Six years of wild bee monitoring shows dramatic seasonal shifts in
biodiversity and species declines
Abstract
Wild bees form diverse communities that pollinate plants in both native
and agricultural ecosystems making them both ecologically and
economically important. The growing evidence of bee declines has sparked
increased interest in monitoring bee community and population dynamics
using standardized methods. Here, we studied the dynamics of bee
biodiversity within and across years by monitoring wild bees adjacent to
four apple orchard locations in Southern Pennsylvania, USA. We collected
bees using passive Blue Vane traps continuously from April to October
for six years amassing over 26,000 bees representing 144 species. We
quantified total abundance, richness, diversity, composition, and
phylogenetic structure. There were large seasonal changes in all
measures of biodiversity with month explaining an average of 72% of the
variation in our models. Changes over time were less dramatic with years
explaining an average of 44% of the variation in biodiversity metrics.
We found declines in all measures of biodiversity especially in the last
3 years. Analyses of population trends over time for the 40 most
abundant species indicate that about one third of species showed at
least some evidence for declines in abundance. Bee family explained
variation in species-level seasonal patterns but we found no consistent
family-level patterns in declines, though bumble bees and sweat bees
were groups that declined the most. Overall, our results show that
season-wide standardized sampling across multiple years can reveal
nuanced patterns in bee biodiversity, phenological patterns of bees, and
population trends over time of many co-occurring species. These datasets
could be used to quantify the relative effects that different aspects of
environmental change have on bee communities and to help prioritize
conservation efforts.