Pan traps: An effective tool for monitoring phenological changes in insect floral visitors and their relationship with floral resources in a coastal Mediterranean forest

Abstract

Precise monitoring of insect floral visitors and their relationship with floral resources throughout the flowering season provides baseline information to help us understand long-term changes in plant-pollinator interactions and improve pollinator conservation strategies. Pan traps are one of the methods most used for monitoring insect floral visitors and several studies have already linked the abundance and richness of these floral visitors with floral resources. However, less research has been conducted into the effectiveness of pan traps for monitoring phenological changes in the floral visitor community with regard to floral resources. We used pan traps to study the species composition and the abundance of insect floral visitors and their relationship with flower richness in a coastal forest throughout the entire flowering season for two consecutive years. Captures were confirmed to be floral visitors through field survey studies. Pan traps were effective for revealing changes in the abundance and species composition of floral visitor communities during and between years that correlated with changes in floral richness and species composition. Changes in floral visitor abundance showed a different bias in their association with floral richness. Thus, while Hymenoptera and Diptera abundance tended to be negatively correlated with floral richness, Coleoptera abundance tended to be positively correlated, although such correlations could change from year to year. There were two significantly different groups of flowering plant and floral visitor species: one in spring and the other in summer. Each period was characterized by unique overlap between some floral visitors and their floral resources, suggesting that to monitor floral visitors effectively both communities need to be considered. Interestingly, the floral phenology in this coastal forest extended longer than that of more inland communities, so reliable monitoring of floral visitors throughout the floral season may help us to better understand the role of coastal plant communities in the stabilization of the pollinator networks of more inland communities. Overall, phenology patterns need to be taken into account for pan trapping to become an effective methodology for monitoring floral visitor communities, considering both intra-year (spring and summer communities) and inter-year variations.