Data from: Monitoring insect pollinators and flower visitation: the effectiveness and feasibility of different survey methods

1. The status of pollinating insects is of international concern, but
knowledge of the magnitude and extent of declines is limited by a lack of
systematic monitoring. Standardised protocols are urgently needed,
alongside a better understanding of how different methods and recorders
(data collectors) influence estimates of pollinator abundance and
diversity. 2. We compared two common methods for sampling wild pollinating
insects (solitary bees, bumblebees and hoverflies), pan traps and
transects, in surveys of 1km countryside squares (agricultural and
semi-natural habitats) and flowering crop fields across Great Britain,
including the influence of local floral resources (nectar sugar
availability or crop flower density) on the insects sampled. Further, we
compared the performance of recorders with differing expertise
(non-specialist research staff, taxonomic experts and non-expert
volunteers) in applying methods. 3. Pan traps and transects produced
compositionally distinct samples of pollinator communities. In the wider
countryside, pan traps sampled more species of solitary bee and hoverfly.
In flowering crops, transects recorded greater numbers of individual
bumblebees, but fewer species. 4. Across all taxonomic groups and
countryside and crop samples, transects generally had lower rates of
species accumulation per individual collected than pan traps. This
demonstrates that differences between methods in estimating richness are
not due to sampling effort alone. However, recorders possessing greater
taxonomic expertise can produce species accumulation data from transects
that is almost commensurate with pan trapping. 5. The abundance and
species richness of pollinators (except solitary bees) on transects in the
wider countryside was positively related to the availability of estimated
nectar sugar. In crops, pollinator abundance responses to flower densities
were idiosyncratic according to crop type, but overall the response was
positive and negative for transects and pan traps, respectively. 6. Given
these taxonomic and context-specific differences in method performance, we
assess their suitability for monitoring pollinating insect communities and
pollination services. We discuss the relevance of these findings within
the context of achieving standardised, large-scale monitoring of
pollinating insects.