Whether cities are more or less diverse than surrounding environments, and the extent to which non-native species in cities impact regional species pools, remain two fundamental yet unanswered questions in urban ecology. Here we offer a unifying framework for understanding the mechanisms that generate biodiversity patterns across taxonomic groups and spatial scales in urban systems. One commonality between existing frameworks is the collective recognition that species co-occurrence locally is not simply a function of natural colonization and extinction processes. Instead, it is largely a consequence of human actions that are governed by a myriad of social processes occurring across groups, institutions, and stakeholders. Rather than challenging these frameworks, we expand upon them to explicitly consider how human and non-human mechanisms interact to control urban biodiversity and influence species composition over space and time. We present a comprehensive theory of the processes that drive biodiversity within cities, between cities and surrounding non-urbanized areas and across cities, using the general perspective of metacommunity ecology. Armed with this approach, we embrace the fact that humans substantially influence β-diversity by creating a variety of different habitats in urban areas, and by influencing dispersal processes and rates, and suggest ways how these influences can be accommodated to existing metacommunity paradigms. Since patterns in urban biodiversity have been extensively described at the local or regional scale, we argue that the basic premises of the theory can be validated by studying the β-diversity across spatial scales within and across urban areas. By explicitly integrating the myriad of processes that drive native and non-native urban species co-occurrence, the proposed theory not only helps reconcile contrasting views on whether urban ecosystems are biodiversity hotspots or biodiversity sinks, but also provides a mechanistic understanding to better predict when and why alternative biodiversity patterns might emerge.

中文翻译：

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了解生物多样性模式如何在城市生态系统中的多个空间尺度上展开的框架

城市是否比周围环境更加多样化，以及城市中的非本地物种对区域物种库的影响程度，仍然是城市生态学中两个尚未解决的基本问题。在这里，我们提供了一个统一的框架，用于理解在城市系统中跨分类群和空间尺度产生生物多样性模式的机制。现有框架之间的一个共同点是集体承认物种在当地共存不仅仅是自然殖民和灭绝过程的函数。相反，它在很大程度上是人类行为的结果，这些行为受发生在群体、机构和利益相关者之间的无数社会过程的支配。与其挑战这些框架，我们扩展它们以明确考虑人类和非人类机制如何相互作用以控制城市生物多样性并影响物种组成在空间和时间上。我们使用元社区生态学的一般视角，提出了驱动城市内、城市与周边非城市化地区之间以及城市间生物多样性的过程的综合理论。有了这种方法，我们接受了这样一个事实，即人类通过在城市地区创造各种不同的栖息地，并通过影响扩散过程和速率来显着影响 β 多样性，并建议如何将这些影响适应现有的元社区范式。由于城市生物多样性的模式已在地方或区域范围内得到广泛描述，我们认为，该理论的基本前提可以通过研究跨城市区域内部和跨空间尺度的 β 多样性来验证。通过明确整合驱动本地和非本地城市物种共存的无数过程，所提出的理论不仅有助于调和关于城市生态系统是生物多样性热点还是生物多样性汇的不同观点，而且还提供了一种机制理解，以更好地预测何时以及为什么会出现替代的生物多样性模式。