Declines in insect biodiversity and biomass are of global concern, and one of the primary drivers of insect loss is agricultural intensification. One group of particular concern is that of insect pollinators because they provide services to crop species dependent on insect vectors for pollination. At the same time as demands for crops dependent on insect pollination are on the rise, we are losing pollinators in agricultural systems. To further investigate the impact of agriculture on landscape scale pollinator diversity, we collated data from five years and almost 1,000 hours of plant-flower visitor observations across natural, semi-natural, and modified habitat types in Ireland. Our study focuses on plant-pollinator communities in Ireland, because it has the highest proportion of land dedicated to agriculture in the EU-27. This is the largest dataset of plant-insect interactions in Ireland to date.
Results/Conclusions
Across the island, we find an unusual asymmetry: there are consistently more entomophilous plant species than flower-visiting insect species. Across all sites surveyed, there are 1.6 times as many plant as insect species. We find this asymmetry is strongest in agricultural and built habitats in Ireland, where there are 2.4 times more plant species than flower visiting insect species. Natural and semi-natural habitats in Ireland have a less dramatic asymmetry, but still have a much lower number of insect species relative to plant species than observed elsewhere. However, for coastal dune systems, we see a more typical asymmetry (more insect species than plant species). When compared to publicly available data on similarly sized plant-pollinator networks, Ireland stands out as the only plant-pollinator community where plant species outnumber insect species. This also leads to an unusually high unweighted average degree for the insect visitors, and low unweighted degree for the plants, as well as a higher nestedness than other networks of similar size. It is possible that the high proportion of land dedicated to agriculture in Ireland has detrimental effects for the diversity of flower-visiting insects.