Data from: Experimental small-scale flower patches increase species density but not abundance of small urban bees

1. Large flower plantings are often used to combat negative effects of
habitat loss on pollinators, but whether these floral additions are
effective at smaller scales remains unclear, particularly in urban
settings. 2. To test the effectiveness of small-scale floral additions on
enhancing urban bee populations, as well as their impact from one year to
the next, different quantities of potted sweet alyssum (Lobularia
maritima) flowers were placed across sites in Ann Arbor, Michigan for two
consecutive years and the resulting Halictid bee visitors were monitored.
3. Overall we found the number of flowers added at the local level was
significantly and positively correlated with small Halictid bee abundance
and species density in an urban landscape. At smaller flower quantities
dynamics were clearly linear, where incremental increases in number of
flowers showed significant increases in bee abundance and species density.
At larger quantities of floral additions, however, dynamics were nonlinear
in that incremental increases in flower quantity had no effect on bee
abundance and highly variable effects on bee species density. 4. When
comparing the change in small Halictid bee abundance and species density
from one year to the next, we found a significant increase in bee species
density in the second year of small-scale floral additions, but no
significant difference in bee abundance. 5. Synthesis and applications.
Our results show that small flower plantings can have positive effects on
small bee communities in urban systems even over a short period of time,
and therefore confirm that encouraging citizens to plant flowers can be an
effective conservation strategy for certain urban pollinator populations.
In addition, our finding that smaller flower plantings may have higher
impacts on small pollinators than larger plantings suggests resource
managers interested in pollinator conservation should consider spreading
multiple, smaller floral plantings across the urban landscape, rather than
pooling all resources into one large flower patch.29-Nov-2017