Flowering plant communities mediate the effects of habitat composition and configuration on wild pollinator communities

There is strong evidence that landscape-scale factors such as habitat
diversity, composition, and configuration are important drivers of
declines in pollinators and pollination services. However, context and
species-specific responses make it challenging to draw general conclusions
about the most important components of landscapes that support diverse and
abundant pollinator communities. In this study, we took a functional
traits approach to community assembly and tested the hypothesis that
landscape properties act most strongly on pollinators indirectly, through
their influence on flowering plant communities. Using plant and pollinator
data from 96 landscapes in Britain, we tested the associations between
plant and pollinator communities and local environmental factors, such as
habitat cover and configuration, using path analysis based on Mantel and
partial Mantel statistics. When all pollinators were considered, we found
that the environmental factors had stronger links to the composition of
flowering plant communities than to the composition of pollinator
communities. Further, the flowering plant community was strongly linked to
the pollinator community suggesting a mediating role between land use and
pollinators. When separating the pollinator community into taxonomic
groups, we found the same result for hoverflies, but wild bees were linked
to both environmental factors and flowering plants. We further explored
these links with structural equation models using the response-effect
trait framework as a guiding principle. We found strong evidence that land
use composition and configuration influence the trait distribution and
functional diversity of the pollinator community via plant community
composition. These findings suggest that the indirect effect of land use
on pollinators via flowering plants should be considered in informing the
design of pollinator-friendly landscapes and in future research on the
effects of land use and management on wild pollinators.