Comparing diversity to flower-bee interaction networks reveals unsuccessful foraging of native bees in disturbed habitats

Abstract

As land is converted to agriculture (e.g., pastures), natural vegetation is repeatedly disturbed, creating various levels of habitat alteration in which flowering plants and pollinators (e.g., bees) interact. Community structure of flowering plants, bees, and flower-bee interactions may each respond to disturbance, but potentially in different ways or magnitudes. We studied flowering plants, bees, and their interactions across four mechanical disturbance levels in and near Archbold Biological Station, Florida (USA) for one year, using repeated sampling with standard techniques in replicated plots. Data were analyzed for community structure, flower-bee interactions and bipartite network structure. Over 7500 flowering plants (81 species) and almost 5000 bees (48 species) were sampled, representing >80% of estimated species richness. Disturbance altered available flower diversity and both shifted and simplified compositions of floral and bee communities. Importantly, the number of foraging bee species did not decrease with disturbance but fewer bee species interacted with flowers given greater disturbance, indicating that disturbance reduced successful foraging. Interaction networks became simpler with disturbance, and the non-native European honey bee (Apis mellifera) became more dominant as disturbance intensity increased. Flower-bee interactions were most sensitive to disturbance. For some native bees, anthropogenic disturbance may contribute to ecological trap conditions and drive long-term diversity patterns. Attention to interaction networks will help land managers identify plant species to conserve and restore flowering plants that are vital to native pollinator communities.