Abstract
Maintaining the diversity of wild bees is a priority for preserving ecosystem function and promoting stability and productivity of agroecosystems. However, wild bee communities face many threats and beekeeping could be one of them, because honey bees may have a strong potential to outcompete wild pollinators when placed at high densities. Yet, we still know little about how beekeeping intensity affects wild bee diversity and their pollinator interactions. Here, we explore how honey bee density relates to wild bee diversity and the structure of their pollination networks in 41 sites on 13 Cycladic Islands (Greece) with similar landscapes but differing in beekeeping intensity. Our large‐scale study shows that increasing honey bee visitation rate had a negative effect on wild bee species richness and abundance, although the latter effect was relatively weak compared to the effect of other landscape variables. Competition for flowering resources (as indicated by a resource sharing index) increased with the abundance of honey bees, but the effect was more moderate for wild bees in family Apidae than for bees in other families, suggesting a stronger niche segregation in Apidae in response to honey bees. Honey bees also influenced the structure of wild bee pollination networks indirectly, through changes in wild bee richness. Low richness of wild bees in sites with high honey bee abundance resulted in wild bee networks with fewer links and lower linkage density. Our results warn against beekeeping intensification in these islands and similar hotspots of bee diversity, and shed light on how benefits to pollination services of introducing honey bees may be counterbalanced by detriments to wild bees and their ecosystem services.
Highlights
Honey bees, Apis mellifera, are used for honey production and as crop pollinators of choice worldwide (Klein et al 2007, Aizen and Harder 2009), because they are generalists, able to pollinate many different crops, and live in large colonies that are transported (Goulson 2003, Potts et al 2010a)
This replacement is alarming because honey bees can only complement, and never fully substitute, the pollination services provided by wild insects (Ollerton et al 2012, Garibaldi et al 2013, Page et al 2021)
The correlation between number of links and z-score is negative, because the more links in the networks, the more strongly z-scores for linkage density fall below the expectation based on random interactions. In this large-scale study we discovered that increasing honey bee visitation rate had an unambiguous negative effect on wild bee richness and abundance, increased competition for flowering resources and influenced the structure of pollination networks indirectly through an effect on the number of wild bees in the communities
Summary
Apis mellifera, are used for honey production and as crop pollinators of choice worldwide (Klein et al 2007, Aizen and Harder 2009), because they are generalists, able to pollinate many different crops, and live in large colonies that are transported (Goulson 2003, Potts et al 2010a). The number of managed honey bee colonies has increased exponentially in some Mediterranean European countries, such as Greece, Portugal and Spain, despite their decrease elsewhere (Potts et al 2010a, Herrera 2020). Beekeeping intensification in the Mediterranean Basin has led to a gradual replacement of wild bees by honey bees at wild and cultivated flowers in this region (Herrera 2020). This replacement is alarming because honey bees can only complement, and never fully substitute, the pollination services provided by wild insects (Ollerton et al 2012, Garibaldi et al 2013, Page et al 2021). From a conservation perspective it is essential to understand whether the pollination benefit of introducing honey bees is counteracted by negative effects on wild pollinators
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