Data from: Experimental small-scale flower patches increase species density but not abundance of small urban bees

1. Large flower plantings are often used to combat negative effects of habitat loss on pollinators, but whether these floral additions are effective at smaller scales remains unclear, particularly in urban settings. 2. To test the effectiveness of small-scale floral additions on enhancing urban bee populations, as well as their impact from one year to the next, different quantities of potted sweet alyssum (Lobularia maritima) flowers were placed across sites in Ann Arbor, Michigan for two consecutive years and the resulting Halictid bee visitors were monitored. 3. Overall we found the number of flowers added at the local level was significantly and positively correlated with small Halictid bee abundance and species density in an urban landscape. At smaller flower quantities dynamics were clearly linear, where incremental increases in number of flowers showed significant increases in bee abundance and species density. At larger quantities of floral additions, however, dynamics were nonlinear in that incremental increases in flower quantity had no effect on bee abundance and highly variable effects on bee species density. 4. When comparing the change in small Halictid bee abundance and species density from one year to the next, we found a significant increase in bee species density in the second year of small-scale floral additions, but no significant difference in bee abundance. 5. Synthesis and applications. Our results show that small flower plantings can have positive effects on small bee communities in urban systems even over a short period of time, and therefore confirm that encouraging citizens to plant flowers can be an effective conservation strategy for certain urban pollinator populations. In addition, our finding that smaller flower plantings may have higher impacts on small pollinators than larger plantings suggests resource managers interested in pollinator conservation should consider spreading multiple, smaller floral plantings across the urban landscape, rather than pooling all resources into one large flower patch.29-Nov-20171. 大规模花卉种植常被用于缓解栖息地丧失对传粉昆虫（pollinators）造成的负面影响，但这类花卉增补措施在小尺度范围内是否有效仍不明确，在城市环境中这一问题尤为突出。 2. 为验证小尺度花卉增补措施对提升城市蜂群数量的有效性，以及其年度间的影响效应，研究团队在密歇根州安娜堡的多个样地放置了不同数量的盆栽香雪球（Lobularia maritima），实验持续两个连续年度，并对造访的隧蜂（Halictid bee）进行监测。 3. 整体而言，我们发现样地本地新增的花卉数量与城市景观中的隧蜂丰度及物种密度呈显著正相关。在花卉投放量较低的区间，数量变化呈现明显的线性关系：花卉数量每增加一定增量，隧蜂丰度与物种密度均会出现显著提升。但当花卉投放量达到较高水平时，数量变化则呈现非线性关系：花卉数量的增量提升对隧蜂丰度无显著影响，而对物种密度的效应则存在高度变异性。 4. 对比小尺度花卉增补实施前后两年间隧蜂丰度与物种密度的变化，我们发现实验第二年的隧蜂物种密度出现了显著提升，但隧蜂丰度未出现显著差异。 5. 综合与应用。本研究结果表明，即便在较短的时间周期内，小规模花卉种植即可对城市生态系统中的小型蜂类群落产生积极影响，从而证实鼓励市民种植花卉可作为针对特定城市传粉昆虫种群的有效保护策略。此外，我们发现相较于大规模花卉种植，小规模花卉种植对小型传粉昆虫的保护效应更强，这一发现提示致力于传粉昆虫保护的资源管理者，应考虑在城市景观中布局多个小型花卉种植区，而非将所有资源集中于一处大型花境。2017年11月29日