Abstract
Abstract Floral resources are important in limiting pollinator populations, but they are often highly variable across time and space and the effect of this variation on pollinator population dynamics is not well understood. The phenology (timing) of floral resources is thought to be important in structuring pollinator populations, but few studies have directly investigated this. Our study quantifies the landscape composition, seasonal nectar and pollen supply and Bombus terrestris colony density of 12 farms in southwest UK to investigate how landscape composition influences the phenology of floral resources and how both these factors affect colony density. We use this information in a spatially explicit predictive model to estimate the effect of different farmland management scenarios on seasonal resource supplies and colony density. We find that farmland nectar supply during September is a strong predictor of B. terrestris colony density in the following year, explaining over half of all the variation in colony density; no other period of resource availability showed a significant association. Semi‐natural habitat cover was not a good proxy for nectar or pollen supply and showed no significant association with colony density. However, the proportional cover of gardens in the landscape was significantly associated with colony density. The predictive model results suggest that increasing the area of semi‐natural flowering habitat has limited effect on bumblebee populations. However, improving the quality of these habitats through Environmental Stewardship and other management options is predicted to reduce the late‐summer resource bottleneck and increase colony density. Synthesis and Applications. Our study demonstrates the importance of considering the phenology of resources, rather than just total resource availability, when designing measures to support pollinators. Late summer appears to be a resource bottleneck for bumblebees in UK farmland, and consequently management strategies which increase late‐summer nectar availability may be the most effective. These include mowing regimes to delay flowering of field margins until September, planting late‐flowering cover crops such as red clover and supporting late‐flowering wild plant species such as Hedera helix. Our results also suggest that rural gardens may play an important role in supporting farmland bumblebee populations.
Highlights
Floral resources are important in limiting pollinator populations, with a loss of floral resources cited as one of the main factors driving pollinator declines (Goulson et al, 2015; Roulston & Goodell, 2011)
We find that farmland nectar supply during September is a strong predictor of B. terrestris colony density in the following year, explaining over half of all the variation in colony density; no other period of resource availability showed a significant association
Landscape factors significantly associated with colony density were added to the top-ranking floral resource model to test whether they improved its fit to the data
Summary
Floral resources are important in limiting pollinator populations, with a loss of floral resources cited as one of the main factors driving pollinator declines (Goulson et al, 2015; Roulston & Goodell, 2011). Different plant species have distinct flowering times (phenology), and at a landscape-level this gives rise to a seasonal pattern of floral resources, which is likely to shape pollinator communities (Ogilvie & Forrest, 2017). Simplified landscapes such as farmlands, with low plant diversity, are likely to have high variation in their supply of floral resources through the year and the ensuing temporal gaps in resource availability may be limiting pollinator populations in these environments (Timberlake et al, 2019). To our knowledge, no studies have directly compared the relative importance of floral resources in different periods of the year on wild bumblebee populations, though this information should be considered when designing agri-environment schemes for pollinators
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
