Grassy–herbaceous land moderates regional climate effects on honey bee colonies in the Northcentral US

Abstract

The lack of seasonally sustained floral resources (i.e., pollen and nectar) is considered a primary global threat to pollinator health. However, the ability to predict the abundance of flowering resources for pollinators based upon climate, weather, and land cover is difficult due to insufficient monitoring over adequate spatial and temporal scales. Here we use spatiotemporally distributed honey bee hive scales that continuously measure hive weights as a standardized method to assess nectar intake. We analyze late summer colony weight gain as the response variable in a random forest regression model to determine the importance of climate, weather, and land cover on honey bee colony productivity. Our random forest model predicted resource acquisition by honey bee colonies with 71% accuracy, highlighting the detrimental effects of warm, wet regions in the Northcentral United States on nectar intake, as well as the detrimental effect of years with high growing degree day accumulation. Our model also predicted that grassy–herbaceous natural land had a positive effect on the summer nectar flow and that large areas of natural grassy–herbaceous land around apiaries can moderate the detrimental effects of warm, wet climates. These patterns characterize multi-scale ecological processes that constrain the quantity and quality of pollinator nutritional resources. That is, broad climate conditions constrain regional floral communities, while land use and weather act to further modify the quantity and quality of pollinator nutritional resources. Observing such broad-scale trends demonstrates the potential for utilizing hive scales to monitor the effects of climate change on landscape-level floral resources for pollinators. The interaction of climate and land use also present an opportunity to manage for climate-resilient landscapes that support pollinators through abundant floral resources under climate change.

Examining spatial and temporal drivers of pollinator nutritional resources: evidence from five decades of honey bee colony productivity data

“…Our findings likewise indicate that climate is closely associated with honey production, likely through climate effects on floral resources. A recent study on colony productivity across the North Central US likewise identified climate conditions as the most important factor for describing honey bee colony weights, as compared to land use and annual weather [22]. Similar to our findings, the authors describe greater colony weight gain in the cool, dry regions of the study [22].…”

“…A recent study on colony productivity across the North Central US likewise identified climate conditions as the most important factor for describing honey bee colony weights, as compared to land use and annual weather [22]. Similar to our findings, the authors describe greater colony weight gain in the cool, dry regions of the study [22]. Warm and cool climates are likely not intrinsically supportive of floral resources.…”

“…nectar volume) [19]. Honey bee (Apis mellifera) colonies are uniquely suited as a sentinel for monitoring long-term, broad scale environmental effects on floral resources [21][22][23]. Honey bees store abundant nectar resources as honey and recruit nestmates to high quality resources [24], are generalist foragers whose dietary niche overlaps with many specialist and generalist pollinators, and are capable of foraging over long distances [25].…”

Modelling daily weight variation in honey bee hives

“…The amount of food collected by bees in each trip m allows for a better assessment of foraging difficulty and thus of environments that can best support beekeeping operations [ 22 ].…”

“…Directly measuring the number of forager bees is difficult, but the use of new technologies provides opportunities to estimate them from more accessible data [12,21]. Recently developed affordable and precise balances can easily be fitted to hives in the field to study the longterm weight changes [22] and shorter within-day weight variations of hives [12,23]. Withinday hive weight variations are clearly visible and exhibit similar patterns that are consistent across multiple day as shown in Fig 1 . In the morning, rapid weight loss occurs because foragers leave the hive [24].…”