Urban green spaces such as gardens often consist of native and exotic plant species, which provide pollen and nectar for flower-visiting insects. Although some exotic plants are readily visited by pollinators, it is unknown if and at which time of the season exotic garden plants may supplement or substitute for flower resources provided by native plants. To investigate if seasonal changes in flower availability from native vs. exotic plants affect flower visits, diversity and particularly plant–pollinator interaction networks, we studied flower-visiting insects over a whole growing season in 20 urban residential gardens in Germany. Over the course of the season, visits to native plants decreased, the proportion of flower visits to exotics increased, and flower-visitor species richness decreased. Yet, the decline in flower-visitor richness over the season was slowed in gardens with a relatively higher proportion of flowering exotic plants. This compensation was more positively linked to the proportion of exotic plant species than to the proportion of exotic flower cover. Plant–pollinator interaction networks were moderately specialized. Interactions were more complex in high summer, but interaction diversity, linkage density, and specialisation were not influenced by the proportion of exotic species. Thus, later in the season when few native plants flowered, exotic garden plants partly substituted for native flower resources without apparent influence on plant–pollinator network structure. Late-flowering garden plants support pollinator diversity in cities. If appropriately managed, and risk of naturalisation is minimized, late-flowering exotic plants may provide floral resources to support native pollinators when native plants are scarce.

诸如花园之类的城市绿色空间通常由本地和外来植物组成，这些植物提供花粉和花蜜来造花昆虫。尽管传粉者很容易参观一些外来植物，但尚不清楚是否以及在季节的哪个时间外来园林植物可以补充或替代本地植物提供的花卉资源。为了研究本地植物和外来植物的可用花的季节性变化是否会影响花访，多样性以及尤其是植物与授粉媒介的相互作用网络，我们在德国20个城市住宅花园中研究了整个生长季节的访花昆虫。在整个季节中，对本地植物的访问减少了，对异国情调的花朵访问的比例增加了，而花访者物种的丰富度降低了。然而，在开花异国植物比例相对较高的花园中，访花者丰富度随季节下降的速度有所放缓。这种补偿与外来植物物种的比例相比，与外来花朵覆盖的比例更正相关。植物-授粉媒介相互作用网络是中等专业化的。在盛夏，相互作用更为复杂，但相互作用的多样性，连锁密度和专业化不受外来物种比例的影响。因此，在本季晚些时候开花的原生植物很少的情况下，外来园林植物部分替代了原生花卉资源，而对植物-授粉媒介的网络结构没有明显影响。晚开花的园林植物支持城市中的传粉媒介多样性。如果管理得当，并且归化的风险降到最低，