Relative abundance of an invasive alien plant affects insect–flower interaction networks in Ireland

• Insect-flower interaction networks were created in sites invaded by Rhododendron ponticum.
• There were no differences in insect abundance, richness or diversity among sites.
• Insect community structure varied between sites.
• Floral abundance was related to insect–flower interaction network structure.

1.Invasive alien flowering plants may affect native plant pollinator interactions and have knock on impacts on populations of native plants and animals. The magnitude of these impacts, however, may be modified by the relative abundance of the invasive plant and the number of flowers it presents.2.We tested this by examining the structure of insect–flower interaction networks in six sites with increasing levels of invasion by Rhododendron ponticum in Ireland.3.Neither flower-visiting insect abundance, species richness nor diversity were related to R. ponticum flower abundance, but the composition of insect communities was. The total number of flowers in a site increased with the relative abundance of R. ponticum flowers but the number of co-flowering native plant species in these sites was low (<6), making interaction networks relatively small.4.As a result, changes in interaction network properties (connectance, interaction evenness and network level specialisation), which correlated with R. ponticum flower abundance, were a result of the small network size rather than due to changes in the resilience of networks.5.Overall, we conclude that the impacts of invasive alien plants on native plant-pollinator interactions are not only species specific, but site specific, according to the abundance of flowers produced by both the invasive and the native plants.