Keystone resources available to wild pollinators in a winter‐flowering tree crop plantation

Abstract

1 Homogeneous tree crop plantations can adversely impact wild pollinator communities by limiting the temporal continuity of food and the availability of nesting sites. Identifying how structural differences between plantations and natural vegetation influence pollinator communities is necessary for ecological management of agroecosystems. 2 Communities of potential wild pollinators (native bees, wasps, flies) were compared between monoculture almond plantations and native vegetation in a semi-arid region of southern Australia, before, during and after the late winter almond flowering period. Abundance and richness of each insect group were related to site heterogeneity and keystone structural resources at each site, focusing on food and nesting resources. 3 Relationships with site heterogeneity varied between taxa and across months. Native bee abundance and richness were strongly associated with specific keystone resources, despite showing no association with site heterogeneity. 4 The present study highlights the value of focusing on biologically meaningful resources when investigating relationships between insects and habitat, rather than on generalized heterogeneity metrics. The results suggest that maintaining keystone resources in agroecosystems can support the conservation of insects and ecosystem services, especially in areas where homogeneous agricultural systems overlap dynamic natural ecosystems.

Floral resource wastage: Most nectar produced by the mass‐flowering crop oilseed rape (Brassica napus) is uncollected by flower‐visiting insects

“…Indeed, insect density was consistently low at our study sites (mean 1.1 insects per 50 m transect). As a result, seemingly helpful suggestions to breed cultivars of OSR that produce greater quantities of nectar may be unneeded (Carruthers, 2016; Prasifka et al., 2018) as it would increase the surplus. Additionally, other UK MFCs primarily flower in spring (Figure 2a), indicating that most MFC floral resources are available during months of lower competition, where nectar supply is estimated to exceed demand even in the absence of MFCs (Timberlake et al., 2019).…”

“…Our results show that a high percentage of nectar produced by OSR is not collected by flower‐visiting insects. Although OSR floral resource production has been quantified previously (Carruthers, 2016; Carruthers et al., 2017; Fairhurst et al., 2021; Thom et al., 2016), no study had measured this in relation to the demand by the insect community that use it. Our results demonstrate that although certain food sources or periods may be characterised by abundant floral resources, the value will also depend on the demand by the flower‐visiting insect community.…”

“…Flowering OSR is visited by honeybees, bumblebees, solitary bees, and flies (Elzay & Baum, 2021; Jauker, Bondarenko, et al., 2012; Jauker, Peter, et al., 2012; Nedić et al., 2013; Westphal et al., 2009) and can enhance insect abundance and fitness during (Westphal et al., 2009) and after (Jauker, Peter, et al., 2012; Riedinger et al., 2015) bloom. Due to the reported benefits of OSR to insect fitness, some authors have suggested that further increasing nectar production via plant breeding programmes can further benefit insects by reducing floral resource shortages in otherwise resource‐poor agricultural landscapes (Carruthers, 2016; Carruthers et al., 2017; Fairhurst et al., 2021; Thom et al., 2016).…”

“…Although OSR and other MFCs have been shown to produce abundant nectar and pollen (Carruthers, 2016; Carruthers et al., 2017; Thom et al., 2016), floral resource production in relation to demand by flower‐visiting insects has not yet been examined. To better understand the use and possible wastage of floral resources from MFCs, we estimated the percentage of nectar and pollen produced by four spring blooming OSR fields per year over 2 years in Sussex, southeast England, which were uncollected by the flower‐visiting insect community.…”

“…Mass‐flowering crops (MFCs) such as field bean ( Vicia faba ) and clover ( Trifolium spp.) produce superabundant pollen and nectar while flowering (Bailes et al., 2015; Carruthers, 2016; Westphal et al., 2009). In the United Kingdom and other temperate countries, one of the most grown MFCs is oilseed rape ( Brassica napus , OSR) which is used for vegetable oil, livestock feed and biofuel (Nedić et al., 2013).…”