By Dr. Gail MacInnis, The National Bee Diagnostic Centre, Alberta, Canada
This blog is part of the ‘Dispatches from Researchers’ series, which features guest articles written by experts in pollination and related fields.
Our study
On the Island of Montréal, Canada there has been a particularly large increase in beekeeping across the city. The number of hives increased more than 12-fold between 2013 and 2020, with an influx of almost three thousand honey bee colonies to the city.
In 2012 and 2013, studies took place to assess wild bee diversity in the city. These surveys (conducted 7 and 8 years prior to our study) provided a unique opportunity to examine the effects of honey bee abundance on the urban wild bee community, and compare the bee communities at the same sites before and after the large influx of honey bees. As wild bee community dynamics are affected by many other factors such as habitat loss and availability of pollen and nectar, the study also attempted to account for environmental variables that may have contributed to wild bee species decline.
Key findings
Cities can support a surprising diversity of wild pollinators, especially compared to agricultural landscapes. This is due to the diversity of land use, relatively low agrochemical use, and abundance of flowers – often in parks and gardens.
Urban beekeeping is often mistakenly perceived as an environmentally friendly practice or a way to combat pollinator declines. However, native bee species are in decline at global scales, and honey beekeeping can negatively affect their populations by outcompeting them for floral resources (food). Indeed, we found a negative relationship between urban beekeepingand wild bee species richness. In our study, sites that saw the greatest increase in honey bees had the fewest wild bee species. Our results also showed that the amount of white clover pollen decreased as honey bees increased across sites. This suggests that the decline in wild bee species richness may be due to insufficient floral resources.
City garden sampling
We found that honey bee abundance had the strongest negative effect on the species richness of small solitary bee species. Small bee species may be at higher risk in areas with abundant honey bee populations. Although small bees require fewer floral resources than large bees, they do not have the ability to forage long distances in times of increased competition. While large bees (especially bumblebees) require more sustenance, they can often forage earlier in the day and in colder conditions than most smaller bees.
To facilitate future research and mitigate the formation of high-density colony sites, it is imperative for cities to maintain a registry of beekeepers with hive locations, so we can develop a better understanding of hive densities, locations, and the honey bee colony carrying capacities of city greenspaces.
Beekeeping can be considered a form of livestock management, but unlike most livestock animals, a beekeeper is not required to provide sustenance for their bees. Honey bees are highly mobile organisms that are free to roam and make use of flowers in their environment. As such, the introduction of honey bee colonies in cities usually does not coincide with an increase in the pollen and nectar required to sustain the wild bee community in addition to burgeoning honey bee populations. High-density beekeeping can also have a negative influence on wild bee populations through the transfer of pathogens and other diseases. Further research on the influence of urban beekeeping on wild pollinators, coupled with evidence-based beekeeping regulations, is essential to ensure cities contain sufficient resources to support wild bees and managed honey bees.
Dr. Gail MacInnis, the National Bee Diagnostic Centre, Alberta, Canada
