Simple and informative: applying a basic Anthophila monitoring scheme in a simplified insular ecosystem

The decline of pollinators and the consequent decay of pollination services call for the establishment of monitoring schemes for several groups of pollinators. For Anthophila (Hymenoptera), the design of monitoring schemes is still under development. The main difficulties lie in combining a reliable but field-feasible taxonomic identification with the collection of informative data about the consistency and functional role of pollinator populations. Here we report on the application of the Italian monitoring scheme for pollinators recently defined by ISPRA and the University of Turin in agreement with the European Pollinators Monitoring Scheme on the small island of Giannutri (Tuscany), a simplified insular ecosystem with a virtually unknown pollinator community. This island has recently experienced a drastic change in its bee community, as since 2018 honey bee (Apis mellifera L.) hives are regularly moved every year to the island for breeding purposes. In the spring 2021 we established six 250 m long fixed transects and performed a total of 48 surveys (8 for each transect), recording more than 2300 observations of 9 Anthophila bee taxa and the flowers they visited. By using generalised additive mixed models, we showed that the monitoring protocol has a good potential for monitoring Anthophila, as we could verify several expected relationships between Anthophila abundance and abiotic factors (season, hour of the day, distance from the apiary) and biotic factors (abundance of flower resources). More importantly, we verified that A. mellifera represents by far the most frequent Anthophila taxon. Our data do not show evidence for spatial partition between A. mellifera and the other most frequent taxa (Bombus terrestris L. and Anthophora spp.). The visit network based on transect observations also showed that these taxa largely overlapped in terms of visits to flower resources. Overall, our data showed that the monitoring protocol allows gathering informative data about Anthophila taxa abundance, interactions and flower-visits. Moreover, the spatial and flower-visit overlap suggest potential for competition between honey bees and wild pollinators, with a potential consequent resource depletion for the latter. While this hypothesis could only be assessed by a long-term monitoring and ad hoc honey bee removal experiments, our data show that this basic monitoring protocol produces rapid and valuable information about Anthophila community and dynamics.