Plant interactions shape pollination networks via nonadditive effects

Plants grow in communities where they interact with other plants and with other living organisms such as pollinators. On the one hand, studies of plant-plant interactions rarely consider how plants interact with other trophic levels such as pollinators. On the other, studies of plant-animal interactions rarely deal with interactions within trophic levels such as plant-plant competition and facilitation. Thus, to what degree plant interactions affect biodiversity and ecological networks across trophic levels is poorly understood. We manipulated plant communities driven by foundation species facilitation and sampled plant-pollinator networks at fine spatial scale in a field experiment in Sierra Nevada, Spain. We found that plant-plant facilitation shaped pollinator diversity and structured pollination networks. Nonadditive effects of plant interactions on pollinator diversity and interaction diversity were synergistic in one foundation species networks while they were additive in another foundation species. Nonadditive effects of plant interactions were due to rewiring of pollination interactions. In addition, plant facilitation had negative effects on the structure of pollination networks likely due to increase in plant competition for pollination. Our results empirically demonstrate how different network types are coupled, revealing pervasive consequences of interaction chains in diverse communities.