Increased bumblebee abundance along the margins of a mass flowering crop: evidence for pollinator spill‐over

Abstract

Although the practice of cultivating mass fl owering crops (MFCs) is seen as a means of counteracting the widespread decline of insect pollinators, no study to-date has evaluated whether the increased pollinator abundance associated with MFCs infl uences pollinator visits to assemblages of adjacent native, non-crop plant species (pollinator ' spill-over ' ). In this study we quantifi ed bumblebee abundance along hedgerow transects in MFC (fi eld bean) vs non-MFC (wheat) margins. Surveys were conducted on east and west-facing margins twice daily (morning and afternoon) for three or four days during the main MFC fl owering period (June) over four years involving paired bean and wheat fi elds in Devon and Cornwall, southwest England. Although no single bumblebee species showed any consistent change in relative frequency, when taken across all years and bumblebee species combined, we observed twice as many bumblebees visiting fl owers adjacent to the MFC. However, when we compared bumblebee activity along hedgerow transects two weeks after bean fl owering, there was no diff erence between crops. We thus conclude that although there is evidence for pollinator spillover from the bean MFC to nearby semi-natural habitat, the eff ect is comparatively short lived and not specifi c to any single bumblebee species. We also suggest that while pollinator services to native plant species might be briefl y enhanced by MFC cultivation, the possible repercussions of bumblebee spill-over from MFCs to semi-natural habitats and the other pollinator groups they support should be evaluated before MFC cultivation is considered as a means of conserving declining bumblebee populations.

Massively Introduced Managed Species and Their Consequences for Plant–Pollinator Interactions

“…In addition to Westphal et al (2003), who reported that increased bumblebee densities in MFC resulted in higher visitation rates in P. tanacetifolia, other studies using phytometers b found that MFC facilitated a pollinator spillover. Cussans et al (2010) found that fruit set of Lotus corniculatus increased when planted close to oilseed rape and Hanley et al (2011) observed higher effectiveness of bumblebees visiting flower margins adjacent to MFC during the flowering period. However, the positive effect of MFC on native communities appears to be limited to a restricted number of insect species (Le F eon et al, 2010; Rollin et al, 2013 and to be limited in time (Hanley et al, 2011;Westphal et al, 2009).…”

“…Cussans et al (2010) found that fruit set of Lotus corniculatus increased when planted close to oilseed rape and Hanley et al (2011) observed higher effectiveness of bumblebees visiting flower margins adjacent to MFC during the flowering period. However, the positive effect of MFC on native communities appears to be limited to a restricted number of insect species (Le F eon et al, 2010; Rollin et al, 2013 and to be limited in time (Hanley et al, 2011;Westphal et al, 2009). Contrary to studies on alien plant species, the underlying mechanisms of facilitation are rarely investigated.…”

“…Short-term effects (during vs after MFC flowering) as well as long-term effects via crop rotations that result in annual changes in the distribution of MFC fields might modify the interactions between plant MIMS and natural plant communities. For example, we may observe transient impact of MFC on pollinator populations and wild plant pollination during the flowering that does not necessarily remain after the flowering season (Hanley et al, 2011;Jauker et al, 2012). Furthermore, by influencing pollinator population dynamics, plant MIMS might induce competition for pollinators during mass flowering that potentially translate into facilitation at larger time scales.…”

Pollination services from field-scale agricultural diversification may be context-dependent

“…Pulses of highly attractive floral resources can create dilution effects, drawing species away from adjacent seminatural habitat and reducing pollination services there (Holzschuh et al, 2011). Yet in spite of the attractiveness of MFC fields, wild bee abundance and richness has been found to be higher in habitats, including hedgerows, in closer proximity to MFC fields (Hanley et al, 2011;Le Féon et al, 2013). The effects of MFCs may be species-specific, with some exhibiting higher preference for MFCs over other resources (Rollin et al, 2013).…”

Contribution of organic farming to public goods in Denmark

“…Flowering legumes are attractive food sources for pollinators (Hanley et al 2011;Knight et al 2009). Besides, organic farms have more perennial grass fields with low yield and higher diversity of wild plants than conventional farms (Aude et al 2003;Henriksen 2013;Petersen et al 2006).…”