Wild bee functional diversity and plant associations in native and conventional plant nurseries

An ongoing challenge in ecology is predicting how characteristics of
communities correspond to habitat features. Examining variation in
functional traits across species may reveal patterns not discernible from
measures of mere abundance or richness. For beneficial insects like wild
bees, functional trait-based approaches are often used to characterize
communities in different agricultural habitats. However, no such approach
has yet been applied in horticultural plant nurseries, which represent
intensively managed artificial flowering plant assemblages. Certain
nurseries mostly cultivate regionally native flowering plants, allowing
one to test how differences between local plant assemblages may correlate
with bee functional traits. We surveyed bee assemblages at native and
conventional plant nurseries in southern California from spring through
autumn over two years, while also documenting the native status of
blooming plants in sampling plots. Bees were classified into different
functional categories based on their diet breadth, nesting location, and
social organization. At native plant nurseries, we netted proportionally
more specialist bee species and fewer generalist species than at
conventional nurseries. Nesting location and social organization of bee
samples did not differ between nursery types. Meanwhile, landscape-level
features were not associated with any observed functional trait metrics of
bee collections. Furthermore, network-level specialization of bee-plant
interactions was higher at conventional nurseries. Our results suggest
that a horticultural cultivation practice is quantifiably correlated with
the functional distribution of resident bee assemblages. These results are
important and encouraging to pollinator conservation efforts in nursery
systems and other human-modified landscapes dominated by ornamental
plants.