ABSTRACT Aim Urbanization is a major driver of biotic homogenization (BH), reducing biodiversity through species invasions and extinctions. However, the drivers and mechanisms remain poorly understood, and urban ecosystems may also exhibit biotic differentiation (BD). This study uses a meta‐analysis to examine BH and BD patterns, underlying processes and key drivers across regions and taxa. Location Global. Time Period 2004–2023. Major Taxa Studied Arthropods, amphibians, birds and plants. Methods We conducted a global meta‐analysis integrating 110 effect sizes from 45 publications to evaluate urban biotic homogenization within and between cities. We quantified β‐diversity and its turnover and nestedness components across urbanization levels. Within cities, we evaluated changes in β‐diversity along urban levels, whereas between cities we assessed similarity among urban assemblages. We then examined how environmental, urban, and biotic factors (e.g., climate, impervious cover, non‐native richness) influenced homogenization. Results Across studies, β‐diversity responses to urbanization were heterogeneous but revealed clear patterns. Birds showed the strongest within‐city homogenization, particularly in North America, whereas amphibians, arthropods, and plants exhibited weaker or inconsistent trends. Turnover was the dominant β‐diversity component (> 65%), yet declined with increasing urbanization, especially in birds and plants. Nestedness increased with urbanization, reflecting species loss in some contexts. Among potential drivers, non‐native species richness consistently predicted homogenization, whereas climatic and geographic variables had context‐dependent or negligible effects. Between‐city analyses revealed biotic homogenization only in certain taxa and regions, whereas cities remained more similar within regions than among regions. Main Conclusions Urbanization influences β‐diversity through context‐dependent processes, with turnover decline emerging as the primary mechanism of homogenization. Non‐native species richness acts as a consistent driver, whereas other factors show idiosyncratic effects. Although homogenization is evident in some taxa and regions, it is not universal. This highlights an opportunity to conserve the remaining biogeographic distinctiveness of some urban assemblages and prevent further homogenization.
Zuñiga‐Palacios et al. (Sun,) studied this question.