Pollen Transport Networks Help Reveal the Importance of Dipteran Pollinators in Coastal Plant Communities

Abstract

The contribution of dipterans to pollination in tropical communities has been scarcely studied. Although some studies have evaluated dipteran pollination in crops and wild species, limited attention has been paid to their role in pollination networks. In particular, their role in pollen transport has been neglected. Integrating their role as floral visitors and their importance in pollen transport through interaction networks may help reveal their importance in pollination in tropical co-flowering communities. We constructed visitation and pollen transport networks from the analysis of pollen carried on dipteran bodies in two tropical coastal communities to test the prediction that pollen transport networks would reveal fewer but more specialised interactions than visitation networks. We estimated parameters describing the network topology and the main estimators of the roles of each species. We recorded 1372 floral visits and counted 46,001 pollen grains. Our results showed that the visitation and pollen transport networks exhibited similar pollination network structures (e.g., nestedness, specialisation, and modularity). However, the pollen transport network suggested a higher level of specialisation between dipterans and plants in both communities. In addition, the networks' modular structure suggested contrasting species grouping according to network type. Moreover, most dipterans were classified as peripheral species in pollen transport networks, suggesting high within-module interactions. Although some estimators of dipteran role through visitation (nestedness contribution and resource range) can be used as indicators of pollen transport, we found that pollen transport is a better descriptor of dipteran specialisation or the role of the species in the modular structure of the network. This work is the first to explore the importance of dipterans using visitation and pollen transport data in the tropics. Overall, our results suggest that a better understanding of the dipteran's importance in pollination networks is necessary to add information on their role in pollen transport.