Data from: When beggars are choosers-How nesting of a solitary bee is affected by temporal dynamics of pollen plants in the landscape

Wild bees are declining in intensively farmed regions worldwide, threatening pollination services to flowering crops and wild plants. To halt bee declines, it is essential that conservation actions are based on a mechanistic understanding of how bee species utilize landscapes. We aimed at teasing apart how foraging resources in the landscape through the nesting season affected nesting and reproduction of a solitary bee in a farmland region. We investigated how availability of floral resources and potentially resource‐rich habitats surrounding nests affected nest provisioning and reproduction in the solitary polylectic bee Osmia bicornis. The study was performed in 18 landscape sectors dominated by agriculture, but varying in agricultural intensity in terms of proportion of organic crop fields and seminatural permanent pastures. Pasture‐rich sectors contained more oak (Quercus robur), which pollen analysis showed to be favored forage in early season. More oaks ≤100 m from nests led to higher proportions of oak pollen in nest provisions and increased speed of nest construction in early season, but this effect tapered off as flowering decreased. Late‐season pollen foraging was dominated by buttercup (Ranunculus spp.), common in various noncrop habitats. Foraging trips were longer with more oaks and increased further through the season. The opposite was found for buttercup. Oak and buttercup interacted to explain the number of offspring; buttercup had a positive effect only when the number of oaks was above the mean for the studied sectors. The results show that quality of complex and pasture‐rich landscapes for O. bicornis depends on preserving existing and generating new oak trees. Lignose plants are key early‐season forage resources in agricultural landscapes. Increasing habitat heterogeneity with trees and shrubs and promoting suitable late‐flowering forbs can benefit O. bicornis and other wild bees active in spring and early summer, something which existing agri‐environment schemes seldom target.全球范围内集约化农业区域的野生蜂类种群正持续下降，对开花作物与野生植物的传粉服务构成威胁。为遏制蜂类种群衰退，保护行动需基于对蜂类物种如何利用景观格局的机制性认知，这一点至关重要。本研究旨在剖析筑巢季内景观中的觅食资源，如何影响农田区域内一种广食性独居蜂的筑巢与繁殖行为。本研究以广食性独居蜂凹唇壁蜂（Osmia bicornis）为研究对象，探究巢周边的花资源可获得性与潜在的资源丰富型生境，如何影响其巢内食物储备与繁殖表现。本研究在18个以农业为主导的景观单元中开展，各单元的农业集约化程度存在差异，差异体现为有机农田与半自然永久牧场的占比不同。牧场占比高的景观单元中夏栎（Quercus robur）分布更多，花粉分析显示，夏栎花粉是该蜂早期觅食的偏好性食物。巢周边100米范围内的夏栎数量越多，巢内食物储备中的夏栎花粉占比越高，且早期筑巢速度越快，但随着花期结束，这一效应逐渐减弱。季末的花粉觅食则以毛茛属（Ranunculus spp.）为主，该植物广泛分布于各类非农田生境中。巢周边夏栎数量越多，觅食往返时长越长，且该时长随季节推进进一步增加；而毛茛的情况则恰好相反。夏栎与毛茛的交互作用可解释子代数量的变化：仅当研究单元内夏栎数量高于均值时，毛茛才对子代数量产生正向影响。研究结果表明，对于凹唇壁蜂而言，复合型且牧场占比高的景观质量，取决于对现有夏栎的保护与新夏栎的种植。木本植物是农业景观中关键的早期季觅食资源。通过种植乔灌木提升生境异质性，并推广适宜的晚开花草本植物，可惠及凹唇壁蜂以及其他春季和初夏活动的野生蜂类，而现有农业环境计划极少涵盖此类举措。