Lokatis Sophie, Jeschke Jonathan M
Institute of Biology, Freie Universität Berlin, Berlin, Germany.
Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
Ecol Appl. 2022 Dec;32(8):e2703. doi: 10.1002/eap.2703. Epub 2022 Sep 25.
Urbanization is restructuring ecosystems at an unprecedented pace, with complex and profound consequences for life on Earth. One of the hypothesized trajectories of urban ecosystems and species communities is biotic homogenization, possibly leading to very similar species assemblages in cities across the globe. Urbanization can, however, also have the opposite effect: biotic diversification, with cities, at least at the local scale, becoming biologically more diverse, mainly as a consequence of high species introduction rates and habitat diversification. Applying the hierarchy-of-hypotheses approach, we systematically map and structure the comprehensive body of literature on the urban biotic homogenization (UBH) hypothesis, comprising 225 individual studies (i.e., tests of the hypothesis) retrieved from 145 publications. The UBH hypothesis is studied at multiple levels with a multitude of approaches and underlying assumptions. We show that UBH is generally used with two very different connotations: about half of the studies investigated a potential increase in community similarity across cities, whereas the other half investigated biotic homogenization within cities, the latter being supported more frequently. We also found strong research biases: (1) a taxonomic bias towards birds and plants, (2) a bias towards small and medium distances (<5000 km) in comparisons across cities, (3) a dominance of studies substituting space for time versus true temporal studies, (4) a strong focus on terrestrial versus aquatic systems, (5) more extraurban (including periurban) areas than natural or rural ecosystems for comparison to urban systems, (6) a bias towards taxonomic versus functional, phylogenetic, and temporal homogenization, and (7) more studies undertaken in Europe and North America than in other continents. The overall level of empirical support for the UBH hypothesis was mixed, with 55% of the studies reporting supporting evidence. Results significantly differed when a natural/nature reserve, an extraurban, or rural/agricultural area served as reference to infer biotic homogenization, with homogenization being detected least frequently when urban systems were compared to agricultural, i.e., other anthropogenically influenced, study sites. We provide an evidence map and a bibliographic network and identify key references on UBH with the goal to enhance accessibility and orientation for future research on this topic.
城市化正在以前所未有的速度重塑生态系统，对地球上的生命产生复杂而深远的影响。城市生态系统和物种群落的一种假设发展轨迹是生物同质化，这可能导致全球城市中出现非常相似的物种组合。然而，城市化也可能产生相反的效果：生物多样化，至少在局部尺度上，城市的生物多样性变得更高，这主要是由于物种引入率高和栖息地多样化。应用假设层次法，我们系统地梳理并构建了关于城市生物同质化（UBH）假设的综合文献体系，其中包括从145篇出版物中检索到的225项独立研究（即该假设的检验）。UBH假设在多个层面上通过多种方法和潜在假设进行研究。我们发现，UBH通常有两种截然不同的含义：大约一半的研究调查了城市间群落相似性的潜在增加，而另一半研究调查了城市内部的生物同质化，后者得到的支持更为频繁。我们还发现了强烈的研究偏差：（1）对鸟类和植物的分类学偏差；（2）城市间比较中对中小距离（<5000公里）的偏差；（3）用空间替代时间的研究占主导地位，而不是真正的时间研究；（4）对陆地系统与水生系统的强烈关注；（5）与城市系统进行比较时，更多的是城市外（包括城郊）区域，而不是自然或农村生态系统；（6）对分类学同质化与功能、系统发育和时间同质化的偏差；（7）在欧洲和北美进行的研究比其他大陆更多。对UBH假设的实证支持总体上参差不齐，55%的研究报告了支持证据。当以自然/自然保护区、城市外区域或农村/农业区域作为推断生物同质化的参考时，结果存在显著差异，与农业（即其他受人为影响的）研究地点相比，将城市系统与之比较时，检测到同质化的频率最低。我们提供了一个证据图和一个文献网络，并确定了关于UBH的关键参考文献，目的是提高该主题未来研究的可及性和导向性。
