Flower strips enhance abundance of bumble bee queens and males in landscapes with few honey bee hives

Riccardo Bommarco,Sandra A.M Lindström,Chloé A Raderschall,Vesna Gagic,Ola Lundin

doi:10.1016/j.biocon.2021.109363

Riccardo Bommarco, Sandra A.M Lindström + Show 3 more

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https://doi.org/10.1016/j.biocon.2021.109363

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Abstract

Wild bee declines in agricultural landscapes have led farmers to supplement crops with honey bees. Simultaneously, environmental subsidy and conservation programmes have incentivized farmers to establish flower strips to support wild and managed pollinators. To find out if flower strips enhance, and competition from honey bees suppresses, wild bees in the landscape and across seasons, we surveyed bumble bee and honey bee abundances in 16 sites in Sweden in summer 2018. The centre of each site (2 km radius) was with or without an annual flower strip, and with or without added honey bee hives. We surveyed bees in each flower strip and in linear habitats in the landscape around each site, such as field edges and road verges. In the following spring, we surveyed bumble bee queen abundance in each site. We show that adding flower strips benefits bumble bee queen abundance the following year, but this effect is diminished if honeybee hives are added. In sites with flower strips, added honey bee hives reduced male bumble bee abundance. Our relatively small flower strip areas bolstered bumble bee population growth across seasons, probably by relieving a resource bottleneck. Adding honey bee hives in combination with flower strips to landscapes with few floral resources should be avoided as it cancelled the positive effect of flower strips.

Highlights

Agricultural intensification is a main driver for biodiversity decline (Díaz et al, 2019)
Analysing only sites with flower strips, we found that the honey bee hive treatment increased honey bee abundance, and did so more in the flower strip than in the linear landscape habitats (Fig. S2b, Table 2)
We show positive legacy effects of annual flower strips on queen bumble bee abundance in the subsequent spring, but honey bee hives counteracted this effect

Summary

Introduction

Agricultural intensification is a main driver for biodiversity decline (Díaz et al, 2019). The loss of wild bees (Bartomeus et al, 2013; Biesmeijer et al, 2006; Zattara and Aizen, 2021) has weakened crop pollination in intensively cropped landscapes (Kennedy et al, 2013; Potts et al, 2016) deprived of semi-natural habitat and with large fields of few crop species (Senapathi et al, 2015) Such homogeneous land scapes are problematic for wild pollinators as they lose continuity of nesting and foraging resources needed for them to complete their life cycle (Carvell et al, 2006; Schellhorn et al, 2015). Bumble bees are important crop pollinators (Kleijn et al, 2015) They are central-place foragers that routinely forage within 1.5 km from their nests (Osborne et al, 2008) and require access to pollen and nectar within flight range throughout the season. Reproductive castes, in contrast to workers, contribute to bumble bee population persistence, making it important to measure caste-specific effects of interventions on bumble bees

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