependence of mutualistic partners, properties that can be assessed through complex networks, depends on the method used for interaction record. The main objective of this study was to compare a floral-visitation network and a pollen-transport network constructed from interactions between plants and bees sampled in 16 plots in early successional areas in the Atlantic Forest, in Antonina, Paraná, southern Brazil. We initially recorded these interactions by focal observation and we sampled the pollen grains on the bees’ body of six bees, and the two networks were restricted to the interactions of these six species. We subdivided the pollen-transport network into a feeding-pollen network, using only the pollen adhered to the bees' corbicules or scopes, and a pollination network, with the pollen present on the bees’ body, except the legs. These networks were compared in relation to the degree (k), the specialization index (d') and species strength (F), through paired t-tests. The pollen-transport network showed a higher number of interactions, higher k, lower d' and a greater number of plant species than the floral visitation network. There was no variation in F. The feeding-and pollination networks presented similar properties. Pollen analysis revealed that bees tend to perform exclusive foraging flights on pollen flowers. The interactions added from the pollen analysis resulted in differences in the metrics evaluated and complemented the record of the interactions observed in the community. Therefore, the associated information of both types of networks can broaden the understanding of the interactions, thus approaching the actual network description.