Elevated pan traps optimise the sampling of bees, including when the availability of floral resources is high

Abstract

Abstract To sample bee communities, a combination of methods is necessary, the most common being hand netting (HN) and pan traps (PT). However, there has been little exploration into how vertical distribution of PT can improve their sampling efficiency, also taking the temporal variation of floral resources into account. Here, we analysed the properties of bee communities sampled with PT at different heights (1.6 and 4.0 m) compared with PTs close to the ground, HN and large blue bucket trap (BB). In addition, we tested the effect of variation in the availability of floral resources on the performance of each method. Bees were collected in fragments of the Brazilian Caatinga. We captured 60 bee species with PTs, HN and BB, with significant increases in the sample coverage with elevated bowls (BB = 56.7%, HN = 60.0%, PT0.3 m = 23.3%, PT1.6 m = 36.7%, PT4.0 m = 50.0%). Elevating the bowls increased the sampling of bees with larger body size. Considering the three heights, PTs registered similar richness compared to HN and BB, but differed in the composition of species and ecological traits. When floral resource availability was greater, the abundance and richness of bees caught in PTs decreased, however, the elevated PT increased their ecological uniqueness (degree of uniqueness of the samples in terms of community composition). Thus, elevating PTs enables the capture of bees that forage at a specific height when floral resources increase. Our results highlight the importance of the vertical distribution of PT for sampling bees, since it improves their performance and its complementarity with other methods.