The impact of managed honeybees on wild bee diversity in semi-natural grasslands

Abstract

Introductions of managed honeybees has been shown to negatively affect wild bees due to increased competition for resources, which threatens to dismantle key ecosystem functions such as pollination. This thesis aims to assess the influence of hive proximity on wild bee richness and abundance, as well as niche overlap, and if these processes are mediated by functional traits and environmental factors. To test this, honeybee apiaries were experimentally added to eight semi-natural grasslands. Wild bees were then surveyed along transects at four distances of increasing distance to apiaries (0m, 500m, 1000m & 2000m). The effect of hive proximity, in conjunction with season and local and landscape floral availability (grassland plant richness and area of semi-natural habitats (SNH)), was then tested on richness, abundance of wild bee community, and their niche overlap with honeybees. Additionally, the influence of functional traits (body size, specialisation, and sociality) of wild bees on their niche overlap with honeybees was quantified.

A total of 56 bee species were collected during the field season, consisting of 14 bumblebee species, and 42 solitary bee species. Hive proximity had a negative impact on bumblebee richness, particularly in areas of low SNH. Functional traits and environmental factors (sampling round, SNH & plant richness) were important drivers of niche overlap, with large social bees, as well as oligolectic species in areas of high SNH, overlapping the most with honeybees. Oligolectic species and bumblebees may be most vulnerable where honeybees forage, primarily in semi-natural habitats, since their higher niche overlap may give rise to resource competition. Further research should focus on the direct effects on fitness and reproductive success to facilitate conservation efforts.

Popular Abstract

Do honeybees cause wild bee diversity to decline?

Pollinators are important for ecosystems to maintain biodiversity, and their decline has been associated with climate change, loss of habitat and introduction of managed honeybees. My study focuses on the impact of honeybees on wild bee communities in grasslands, with competition for floral resources and hive proximity being the main possible causes.

In 2022, throughout Skåne County, Sweden, a field experiment was undertaken in which apiaries were introduced into semi-natural grasslands. The wild bee community and the flowering plants on which they feed, were then identified at increasing distances from the apiaries, to assess if patterns in wild bee diversity, as well as how much wild bee species overlap in their diet with honeybees, was structured by their proximity to honeybee apiaries, as well as additional factors (flowering plant diversity within grasslands, time of the year, availability of semi-natural habitats). Furthermore, to assess if diet overlap was affected by traits that affect how bees forage (body size, diet specialisation, and sociality), data for each wild bee species was collected.

A total of 56 wild bee species were collected, highlighting the importance of these areas for wild bee conservation. However, we found that hive proximity had limited negative impacts on wild bee diversity, only affecting the number of bumblebee species when the surrounding landscape consisted of low levels of other semi-natural habitats. This implies that the higher densities of honeybees close to hives negatively affect wild bumblebees mainly when resources are limited in the landscape, and may force some bumblebee species to forage in other areas to avoid honeybees.

In contrast, overlap in diet between honeybees and wild bees, differed considerably depending on the traits of wild bees. Overall, large social bees (i.e., bumblebees), as well as bees with specialised diets (i.e., only foraging on one or a few plant species), exhibited the most overlap with honeybees. As a result, these wild bee groups may be more vulnerable to competition for food, where resources become limited. In particular, specialist bees overlapped the most with honeybees in landscapes with greater availability of semi-natural habitats. In these areas, honeybees are more likely to forage in natural areas, due to a lower availability of flowering agricultural crops, thereby increasing the likelihood that honeybees use the few resources that specialist bees rely on, and increasing the risk of competitive impacts.

Lastly, wild bee biodiversity was strongly affected by the time of the year, grassland plant richness and the amount of semi-natural habitats in the surrounding landscape, highlighting that patterns in bee biodiversity are structured by changes in food availability in time and space. In conclusion, honeybees have highly variable impacts on wild bee communities in semi-natural grasslands, and these effects should be considered in apiary management to ensure that honeybees and wild bees can live in harmony.



Master’s Degree Project in Biology 30 credits 2024
Department of Biology, Lund University

Advisor: Liam Kendall
Centre for Environmental and Climate Science (CEC), Lund University

• author: Jakobsson, Karin
• supervisor: Liam Kendall
• organization: Degree Projects in Biology
• course: BIOM02 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9175890
• date added to LUP: 2024-10-02 16:14:04
• date last changed: 2024-10-02 16:14:04