PREMISE In arid ecosystems, shrub facilitation is a critical process driving plant community structure and assembly, often resulting in increased densities of annual plants beneath shrub canopies. Pollinator-mediated interactions can have fitness consequences for both plant interactors but are largely unexplored as an indirect consequence of direct shrub-annual facilitation. METHODS We tested the capacity of the geographically widespread creosote bush (Larrea tridentata) to influence pollinator visitation to its annual understory during its phenological shift into spring flowering. We used small video cameras to record pollinator visitation and foraging behavior on potted transplants of a representative flowering annual. We concurrently evaluated L. tridentata's positive role as a foundation plant in this system by measuring the associated plant and arthropod communities and deploying data loggers to measure understory microclimates. RESULTS Pollinator visitation to the flowering annual desert dandelion, Malacothrix glabrata, was lower when beneath the canopy of L. tridentata, and further declined throughout the study site as L. tridentata entered full bloom. We confirmed the role of L. tridentata as a foundation species in this system through its concurrent, positive effects on annual plant cover (a proxy for biomass), the abundance and richness of the understory arthropod community and its ability to create stable microclimates. CONCLUSIONS Direct and indirect shrub effects on other species function simultaneously to shift net outcomes even within predominantly net positive facilitation complexes.

中文翻译：

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用一粒盐促进：减少传粉媒介访问是与基础物种杂酚油灌木（Larrea tridentata）相关的间接成本

前提在干旱生态系统中，灌木促进是推动植物群落结构和组装的关键过程，通常会导致灌木冠层下一年生植物的密度增加。传粉媒介介导的相互作用可以对植物相互作用者产生适应性后果，但作为直接灌木一年生促进的间接结果，在很大程度上未被探索。方法我们测试了地理上广泛分布的杂酚油灌木（Larrea tridentata）在其物候转变为春季开花期间影响传粉媒介访问其年度林下的能力。我们使用小型摄像机记录了具有代表性的一年生开花盆栽移植的传粉者访问和觅食行为。我们同时评估了 L. tridentata' 通过测量相关植物和节肢动物群落并部署数据记录器来测量林下小气候，作为该系统中的基础植物发挥积极作用。结果 授粉者对一年生开花的沙漠蒲公英的访问量在三齿草的树冠下较低，随着三齿草进入盛开，在整个研究地点进一步下降。我们通过其对一年生植物覆盖率（生物量的代表）、林下节肢动物群落的丰度和丰富度及其创造稳定小气候的能力的并发积极影响，证实了三齿龙舌兰在该系统中作为基础物种的作用。结论 灌木对其他物种的直接和间接影响同时作用于改变净结果，即使在主要是净正促进复合体中也是如此。