Buzzing Controversy: Do Honeybees Harm Wild Pollinators? A Surprising Answer from Canadian Grasslands

In a world where honeybees (Apis mellifera) play a vital role in plant pollination and honey production, different concerns have arisen regarding their dominance over wild pollinators. Previous studies have shown that honeybees, now a widespread introduced species in the Americas and Oceania, can lead to a decline in the richness and abundance of native pollinators and, thus, an overall decrease in floral resource utilisation.

Such a negative effect likely occurs because honeybees compete intensively with native pollinators for resources such as nectar and pollen, reducing the resources available for wild species. Additionally, the presence of honeybees can alter the foraging behaviour of native species, causing them to avoid certain areas due to the honeybees’ aggressive behaviour. However, the details of how honeybees may change or influence wild pollinators still need to be fully understood.

To help fill this gap, Sydney H. Worthy and their team conducted a recent study to evaluate whether honeybees compete with wild pollinators for the same resources and how this affected plant-pollinator interactions at the community level. They conducted a field experiment in Western Canada, where they installed three beehives and collected data on insect-flower interactions in transects located at 100, 500 and 5000 metres from the hives. All these observations took place in the summer of 2019. 

To analyse their results, they used a tool called “interaction networks”, which represents the set of interactions occurring in a given ecosystem. In this type of analysis, when a plant species and pollinator interact, a connection is drawn between them, and as species rarely interact with a single species, these multiple connections create a network that brings together all the detected interactions. These networks allow the visualisation of species interactions and the calculation of numerical indices, known as “network metrics“, that inform researchers about how intricate and resilient these networks are. Particularly the work of Worthy and colleagues focus on indices of resource use, that is, how the resources available in an ecosystem are used by pollinators.

By the end of the study, the researchers recorded 1,814 interactions, composed of 281 pollinator species and 37 plant species. Not surprisingly, honeybees significantly contributed to this number of interactions, especially in the transects closest to the hives. That is, honeybees accounted for nearly a quarter of the interactions in transects 100 m apart and 15% of interactions in transects 500 m away. This, in turn, implies that when honeybees are present, they indeed make up a great part of the number of plant-pollinator interactions occurring in a given community.

The authors also found that high honeybee abundance led to changes in some network metrics. Specifically, they found that if you only use honeybee abundance as a predictor variable, then you find distinct patterns in pollinator behaviour in how they use resources. This phenomenon arises from the competitive dynamics between wild pollinators and honeybees, wherein wild pollinators are potentially compelled to seek alternative floral resources, consequently adopting more specialized foraging strategies. Notably, the study also revealed that as honeybee abundance rises, interactions within the ecosystem become less uniform. This suggests a scenario where heightened honeybee populations might deplete resources, prompting certain species of wild pollinators to intensify their interactions with specific plant species while others reduce their engagement. 

However, unexpectedly, when honeybee interactions were excluded from the analysis, the previous influence of bee abundance on these network metrics vanished, suggesting that honeybee abundance may not be the primary driver of variations in how plants and pollinators interact. This finding was strengthened when the authors considered additional variables in their models, such as flower abundance, flower species richness and the total number of collection rounds. With such models, it became evident that honeybee abundance was not the predominant factor shaping these outcomes; instead, it was the richness of flowers and the frequency of collections that were the best drivers of the variations.

READ THE ARTICLE:

Worthy, S. H., Acorn, J. H., & Frost, C. M. (2023). Honey bees (Apis mellifera) modify plant-pollinator network structure, but do not alter wild species’ interactions. PLOS One, 18(7), e0287332. https://doi.org/10.1371/journal.pone.0287332

Victor H. D. Silva is a biologist passionate about the processes that shape interactions between plants and pollinators. He is currently focused on understanding how plant-pollinator interactions are influenced by urbanization and how to make urban green areas more pollinator-friendly. For more information, follow him on X as @another_VDuarte

Portuguese version by Victor H. D. Silva.

Cover Image by Muhammad Mahdi Karim, Wikicommons