Annual variation across functional traits: The effects of precipitation and land use on four wild bee species

Understanding the impacts of urbanization and climate change on organisms
has become increasingly critical in ecology and conservation as these
anthropogenic stressors negatively impact wildlife biodiversity,
especially pollinators such as bees. We analyzed the demographic
(abundance and sex ratio) and morphological (body size and wing wear)
responses to urbanization and inter-annual variation of four common wild
bee species across an urban gradient in Toronto, Canada. We
observed more significant shifts in bee demography with inter-annual
precipitation variation than with urbanization, with diverse patterns
depending on species. The drier active season saw a decrease in abundance
for Agapostemon virescens and Ceratina calcarata whereas Bombus
impatiens and Xenoglossa pruinosa increased when compared to the previous
year Wetter active seasons resulted in smaller body sizes and greater wing
wear for all bee species examined. For larger bees (A. virescens,
B. impatiens, and X. pruinosa), increasing urbanization resulted in
significantly larger females only for A. virescens, whereas foraging
effort reduced as urban intensity increased. The small, cavity-nesting
bee, C. calcarata exhibited reduced body sizes and increased
foraging effort with increasing urbanization. Moderate
urbanization better supported most wild bee assemblages and morphology
suggesting that moderate land use intensity provide green spaces and
adequate resources for these bee species.