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群数量持续下降，对显花作物与野生植物的授粉服务构成严重威胁。若要遏制蜂群衰退趋势，保护举措必须建立在对蜂类物种如何利用景观格局的机制性认知基础之上。本研究旨在厘清筑巢季内景观中的觅食资源如何影响农田区域独居蜂的筑巢与繁殖行为。我们以广食性独居蜂凹唇壁蜂（Osmia bicornis）为研究对象，探究了巢穴周边的花资源可获得性与潜在高资源生境，如何影响该蜂的巢内花粉供给与繁殖表现。本研究在18个以农业为主的景观单元中开展，各单元的农业集约化程度存在差异，差异体现在有机农田与半自然永久牧场的占比上。牧场占比高的景观单元内夏栎（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。距离巢穴100米以内的夏栎数量越多，巢内花粉供给中的夏栎花粉占比越高，且早期筑巢速度越快，但随着花期推进，该效应逐渐减弱。觅食季后期的花粉采集则以毛茛属（Ranunculus spp.）为主，该植物广泛分布于各类非农田生境中。夏栎数量越多，单次觅食往返的时长越长，且该时长随觅食季推进进一步增加；而毛茛则呈现出相反的趋势。夏栎与毛茛的交互作用可解释子代数量的变化：仅当研究单元内的夏栎数量高于均值时，毛茛才会对子代数量产生正向影响。研究结果表明，提升凹唇壁蜂适宜的复杂型、高牧场占比景观质量，需依托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觅食资源。通过增加树木与灌木以提升生境异质性，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（agri-environment schemes）极少将此类措施纳入目标范畴。