Plant-solitary bee networks have stable cores but variable peripheries under differing agricultural management: Bioindicator nodes unveiled

Abstract

• Plant-solitary bee networks have a stable core but a variable periphery. • Osmia caerulescens is a good bioindicator of management types. • Osmia bicornis is a good bioindicator of ecosystem recovery. • Aboveground cavity-nesting bees pollinate many wild herb plants in olive orchards. • Plant species identified at the core are of conservation priority for bees. The identification of important nodes structuring pollination networks represents a key contribution to biodiversity conservation and pollination functioning. Understanding how species and their importance covary with management is essential if we aim to predict anthropic effects on the environment. In this study we used 96 bee trap nests to sample plant (pollen)-solitary bee interaction networks in 18 pairs of olive groves employing differing management techniques (intensive vs. organic). We applied a novel dual analytical approach consisting of identifying important nodes from two different perspectives: nodes that strongly determine the topological structure of the network and nodes that sustain rare or infrequent interactions. We employed this analytical approach to identify important nodes for the conservation of these networks and to study how different agricultural management practices modify the importance of the nodes. Specifically, Osmia caerulescens appeared in the core of the network of organic farms and acts as a good bioindicator of agricultural management types. As well, O. bicornis participated in important singular interactions but only on organic farms and so can be considered as a good bioindicator of ecosystem recovery. Our results highlight the species that should be prioritized for conservation or restoration and reveal a core-periphery structure in networks, in which, despite most structuring species remaining constant across management types, certain important singular interactions differ. We demonstrate that the switch from intensive to organic farming on olive farms can restore the structure of these plant-solitary bee networks, mainly through the recovery of certain species and rare or infrequent interactions.