There is increasing recognition that alien species may be ‘sleepers’, becoming invasive with favourable changes in conditions, yet these changes remain difficult to predict. As populations of frugivorous birds shift with urbanisation and climate change, they could provide dispersal services for introduced fruiting plants that have previously been considered benign. This is likely to be especially problematic at higher latitudes where bird migration phenologies are altering rapidly. However, any consequences for fruit dispersal have not yet been explored. Here, we use Helsinki, Finland, to investigate whether (i) streetscapes provide birds with a fruit resource that differs from urban forest fragments and (ii) the chances for dispersal of alien species (i.e., preferential consumption of native fruits). While there were both more fruits and birds in streetscapes (replicated across multiple years), fruits were not consumed preferentially according to origin. Additionally, seed analysis from faecal samples of blackbird Turdus merula L., a previously migratory but increasingly resident species, suggested that alien and native plants are equally likely to be dispersed. These results indicate that birds could be dispersing alien species more frequently than previously thought and highlight the complex effects of changing climates on potentially invasive species.

中文翻译：

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鸟类迁徙模式的变化有可能加强外来植物从城市中心的传播


人们越来越认识到，外来物种可能是“沉睡者”，随着条件的有利变化而变得具有侵略性，但这些变化仍然难以预测。随着城市化和气候变化，食果鸟类的数量发生了变化，它们可以为以前被认为是良性的引入的果园植物提供驱散服务。这在高纬度地区可能尤其成问题，因为鸟类的迁徙方式正在迅速变化。然而，尚未探讨水果传播的任何后果。在这里，我们以芬兰赫尔辛基为例，调查 （i） 街景是否为鸟类提供了不同于城市森林碎片的水果资源，以及 （ii） 外来物种扩散的机会（即优先食用本地水果）。虽然街景中的水果和鸟类都更多（多年复制），但水果并没有根据原产地被优先食用。此外，对黑鸫 Turdus merula L. 的粪便样本的种子分析表明，外来植物和本地植物同样有可能被分散。这些结果表明，鸟类可能比以前认为的更频繁地传播外来物种，并突出了气候变化对潜在入侵物种的复杂影响。